long-tern leaching behaviors of cement composites
LONG-TERN LEACHING BEHAVIORS OF CEMENT COMPOSITES PREPARED BY HAZARDOUS WASTES ZHENZHOU YANG*, LILI LIU*, XIDONG WANG* AND ZUOTAI ZHANG**,° * Beijing Key Laboratory for Solid Waste Utilization and Management and Department of Energy and Resource Engineering, College of Engineering, Peking University, Beijing 100871, P.R. China ** School of Environmental Science and Engineering, Southern University of Science and Technology of ° The Key Laboratory of Municipal Solid Waste Recycling Technology and Management of Shenzhen City, Shenzhen, 518055, P.R. China
SUMMARY: In the present study, long-term environmental impacts of compact and ground cement composites prepared by municipal sewage sludge (MSS) and hazardous wastes (HW), were investigated for use in building industry. Consecutive leaching tests over a time span of 180 days were performed in acid water, deionized water, and saline water, respectively, with the accumulative concentration of different elements determined in the leachate. Vanadium (V), barium (Ba), and stannum (Sn) were the three critical elements influencing the long-term environmental impact of the cement composites prepared. Higher concentrations of V in the leachate were observed from the compact cement composites than those from the ground ones. The concentration of Ba in the leachate increased with the decrease of particle size of the cement composites, and an initial increase in the leaching efficiency of Sn was followed by a clear decline with the leaching time. In addition, kinetic study revealed that the leaching behaviors of heavy metals follows a second-order model. The results demonstrated that the addition of MSS and HW into cement is considered to be irresistible against saline water, and the application of such materials in marine condition should be paid attention.
1. INTRODUCTION With the rapid urbanization and industrialization of China, a large quantity of municipal sewage sludge (MSS) and hazardous wastes (HW) are produced in China. It was estimated that more than 200 million tons of MSS in China were generated per year with an annual increase rate of 8-10% (Li et al., 2012; Shi and Kan, 2009), while the output HW has reached 15.87 million tons in 2011 and is rapidly increasing nowadays (Yang et al., 2016). Consequently, the timely and effective disposal of these two wastes has become a severe environmental issue. The most common ways to deal with these two wastes in China are agriculture, landfilling, and incineration (Folgueras et al., 2013; Murakami et al., 2009; Zhou et al., 2014). However, the reduced availability of land and the increasing concerns of environmental risks from general population restrict the applications these methods. Thus, an appropriate approach for the
Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
innocuous disposal of these two wastes is urgently needed. The co-processing of wastes in cement kiln seems to be a promising method, which can completely destroy the hazardous substance, save the resource and energy in addition to the additional revenue of governmental subsidy. The potential of cement kilns to use these solid wastes as raw materials seems to be large. However, it is worth mentioning that the application of materials involving wastes is possible when they possess the proper technical characteristics and satisfy the demand relating to healthy and the environmental field (Drinčić et al., 2017; Šturm et al., 2009). Therefore, it is necessary to evaluate the environmental impact, mainly caused by the release of heavy metals, of the final stabilization products of MSS and HW with cement-based materials during their whole life span. Many current researches have focused on the effect of MSS or HW addition on the mechanical strength of the as-derived cementitious materials (Bertolini et al., 2004; Jiang-Shan et al., 2013; Kai et al., 2011; Li et al., 2012; Pan et al., 2008). Besides, some researches were also conducted on the leaching behaviors of heavy metals during the usage of cementitious materials added with MSS or HW. For example, Bie et al. discovered that the leaching concentration of heavy metal of cement composites prepared by HW could be reduced significantly after 64 hours’ leaching (Bie et al., 2016), while Shi and Yuan also found the similar results when the leaching time increases to 60 days (Shi and Ling, 2003). Few studies have ever stressed on the long-term environmental impact when using cementitious materials added with HW is applied in practice. In general, the leaching test NEN 7375 based on diffusion is used to evaluate the leaching characteristics of moulded or monolithic building and waste materials, which used the replenished leaching solution to estimate the diffusion of inorganic components from composites at the particular time (from 6 h to 64 days) (Hohberg et al., 2000). To assess the long-term environmental impacts, the modified NEN 7375 protocol was applied in this study, which used the not replenished leaching solution to simulate the diffusion and dissolution of contaminants, as reported by Ana Drincˇic et al. (2017). The aim of this study is to evaluate the potential of using MSS and HW as alternative raw materials and fuel for the cement production. In order to investigate the long-term environmental impacts of such products, leaching test lasting 180 days based on diffusion and dissolution of contaminants was applied. Besides, three leaching solvent, which simulate different acid rain, surface water and marine conditions were also applied to the cement composites prepared by MSS and HW, in different forms (compact, ground coarse particle and ground fine particle) during the leaching test. Based on the experimental data, the environmental evaluation can be made on the application of such cement composites containing waste materials.
2. MATERIALS AND METHODS 2.1 Materials The cement used in this study is Eco-Ordinary Portland Cement (EOPC) from a cement plant co-processing MSS and HW, which is classified in P.O. 42.5 according to standard GB1752007. This cement plant integrates the uses of MSS and HW as raw materials, and adds alternative fuel to produce cement clinker with a disposal capacity of 500 t·d-1 and 130 t·d-1, respectively. MSS is collected from the Beijing sewage treatment plants with the moisture content of 80% while the adopted HW is a mixture of several hazardous wastes from different sectors, including electroplating sludge, waste mineral oil, printing ink, paint sludge, waste
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
chemicals and cosmetic, and with the moisture contents of 95% and 60%, respectively. The characteristics of raw materials, MSS and HW used to produce cement has been described by our previous studies (Yang et al., 2016). 2.2 Materials characterization X-ray fluorescence spectrometer (XRF, S4-Explore, Bruker) spectrometry was used to determine the chemical composition of EOPC, and the mineral compositions of sample is identified by using an X-ray diffractometer (XRD, D/Max 2500, Rigaku). Concentrations of heavy metals in the EOPC are determined by using an inductively coupled plasma mass spectrometry (ICP-MS, XSERIES 2, Thermo Scientific). The quality control of heavy metals measurements is checked by multiple analysis of the examined samples and the certified reference materials, which are described in detailed in SI (supplementary information). Prior to the measurement of heavy metals in the EOPC sample, a microwave digestion is applied to the sample following a method described in literature (Qi et al., 2016). The potential leachability of EOPC is evaluated according to the toxicity characteristic leaching procedure (TCLP) described in US EPA method 1311 (Amlan Ghosh et al., 2004). Concentrations of heavy metals in the leachate from TCLP tests are also determined by ICP-MS. In order to characterize the porosity of cement composites, the pore size distribution of the compact cement composites was measured by using mercury intrusion porosimetry (MIP, Autopore IV 9510, Micromeritics). 2.3 Cement composites preparation In the experiment, cement composites were prepared by EOPC, aggregate and deionized water. The aggregate in cement composites is the China standard sand produced by Xiamen ISO Standard Sand Co., LTD, and deionized water is used to make and cure cement composites. The cement/aggregate/water ratio, calculated based on dry weight in mortar, is 1:3:0.5. The size of the composite cast is 4 cm × 4 cm × 16 cm. The test of mechanical property of the composites is conducted according to the GB/T 17671-1999. In this study, compact and ground composites are prepared. The ground composites can be classified into coarse particle (particle size ~1 cm), and fine particle (particle size ~1 mm) based on their particle size. The compact composites simulated the intact mortar, while the ground composites with different particle sizes simulated the mortar under different stages of decomposition over time upon usage in buildings. 2.4 Long-term leaching test To assess the long-term environmental impacts during the usage of cement materials, the leaching test based on the diffusion is applied, which combined both diffusion and dissolution of contaminants. The leaching solvent in this study is acid solution, deionized water and saline water, which simulate the acid rain, surface water and marine condition, respectively. Acid solution is prepared by mixing H2SO4 and HNO3 at a mass ratio of 2:1, with the pH value adjusted to 3.2 using deionized water (Lu et al., 2016); while saline water is prepared according to the standard GB8650-88. The leaching experiment is carried out in a polyethylene vessel and the volume ratio of leaching solvent to mortar was 5:1, based on the modified NEN 7375 procedure. During the leaching process, every 10 mL of leachate is sampled after 3, 7, 14, 30, 60, 90, 120, 150 and 180 days for the determination of pH value, conductivity, and concentration of heavy metals by
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
using pH meter (MP 220, Mettler-Toledo), conductivity meter (FE 30, Mettler-Toledo) and ICPMS, respectively. In addition, the mechanical strength of the compact composites after leaching is also tested based on the GB/T 17671-1999.
3. RESULTS AND DISCUSSION 3.1 Characterization of OPEC Elemental composition and the heavy metals contents of OPEC are shown in Table 1. It can be seen that the main elements, expressed in the form of oxides, contained in OPEC are CaO, SiO2 and Al2O3. Besides, the results also show that the contents of Mn, Zn, Ba, and As are notably high in the OPEC. XRD patterns (Fig. 1) shows that ricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), tetra-calcium aluminoferrite (C4AF) and gypsum (CaSO4) are the dominant mineral phases in the EOPC sample, which is similar with the commercial cement (Yang et al., 1996). Table 2 presents the leaching behavior of heavy metals in the EOPC by using the TCLP method. The TCLP results show that the concentration of the targeted heavy metals in the leachate from EOPC are well within the regulatory limits, indicating that they can be classified as non-hazardous. Table 1 Main chemical composition of EOPC (wt% by weight). Sample
CaO
SO3
SiO2
MgO
Al2O3
Na2O
TiO2
K 2O
P 2O 5
LOI
EOPC
53.8
2.8
22.6
4.1
8.0
0.8
0.5
0.8
0.2
3.2
EOPC
As
Ba
Cd
Co
Cr
Cu
Ni
Pb
Zn
Mn
V
Sn
94
157
0.6
3
4.4
19
9
23
101
673
30
Nd
Nd: not detected.
Table 2 TCLP leaching concentrations (mg/L) of heavy metals in the EOPC (μg/L) As
Ba
Cd
Co
Cr
Cu
Ni
Pb
Zn
Mn
V
Sn
EOPC
Nd
1
Nd
Nd
Nd
Nd
Nd
Nd
0.06
Nd
0.07
Nd
GB 5085.3
5
100
1
~
15
100
5
5
100
~
~
~
-2007
Nd: not detected; ~: not regulated.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
♣
♣ C3S
♦ C2S
♦ ♣ ♣ ♦ ♣
♥ C3A
♠ C4AF
• CaSO4·2H2O
♦ ♣
•
♣ ♠ ♥ • •
20
♣
♦ ♣♣ ♣
40
60
2-theta (deg.)
Fig. 1 XRD pattern of EOPC 3.2 Long-term environmental impact of the EOPC composite In order to assess the long-term environmental impacts of cement composites that prepared by HW, the leaching test based on diffusion and dissolution of contaminants is conducted on the EOPC composites, together with the compact and ground cement composites. The concentration ranges of elements in the leachate under different conditions and the maximum values set by the corresponding regulation are shown in Table S1. It can be seen that, the concentration of most elements (Co, Ni and Pb et al.) in the leachate from ground composites are higher than those from compact composites. Besides, these elements also show higher solubility in the fine particle than those in coarse particle, which can be attributed to the higher specific area in ground composites and fine particles. Furthermore, the concentration of most heavy metals are below the limitation of regulation, except for arsenic under the saline water condition. This indicates that the pollution of arsenic must be paid attention when this kind of material is used under the marine condition. The pH and conductivity values of the leachate are displayed in Table S2. It can be seen that, pH value of the leachate is quite high due to the presence of calcium in the cement, ranging from 11 to 13. The pH values of leachate from ground composites are clearly higher than that in the compact composites, which can be ascribed to the higher specific area in the ground composites, and thus higher leachability of alkaline phases. Conductivity can be used as an indicator of the ionic strength of samples and the conductivity of the leachate from saline water is much higher than those from acid solution and deionized water and is a little lower for the compact composites than the ground composites. Correspondingly, pH value in the leachate from saline water is higher than those from acid solution and deionized water, indicating that the higher ionic strength of saline water can increase the leachability of alkaline components from cement composites compared to acid solution and deionized water. In addition, pH value of all leachates decline slowly with the leaching time, which is likely associated with the aqueous carbonation effect. In this study, different leaching behaviors are found in V, Ba, and Sn, which are presented in Figs. 2-4, respectively.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
The leachability of V under different conditions is shown in Fig. 2. It can be seen that the leaching concentration of V is much higher in the saline water than acid solution and deionized water. It is worth mentioning that the leaching concentration of V from compact cement composites is significantly higher than that from ground ones. This phenomenon can be attributed to the high leachability of Ca2+ for ground composites, which could promote the reaction between Ca2+ and vanadate, and thus the formation insoluble calcium vanadate (Shahnazi et al., 2012). Therefore, a lower leaching concentration of V is observed in the case of the ground composites. Different phenomenon is observed in the case of Ba, which is shown in Fig. 3. It can be seen that the concentration of Ba in the leachate of ground composites is much higher than that of compact composites, and the solubility of Ba also increases with smaller particle sizes of ground composites. These indicate that the leaching behavior of different Ba is related to the surface area of the cement composite. Ba is in the form of soluble Ba(OH)2 under alkaline condition and becomes more soluble under higher alkaline condition. The concentration of Ba in the leachate reached a stable value after approximately 150 days of leaching. Based on the observation above, in order to prevent the leaching of Ba, the crushed composites prepared by HW should be forbidden, unless included into other compact building materials. The leaching behavior of Sn under different conditions is displayed in Fig. 4. It can be seen that the increase in leaching efficiencies of Sn is followed by a clear decline with the leaching time in both the acid water and the deionized water conditions. The decline can be attributed to the decrease of pH values in the leachate with the leaching time, which can facilitate the precipitation of heavy metals under the condition of high alkalinity. In addition, some heavy metals such as iron and manganese, can be also presented as hydroxide in the alkaline environment and this gel-like precipitates might also act as adsorbents and impede the leaching of heavy metals (Tang and Steenari, 2016). 8
6
a)
Compact Coarse particle Fine particle
7 Concentration of V (µg/L)
Concentration of V (µg/L)
7
5 4 3 2
6
300
b)
Compact Coarse particle Fine particle
Concentration of V (µg/L)
8
5 4 3 2
c)
Compact Coarse particle Fine particle
250 200 150 100 50
1
1 0
0
3
7
14
30
60 90 Time (days)
120
150
180
0
3
7
14
30
60 90 Time (days)
120
150
180
3
7
14
30
60
90
120
150
180
Fig. 2 Leaching of V with acid water, deionized water and saline water over time, from the tested compact, coarse particle and fine particle: (a) acid water; (b) deionized water; (c) saline water
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
6000 4500
4000
Compact Coarse particle Fine particle
4000
3000
2000
1000
3500 3000 2500 2000 1500 1000
3
7
14
30
60 90 Time (days)
120
150
4000 3000 2000 1000
500
0
0
180
Compact Coarse particle Fine particle
5000 Concentration of Ba (µg/L)
Compact Coarse particle Fine particle
Concentration of Ba (µg/L)
Concentration of Ba (µg/L)
5000
3
7
14
30
60 90 Time (days)
120
150
0
180
3
7
14
30
60 90 Time (days)
120
150
180
Fig. 3 Leaching of Ba with acid water, deionized water and saline water over time, from the tested compact, coarse particle and fine particle: (a) acid water; (b) deionized water; (c) saline water
0.6
0.4
0.2
0.30
Concentration of Sn (µg/L)
Concentration of Sn (µg/L)
Concentration of Sn (µg/L)
0.8
0.25 0.20 0.15 0.10
3
7
14
30
60 90 Time (days)
120
150
180
Compact Coarse particle Fine particle
0.8
0.6
0.4
0.2
0.05 0.0
1.0
Compact Coarse particle Fine particle
0.35
Compact Coarse particle Fine particle
1.0
0.00 3
7
14
30
60 90 Time (days)
120
150
180
0.0
3
7
14
30
60 90 Time (days)
120
150
180
Fig. 4 Leaching of Sn with acid water, deionized water and saline water over time, from the tested compact, coarse particle and fine particle: (a) acid water; (b) deionized water; (c) saline water
3.3 Kinetic study A kinetic study on the leaching characteristics of heavy metals in the cement composites under different conditions is performed. For a liquid-solid reaction system, the reaction rate is generally controlled by the following steps: diffusion of ions through the water film, product layer and solid matrix; the chemical reaction at the surface of solid particles, or the combined of diffusion and chemical reactions. Here, multiple kinetic models, such as reaction-controlled and diffusion-controlled models are employed to describe the leaching process. However, our results show that those kinetic model did not fit the experimental data very well. Therefore, another kinetic model should be employed to describe the leaching process in this study.
t 1 t = + (1) 2 Ct KCs Cs Considering the observation from this study that, most heavy metals in the cement composites are released quickly at first, and then experienced a slow releasing process before
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
reaching the equilibrium state, indicating that the kinetic model describing the leaching behavior of cement composites might follow the second-order law. The general form of the second-order kinetic model is described previously by Le et al. (Lee et al., 2005), which is shown in Eq. (1). Accordingly, the slope 1/Cs and the intercept 1/KC2s can be experimentally determined by a linear fitting of the plot between the value t/Ct and the corresponding time t. Here, Ct (mL/L) is the concentration of the heavy metal leached out at a given time of t (min), Cs (mL/L) is the concentration of the heavy metal at the equilibrium state, and K (L/mg·min) is the second-order rate constant. Fig. 5 shows the fitting results for Ba at different leaching conditions. Most coefficients of determination (R2) between the theoretically-fitted value and the experimentallydetermined value passed 0.95, showing very good agreements. As a kind of porous materials, cement composites contains a large number of intercommunicating pores and closed pores (Fig. S1). Therefore, the leaching process of heavy metals in cement composites probably happens according to the following steps. Firstly, the heavy metals concentrated on the surface of cement composites dissolve rapidly into the leaching solvent during the leaching process. Meanwhile, the inter-communicating pores at the surface of cement composites will be quickly filled with the leaching solvent, and then the diffusion of heavy metals between the liquid in the intercommunicating pores and the liquid outside the cement composites will be completed in a short time. Thus, the concentrations of heavy metals in the leachate will be increased rapidly at first. Secondly, the elevated concentration of heavy metals in the leachate could weak the drive of mass transfer. Besides, those refractory phases in the cement composites, will serve as blocking layers, impeding the outward diffusion of heavy metals adsorbed in the closed pores or embedded inside the matrix of cement composites. Lastly, the hydration of cement composites all the way lasts during the whole leaching process, which will lead to a denser structure of cement composites and thus increase the diffusion resistance. Therefore, the leaching rate of heavy metals is much slower in the second stage than that in the first stage. Besides, it also can be seen that the slope of the fitting line decrease with the decrease of particle sizes, indicating that concentration of Ba at the equilibrium state increases with the decrease of particle sizes.
1.2
R =0.959 Coarse particles: y=2.639E-4x+0.005
y=0.006x+0.252 2
a)
2
Fine particles:
R =0.998 y=1.861E-4x+0.006
Compact Coarse particle Fine particle
2
R =0.997
0.8
Compact:
1.6
R =0.958 Coarse particles: y=2.523E-4x+0.006
y=0.008x+0.194
1.4 t/Ct (d·L/µg)
t/Ct (d·L/µg)
1.0
0.8
1.8
0.6
Fine particles:
1.2
Compact:
2
0.7
2
0.6
b)
R =0.993 y=1.812E-4x+0.007 2
R =0.994
1.0
Compact Coarse particle Fine particle
0.6
0.4
0.4
20
40
60
80
100
120
Time (days)
140
160
180
200
R =0.952 y=1.689E-4x+0.004
c)
2
R =0.976
0.4 0.3
Compact Coarse Partcile Fine Particle
0.1
0.2 0
2
Fine particles:
0.2
0.2 0.0
2
R =0.981 Coarse particles: y=1.827E-4x+0.005
0.5
0.8
y=0.004x-0.005
Compact:
t/Ct (d· L/µg)
1.4
0.0
0.0 0
20
40
60
80
100
120
140
Time (days)
160
180
200
0
20
40
60
80 100 120 Time (days)
140
160
180
200
Fig. 5 Second-order reaction kinetics of barium under different leaching conditions: (a) acid water; (b) deionized water; (c) saline water
3.4 The mechanical property of cement composites The mechanical strength of the compact cement composites after the leaching test is determined in Fig. 6. It is known that the leaching medium can influence the strength of cement composites from two opposite aspects (Makhloufi et al., 2012). Firstly, H+ in the leachate can react with cement composites, destroying the structure and thus decreasing the strength of cement composites. Secondly, the leachate can provide the environment for the hydration of
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
cement, which will increase the strength of cement composites. In this study, the effect of H+ on the structure of cement composites will be limited due to highly alkaline environment in the leachate. Therefore, the ongoing hydration reaction during the leaching process could increase the strength of cement composites, especially for the comprehensive strength, as shown in Fig. 6. It also can be seen that the strength of cement composites leached in the saline water are obviously lower than those leached in the acid solution and deionized water, indicating that the saline water can cause the adverse effect on the mechanical strength of cement composites. Besides, the criterion for classifying as material as resistant/durable is expressed as a corrosion index (Ic), which represents the relative strength of samples stored in an aggressive-solution in comparison to a water-stored sample (Frias et al., 2013). Ic of the cement composites prepared by EOPC is 0.8, which can be considered to be irresistible against saline water. Since porosity is an essential parameter for the description of physical properties of any material (Gallé, 2001), MIP tests are performed at the end of the study on the compact cement composites after the leaching test (Table S3 and Fig. S2). It can be seen that the total MIP porosity of the cement composites leached in saline water had the highest overall porosity, indicating that saline water can cause the corrosion of cement composites. Therefore, our results indicate that the cement composites prepared by EOPC should be carefully used in the marine environment.
6
4
2
70 60
b)
50 40
Flexural strength (Mpa)
8
80
Compressive strength (Mpa)
a)
10
30 20 10 0
0 EOPC
EOPC-acid water EOPC-water
EOPC-salt water
EOPC
EOPC-acid water EOPC-water
EOPC-salt water
Fig. 6 The mechanical properties of OPEC under different leaching environment: (a) flexural strength (b) compressive strength
4. CONCLUSION The long-term leaching behaviors of cement composites prepared by EOPC are investigated in this study. Compact and ground (coarse particle and fine particle) cement composites are prepared and the leaching test based on the modified NEN 7375 procedure is conducted in acid water, deionized water and saline water over a time period of 180 days. Our results show that concentration of most heavy metals are below the limitation of corresponding regulation, except for arsenic in the leachate from the cement composites under the saline water condition. Besides, the elevated concentration of V is observed in the leachate of compact cement composites than ground composites. The increased concentration of Ba in the leachate is observed with the decrease of particle size of cement composites. The concentration of Sn increases firstly but decline afterward in the acid water and deionized water and the kinetic
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
study indicated that the leaching of heavy metals follows a second-order model. Furthermore, our results point out that the cement composites prepared by EOPC should be carefully used in the marine environment.
ACKNOWLEDGEMENTS This study was supported by National Science Fund for Distinguished Young Scholars (51522401) and National Natural Science Foundation of China (51472007). This work was also supported financially by Research Funding supported by Shenzhen Science and Technology Innovation Committee (ZDSYS201602261932201).
REFERENCES Amlan Ghosh, Muhammed Mukiibi, A., Ela, W., (2004). TCLP Underestimates Leaching of Arsenic from Solid Residuals under Landfill Conditions. Environ. Sci. Technol. 38, 4677-4682. Bertolini, L., Carsana, M., Cassago, D., Curzio, A.Q., Collepardi, M., (2004) MSWI ashes as mineral additions in concrete. Cement & Concrete Research 34, 1899-1906. Bie, R., Chen, P., Song, X., Ji, X., (2016) Characteristics of municipal solid waste incineration fly ash with cement solidification treatment. Journal of the Energy Institute 89, 704-712. Drinčić, A., Nikolić, I., Zuliani, T., Milačič, R., Ščančar, J., (2017) Long-term environmental impacts of building composites containing waste materials: Evaluation of the leaching protocols. Waste Manage., 340-349. Folgueras, M.B., Alonso, M., Díaz, R.M., (2013) Influence of sewage sludge treatment on pyrolysis and combustion of dry sludge. Energy 55, 426-435. Frias, M., Goñi, S., García, R., Villa, R.V.D.L., (2013) Seawater effect on durability of ternary cements. Synergy of chloride and sulphate ions. Composites Part B Engineering 46, 173–178. Gallé, C., (2001) Effect of drying on cement-based materials pore structure as identified by mercury intrusion porosimetry : A comparative study between oven-, vacuum-, and freezedrying. Cement & Concrete Research 31, 1467-1477. Hohberg, I., Groot, G.J.D., Veen, A.M.H.V.D., Wassing, W., (2000) Development of a leaching protocol for concrete. Waste Manage. 20, 177-184. Jiang-Shan, L.I., Qiang, X., Zhu-Yun, H.U., Xian-Wang, L.I., (2013) Study of strength stability of municipal solid waste incinerator fly ash solidified by cement. Rock & Soil Mechanics 34, 751756. Kai, W., Shi, H., Guo, X., (2011) Utilization of municipal solid waste incineration fly ash for sulfoaluminate cement clinker production. Waste Manage. 31, 2001-2008. Lee, I.H., Wang, Y.J., Chern, J.M., (2005) Extraction kinetics of heavy metal-containing sludge. J. Hazard. Mater. 123, 112. Li, X.G., Lv, Y., Ma, B.G., Chen, Q.B., Yin, X.B., Jian, S.W., (2012) Utilization of municipal solid waste incineration bottom ash in blended cement. J. Clean. Prod. 32, 96-100. Lu, H., Wei, F., Tang, J., Giesy, J.P., (2016) Leaching of metals from cement under simulated environmental conditions. Journal of Environmental Management 169, 319.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Makhloufi, Z., Kadri, E.H., Bouhicha, M., Benaissa, A., Bennacer, R., (2012) The strength of limestone mortars with quaternary binders: Leaching effect by demineralized water. Construction & Building Materials 36, 171-181. Murakami, T., Suzuki, Y., Nagasawa, H., Yamamoto, T., Koseki, T., Hirose, H., Okamoto, S., (2009) Combustion characteristics of sewage sludge in an incineration plant for energy recovery. Fuel Process Technol. 90, 778-783. Pan, J.R., Huang, C., Kuo, J.J., Lin, S.H., (2008) Recycling MSWI bottom and fly ash as raw materials for Portland cement. Waste Manage. 28, 1113-1118. Qi, L., Zhang, Y., Ma, Y., Chen, M., Ge, X., Ma, Y., Zheng, J., Wang, Z., Li, S., (2016) Source identification of trace elements in the atmosphere during the second Asian Youth Games in Nanjing, China: Influence of control measures on air quality. Atmospheric Pollution Research 7, 547-556. Shahnazi, A., Rashchi, F., Vahidi, E., (2012) A Kinetics Study on the Hydrometallurgical Recovery of Vanadium from LD Converter Slag in Alkaline Media. John Wiley & Sons, Inc. Shi, H., Ling, Y., (2003) cementitious reactivity of municipal solid waste incineration fly ash and immobolization effect by cement. Journal of the Chinese Ceramic Society. Shi, H.S., Kan, L.L., (2009) Characteristics of municipal solid wastes incineration (MSWI) fly ash–cement matrices and effect of mineral admixtures on composite system. Construction & Building Materials 23, 2160-2166. Šturm, T., Milačič, R., Murko, S., Vahčič, M., Mladenovič, A., Šuput, J.S., Ščančar, J., (2009) The use of EAF dust in cement composites: Assessment of environmental impact. J. Hazard. Mater. 166, 277. Tang, J., Steenari, B.M., (2016) Leaching optimization of municipal solid waste incineration ash for resource recovery: A case study of Cu, Zn, Pb and Cd. Waste Manage 48, 315-322. Yang, S., Song, H., Xie, R., (1996) XRD Study of Hydration Rate of Cement. Journal of Instrumental Analysis. Yang, Z., Yan, C., Sun, Y., Liu, L., Zhang, Z., Ge, X., (2016) The partitioning behavior of trace element and its distribution in the surrounding soil of a cement plant integrated utilization of hazardous wastes. Environ. Sci. Pollut. R. 23, 13943. Zhou, H.B., Ma, C., Gao, D., Chen, T.B., Zheng, G.D., Chen, J., Pan, T.H., (2014) Application of a recyclable plastic bulking agent for sewage sludge composting. Bioresource Technol. 152, 329.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
SUPPLEMENTARY INFORMATION Table S1 The concentration (μg/L) ranges of the elements in the acidic, deionized and saline leachates from compact, coarse particle and fine particle composites prepared with EOPC during the course of the experiment (180 days).
Element
Acidic Acidic Acidic water water (coarse water (fine (compact) particle) particle)
Deionized water (compact)
Deionized water (coarse particle)
Deionized water (fine particle)
Saline water (compact)
Saline water (coarse
Saline water (fine
particle)
particle)
Maximum permitted values
Cr
0.8-3.5
0.6-2.3
1.1-3.2
0.9-3.5
0.7-1.4
1.1-2.2
41.3-49.3
34.8-55.8
36.3-44.5
300
Mn
0.01-0.2
0.01-0.2
0.01-0.2
0.01-0.5
0.01-0.09
0.01-0.08
0.01-1.1
0.01-0.2
0.01-0.1
1000
Co
0.2-1.6
2.6-11.4
4.2-11.4
0.3-1.6
2.7-11.6
3.3-11.5
0.3-2.1
3.3-12.8
5.2-11.4
/
Ni
2.6-17.6
23.4-126.2
34.4-131.6
3.7-17.3
21.1-103.3
30.4-142.3
34.4-61.4
55.2-93.5
59.5-95.8
300
Cu
1.6-3.0
5.1-12.3
4.5-11.2
1.3-4.5
4.7-13.0
3.8-14.1
12.9-24.9
19.5-35.2
20.4-33.3
1000
Zn
0.01-8.5
0.01-12.9
0.01-10.2
0.01-8.5
0.01-10.3
0.01-14.0
0.01-11.6
0.01-14.9
0.01-8.4
1000
As
0.06-0.5
0.01-0.6
0.01-0.6
0.01-0.6
0.01-0.7
0.01-0.7
0.01-364
0.01-274
0.01-361
100
Cd
0.01-0.02
0.01-0.02
0.01-0.04
0.01-0.02
0.01-0.04
0.01-0.04
0.01-0.1
0.1-0.7
0.3-0.8
100
Pb
0.01-0.08
0.2-2.9
0.3-3.5
0.01-0.04
0.3-3.0
0.2-3.6
0.2-0.8
0.2-5.2
0.3-5.5
300
Sb
0.09-0.3
0.01-0.08
0.01-0.05
0.05-0.3
0.03-0.07
0.02-0.07
0.02-0.07
0.2-0.4
0.2-0.4
/
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Table S2 The pH and electrical conductivity of leachates during the course of the experiment of 180 days
Sample
Time (days)
Parameter
3
7
14
30
60
90 120
150
180
pH
11.5
11.5
11.5
11.5
11.4
11.2
11
11.5
11.5
Conductivity (mS cm-1)
0.5
0.7
0.8
1.0
1.0
0.9
0.9
0.9
0.9
pH
12.2
12.3
12.3
12.1
12
11.6
11.6
11.8
11.8
Conductivity (mS cm-1)
3.2
4.9
5.8
6.2
6.7
6.7
6.7
6.2
6.0
pH
12.4
12.4
12.3
12.2
12.1
11.8
11.6
11.8
11.8
Conductivity (mS cm-1)
3.8
4.7
6.5
6.9
7.5
7.0
7.1
6.8
6.6
pH
11.7
11.6
11.5
11.6
11.5
11.2
11.3
11.4
11.4
Conductivity (mS cm-1)
0.6
0.8
0.9
1.0
0.9
1.0
.0
1.0
0.9
pH
12.3
12.4
12.2
12.3
12.2
12
11.8
11.8
11.8
Conductivity (mS cm-1)
3.3
4.8
5.8
6.4
6.7
6.5
6.1
6.1
5.7
pH
12.5
12.4
12.3
12.2
12.2
12.1
11.9
11.8
11.8
Conductivity (mS cm-1)
3.4
4.2
6.4
7.4
7.5
7.1
6.7
6.7
6.6
pH
11.8
11.9
11.9
11.5
12
11.9
11.6
11.8
11.8
Conductivity (mS cm-1)
44.6
44.7
44.1
42.1
41.3
40.4
39.0
39.8
39.0
pH
12.4
12.3
12.4
12.2
12.3
12.3
11.8
12.1
12.1
Conductivity (mS cm-1)
47.0
46.8
46.7
45.0
44.0
42.7
43.5
43.6
42.3
pH
12.4
12.4
12.4
12.2
12.3
12.3
11.9
12.1
12.1
Conductivity (mS cm-1)
47.0
46.9
47.1
45.3
44.2
42.9
43.7
44.0
42.6
Acidic water: Compact Cc
Coarse Cc
Fine Cc Deionized water: Compact Cc
Coarse Cc
Fine Cc Saline water: Compact Cc
Coarse Cc
Fine Cc
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Table S3 The porosity, average pore diameter and total instrusion volume of compact compistesprepared with EOPC, after 180 days of exposure to acid water, deionized water and saline water.
Sample
Porosity (%)
Average pore diameter (nm)
Total pore volume (mL/g)
Cc (Acid water) Cc (Deionized water) Cc (Saline water)
16.0 12.7
28.6 27.9
0.073 0.064
11.7
33.7
0.051
Fig. S1 Sketch of the leaching behavior of heavy metals in cement composites
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
0.14
Acid water Deionized water Saline water
0.10 0.08
-1
Pore volume (mL· g )
0.12
0.06 0.04 0.02 0.00
1
10
100 1000 Pore size diameter (nm)
10000
Fig. S2 Pore size distribution curves, determinend by MIP, for the investigated compact composites preparedby EOPC, afeter 180 days of exposure to acid water, deinoized water and saline water.
SUMMARY: In the present study, long-term environmental impacts of compact and ground cement composites prepared by municipal sewage sludge (MSS) and hazardous wastes (HW), were investigated for use in building industry. Consecutive leaching tests over a time span of 180 days were performed in acid water, deionized water, and saline water, respectively, with the accumulative concentration of different elements determined in the leachate. Vanadium (V), barium (Ba), and stannum (Sn) were the three critical elements influencing the long-term environmental impact of the cement composites prepared. Higher concentrations of V in the leachate were observed from the compact cement composites than those from the ground ones. The concentration of Ba in the leachate increased with the decrease of particle size of the cement composites, and an initial increase in the leaching efficiency of Sn was followed by a clear decline with the leaching time. In addition, kinetic study revealed that the leaching behaviors of heavy metals follows a second-order model. The results demonstrated that the addition of MSS and HW into cement is considered to be irresistible against saline water, and the application of such materials in marine condition should be paid attention.
1. INTRODUCTION With the rapid urbanization and industrialization of China, a large quantity of municipal sewage sludge (MSS) and hazardous wastes (HW) are produced in China. It was estimated that more than 200 million tons of MSS in China were generated per year with an annual increase rate of 8-10% (Li et al., 2012; Shi and Kan, 2009), while the output HW has reached 15.87 million tons in 2011 and is rapidly increasing nowadays (Yang et al., 2016). Consequently, the timely and effective disposal of these two wastes has become a severe environmental issue. The most common ways to deal with these two wastes in China are agriculture, landfilling, and incineration (Folgueras et al., 2013; Murakami et al., 2009; Zhou et al., 2014). However, the reduced availability of land and the increasing concerns of environmental risks from general population restrict the applications these methods. Thus, an appropriate approach for the
Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
innocuous disposal of these two wastes is urgently needed. The co-processing of wastes in cement kiln seems to be a promising method, which can completely destroy the hazardous substance, save the resource and energy in addition to the additional revenue of governmental subsidy. The potential of cement kilns to use these solid wastes as raw materials seems to be large. However, it is worth mentioning that the application of materials involving wastes is possible when they possess the proper technical characteristics and satisfy the demand relating to healthy and the environmental field (Drinčić et al., 2017; Šturm et al., 2009). Therefore, it is necessary to evaluate the environmental impact, mainly caused by the release of heavy metals, of the final stabilization products of MSS and HW with cement-based materials during their whole life span. Many current researches have focused on the effect of MSS or HW addition on the mechanical strength of the as-derived cementitious materials (Bertolini et al., 2004; Jiang-Shan et al., 2013; Kai et al., 2011; Li et al., 2012; Pan et al., 2008). Besides, some researches were also conducted on the leaching behaviors of heavy metals during the usage of cementitious materials added with MSS or HW. For example, Bie et al. discovered that the leaching concentration of heavy metal of cement composites prepared by HW could be reduced significantly after 64 hours’ leaching (Bie et al., 2016), while Shi and Yuan also found the similar results when the leaching time increases to 60 days (Shi and Ling, 2003). Few studies have ever stressed on the long-term environmental impact when using cementitious materials added with HW is applied in practice. In general, the leaching test NEN 7375 based on diffusion is used to evaluate the leaching characteristics of moulded or monolithic building and waste materials, which used the replenished leaching solution to estimate the diffusion of inorganic components from composites at the particular time (from 6 h to 64 days) (Hohberg et al., 2000). To assess the long-term environmental impacts, the modified NEN 7375 protocol was applied in this study, which used the not replenished leaching solution to simulate the diffusion and dissolution of contaminants, as reported by Ana Drincˇic et al. (2017). The aim of this study is to evaluate the potential of using MSS and HW as alternative raw materials and fuel for the cement production. In order to investigate the long-term environmental impacts of such products, leaching test lasting 180 days based on diffusion and dissolution of contaminants was applied. Besides, three leaching solvent, which simulate different acid rain, surface water and marine conditions were also applied to the cement composites prepared by MSS and HW, in different forms (compact, ground coarse particle and ground fine particle) during the leaching test. Based on the experimental data, the environmental evaluation can be made on the application of such cement composites containing waste materials.
2. MATERIALS AND METHODS 2.1 Materials The cement used in this study is Eco-Ordinary Portland Cement (EOPC) from a cement plant co-processing MSS and HW, which is classified in P.O. 42.5 according to standard GB1752007. This cement plant integrates the uses of MSS and HW as raw materials, and adds alternative fuel to produce cement clinker with a disposal capacity of 500 t·d-1 and 130 t·d-1, respectively. MSS is collected from the Beijing sewage treatment plants with the moisture content of 80% while the adopted HW is a mixture of several hazardous wastes from different sectors, including electroplating sludge, waste mineral oil, printing ink, paint sludge, waste
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
chemicals and cosmetic, and with the moisture contents of 95% and 60%, respectively. The characteristics of raw materials, MSS and HW used to produce cement has been described by our previous studies (Yang et al., 2016). 2.2 Materials characterization X-ray fluorescence spectrometer (XRF, S4-Explore, Bruker) spectrometry was used to determine the chemical composition of EOPC, and the mineral compositions of sample is identified by using an X-ray diffractometer (XRD, D/Max 2500, Rigaku). Concentrations of heavy metals in the EOPC are determined by using an inductively coupled plasma mass spectrometry (ICP-MS, XSERIES 2, Thermo Scientific). The quality control of heavy metals measurements is checked by multiple analysis of the examined samples and the certified reference materials, which are described in detailed in SI (supplementary information). Prior to the measurement of heavy metals in the EOPC sample, a microwave digestion is applied to the sample following a method described in literature (Qi et al., 2016). The potential leachability of EOPC is evaluated according to the toxicity characteristic leaching procedure (TCLP) described in US EPA method 1311 (Amlan Ghosh et al., 2004). Concentrations of heavy metals in the leachate from TCLP tests are also determined by ICP-MS. In order to characterize the porosity of cement composites, the pore size distribution of the compact cement composites was measured by using mercury intrusion porosimetry (MIP, Autopore IV 9510, Micromeritics). 2.3 Cement composites preparation In the experiment, cement composites were prepared by EOPC, aggregate and deionized water. The aggregate in cement composites is the China standard sand produced by Xiamen ISO Standard Sand Co., LTD, and deionized water is used to make and cure cement composites. The cement/aggregate/water ratio, calculated based on dry weight in mortar, is 1:3:0.5. The size of the composite cast is 4 cm × 4 cm × 16 cm. The test of mechanical property of the composites is conducted according to the GB/T 17671-1999. In this study, compact and ground composites are prepared. The ground composites can be classified into coarse particle (particle size ~1 cm), and fine particle (particle size ~1 mm) based on their particle size. The compact composites simulated the intact mortar, while the ground composites with different particle sizes simulated the mortar under different stages of decomposition over time upon usage in buildings. 2.4 Long-term leaching test To assess the long-term environmental impacts during the usage of cement materials, the leaching test based on the diffusion is applied, which combined both diffusion and dissolution of contaminants. The leaching solvent in this study is acid solution, deionized water and saline water, which simulate the acid rain, surface water and marine condition, respectively. Acid solution is prepared by mixing H2SO4 and HNO3 at a mass ratio of 2:1, with the pH value adjusted to 3.2 using deionized water (Lu et al., 2016); while saline water is prepared according to the standard GB8650-88. The leaching experiment is carried out in a polyethylene vessel and the volume ratio of leaching solvent to mortar was 5:1, based on the modified NEN 7375 procedure. During the leaching process, every 10 mL of leachate is sampled after 3, 7, 14, 30, 60, 90, 120, 150 and 180 days for the determination of pH value, conductivity, and concentration of heavy metals by
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
using pH meter (MP 220, Mettler-Toledo), conductivity meter (FE 30, Mettler-Toledo) and ICPMS, respectively. In addition, the mechanical strength of the compact composites after leaching is also tested based on the GB/T 17671-1999.
3. RESULTS AND DISCUSSION 3.1 Characterization of OPEC Elemental composition and the heavy metals contents of OPEC are shown in Table 1. It can be seen that the main elements, expressed in the form of oxides, contained in OPEC are CaO, SiO2 and Al2O3. Besides, the results also show that the contents of Mn, Zn, Ba, and As are notably high in the OPEC. XRD patterns (Fig. 1) shows that ricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), tetra-calcium aluminoferrite (C4AF) and gypsum (CaSO4) are the dominant mineral phases in the EOPC sample, which is similar with the commercial cement (Yang et al., 1996). Table 2 presents the leaching behavior of heavy metals in the EOPC by using the TCLP method. The TCLP results show that the concentration of the targeted heavy metals in the leachate from EOPC are well within the regulatory limits, indicating that they can be classified as non-hazardous. Table 1 Main chemical composition of EOPC (wt% by weight). Sample
CaO
SO3
SiO2
MgO
Al2O3
Na2O
TiO2
K 2O
P 2O 5
LOI
EOPC
53.8
2.8
22.6
4.1
8.0
0.8
0.5
0.8
0.2
3.2
EOPC
As
Ba
Cd
Co
Cr
Cu
Ni
Pb
Zn
Mn
V
Sn
94
157
0.6
3
4.4
19
9
23
101
673
30
Nd
Nd: not detected.
Table 2 TCLP leaching concentrations (mg/L) of heavy metals in the EOPC (μg/L) As
Ba
Cd
Co
Cr
Cu
Ni
Pb
Zn
Mn
V
Sn
EOPC
Nd
1
Nd
Nd
Nd
Nd
Nd
Nd
0.06
Nd
0.07
Nd
GB 5085.3
5
100
1
~
15
100
5
5
100
~
~
~
-2007
Nd: not detected; ~: not regulated.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
♣
♣ C3S
♦ C2S
♦ ♣ ♣ ♦ ♣
♥ C3A
♠ C4AF
• CaSO4·2H2O
♦ ♣
•
♣ ♠ ♥ • •
20
♣
♦ ♣♣ ♣
40
60
2-theta (deg.)
Fig. 1 XRD pattern of EOPC 3.2 Long-term environmental impact of the EOPC composite In order to assess the long-term environmental impacts of cement composites that prepared by HW, the leaching test based on diffusion and dissolution of contaminants is conducted on the EOPC composites, together with the compact and ground cement composites. The concentration ranges of elements in the leachate under different conditions and the maximum values set by the corresponding regulation are shown in Table S1. It can be seen that, the concentration of most elements (Co, Ni and Pb et al.) in the leachate from ground composites are higher than those from compact composites. Besides, these elements also show higher solubility in the fine particle than those in coarse particle, which can be attributed to the higher specific area in ground composites and fine particles. Furthermore, the concentration of most heavy metals are below the limitation of regulation, except for arsenic under the saline water condition. This indicates that the pollution of arsenic must be paid attention when this kind of material is used under the marine condition. The pH and conductivity values of the leachate are displayed in Table S2. It can be seen that, pH value of the leachate is quite high due to the presence of calcium in the cement, ranging from 11 to 13. The pH values of leachate from ground composites are clearly higher than that in the compact composites, which can be ascribed to the higher specific area in the ground composites, and thus higher leachability of alkaline phases. Conductivity can be used as an indicator of the ionic strength of samples and the conductivity of the leachate from saline water is much higher than those from acid solution and deionized water and is a little lower for the compact composites than the ground composites. Correspondingly, pH value in the leachate from saline water is higher than those from acid solution and deionized water, indicating that the higher ionic strength of saline water can increase the leachability of alkaline components from cement composites compared to acid solution and deionized water. In addition, pH value of all leachates decline slowly with the leaching time, which is likely associated with the aqueous carbonation effect. In this study, different leaching behaviors are found in V, Ba, and Sn, which are presented in Figs. 2-4, respectively.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
The leachability of V under different conditions is shown in Fig. 2. It can be seen that the leaching concentration of V is much higher in the saline water than acid solution and deionized water. It is worth mentioning that the leaching concentration of V from compact cement composites is significantly higher than that from ground ones. This phenomenon can be attributed to the high leachability of Ca2+ for ground composites, which could promote the reaction between Ca2+ and vanadate, and thus the formation insoluble calcium vanadate (Shahnazi et al., 2012). Therefore, a lower leaching concentration of V is observed in the case of the ground composites. Different phenomenon is observed in the case of Ba, which is shown in Fig. 3. It can be seen that the concentration of Ba in the leachate of ground composites is much higher than that of compact composites, and the solubility of Ba also increases with smaller particle sizes of ground composites. These indicate that the leaching behavior of different Ba is related to the surface area of the cement composite. Ba is in the form of soluble Ba(OH)2 under alkaline condition and becomes more soluble under higher alkaline condition. The concentration of Ba in the leachate reached a stable value after approximately 150 days of leaching. Based on the observation above, in order to prevent the leaching of Ba, the crushed composites prepared by HW should be forbidden, unless included into other compact building materials. The leaching behavior of Sn under different conditions is displayed in Fig. 4. It can be seen that the increase in leaching efficiencies of Sn is followed by a clear decline with the leaching time in both the acid water and the deionized water conditions. The decline can be attributed to the decrease of pH values in the leachate with the leaching time, which can facilitate the precipitation of heavy metals under the condition of high alkalinity. In addition, some heavy metals such as iron and manganese, can be also presented as hydroxide in the alkaline environment and this gel-like precipitates might also act as adsorbents and impede the leaching of heavy metals (Tang and Steenari, 2016). 8
6
a)
Compact Coarse particle Fine particle
7 Concentration of V (µg/L)
Concentration of V (µg/L)
7
5 4 3 2
6
300
b)
Compact Coarse particle Fine particle
Concentration of V (µg/L)
8
5 4 3 2
c)
Compact Coarse particle Fine particle
250 200 150 100 50
1
1 0
0
3
7
14
30
60 90 Time (days)
120
150
180
0
3
7
14
30
60 90 Time (days)
120
150
180
3
7
14
30
60
90
120
150
180
Fig. 2 Leaching of V with acid water, deionized water and saline water over time, from the tested compact, coarse particle and fine particle: (a) acid water; (b) deionized water; (c) saline water
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
6000 4500
4000
Compact Coarse particle Fine particle
4000
3000
2000
1000
3500 3000 2500 2000 1500 1000
3
7
14
30
60 90 Time (days)
120
150
4000 3000 2000 1000
500
0
0
180
Compact Coarse particle Fine particle
5000 Concentration of Ba (µg/L)
Compact Coarse particle Fine particle
Concentration of Ba (µg/L)
Concentration of Ba (µg/L)
5000
3
7
14
30
60 90 Time (days)
120
150
0
180
3
7
14
30
60 90 Time (days)
120
150
180
Fig. 3 Leaching of Ba with acid water, deionized water and saline water over time, from the tested compact, coarse particle and fine particle: (a) acid water; (b) deionized water; (c) saline water
0.6
0.4
0.2
0.30
Concentration of Sn (µg/L)
Concentration of Sn (µg/L)
Concentration of Sn (µg/L)
0.8
0.25 0.20 0.15 0.10
3
7
14
30
60 90 Time (days)
120
150
180
Compact Coarse particle Fine particle
0.8
0.6
0.4
0.2
0.05 0.0
1.0
Compact Coarse particle Fine particle
0.35
Compact Coarse particle Fine particle
1.0
0.00 3
7
14
30
60 90 Time (days)
120
150
180
0.0
3
7
14
30
60 90 Time (days)
120
150
180
Fig. 4 Leaching of Sn with acid water, deionized water and saline water over time, from the tested compact, coarse particle and fine particle: (a) acid water; (b) deionized water; (c) saline water
3.3 Kinetic study A kinetic study on the leaching characteristics of heavy metals in the cement composites under different conditions is performed. For a liquid-solid reaction system, the reaction rate is generally controlled by the following steps: diffusion of ions through the water film, product layer and solid matrix; the chemical reaction at the surface of solid particles, or the combined of diffusion and chemical reactions. Here, multiple kinetic models, such as reaction-controlled and diffusion-controlled models are employed to describe the leaching process. However, our results show that those kinetic model did not fit the experimental data very well. Therefore, another kinetic model should be employed to describe the leaching process in this study.
t 1 t = + (1) 2 Ct KCs Cs Considering the observation from this study that, most heavy metals in the cement composites are released quickly at first, and then experienced a slow releasing process before
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
reaching the equilibrium state, indicating that the kinetic model describing the leaching behavior of cement composites might follow the second-order law. The general form of the second-order kinetic model is described previously by Le et al. (Lee et al., 2005), which is shown in Eq. (1). Accordingly, the slope 1/Cs and the intercept 1/KC2s can be experimentally determined by a linear fitting of the plot between the value t/Ct and the corresponding time t. Here, Ct (mL/L) is the concentration of the heavy metal leached out at a given time of t (min), Cs (mL/L) is the concentration of the heavy metal at the equilibrium state, and K (L/mg·min) is the second-order rate constant. Fig. 5 shows the fitting results for Ba at different leaching conditions. Most coefficients of determination (R2) between the theoretically-fitted value and the experimentallydetermined value passed 0.95, showing very good agreements. As a kind of porous materials, cement composites contains a large number of intercommunicating pores and closed pores (Fig. S1). Therefore, the leaching process of heavy metals in cement composites probably happens according to the following steps. Firstly, the heavy metals concentrated on the surface of cement composites dissolve rapidly into the leaching solvent during the leaching process. Meanwhile, the inter-communicating pores at the surface of cement composites will be quickly filled with the leaching solvent, and then the diffusion of heavy metals between the liquid in the intercommunicating pores and the liquid outside the cement composites will be completed in a short time. Thus, the concentrations of heavy metals in the leachate will be increased rapidly at first. Secondly, the elevated concentration of heavy metals in the leachate could weak the drive of mass transfer. Besides, those refractory phases in the cement composites, will serve as blocking layers, impeding the outward diffusion of heavy metals adsorbed in the closed pores or embedded inside the matrix of cement composites. Lastly, the hydration of cement composites all the way lasts during the whole leaching process, which will lead to a denser structure of cement composites and thus increase the diffusion resistance. Therefore, the leaching rate of heavy metals is much slower in the second stage than that in the first stage. Besides, it also can be seen that the slope of the fitting line decrease with the decrease of particle sizes, indicating that concentration of Ba at the equilibrium state increases with the decrease of particle sizes.
1.2
R =0.959 Coarse particles: y=2.639E-4x+0.005
y=0.006x+0.252 2
a)
2
Fine particles:
R =0.998 y=1.861E-4x+0.006
Compact Coarse particle Fine particle
2
R =0.997
0.8
Compact:
1.6
R =0.958 Coarse particles: y=2.523E-4x+0.006
y=0.008x+0.194
1.4 t/Ct (d·L/µg)
t/Ct (d·L/µg)
1.0
0.8
1.8
0.6
Fine particles:
1.2
Compact:
2
0.7
2
0.6
b)
R =0.993 y=1.812E-4x+0.007 2
R =0.994
1.0
Compact Coarse particle Fine particle
0.6
0.4
0.4
20
40
60
80
100
120
Time (days)
140
160
180
200
R =0.952 y=1.689E-4x+0.004
c)
2
R =0.976
0.4 0.3
Compact Coarse Partcile Fine Particle
0.1
0.2 0
2
Fine particles:
0.2
0.2 0.0
2
R =0.981 Coarse particles: y=1.827E-4x+0.005
0.5
0.8
y=0.004x-0.005
Compact:
t/Ct (d· L/µg)
1.4
0.0
0.0 0
20
40
60
80
100
120
140
Time (days)
160
180
200
0
20
40
60
80 100 120 Time (days)
140
160
180
200
Fig. 5 Second-order reaction kinetics of barium under different leaching conditions: (a) acid water; (b) deionized water; (c) saline water
3.4 The mechanical property of cement composites The mechanical strength of the compact cement composites after the leaching test is determined in Fig. 6. It is known that the leaching medium can influence the strength of cement composites from two opposite aspects (Makhloufi et al., 2012). Firstly, H+ in the leachate can react with cement composites, destroying the structure and thus decreasing the strength of cement composites. Secondly, the leachate can provide the environment for the hydration of
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
cement, which will increase the strength of cement composites. In this study, the effect of H+ on the structure of cement composites will be limited due to highly alkaline environment in the leachate. Therefore, the ongoing hydration reaction during the leaching process could increase the strength of cement composites, especially for the comprehensive strength, as shown in Fig. 6. It also can be seen that the strength of cement composites leached in the saline water are obviously lower than those leached in the acid solution and deionized water, indicating that the saline water can cause the adverse effect on the mechanical strength of cement composites. Besides, the criterion for classifying as material as resistant/durable is expressed as a corrosion index (Ic), which represents the relative strength of samples stored in an aggressive-solution in comparison to a water-stored sample (Frias et al., 2013). Ic of the cement composites prepared by EOPC is 0.8, which can be considered to be irresistible against saline water. Since porosity is an essential parameter for the description of physical properties of any material (Gallé, 2001), MIP tests are performed at the end of the study on the compact cement composites after the leaching test (Table S3 and Fig. S2). It can be seen that the total MIP porosity of the cement composites leached in saline water had the highest overall porosity, indicating that saline water can cause the corrosion of cement composites. Therefore, our results indicate that the cement composites prepared by EOPC should be carefully used in the marine environment.
6
4
2
70 60
b)
50 40
Flexural strength (Mpa)
8
80
Compressive strength (Mpa)
a)
10
30 20 10 0
0 EOPC
EOPC-acid water EOPC-water
EOPC-salt water
EOPC
EOPC-acid water EOPC-water
EOPC-salt water
Fig. 6 The mechanical properties of OPEC under different leaching environment: (a) flexural strength (b) compressive strength
4. CONCLUSION The long-term leaching behaviors of cement composites prepared by EOPC are investigated in this study. Compact and ground (coarse particle and fine particle) cement composites are prepared and the leaching test based on the modified NEN 7375 procedure is conducted in acid water, deionized water and saline water over a time period of 180 days. Our results show that concentration of most heavy metals are below the limitation of corresponding regulation, except for arsenic in the leachate from the cement composites under the saline water condition. Besides, the elevated concentration of V is observed in the leachate of compact cement composites than ground composites. The increased concentration of Ba in the leachate is observed with the decrease of particle size of cement composites. The concentration of Sn increases firstly but decline afterward in the acid water and deionized water and the kinetic
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
study indicated that the leaching of heavy metals follows a second-order model. Furthermore, our results point out that the cement composites prepared by EOPC should be carefully used in the marine environment.
ACKNOWLEDGEMENTS This study was supported by National Science Fund for Distinguished Young Scholars (51522401) and National Natural Science Foundation of China (51472007). This work was also supported financially by Research Funding supported by Shenzhen Science and Technology Innovation Committee (ZDSYS201602261932201).
REFERENCES Amlan Ghosh, Muhammed Mukiibi, A., Ela, W., (2004). TCLP Underestimates Leaching of Arsenic from Solid Residuals under Landfill Conditions. Environ. Sci. Technol. 38, 4677-4682. Bertolini, L., Carsana, M., Cassago, D., Curzio, A.Q., Collepardi, M., (2004) MSWI ashes as mineral additions in concrete. Cement & Concrete Research 34, 1899-1906. Bie, R., Chen, P., Song, X., Ji, X., (2016) Characteristics of municipal solid waste incineration fly ash with cement solidification treatment. Journal of the Energy Institute 89, 704-712. Drinčić, A., Nikolić, I., Zuliani, T., Milačič, R., Ščančar, J., (2017) Long-term environmental impacts of building composites containing waste materials: Evaluation of the leaching protocols. Waste Manage., 340-349. Folgueras, M.B., Alonso, M., Díaz, R.M., (2013) Influence of sewage sludge treatment on pyrolysis and combustion of dry sludge. Energy 55, 426-435. Frias, M., Goñi, S., García, R., Villa, R.V.D.L., (2013) Seawater effect on durability of ternary cements. Synergy of chloride and sulphate ions. Composites Part B Engineering 46, 173–178. Gallé, C., (2001) Effect of drying on cement-based materials pore structure as identified by mercury intrusion porosimetry : A comparative study between oven-, vacuum-, and freezedrying. Cement & Concrete Research 31, 1467-1477. Hohberg, I., Groot, G.J.D., Veen, A.M.H.V.D., Wassing, W., (2000) Development of a leaching protocol for concrete. Waste Manage. 20, 177-184. Jiang-Shan, L.I., Qiang, X., Zhu-Yun, H.U., Xian-Wang, L.I., (2013) Study of strength stability of municipal solid waste incinerator fly ash solidified by cement. Rock & Soil Mechanics 34, 751756. Kai, W., Shi, H., Guo, X., (2011) Utilization of municipal solid waste incineration fly ash for sulfoaluminate cement clinker production. Waste Manage. 31, 2001-2008. Lee, I.H., Wang, Y.J., Chern, J.M., (2005) Extraction kinetics of heavy metal-containing sludge. J. Hazard. Mater. 123, 112. Li, X.G., Lv, Y., Ma, B.G., Chen, Q.B., Yin, X.B., Jian, S.W., (2012) Utilization of municipal solid waste incineration bottom ash in blended cement. J. Clean. Prod. 32, 96-100. Lu, H., Wei, F., Tang, J., Giesy, J.P., (2016) Leaching of metals from cement under simulated environmental conditions. Journal of Environmental Management 169, 319.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Makhloufi, Z., Kadri, E.H., Bouhicha, M., Benaissa, A., Bennacer, R., (2012) The strength of limestone mortars with quaternary binders: Leaching effect by demineralized water. Construction & Building Materials 36, 171-181. Murakami, T., Suzuki, Y., Nagasawa, H., Yamamoto, T., Koseki, T., Hirose, H., Okamoto, S., (2009) Combustion characteristics of sewage sludge in an incineration plant for energy recovery. Fuel Process Technol. 90, 778-783. Pan, J.R., Huang, C., Kuo, J.J., Lin, S.H., (2008) Recycling MSWI bottom and fly ash as raw materials for Portland cement. Waste Manage. 28, 1113-1118. Qi, L., Zhang, Y., Ma, Y., Chen, M., Ge, X., Ma, Y., Zheng, J., Wang, Z., Li, S., (2016) Source identification of trace elements in the atmosphere during the second Asian Youth Games in Nanjing, China: Influence of control measures on air quality. Atmospheric Pollution Research 7, 547-556. Shahnazi, A., Rashchi, F., Vahidi, E., (2012) A Kinetics Study on the Hydrometallurgical Recovery of Vanadium from LD Converter Slag in Alkaline Media. John Wiley & Sons, Inc. Shi, H., Ling, Y., (2003) cementitious reactivity of municipal solid waste incineration fly ash and immobolization effect by cement. Journal of the Chinese Ceramic Society. Shi, H.S., Kan, L.L., (2009) Characteristics of municipal solid wastes incineration (MSWI) fly ash–cement matrices and effect of mineral admixtures on composite system. Construction & Building Materials 23, 2160-2166. Šturm, T., Milačič, R., Murko, S., Vahčič, M., Mladenovič, A., Šuput, J.S., Ščančar, J., (2009) The use of EAF dust in cement composites: Assessment of environmental impact. J. Hazard. Mater. 166, 277. Tang, J., Steenari, B.M., (2016) Leaching optimization of municipal solid waste incineration ash for resource recovery: A case study of Cu, Zn, Pb and Cd. Waste Manage 48, 315-322. Yang, S., Song, H., Xie, R., (1996) XRD Study of Hydration Rate of Cement. Journal of Instrumental Analysis. Yang, Z., Yan, C., Sun, Y., Liu, L., Zhang, Z., Ge, X., (2016) The partitioning behavior of trace element and its distribution in the surrounding soil of a cement plant integrated utilization of hazardous wastes. Environ. Sci. Pollut. R. 23, 13943. Zhou, H.B., Ma, C., Gao, D., Chen, T.B., Zheng, G.D., Chen, J., Pan, T.H., (2014) Application of a recyclable plastic bulking agent for sewage sludge composting. Bioresource Technol. 152, 329.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
SUPPLEMENTARY INFORMATION Table S1 The concentration (μg/L) ranges of the elements in the acidic, deionized and saline leachates from compact, coarse particle and fine particle composites prepared with EOPC during the course of the experiment (180 days).
Element
Acidic Acidic Acidic water water (coarse water (fine (compact) particle) particle)
Deionized water (compact)
Deionized water (coarse particle)
Deionized water (fine particle)
Saline water (compact)
Saline water (coarse
Saline water (fine
particle)
particle)
Maximum permitted values
Cr
0.8-3.5
0.6-2.3
1.1-3.2
0.9-3.5
0.7-1.4
1.1-2.2
41.3-49.3
34.8-55.8
36.3-44.5
300
Mn
0.01-0.2
0.01-0.2
0.01-0.2
0.01-0.5
0.01-0.09
0.01-0.08
0.01-1.1
0.01-0.2
0.01-0.1
1000
Co
0.2-1.6
2.6-11.4
4.2-11.4
0.3-1.6
2.7-11.6
3.3-11.5
0.3-2.1
3.3-12.8
5.2-11.4
/
Ni
2.6-17.6
23.4-126.2
34.4-131.6
3.7-17.3
21.1-103.3
30.4-142.3
34.4-61.4
55.2-93.5
59.5-95.8
300
Cu
1.6-3.0
5.1-12.3
4.5-11.2
1.3-4.5
4.7-13.0
3.8-14.1
12.9-24.9
19.5-35.2
20.4-33.3
1000
Zn
0.01-8.5
0.01-12.9
0.01-10.2
0.01-8.5
0.01-10.3
0.01-14.0
0.01-11.6
0.01-14.9
0.01-8.4
1000
As
0.06-0.5
0.01-0.6
0.01-0.6
0.01-0.6
0.01-0.7
0.01-0.7
0.01-364
0.01-274
0.01-361
100
Cd
0.01-0.02
0.01-0.02
0.01-0.04
0.01-0.02
0.01-0.04
0.01-0.04
0.01-0.1
0.1-0.7
0.3-0.8
100
Pb
0.01-0.08
0.2-2.9
0.3-3.5
0.01-0.04
0.3-3.0
0.2-3.6
0.2-0.8
0.2-5.2
0.3-5.5
300
Sb
0.09-0.3
0.01-0.08
0.01-0.05
0.05-0.3
0.03-0.07
0.02-0.07
0.02-0.07
0.2-0.4
0.2-0.4
/
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Table S2 The pH and electrical conductivity of leachates during the course of the experiment of 180 days
Sample
Time (days)
Parameter
3
7
14
30
60
90 120
150
180
pH
11.5
11.5
11.5
11.5
11.4
11.2
11
11.5
11.5
Conductivity (mS cm-1)
0.5
0.7
0.8
1.0
1.0
0.9
0.9
0.9
0.9
pH
12.2
12.3
12.3
12.1
12
11.6
11.6
11.8
11.8
Conductivity (mS cm-1)
3.2
4.9
5.8
6.2
6.7
6.7
6.7
6.2
6.0
pH
12.4
12.4
12.3
12.2
12.1
11.8
11.6
11.8
11.8
Conductivity (mS cm-1)
3.8
4.7
6.5
6.9
7.5
7.0
7.1
6.8
6.6
pH
11.7
11.6
11.5
11.6
11.5
11.2
11.3
11.4
11.4
Conductivity (mS cm-1)
0.6
0.8
0.9
1.0
0.9
1.0
.0
1.0
0.9
pH
12.3
12.4
12.2
12.3
12.2
12
11.8
11.8
11.8
Conductivity (mS cm-1)
3.3
4.8
5.8
6.4
6.7
6.5
6.1
6.1
5.7
pH
12.5
12.4
12.3
12.2
12.2
12.1
11.9
11.8
11.8
Conductivity (mS cm-1)
3.4
4.2
6.4
7.4
7.5
7.1
6.7
6.7
6.6
pH
11.8
11.9
11.9
11.5
12
11.9
11.6
11.8
11.8
Conductivity (mS cm-1)
44.6
44.7
44.1
42.1
41.3
40.4
39.0
39.8
39.0
pH
12.4
12.3
12.4
12.2
12.3
12.3
11.8
12.1
12.1
Conductivity (mS cm-1)
47.0
46.8
46.7
45.0
44.0
42.7
43.5
43.6
42.3
pH
12.4
12.4
12.4
12.2
12.3
12.3
11.9
12.1
12.1
Conductivity (mS cm-1)
47.0
46.9
47.1
45.3
44.2
42.9
43.7
44.0
42.6
Acidic water: Compact Cc
Coarse Cc
Fine Cc Deionized water: Compact Cc
Coarse Cc
Fine Cc Saline water: Compact Cc
Coarse Cc
Fine Cc
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Table S3 The porosity, average pore diameter and total instrusion volume of compact compistesprepared with EOPC, after 180 days of exposure to acid water, deionized water and saline water.
Sample
Porosity (%)
Average pore diameter (nm)
Total pore volume (mL/g)
Cc (Acid water) Cc (Deionized water) Cc (Saline water)
16.0 12.7
28.6 27.9
0.073 0.064
11.7
33.7
0.051
Fig. S1 Sketch of the leaching behavior of heavy metals in cement composites
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
0.14
Acid water Deionized water Saline water
0.10 0.08
-1
Pore volume (mL· g )
0.12
0.06 0.04 0.02 0.00
1
10
100 1000 Pore size diameter (nm)
10000
Fig. S2 Pore size distribution curves, determinend by MIP, for the investigated compact composites preparedby EOPC, afeter 180 days of exposure to acid water, deinoized water and saline water.
