水泥-过磷酸钙复合材料固化铅污染土的浸出和力学特性
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摘要
水泥是铅污染土固稳修复常用的固化剂,在修复重度铅污染土时效果较差。而过磷酸钙在稳定铅污染土方面具有溶出风险低、长期稳定性好和环境安全性高的优点。为了研究水泥-过磷酸钙复合材料固化后铅污染土的浸出和力学特性,采用水泥-过磷酸钙复合材料对铅污染土进行固化/稳定化处理,通过浸出试验、无侧限抗压强度试验和渗透试验对固化前后的铅污染土固化体进行浸出和力学特性变化特征对比分析,分别探讨了水泥和过磷酸钙添加量对固化土浸出和力学特性的影响规律。结果表明:水泥可显著改善铅污染土的强度和渗透特性,当水泥的添加量从5%增加到30%时,固化土的抗压强度从0.56 MPa增加到4.78 MPa;渗透系数从8.2×10-7cm/s减小到2.2×10-8cm/s。但水泥在固稳高浓度铅污染土效果较差,当水泥的添加量从5%增加到30%时,固化土的浸出浓度从56.3 mg/L减少到19.8 mg/L,固化土的浸出浓度远高于我国危险废弃物鉴别标准(GB/T 5085.3—2007)。过磷酸钙可显著降低污染土中铅的浸出特性,固化土的浸出浓度从43.5 mg/L减少到0.17mg/L;但过磷酸钙会降低固化土的力学性能。随着过磷酸钙添加量从1%增加到5%,固化土的抗压强度从1.17MPa降低到0.42 MPa;渗透系数从3.0×10-7cm/s增加到1.3×10-6cm/s。因此,在铅污染土实际工程中应根据实际的场地工况和修复目标,合理选择水泥和过磷酸钙的配比,保证修复后的铅污染土强度特性和浸出特性均满足修复标准。
Ordinary portland cement(OPC) stabilization was one of practical approaches to remediate soil contaminated with high levels of lead(Pb),however,the OPC had less effective on high levels Pb-contaminated soil. Calcium superphosphate was commonly used for the remediation of high levels Pb-contaminated soils mostly due to its lower leachability,relatively effective and high environmental safety. Cement-calcium superphosphate composite material was used to stabilize/solidify lead-contaminated soils. Leaching test,unconfined compressive strength test and permeability test were conducted to investigate effects of cement and calcium superphosphate dosages on mechanical and leaching properties of cement-calcium superphosphate composite material treated Pb-contaminated soils. Results showed that cement had an inefficient effect on highly concentrated contaminated soil,and the unconfined compressive strength and hydraulic conductivity were improved significantly with the increase in cement dosage. The unconfined compressive strength increased from 0.56 MPa to 4.78 MPa and the hydraulic conductivity decreased from 8.2× 10-7 cm/s to 2.2×10-8 cm/s,while the leaching concentration decreased from 56.3 mg/L to 19.8 mg/L when the cement dosage increased from 5% to 30%. The leaching concentration was above the identification standards for hazardous wastes in China. Cement-calcium superphosphate composite material had an efficient effect on highly concentrated contaminated soil,and leaching concentration decreased significantly with the increase in calcium superphosphate dosage. However,calcium superphosphate could lowered mechanical properties of solidified soil. The unconfined compressive strength decreased from 1.17 MPa to 0.42 MPa,and the hydraulic conductivity increased from 3.0×10-7 cm/sto 1.3×10-6 cm/s when the calcium superphosphate dosage was increased from 0% to 5%. Therefore,the effects of calcium superphosphate on mechanical properties of solidified soil should be completely considered when stabilizing the Pb-contaminated soil using calcium superphosphate.
Ordinary portland cement(OPC) stabilization was one of practical approaches to remediate soil contaminated with high levels of lead(Pb),however,the OPC had less effective on high levels Pb-contaminated soil. Calcium superphosphate was commonly used for the remediation of high levels Pb-contaminated soils mostly due to its lower leachability,relatively effective and high environmental safety. Cement-calcium superphosphate composite material was used to stabilize/solidify lead-contaminated soils. Leaching test,unconfined compressive strength test and permeability test were conducted to investigate effects of cement and calcium superphosphate dosages on mechanical and leaching properties of cement-calcium superphosphate composite material treated Pb-contaminated soils. Results showed that cement had an inefficient effect on highly concentrated contaminated soil,and the unconfined compressive strength and hydraulic conductivity were improved significantly with the increase in cement dosage. The unconfined compressive strength increased from 0.56 MPa to 4.78 MPa and the hydraulic conductivity decreased from 8.2× 10-7 cm/s to 2.2×10-8 cm/s,while the leaching concentration decreased from 56.3 mg/L to 19.8 mg/L when the cement dosage increased from 5% to 30%. The leaching concentration was above the identification standards for hazardous wastes in China. Cement-calcium superphosphate composite material had an efficient effect on highly concentrated contaminated soil,and leaching concentration decreased significantly with the increase in calcium superphosphate dosage. However,calcium superphosphate could lowered mechanical properties of solidified soil. The unconfined compressive strength decreased from 1.17 MPa to 0.42 MPa,and the hydraulic conductivity increased from 3.0×10-7 cm/sto 1.3×10-6 cm/s when the calcium superphosphate dosage was increased from 0% to 5%. Therefore,the effects of calcium superphosphate on mechanical properties of solidified soil should be completely considered when stabilizing the Pb-contaminated soil using calcium superphosphate.
引文
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[2]WEI M L,DU Y J,REDDY K R,et al. Effects of freeze-thaw on characteristics of new KMP binder stabilized Zn-and Pb-contaminated soils[J]. Environmental Science and Pollution Research,2015,22(24):19473-19484.
[3]张亭亭,李江山,王平,等.磷酸镁水泥固化铅污染土的应力-应变特性研究[J].岩土力学,2016,37(S1):215-224.ZHANG T T,LI J S,WANG P,et al. Experimental study of stress-strain properties of lead-contaminated soils treated by magnesium phosphate cement[J]. Rock and Soil Mechanics,2016,37(S1):215-224.
[4]LI J S,XUE Q,WANG P. Comparison of solidification/stabilization of lead contaminated soil between magnesia-phosphate cement and ordinary portland cement under the same dosage[J]. Environmental Progress&Sustainable Energy,2016,35(1):88-94.
[5]YIN C Y,MAHMUD H B,SHAABAN M G. Stabilization/solidification of lead-contaminated soil using cement and rice husk ash[J]. Journal of Hazardous Materials, 2006, 137(3):1758-1764.
[6]CHO J H,EOM Y,LEE T G. Stabilization/solidification of mercury-contaminated waste ash using calcium sodium phosphate(CNP)and magnesium potassium phosphate(MKP)processes[J]. Journal of Hazardous Materials,2014,278:474-482.
[7]ZHANG Z,GUO G,TENG Y,et al. Screening and assessment of solidification/stabilization amendments suitable for soils of leadacid battery contaminated site[J]. Journal of Hazardous Materials,2015,88:140-146.
[8]张亭亭,李江山,王平,等.磷酸镁水泥固化铅污染土的力学特性试验研究及微观机制[J].岩土力学,2016,37(S2):279-286.ZHANG T T,LI J S,WANG P,et al. Experimental study of mechanical and microstructure properties of magnesium phosphate cement lead contaminated soils[J]. Rock and Soil Mechanics,2016,37(S2):279-286.
[9]孙芳利,PROSPER N K,吴华平,等.木竹材防腐技术研究概述[J].林业工程学报,2017,2(5):1-8.SUN F L,PROSPER N K,WU H P,et al. A review on the development of wood and bamboo preservation[J]. Journal of Forestry Engineering,2017,2(5):1-8.
[10]杜延军,蒋宁俊,王乐,等.水泥固化锌污染高岭土强度及微观特性研究[J].岩土工程学报,2012,34(11):2114-2120.DU Y J,JIANG N J,WANG L,et al. Strength and microstructurecharacteristics of cement-based solidified/stabilized zinc-contaminated kaolin[J]. Chinese Journal of Geotechnical Engineering,2012,34(11):2114-2120.
[11]BOARDMAN D J. Lime stabilization:clay-metal-lime interactions[D]. Leicestershire:Loughborough University,1999.
[12]BASTA N T,MCGOWEN S L. Evaluation of chemical immobilization treatments for reducing heavy metal transport in a smelter-contaminated soil.[J]. Environmental Pollution,2004,127(1):73-82.
[13]WANG A J,ZHANG J,LI J M,et al. Effect of liquid-to-solid ratios on the properties of magnesium phosphate chemically bonded ceramics[J]. Materials Science&Engineering C,2013,33(5):2508-2512.
[14] MALONE P G,JONES L W,LARSON R J. Guide to the disposal of chemically stabilized and solidified wastes[M]. Municipal Environmental Research Laboratory,Office of Research and Development,US Environmental Protection Agency,1980.
[15]XUE Q,LI J,LIU L. Effect of compaction degree on solidification characteristics of Pb-contaminated soil treated by cement[J].CLEAN-Soil,Air,Water,2014,42(8):1126-1132.
[16]DU Y J,WEI M L,REDDY K R,et al. New phosphate-based binder for stabilization of soils contaminated with heavy metals:Leaching, strength and microstructure characterization[J].Journal of Environmental Management,2014,146:179-188.
[17]TAN H,MA B,LI X,et al. Effect of competitive adsorption between sodium tripolyphosphate and naphthalene superplasticizer on fluidity of cement paste[J]. Journal of Wuhan University of Technology(Materials Science Edition), 2014, 29(2):334-340.
[18]LTIFI M. Effects of sodium tripolyphosphate on the rheology and hydration rate of Portland cement pastes[J]. Advances in Cement Research,2012,24(6):325-335.
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