淋滤条件下水泥固化铅污染高岭土的强度及 微观特性的研究

通过半动态淋滤试验,研究淋滤液初始pH=2,4,7时水泥固化铅污染土的强度、微观和钙溶出特性。无侧限抗压强度试验及钙溶出率（CFR_Ca）结果表明：半动态淋滤试验使试样无侧限抗压强度（q_u）较标准养护39 d试样降低了1%～42%；淋滤液初始pH=2时,CFR_Ca为pH=4或7时的2～7倍,而pH=4与7时q_u及CFR_Ca差别均不明显；水泥掺量由12%提高到18%时,q_u增大了35%～98%,CFR_Ca降低了40%～58%；固化铅污染土较固化未污染土,其q_u小50%～68%,而CFR_Ca大29%～175%。试样无侧限抗压强度比q_r（淋滤后试样q_u/标准养护39 d试样q_u）与CFR_Ca在双对数坐标下呈现良好线性关系：随CFR_Ca增大,q_r减小,说明钙的溶出是控制固化污染土/未污染土强度的主要因素之一。X射线衍射、扫描电镜及压汞试验结果表明,高浓度铅抑制水泥水化/火山灰反应,固化铅污染土与固化未污染土孔隙分布分别呈单峰和双峰特征,固化铅污染土中铅形成Si-O-Pb结合体、PbAl₂O₄、CaPbO₃等沉淀是铅固化稳定化的主要机理之一。     

酸雨环境下磷酸镁水泥固化锌污染土溶出特性研究

通过对磷酸镁水泥(简称MPC)固化锌污染土进行半动态淋滤试验,以研究酸雨作用下重金属的溶出特性,通过更新淋滤液试验组的浸出液电导率和pH的测试来再次印证Zn~(2+)在半动态淋滤试验中的淋滤特性,并添加普通硅酸盐水泥(简称CEMI)固化土试验组进行对比。通过对MPC固化锌污染土半动态淋滤后浸出液中锌离子浓度的测试,分析淋滤液初始pH值、固化剂类型对MPC固化污染土累积锌溶出特性的影响规律。试验结果表明,CEMI组试样累积锌溶出质量大于MPC组试样;初始淋滤液pH=2时的试样表面溶出锌总量普遍高于pH为4和7,而pH=4和7时的试样表面溶出锌总量比较接近;采用更新淋滤液方式的3组试样溶出的Zn~(2+)量均大于不更新淋滤组;氧化镁与磷酸盐的比值(M/P)为6∶1的试样固化效果优于M/P为3∶1的试样。通过试验数据计算分析,得到了有效扩散系数De;锌的De会随酸雨初始pH的下降而增大,淋滤液初始pH=2时的锌的De普遍大于pH=4,7时的De几个数量级。研究结果表明,酸雨作用下影响磷酸镁水泥固化锌污染土溶出特性的主要因素为水泥固化剂的种类以及酸雨的pH值。     

碳化作用对水泥固化/稳定化铅污染土渗透特性的影响

采用人工配制铅污染土的方法制备不同水泥掺量和不同铅浓度的土样,开展碳化前后水泥固化/稳定化铅污染土的渗透试验,并分析试样的宏观渗透系数和微观孔隙结构之间的内在联系。研究结果表明,水泥掺量增加会降低试样的渗透系数;水泥掺量为7.5%时,碳化作用下渗透系数提高;水泥掺量为15%时,碳化作用下渗透系数降低。铅浓度越高,试样的渗透系数越高,而碳化作用又会增大试样的渗透系数。水泥掺量增加会显著降低试样的孔隙率;碳化作用使得试样中孔径小于0.1μm的孔隙增多,大于0.1μm的孔隙减少。     

磷矿粉稳定铅污染土的溶出特性研究

采用磷矿粉作为稳定剂对铅污染土进行修复处理。通过毒性浸出试验（TCLP）,研究磷矿粉稳定铅污染土的溶出特性,探讨了不同磷矿粉掺量和养护龄期对铅、钙溶出量的影响,分析不同初始铅浓度作用下铅、钙的溶出规律。结果表明：铅溶出量随磷矿粉掺量和养护龄期的增加而减小,钙溶出规律与之相反,钙溶出量与铅溶出量存在线性负相关性;稳定污染土和浸出液的pH值受初始铅浓度影响显著,并随着磷矿粉掺量增加而逐渐增大。     

碱激发高炉矿渣固化铅污染土酸缓能力、强度及微观特性研究

采用碱激发高炉矿渣对铅污染土进行固化稳定处理,并研究其固化稳定机理。结果表明:随着固化剂掺量提高,GGBS-MgO固化铅污染土酸缓能力的固化污染土酸缓冲系数β随之提高;铅能够抑制GGBS-MgO进行水化反应,致使GGBS-MgO固化铅污染土比表面积远低于同掺量的固化未污染土;GGBS-MgO固化铅污染土q_u均低于相同掺量下固化未污染土,且无侧限抗压强度与其比表面积间存在明显的线性关系;SEM和XRD结果显示,GGBS-MgO固化铅污染土和固化未污染土的试样,主要水化产物都为C-S-H与Ht;累积进汞量和孔径直径结果显示,GGBS-MgO固化未污染土累积进汞量高于固化铅污染土。     

水泥固化重金属铅污染土的强度特性研究

污染场地中开挖出来的污染土利用水泥固化处理（S/S法）后,其污染物质的淋滤特性和土体的强度得到改善,可用于场地的回填和堤坝的填筑等。针对该项技术,对水泥固化稳定后的重金属铅污染土的强度特性进行了研究。试验所用的铅污染土通过将硝酸铅溶液加入干土中人工制备而成,并考虑了不同铅离子含量和水泥掺量对水泥固化污染土强度特性的影响。试验结果表明：水泥固化污染土的无侧限抗压强度随着水泥掺量以及龄期的增长而提高;与常规水泥土（不含重金属污染物）强度相比,污染土中铅离子含量较低时,强度略有提高,铅离子含量较高时,强度显著降低;不同铅含量水泥土试样的应力应变关系均表现为强度越高,破坏应变越小;试样28 d龄期的变形模量与强度呈较好的线性对应关系。     

酸溶液淋溶作用下重金属污染土固化体浸出特性及机理

采用KH_2PO_4—水泥复合材料对铅污染土进行固化/稳定化处理,为了研究酸雨淋溶对铅污染土固化体浸出特性的影响规律及其机理,开展了不同KH_2PO_4添加量、浸出时间和淋溶液pH对Pb浸出行为的影响规律试验研究。探讨了铅污染土固化体浸出机理。结果表明,KH_2PO_4对铅污染土有良好的稳定作用。酸溶液淋溶作用下固化体中Pb的释放行为与pH直接相关,强酸作用下Pb的溶出量大。固化体中Pb的浸出也与浸出液pH相关,强碱性有利于Pb的迁移。浸出液pH与固化体中的碱性水化产物释放量有关。对于pH=2和5溶液,Pb的累积浸出率随时间呈线性变化,而对于pH=3溶液,Pb的累积浸出率随时间呈两阶段线性变化。固化体在pH=2溶液浸泡下,Pb的释放机理为溶解控制;对于pH=3溶液浸泡,机理则为先溶解控制再表面冲刷;而对于pH=5溶液浸泡,Pb的释放机理为扩散控制。     

含磷材料固化锌、铅污染土的路用性能试验研究

采用新型含磷材料(KMP)及水泥(PC)分别对锌、铅污染土进行固化处理。通过无侧限抗压强度、水稳性、回弹模量和压汞试验,探究固化污染土作为路基填料的力学及耐久特性。结果表明:常规养护条件下,KMP和PC固化污染土强度随龄期和掺量增长而提高,强度越大;锌、铅复合污染条件下,固化污染土强度最低。经过泡水试验,固化试样强度均有所下降且7d强度损失较高;铅、锌复合污染条件下,强度降低幅度最高,水稳系数为0.52~0.58。固化污染土回弹模量低于固化未污染土但高于未固化污染土回弹模量,且KMP试样回弹模量高于水泥试样回弹模量的6.7%~24.2%。相对PC固化污染土,KMP试样微孔隙多、中、大孔隙较少,结构致密。     

酸雨入渗对水泥固化铅污染土淋滤特性的影响研究

以水泥固化铅污染土（Pb-CHMS）为研究对象，通过Batch淋滤试验和柔性壁土柱酸雨入渗试验，对Pb-CHMS在酸雨作用下的淋滤特性进行了研究。Batch试验结果表明，当酸雨pH=2.5时，滤出液pH显著降低，钙（Ca）浓度显著增加；铅（Pb）浓度则随pH降低而减小。柔性壁土柱酸雨入渗试验结果表明，Pb-CHMS渗透系数随渗透量和时间增加而降低，酸雨入渗导致渗透系数降低速率减缓；pH、Ca和Pb溶出量随渗透量降低；并建立了Pb-CHMS室内土柱酸雨入渗时间与所模拟的固化污染土体酸雨入渗时间的关系。     

NaOH对固化海涂淤泥强度和变形特性的影响研究

在海涂淤泥中掺入不同量NaOH改变淤泥孔隙溶液的pH值,再掺入等量水泥做固化试验.通过室内试验测试淤泥固化土的基本力学性质,探讨NaOH对仅用水泥固化淤泥的改善作用,研究无侧限抗压强度与NaOH掺量的关系和各个龄期淤泥固化土的应力一应变关系,并分析固化淤泥的微观结构特征.研究表明,NaOH掺量不大于0.8%时,孔隙溶液pH值的改变对Ca (OH)<,2>浓度影响很小,对固化强度的改善效果不明显;NaOH掺量大于1.6%时,随着掺量的增大,可以较大地提高淤泥固化强度,破坏应变较小,具有脆性破坏性质;NaOH掺量为3.2%时,90d强度约为不掺NaOH固化淤泥的2倍;微观结构反映出各种状态水化产物形成网状骨架并且填充孔隙,使得固化土具有一定的强度.     

酸雨作用下含磷固化剂处理铅锌镉复合污染土的半动态浸出试验研究

酸雨pH可显著影响固化重金属污染土的浸出量。定量评价固化污染土在暴露条件下(例如酸雨)对周边水土体环境的影响,需要明确固化污染土的有效扩散系数和阻滞因子这两个关键参数。现有研究多集中在固化污染土的浸出特性和表观扩散系数,有关有效扩散系数和阻滞因子的研究很少。本次研究旨在研究改进的KMP固化剂固化重金属Pb、Zn、Cd复合污染土在酸雨作用下的有效扩散系数和阻滞因子。解吸附试验表明,随着污染土中重金属Pb、Zn、Cd浓度增加,固化污染土的解吸附量增大,且解吸附曲线满足Freundlich平衡吸附/解吸附方程。半动态浸出试验结果表明,污染土中重金属Pb、Zn、Cd浸出机制主要由扩散控制,且拟合曲线斜率分别为0.60,0.56和0.61,表观扩散系数Dobs为1.05×10~(-16),7.84×10~(-13)和2.11×10~(-12) m~2/s。结合解吸附试验和半动态浸出试验结果可知,Pb、Zn、Cd的阻滞因子Rd分别为17165.6,254.6和109.3,有效扩散系数De分别为1.82×10~(-12),1.96×10~(-10),2.34×10~(-10) m~2/s。与其他学者结果相比,固化污染土中Pb的有效扩散系数低于其他学者的两个数量级,而Zn和Cd的求算结果与其他学者一致。     

Stabilisation/solidification of lead-contaminated soil by using ladle furnace slag and carbon dioxide

Global sustainable development faces challenges in greenhouse gas emission, consumption of non-renewable resource and energy, waste landfilling, and environmental pollution. Geotechnical engineering also faces similar challenges; for example, the use of cement and lime for stabilisation/solidification (S/S) of contaminated soil is associated with carbon dioxide (CO₂) emission and consumption of limestone and energy. In this context, this study introduces a sustainable S/S method by using an industrial waste, ladle furnace slag (LFS), and a greenhouse gas, CO₂, to replace common additives for S/S of lead (Pb)-contaminated soil. LFS was first mixed with Pb-contaminated soils and then CO₂ was introduced into the soil for carbonation. The results showed that LFS-stabilised Pb-contaminated soils could achieve CO₂ uptake up to 18% of LFS mass. After carbonation, the concentration of leached Pb from contaminated soils was reduced by three orders of magnitude than that without carbonation, demonstrating higher S/S efficacy than cement, lime, and magnesia. Additionally, this method can improve soil strength, as well as reduce non-renewable resource consumption, energy use, LFS landfilling, and additive cost.     

硫酸钠溶液pH值对硅酸盐水泥砂浆析钙及侵蚀产物的影响

将水泥砂浆浸泡在pH值为5,9,13的Na_2SO_4溶液中至330d,采用化学滴定法测定砂浆中Ca~(2+),OH~-的析出量,采用X射线衍射(XRD)仪和差示扫描量热法(DSC)对不同侵蚀龄期下侵蚀产物进行半定量分析,并通过扫描电子显微镜(SEM)对钙硅比和微结构进行了分析.结果表明:溶液pH值越低,Ca~(2+)析出速率越快、析出量越大,且低pH值条件下Ca~(2+)的大量析出有助于其与侵入的SO_4~(-2)结合,形成更多低溶解度的CaSO_4·2H_2O,从而加速Ca~(2+)析出和SO_4~(-2)扩散渗入;低pH值环境下大量石膏的形成伴随着Ca(OH)_2的大量消耗,且会引起C-S-H凝胶的脱钙,导致水泥砂浆的胶凝性降低,引起试件的软化和剥落.     

Heavy metal stabilization in contaminated road-derived sediments

There is increasing interest in the stabilization of heavy metals in road-derived sediments (RDS), to enable environmentally responsible reuse applications and circumvent the need for costly landfill disposal. To reduce the mobility of heavy metals (i.e. Cu, Pb and Zn) the effectiveness of amendments using phosphate, compost and fly ash addition were investigated using batch leaching experiments. In general, phosphate amendments of RDS were found to be ineffective at stabilizing heavy metals, despite being used successfully in soils. Phosphate amendment resulted in enhanced concentrations of dissolved organic carbon (DOC), which increased the solubilisation of heavy metals via complexation. Amendment with humified organic matter (compost) successfully stabilized Cu and Pb in high DOC leaching RDS with an optimum loading of 15-20% (w/w). Compost, however, was ineffective at stabilizing Zn. Increasing the pH by amending RDS/compost blends with 2.5-15% (w/w) coal fly ash resulted in the stabilization of Zn, Cu and Pb. However, above a pH of ∼ 7.5 and 8 enhanced leaching of organic matter resulted in an increase in leached Cu and Pb, respectively. Accordingly, the optimum level of fly ash amendment for the RDS/compost blends was estimated to be ca. 10%. Boosted regression trees analysis (BRT) of the data revealed that DOC accounted for 56% and 65% of the Cu and Pb leaching, respectively, whereas pH only accounted for ca. 18% of Cu and Pb leaching. RDS sample characteristics (i.e. metal concentrations, size fractionation and organic matter content) were more important at reconciling the leaching concentrations of copper Cu (27%) than Pb (16%). The most important parameter explaining Zn leaching was pH. Overall, the choice of a suitable stabilization agent/s depends on the composition of RDS with respect to the amount of organic matter present, and the sorption chemistry of the heavy metal of interest.     

Comparative value of phosphate sources on the immobilization of lead, and leaching of lead and phosphorus in lead contaminated soils

The mobility and bioavailability of lead (Pb) in soils can be mitigated by its immobilization using both soluble and insoluble phosphate (P) compounds. The effectiveness of insoluble P sources on Pb immobilization depends on their rate of dissolution which can be enhanced by phosphate solubilizing bacteria (PSB). In this study, the effect of soluble (potassium dihydrogen phosphate) and insoluble (rock phosphate in the presence and absence of PSB) P compounds on the immobilization of Pb, and leaching of Pb and P was examined using both naturally contaminated (SR soil: NH₄NO₃ extractable Pb: 28.7 mg/kg, pH: 5.88, organic matter: 0.7%) and Pb spiked (AH soil: NH₄NO₃ extractable Pb: 42.7 mg/kg, pH: 5.23, organic matter: 10.9%) soils. Phosphate compounds were added at the rate of 200 mg P/kg and 800 mg P/kg for SR and AH soils, respectively. Soluble P treatment immobilized 80% and 57% of Pb in SR and AH soils, respectively. Insoluble rock phosphate immobilized 40% and 9% of Pb without PSB, and 60% and 17% with PSB in SR and AH soils, respectively. Lead leaching was the lowest when soils were amended with rock phosphate in the presence of PSB, which reduced Pb leaching by 36% for SR soil and 18% for AH soil compared to the control. The leaching of Pb increased when the soils were amended with soluble P because soluble P treatment increased dissolved organic carbon (DOC) concentration of soil, thereby increasing Pb mobility. Soluble P treatment significantly increased P leaching and 9% of total added P was leached from low P retaining AH soil. The optimum level of P amendment is a critical issue when soluble P is used as a Pb immobilizing agent because of eutrophication resulting from excessive P leaching to surface and ground water. While the soluble P compound was effective in the immobilization of Pb, it resulted in P leaching which increased with increasing levels of P addition. However, rock phosphate amendment with PSB achieved the immobilization of Pb with a minimum effect on both Pb and P leaching.     

水泥固化重金属污染土的淋滤特性试验研究

固化稳定法是目前处理重金属污染土场地的常用方法之一。经过处理后的污染土,不仅在强度上有所提高,而且重金属污染离子亦能被有效固化稳定下来。目前,这方面的研究成果主要集中在固化污染土的工程性质变化方面,而对固化土中的重金属离子的滤出特性研究较少。通过系统的室内试验,以经水泥固化后的铅和锌污染土为研究对象,着重研究固化污染土中重金属离子的淋滤特性。试验结果表明:水泥固化重金属污染土后,随着固化剂掺量和养护龄期的增加,重金属的滤出率显著降低,并最终趋于稳定。在污染物掺量较低时,水泥对Pb2+的固化效果好于对Zn2+的固化效果;随着污染物掺量的增加,滤出液中Pb2+浓度的增幅要大于Zn2+浓度增幅。在污染物掺量较高时,水泥对Zn2+的固化效果好于对Pb2+的固化效果。