Stabilization-based soil remediation should consider longterm challenges

Soil remediation is of increasing importance globally, especially in developing countries. Among available remediation options, stabilization, which aims to immobilize contaminants within soil, has considerable advantages, including that it is cost-effective, versatile, sustainable, rapid, and often results in less secondary pollution. However, there are emerging challenges regard- ing the long-term performance of the technology, which may be affected by a range of environmental factors. These challenges stem from a research gap regarding the development of accurate, quantitative laboratory simula- tions of long-term conditions, whereby laboratory accel- erated aging methods could be normalized to real field conditions. Therefore, field trials coupled with long-term monitoring are critical to further verify conditions under which stabilization is effective. Sustainability is also an important factor affecting the long-term stability of site remediation. It is hence important to consider these challenges to develop an optimized application of stabilization technology in soil remediation.

Effects of sepiolite on stabilization remediation of heavy metal-contaminated soil and its ecological evaluation

Stabilization in the remediation of heavy metal contaminated soils has been gaining prominence because of its cost-effectiveness and rapid implementation. In this study, microbial properties such as microbial community and enzyme activities, chemical properties such as soil pH and metal fraction, and heavy metal accumulation in spinach （Spinacia oleracea） were considered in assessing stabilization remediation effectiveness using sepiolite. Results showed that soil pH values increased with rising sepiolite concentration. Sequential extraction results indi- cated that the addition of sepiolite converted significant amounts of exchangeable fraction of Cd and Pb into residual form. Treatments of sepiolite were observed to reduce Cd and Pb translocation from the soil to the roots and shoots of spinach. Concentrations of Cd and Pb exhibited 12.6%-51.0% and 11.5%-46.0% reduction for the roots, respectively, and 0.9%-46.2% and 43.0%- 65.8% reduction for the shoots, respectively, compared with the control group. Increase in fungi and actinomycete counts, as well as in catalase activities, indicated that soil metabolic recovery occurred after sepiolite treatments.

Residual effects of tobacco biochar along with different fixing agents on stabilization of trace elements in multi-metal contaminated soils

The residual effect of tobacco biochar(TB≥500°C)mono and co-application with Cahydroxide(CH),Ca-bentonite(CB)and natural zeolite(NZ)on the bio-availability of trace elements TE(s)in alkaline soils has not been deeply studied yet.A pot study that had earlier been investigated TB mono and blended with CH,CB and NZ on the immobilization of Pb,Cu Cd,and Zn by Chinese cabbage.Maize crop in the rotation was selected as test plant to assess the residual impact of amendments on stabilization of Pb,Cu Cd,and Zn in mine polluted(M-P),smelter heavily and low polluted(S-HP and S-LP,respectively)soils.The obtained results showed that stabilization of Pb,Cd,Cu and Zn reached 63.84% with TB+CB,61.19% with TB+CH,83.31% with TB+CH and 35.27% with TB+CH for M-P soil,36.46% with TB+NZ,38.46% with TB+NZ,19.40% with TB+CH and 62.43% with TB+CH for S-LP soil,52.94%TB+NZ,57.65% with TB+NZ,52.94% with TB+NZ,and 28.44% with TB+CH for S-LP soil.Conversely,TB+CH and TB alone had mobilized Pb and Zn up to19.29% and 34.96% in M-P soil.The mobility of Zn reached 8.38% with TB+CB and 66.03% with TB for S-HP and S-LP soils.The uptake and accumulation of Pb,Cd,Cu and Zn in shoot and root were reduced in three polluted soils.Overall,the combination of TB along with CH,CB and NZ has been proven to be effective in Pb,Cd,Cu and Zn polluted mine/smelter soils restoration.

Effect of cyclic drying and wetting on engineering properties of heavy metal contaminated soils solidified/stabilized with fly ash

Solidification/stabilization （S/S） is one of the most effective methods of dealing with heavy metal contaminated soils. The effects of cyclic wetting and drying on solidified/stabilized contaminated soils were investigated. A series of test program, unconfined compressive strength （UCS） test, TCLP leaching test and scanning electron microscopy （SEM） test, were performed on lead and zinc contaminated soils solidified/stabilized by fly ash. Test results show that UCS and the leaching characteristics of heavy metal ions of S/S contaminated soils are significantly improved with the increase of fly ash content. UCS of S/S soils firstly increases with the increase of the times of drying and wetting cycles, after reaching the peak, it decreases with it. When the pollutant content is lower （1 000 mg/kg）, the TCLP concentration first slightly decreases under cyclic drying and wetting, then increases, but the change is minor. The TCLP concentration is higher under a high pollutant content of 5 000 mg/kg, and increases with the increase of the times of drying and wetting cycles. The results of scanning electron microscopy （SEM） test are consistent with UCS tests and TCLP leaching tests, which reveals the micro-mechanism of the variations of engineering properties of stabilized contaminated soils after drying and wetting cycles.

土壤改进剂在重金属污染修复中的应用研究进展

自然和人为活动排放到环境中的重金属可能对人类健康、生态环境、经济和社会发展产生有害影响,因此重金属污染土壤的修复近年来备受关注。在重金属污染土壤的几种修复技术(物理修复、化学修复和生物修复)中,利用土壤改进剂的金属稳定技术受到了相当大的关注,是一种很有前景的土壤化学修复方法。文章综述了近年来国内外土壤改进剂在修复重金属污染土壤方面的研究进展,包括黏土矿物、含磷材料、金属和金属氧化物等无机材料,有机质、城市固体废物和生物炭等有机材料,以及一些有机、无机材料联合施用在重金属污染土壤修复中的应用。这些改进剂通过吸附、络合、沉淀和氧化还原等多种修复过程,有效地降低了土壤中重金属的生物有效性。最后,文章展望了今后的研究方向:应继续加强改进剂的基础理论研究,明确化学稳定过程和重金属修复机制,以促进该领域的发展,为重金属在污染土壤中的稳定修复研究和实践提供有价值的参考。

土壤修复一体机在重金属污染土壤修复中的应用

对于重金属污染土壤,固化稳定化技术具有效率高、修复周期短、普适性强等显著优势,是目前较为有效的修复技术。文章介绍了重金属污染土壤修复设备在工程应用中存在的问题,并介绍了XF150土壤修复一体机。该设备性能满足重金属污染修复的技术指标和要求,已成功应用于多个修复项目。

铅锌冶炼厂土壤污染治理研究

以某铅锌冶炼厂周边土壤为研究对象,综合运用土壤学、环境科学和生态修复技术,探讨了土壤中重金属污染的特征及其治理方法。首先,通过土壤样品采集与实验室分析,确定土壤中主要重金属污染物种类及其含量水平,评估污染程度和空间分布特征。其次,基于污染特征,筛选适宜的物理、化学和生物修复技术,包括土壤固化/稳定化、电动修复、植物修复和微生物修复等,对比分析各种技术的优势与局限性。进一步结合场地条件和污染特征,选择土壤固化/稳定化修复方案。研究结果表明:土壤固化/稳定化修复方案能够有效降低土壤中重金属含量,恢复土壤生态功能,为类似铅锌冶炼厂污染场地的土壤污染治理提供了科学依据和技术支持。

比较三种稳定剂对FeS纳米颗粒的稳定效果及对水土中镉的固定与去除性能的影响

本研究评估了三种多糖稳定剂(羧甲基纤维素钠(CMC)、羧甲基淀粉钠(CMS)和一种水溶性淀粉)用于稳定FeS纳米颗粒的有效性,并测试了相应稳定化纳米颗粒在水和土壤中固定Cd^(2+)的性能。使用0.010 wt%CMC、0.025 wt%CMS或0.065 wt%淀粉可获得完全稳定的FeS纳米颗粒(100 mg/L FeS)。CMC-FeS表现出较高的zeta负电位,淀粉-FeS保持中性,而CMS-FeS则表现出中等负电位。CMCFeS对Cd^(2+)的吸附速率最快,吸附容量也最高。当用100 mg/L CMC-FeS或CMS-FeS处理一种含Cd土壤(58.3 mg/kg Cd)后,Cd的TCLP浸出率分别降低了88.4%和68.0%。CMC-FeS和CMS-FeS均可在模型土壤中运移,显示出其在土壤中原位固定Cd^(2+)方面的潜力。土壤穿透曲线实验表明,CMC-FeS在4.5个孔体积,CMS-FeS在约25个孔体积处几乎完全穿透。柱实验结果表明,当用55个孔体积的CMC-FeS或CMS-FeS悬浮液(100 mg/L)处理该含Cd土壤后,Cd的水浸出率分别降低了98.2%和98.0%。根据目标污染物、材料在土壤中的传输特性和材料成本,可找到这三种稳定剂在土壤修复中的最佳应用。

某铅污染土壤异地修复工程稳定化药剂筛选研究

本研究对某地块异地修复处置项目的碱性含铅污染土壤开展稳定化修复小试实验,实验结果表明含磷酸盐稳定化药剂复合药剂A和复合药剂B均适用于本项目污染土壤的稳定化修复。在单独施用的情况下,复合药剂B的修复效率高于复合药剂A,复配添加少量低浓度柠檬酸能提升复合药剂A的稳定化修复效率。综合考虑两种稳定化药剂的药剂成本和本小试实验结果,建议修复工程选用复合药剂A复配少量低浓度柠檬酸作为改良的复合稳定化药剂。此外实验结果还表明,对于土壤pH值较高的铅污染土壤,偏酸性含磷酸盐稳定化药剂的稳定化修复效果可能比偏碱性含磷酸盐稳定化药剂更佳。

异位固化/稳定化技术修复重金属污染土壤案例分析

采用异位固化稳定化技术对某工业园废弃遗留地块重金属污染土壤进行土壤重金属修复。具体工艺为“废渣土壤+水泥+石灰+稳定剂(氯化铁)”。污染土壤修复流程为:拆除修复地块硬化地坪;清挖污染土壤,转运至地块内遗留车间进行暂存及修复,分批次进行固化稳定化处理;利用修复土壤,通过养护、检验等手段将处理达标的土壤外运用于工业用地或路基填埋。修复后土壤样品的浸出液pH检测最大值为8.56,Cu、Pb、Zn、Cd、As、Ni、Be、Sb、Co检测最大值分别为0.0044、0.0090、0.9989、0.0034、0.0320、0.0052、0.0004、0.0090、0.0209 mg L,达到各重金属修复标准限值。

某冶炼厂重金属污染土壤修复案例研究

重金属是土壤修复工程中常见的污染物之一,重金属污染在土壤中迁移性较弱,现有修复技术很难去除,其易随食物链进入人体,潜在危害大。该文以某冶炼厂重金属污染土壤修复案例为研究重点,对项目概况、修复工艺选择、方案设计及修复自检进行分析,为各地实施类似冶炼厂重金属污染场地修复提供思路和经验参考。

铁基凝胶材料对镉砷复合污染土壤的稳定化效果研究

以镉砷复合污染土壤为研究对象,采用铁盐与海藻酸钠(SA)为原料,通过碱性-交联法制备了一类铁基凝胶稳定材料,考察了不同铁盐类型和铁盐掺入量制备的凝胶材料对污染土壤中Cd和As的同步稳定效果。结果表明:以FeCl_(3)作为铁盐原料,m(FeCl_(3))∶m(SA)=0.88∶1.00条件下制备的铁基凝胶材料F1(1)对Cd和As的同步稳定效果最佳。当铁基凝胶材料F1(1)添加质量比为5%时,土壤中Cd和As的稳定效率分别为87.76%和93.42%,镉砷同步稳定权衡值T显著降低至1.45。稳定15 d后,土壤中Cd的稳定效率降为82.94%,As的稳定效率上升至97.38%,镉砷同步稳定权衡值T为1.55。

固定剂及其在重金属污染土壤修复中的应用

由于人类的过度开发,部分地区土壤重金属污染日趋严重。采用向污染土壤中施加各类固定化试剂,通过其对重金属的吸附、沉淀(共沉淀)、离子交换及络合作用等将重金属固定在土壤中,降低其在环境中的迁移性和生物可利用性,最终达到减少重金属污染环境风险的目标,是修复重金属污染土壤的有效手段之一。本文概述了近年来国内外报道的各种土壤固定剂及其在重金属污染土壤修复中的应用和修复机理,并从构效关系等角度出发,展望了固定剂在土壤修复应用中的未来发展。

生物炭对矿区土壤重金属有效性及形态的影响

为探索生物炭作为改良剂修复矿区重金属污染土壤的可行性,以玉米秸秆为原料在450℃制备生物炭,采用扫描电镜、能谱分析以及傅里叶变换红外光谱等分析与测试手段对其进行表征。采用室内连续培养的方法,研究在不同培养时间条件下,添加不同施用量(0、1%、3%和5%)的生物炭后,对矿区土壤pH,阳离子交换量(CEC),土壤重金属Cu、Zn、Pb和Mn有效性以及重金属不同形态变化的影响。结果表明:生物炭能够提高土壤的pH和CEC,且都随着添加量的增加而增加。56d土壤培养后,与对照相比,1%、3%和5%添加水平下pH分别增加了1.14个、1.42个和1.67个单位,土壤CEC分别增加了2.02cmol/kg、3.60cmol/kg和5.39cmol/kg。添加不同含量生物炭后,土壤中有效态重金属均呈现不同程度的降低,而且生物炭添加量越大,降幅也越大。在5%添加水平下,生物炭分别使Cu、Zn、Pb和Mn有效态下降了49.2%、46.2%、72.5%和26.3%。重金属有效态含量与土壤pH、CEC均呈显著负相关关系。添加生物炭后,土壤中重金属的形态发生了变化,由易迁移的弱酸提取态向更加稳定的残渣态转化,且生物炭添加量越大,钝化效果越显著。综上所述,玉米秸秆生物炭的添加提高了矿区重金属复合污染土壤的pH和CEC,促进了重金属复合污染土壤中Cu、Zn、Pb和Mn的弱酸提取态向化学性质稳定的残渣态转化,降低了土壤重金属的有效性,实现了对重金属复合污染土壤的修复。

磷酸盐修复重金属污染土壤的研究进展

从研究方法、反应机理以及风险评价等方面综述了磷酸盐修复重金属污染土壤的研究进展,分析和讨论了其中存在的问题和不足,提出了今后加强研究的重点。目前磷酸盐修复重金属污染土壤时,使用的主要研究方法有化学形态提取法、化学平衡形态模型法和光谱及显微镜技术,各个方法都有其优缺点,应该结合使用并探索新方法。磷酸盐稳定重金属的作用机理主要有3个:磷酸盐诱导重金属吸附、磷酸盐和重金属生成沉淀或矿物和磷酸盐表面吸附重金属,但磷酸盐与重金属反应的机理十分复杂,人们尚不完全清楚,因此难以有效区分和评价诱导吸附机理和沉淀机理或其它固定机理,相应地对磷酸盐修复重金属的长期稳定性难以预测。磷酸盐修复重金属污染土壤时由于其较高的施用量可能会造成磷的积聚从而引发一些环境风险,如磷淋失造成水体富营养化,营养失衡造成作物必需的中量和微量元素缺乏以及土壤酸化等。所以应该谨慎选择磷肥种类和用量,最好是水溶性磷肥和难溶性磷肥配合、磷肥与石灰物质等配合施用。今后应着重研究磷酸盐与重金属相互作用的机理区分和评价;关注磷酸盐修复重金属污染土壤时存在的潜在风险,特别是加强植物长期不断吸收磷或其它环境条件变化致使土壤磷素持续减少过程中稳定的重金属溶解性和移动性的研究,磷酸盐修复重金属污染土壤的长期田间实践等。

纳米羟基磷灰石钝化修复重金属污染土壤的稳定性研究

为评估纳米羟基磷灰石（Nano-hydroxyapatite,NAP）钝化修复重金属污染土壤的稳定性,采用一次性添加不同用量（0.5%、1%、2%,W/W）的NAP进行水稻盆栽试验,研究了一年和三年后土壤性质、有效态重金属（Cd、Cu、Zn、Pb）含量和水稻体内重金属含量的变化。结果表明：不同NAP施用量下土壤p H值在第一年和第三年分别显著提高了0.71～1.24和0.60～1.16,年际间p H提高幅度的差异较小,表现出较好的稳定性;第三年土壤中有效态Cd、Cu和Zn含量与对照相比降幅（62.7%～96.5%）要显著低于第一年（66.6%～98.4%）,而有效态Pb含量的降幅（百分比）则略有提高,表明随着时间的延长,NAP固定土壤Cd、Cu和Zn含量的能力有所减弱,而对Pb的固定能力有所增强。添加NAP显著降低了水稻根中的重金属含量和糙米中Cd含量,糙米中的Pb、Cu和Zn含量也有所降低。糙米中重金属含量与土壤中有效态重金属含量呈正相关关系,表明NAP通过降低土壤有效态重金属来降低重金属在水稻籽粒中的累积。

湖北某重金属污染土壤稳定化/固化治理工程实例

为保证南水北调水源地水质安全,该项工程对湖北省郧县境内4个关停搬迁企业原址约16万m3重金属污染土壤进行了修复治理。污染土壤清挖标准为《展览会用地土壤环境质量标准》(HJ350—2007)A级标准,污染土壤无害化处理验收标准为浸出液浓度低于《地表水环境质量标准》(GB3838—2002)中IV类水体标准值。工程采用异位稳定化/固化技术对重金属污染土壤进行了无害化处理,所用稳定化/固化药剂为施工单位自主研发的硫系和铁系稳定化药剂;无害化处理后的近20万m3土壤采用安全填埋进行处置。工程的成功实施为南水北调库区水质安全提供了有力保障。

土壤重金属污染的工程危害及修复方法

分析了重金属污染对地基土和地下结构物的危害,比较了电动修复、土壤冲刷、原位土壤淋洗、化学固化修复土壤的优缺点,重点介绍固化/稳定化技术在修复重金属污染土壤中的应用。

稳定化技术对土壤重金属污染修复的试验研究

以两种不同性质土壤为基质,通过添加可溶性的Cd、Zn、Pb、Cu盐形成土壤重金属复合污染。采用USEPA的毒性浸出试验(Toxicity Characteristic Leaching Procedure,TCLP)对由硫化钙、过磷酸钙、氢氧化钙组成的复合修复剂进行试验研究。结果表明:(1)土壤在添加可溶性盐后p H降低。可溶性重金属盐加入越多,p H下降越多。(2)从水溶态的平均百分比来看,Cd(12.9%)>Zn(7.1%)>Cu(3.4%)>Pb(0.7%)。4种重金属中,除Cd的水溶态比例高于10%外,其他3种重金属的水溶态比例均低于10%。(3)试验设计的方案1为:硫化钙0.5%+过磷酸钙1%+氢氧化钙0.1%+去离子水20%。方案2为:硫化钙2%+过磷酸钙1%+氢氧化钙0.5%+去离子水20%。(4)对于Cd和Zn,方案2优于方案1。方案2对土壤重金属消减率[Cd(89.7%)、Zn(99.7%)]大于方案1的消减率[Cd(88.9%)、Zn(95.7%)]。对于Cu和Pb,方案1优于方案2。方案1消减率Cu为67.2%、Pb为53.9%。

Evaluation of immobilizing agents as soil quality conditioners in addition to their metal(loid) immobilizing effect

In trace metal (TM)-contaminated agricultural soils,management of TM availability is important for safe crop production.In addition,maintenance or improvement of soil quality is vital for sustainable crop cultivation.Decreased TM phytoavailability and increased soil quality can be achieved by the application of various immobilizing agents to soil,which can supply both macronutrients and organic matter.This study investigated the long-term influences of four common immobilizing agents on soil biogeochemical properties and the phytoavailability of TMs in mixed metal-contaminated soil from a cultivated upland near an abandoned mining site.Lime (L),gypsum (G),fly ash (F),and animal manure-based compost (C) were applied to pots containing contaminated soil,either individually or in combination.After incubation for three years under sequential cultivation of two crops and fallow,soil biogeochemical properties were determined,and Brassica rapa plant bioassay was performed.The phytoavailability of all TMs (both cationic metals and anionic metalloids) remained significantly lower in soils treated with immobilizing agents even after three years,when compared with the no-agent control (CK) soil.In addition,the soil quality was significantly improved by treatment with immobilizing agents.For instance,the C and L+C treatments were the most effective in improving soil physical (bulk density,porosity,and water-resistant aggregate stability),chemical (pH,organic matter,total nitrogen,cation exchange capacity,and plant-available phosphorus,magnesium,and potassium),and biological (microbial biomass carbon and dehydrogenase activity) properties.The improvement of soil properties and lowering of TM bioavailability were also consistent with the most significant increase in B.rapa biomass production observed in the C treatment,followed by the L+C,G+F,L,G,F,and L+G treatments,as compared with that in CK.These results indicate that the function of the TM-immobilizing agent as a soil quality conditioner,in addition to its TM immobilizing effect,should be considered when selecting such agents for agricultural or ecological applications.