土壤重金属的形态特征及其对蔬菜的影响研究

运用连续提取的方法,对土壤中Pb、cd、cu的水溶态、交换态及碳酸盐结合态、铁锰氧化物结合态、有机物及硫化物结合态和残渣态进行测定,残渣态所占的比例较大。对蔬菜有效性较高的是有机物和硫化物结合态和铁锰氧化物结合态。     

贵州省某村煤中砷含量及赋存状态

基于对贵州兴仁某村煤中砷的含量及赋存状态的研究,得出研究区砷含量分布范围在17.83mg/kg～140.64mg/kg,平均值为93.31mg/kg,远高于中国(4.09mg/kg)和世界(5mg/kg)煤砷含量.其赋存状态复杂多样,煤砷各形态含量比例分布为:残渣态(56.74%)铁锰氧化物结合态(20.74%)硫化物结合态(15.20%)有机结合态(5.07%)碳酸盐结合态(1.73%)水溶态和可交换态(0.52%).煤中砷主要以残渣态形式存在,铁锰氧化物结合态砷含量也较高.其中一个煤样砷含量相对于其他样品较小,有机砷结合态所占比例相对较大,结合前人研究推断:此次研究的煤样多以大分子有机砷结合态存在,但不易提取,导致残渣态砷含量较高.     

柠檬酸对土壤中重金属形态转化的影响

重金属的存在形态对评价其对环境危害的大小具有重要意义。本文采用BCR法分级提取土壤中重金属各种形态:弱酸提取态(水溶态+可交换态+碳酸盐结合态)、可还原态(Fe-Mn氧化物结合态)、可氧化态(有机物和硫化物结合态)和残渣态,研究了柠檬酸对重金属复合污染土壤中Cd、Pb、Cr的化学形态、生物有效性的影响。结果表明随着柠檬酸量的增加,残渣态镉和铅向可还原态和可氧化态转化量也增加,残渣态铬和可还原态铬向可氧化态铬的转化量也缓慢增加,但对弱酸提取态均影响不大。说明施加柠檬酸可活化土壤中的镉铅铬,助力于植物修复技术。     

织金县燃煤区土壤重金属含量及其结合形态

通过Tessier和Shuman法探究了织金县燃煤区土壤中水溶态、离子交换态、碳酸盐结合态、腐殖酸结合态、铁锰氧化物结合态、强有机结合态、残渣态七种形态Zn、Pb、Cd、Ni、Cu、As、Hg等几种重金属的含量,同时测定了其土壤中各种重金属的总含量。结果显示,Zn、Pb、Cd、Ni、Cu、As、Hg等重金属在织金县燃煤区土壤中的结合形态主要以残渣态含量最高,可高达84.15%。     

钝化剂对废弃石煤矿山铀污染土壤修复效果研究

本文采集江西省内某废弃石煤矿区周边实际铀（U）污染土壤为研究对象，选用泥炭和玉米秸秆炭作为有机钝化剂，以及将沸石和蛭石作为无机钝化剂对污染土壤进行钝化处理，以此考察不同钝化剂对污染土壤理化性质和U形态分布的影响。结果表明，四种钝化剂对污染土壤pH值影响不显著，沸石处理的土壤pH值虽有增加，但对U的钝化效果最不理想；泥炭对污染土壤中U的钝化效果最显著，与污染土壤混合培养5周后，铁锰氧化物结合态U占比降低了15.15%，硫化物及有机物结合态U占比增加了22.22%，与原始土壤中U形态分布对比，残余态U和硫化物及有机物结合态U总占比加和明显增加；蛭石对污染土壤中U也具有一定的钝化效果，与污染土壤混合培养3周后，U形态分布基本趋于稳定，铁锰氧化物结合态含量占比出现了较为明显的降低。     

草酸和醋酸作为电动淋洗液对污泥中重金属去除效果的对比

对于污泥中重金属难以去除的问题,本文开展了电动淋洗单因素实验,采用草酸和醋酸作为电动淋洗液调控阴极pH的方法对污泥电动淋洗去除重金属效果进行了探究。阐明了电动淋洗前后重金属形态转化的规律,Cd、Cu的形态由较稳定的残渣态转变为迁移性较高的可交换态、铁锰氧化物结合态等,重金属形态的转变有利于其与污泥的解吸。添加草酸调控阴极pH后Cd、Cu的去除率由11.90 wt.%、12.3 wt.%提高到了33.17 wt.%和28.82 wt.%,使用柠檬酸作为添加剂后Cd、Cu的去除率分别达到了75.50 wt.%、63.23 wt.%。     

水泥硬化体中Cr的形态及分布——改进的Tessier连续浸提法

采用改进的Tessier连续浸提法,结合电感耦合等离子体原子发射光谱、X射线衍射、扫描电子显微镜和能谱等测试手段,分析了不同形态Cr在水泥水化产物中的分布。结果表明:硅酸盐水泥硬化体中可交换态和碳酸盐结合态Cr占其总量的7%～35%,主要以吸附和沉淀形式存在于颗粒表面,对pH变化较为敏感,Cr的溶出对应于Ca(OH)2的溶解和部分水化硅酸钙(C-S-H)的溶解。不容易迁移的铁锰氧化态、硫化物结合态和残渣态的Cr约占总Cr含量的65%～93%,为Cr的主要分布形态,其溶出对应于钙矾石(AFt)和C-S-H和未水化熟料相的分解。随龄期延长,Cr逐渐向迁移能力较强的可交换态和碳酸盐结合态转变。     

城市典型金属加工土壤污染特征及植物毒性研究

研究了金属冷、热加工工艺对Cu、Zn、Pb、As土壤粒径分布规律、种子萌发毒性及植物富集特征影响。结果表明,金属热加工造成的土壤重金属污染浓度较高,重金属在细颗粒土壤中的浓度显著高于粗颗粒土壤。金属热加工土壤Cu、Zn、Pb主要以铁锰氧化物结合态存在,As的主要形态为残渣态;金属冷加工土壤Cu的主要形态为残渣态和有机结合态,Zn、Pb主要形态为铁锰氧化物结合态,As主要形态为残渣态。冷热加工工艺不同粒径土壤培养的小麦种子发芽势和发芽率均大于80%,对种子萌发毒性较小。重金属富集量为：Zn>Cu>Pb>As,植物富集作用和重金属总量、形态分布相关。     

尾矿中锌解吸-电动-硫化钠沉淀联合修复

对某含锌尾矿进行解吸-电动-硫化钠沉淀联合修复,去除尾矿锌重金属,考察了尾矿颗粒微观变化.结果表明,柠檬酸具有酸性和络合作用双重特性,其对锌的解吸率较优,可用作该尾矿解吸剂.较高电压梯度有助于增大电流,加快离子移动,提升去除率,但过高会带来更大能耗,以1.5 V/cm为宜,锌去除率可达67.32%.尾矿中弱酸可提取态锌和铁锰氧化态锌去除率分别为93.18%和63.16%.尾矿颗粒晶体及表面在修复后被破坏,有利于离子移动和修复指标提升.用0.006 mol/L Na_2S沉淀除锌后,阴极液可再次用作阳极补充液.     

剩余污泥中重金属形态分布及浸出特征研究

剩余污泥具有改良土壤结构、增加土壤肥力、促进农作物生长等优点,由于含有有害的重金属等,妨碍其农用。通过对剩余污泥中重金属形态分布及浸出特征研究,结果显示,剩余污泥中Cu、Zn、Ni、Cr及Pb交换态含量都比较少,Cu、Zn、Ni主要以碳酸盐结合态、铁锰氧结合态和硫化物及有机结合态存在,Cr、Cd和Pb主要以残渣态存在;在酸性条件下,交换态、碳酸盐结合态溶出量大,并且溶出量都随浸出时间的延长而增加。     

Electrokinetic remediation of copper mine tailings: Implementing bipolar electrodes

Important process parameters to optimize in electrokinetic soil remediation are those influencing remediation time and power consumption since these directly affect the cost of a remediation action. This work shows how the electrokinetic remediation (EKR) process could be improved by implementing bipolar electrodes in the porous material. The bipolar electrodes in EKR meant two improvements: (1) a shorter migration pathway for the contaminant, and (2) an increased electrical conductivity in the remediation system. All together the remediation proceeded faster with lower electrical resistance than in similar experiments but without the bipolar electrodes.The new electrokinetic remediation design was tested on copper mine tailings with different applied electric fields, remediation times and pre-treatment. The results showed that the copper removal was increased from 8% (applying 20 V for 8 days in sulphuric acidified tailings) without bipolar electrodes to 42% when bipolar electrodes were implemented.Furthermore, the results showed that in this system sulphuric acid addition prior to remediation was better than citric acid addition. In addition, applying a too strong electric field (even with bipolar electrodes) could cause a severe polarization (e.g. a high electrical resistance) in the remediation system.     

EK/Fe0-PRB联合修复实际砷污染土壤的协同机制

以我国某矿区砷污染土壤为研究对象,采用EK/Fe⁰-PRB联合修复工艺去除土壤中的砷,考察了土壤含水率及增强试剂对砷去除的影响,分析了修复前后土壤中砷的迁移分布及砷价态分布变化,并借助X射线光电子能谱（XPS）对修复前后PRB填料Fe⁰进行了表征分析,探讨了EK/PRB修复砷污染的协同机制。结果表明,在EK/PRB联合修复过程中,EK去除作用所占比例为22%～43%,而PRB的去除作用所占比例为52%～71%,以PRB的去除作用为主;未添加增强试剂时,阳极液砷收集含量明显高于阴极液砷收集含量,电动去除机制主要为电迁移作用,添加增强试剂后,阴极液砷收集含量所占比例明显升高;EK/PRB修复后,As（Ⅴ）和As（Ⅲ）在土壤、电极液、PRB中的含量比例基本没有变化,As（Ⅴ）含量比例略微升高,即处理之后土壤中的五价砷并不会经氧化还原作用而转变成毒性较高的三价砷;反应后Fe⁰表面存在As（Ⅲ）和As（Ⅴ）,未发现As（0）的存在,因此砷在PRB中仅通过铁表面氧化物的吸附作用而去除。     

Testing pulsed electric fields in electroremediation of copper mine tailings

Mining processes, prior to pyrometallurgical copper production, generate large amounts of solid waste, which are and have been deposited in mine tailings impoundments. This work is based on three electrodialytic (EDR) and four electrokinetic (EKR) remediation experiments on fresh and aged copper mine tailings using pulsed electric fields. The EDR results are compared to conventional remediation with direct current (dc) electric field. Applying pulsed electric fields in EDR, it was found that the remediation time decreased compared to dc EDR. In the anode side of the cell, 72 h of remediation at 20 V with a frequency ≥28 cycles/day at a fixed time ratio (t_ON/t_OFF) of 20, in terms of copper removal would correspond to around 270 h of dc remediation time. With both EDR and EKR of 120 h, at 14 cycles/day, the copper removal is practically uniform in the whole cell. Increasing the frequency to ≥28 cycles/day, the copper removal in the anode side is improved, and in the cathode side an accumulation is observed. With an EKR of 240 h, a larger copper accumulation in the cathode side was observed due to precipitation of copper hydroxide. In EDR with a pulsed electric field, the transport across the cation exchange membrane becomes the rate determining step. This can be seen from: (a) accumulation in the cathode side when increasing the frequency and (b) similar total copper removal for the three frequencies studied. In EKR, free alkali diffusion into the cell occurred. This generated copper precipitation in the cathode side, and the effect of the pulsed electric field on total copper removal was reduced.     

不同电极电动修复铜镉复合污染土壤的研究

针对铜镉污染土壤问题,研究了不同电极材料对电动修复土壤效果的影响。采用不锈钢、石墨板、钛板、钛网四种不同电极对土壤进行修复。结果显示,石墨板电极对2种重金属的总去除率较好,Cu为40.34%,Cd为95.21%,且Cd的去除率明显高于Cu。另外,不同电极材料对修复过程中电流和处理后重金属形态分布的影响不大,其中石墨板电极电流稳定时的值为42mA,高于其他三种电极。     

Electrodialytic remediation of copper mine tailings with sinusoidal electric field

In this work an electrodialytic remediation cell for copper mine tailings using sinusoidal electric field was analyzed, in order to increase the removal efficiency. The sinusoidal electric field was obtained by applying simultaneously continuous-alternating voltages; in this work an alternating voltage of low frequency was applied. The system was tested considering the effect of: (1) the effective voltage applied to the cell, (2) the period for the alternating voltage, (3) remediation time, and (4) copper complexing capacity of citric acid. According to the conditions studied in this investigation, the laboratory results showed that decreasing the effective voltage improves the remediation action, due to polarity reversal of the system, which reduces polarization during the process, but in terms of the period for the alternating voltage there is no effect. As expected the remediation time and copper complexing capacity of citric acid improves the amount of remediated material and the remediation action in general.     

Enhanced electrokinetic remediation of cadmium-contaminated natural clay using organophosphonates in comparison with EDTA

Soil contamination by metals is a worldwide environmental problem. Electrokinetic extraction is a promising technology for in-situ remediation of contaminated soils of low hydraulic permeability. However, the extraction of metals is usually hindered by the high buffer capacity of natural soils. Organophosphonates are strong metal chelates as ethylenediaminetetraacetic acid(EDTA) which has been widely studied in the enhancement of electrokinetic remediation. In this study, batch desorption experiments and bench-scale electrokinetic extraction experiments were carried out to study the effect of two organophosphonates, i.e.,(nitrilotrimethylene)triphosphonate(NTMP) (ethylenedinitrilo)-tetramethylenephosphonate(EDTMP), on the extraction of cadmium from a natural clay in comparison with EDTA. Results of the batch desorption experiments showed that more than 75% of the sorbed cadmium could be dissolved into solution using 0.1 mol·L~(-1) organophosphonates or EDTA in the wide p H range of 1–11. Results of the electrokinetic extraction experiments showed that the cadmium spiked in the specimen migrated towards the anode with the enhancement of NTMP,EDTMP, and EDTA under a constant voltage gradient of approximately 1.0 V·cm-1. Although cadmium mobilization enhanced by EDTA was more efficient than that by the organophosphonates, accumulation of cadmium was observed in the vicinity of the anode. The average removal efficiencies of cadmium from the soil after approximately 5 days of electrokinetic extraction enhanced by 0.1 mol·L-1 NTMP(22.8%) and EDTMP(22.4%) were higher than that by 0.1 mol·L~(-1) EDTA(15.1%).     

Development of electrokinetic-flushing technology for the remediation of contaminated soil around nuclear facilities

The effects of a flushing by a pump on an electrokinetic-flushing remediation of contaminated soil were estimated. The soils were sampled from the sites around nuclear facilities which were built on a high hydro-conductivity of sandstone. An electrokinetic-flushing equipment with a pump was manufactured to estimate the effect of a flushing on an electrokinetic-flushing remediation. In order to select an optimal reagent suitable to the characteristics of a soil near nuclear facilities, 4 experiments were executed with 4 candidate reagents selected from 12 reagents and the results of the experiments are as follows. The removal efficiencies of cobalt and cesium from the contaminated soil with the acetic acid were the highest, which were 92.1% and 83.1%, respectively. The effluent solution volume generated from an electrokinetic remediation was very smaller and it was 5% below that from a soil washing. Next, the results from a comparison of an electrokinetic-flushing remediation and an electrokinetic remediation revealed that the removal efficiencies of Co²⁺ and Cs⁺ by an electrokinetic-flushing remediation for 5 days were increased by 25% and 35% when compared to those by the electrokinetic remediation, but the effect of a flushing by the electrokinetic-flushing equipment started to decrease after 5 days. The removal efficiencies of Co²⁺ and Cs⁺ by an electrokinetic-flushing remediation for 15 days were increased by 6.8% and 7.7% when compared to that by an electrokinetic remediation. Namely, the higher the hydro-conductivity of a soil was, the larger the effect of a flushing was on an electrokinetic-flushing remediation.     

Pulsed electrokinetic removal of Cd and Zn from fine-grained soil

Pulsed electrokinetics studies were carried out to optimize the removal of Zn and Cd from fine-grained soils and to observe the effects of varying the pulse frequency, pulse time ratio (on/off), and DC voltage gradient. Existing forms of heavy metals in the soil matrix were determined using a sequential extraction method. The strongly bound fraction (bound to organic matter and residuals) that is difficult to remove from the soil matrix comprised 74 and 62% of the total Zn and Cd, respectively. In the electrokinetic remediation experiments, MgSO₄ was employed to increase the ionic strength of the soil for 2 weeks. Transportation of heavy metals was influenced by the frequency, pulse ratio, and the voltage gradient of the pulsed electric field. Extraction efficiency of Zn and Cd near the anode was correlated positively with the voltage gradient at a given pulse and ratio. A high pulse frequency (1,800 cycles/h) enhanced the removal efficiency of the heavy metals compared to a low pulse frequency (1,200 cycles/h) at a supplied voltage gradient of 1 V/cm. Although pulsed electrokinetics was more effective in extracting and desorbing ions near the anode than conventional electrokinetics, its ability to transport heavy metals from the anode to the cathode was relatively small. Total removals with pulsed electrokinetics were 21–31% for Zn and 18–24% for Cd. In summary, pulsed electrokinetics can enhance removal efficiency of heavy metals and is beneficial with regard to electrical energy consumption.     

A new method for remedial treatment of contaminated clayey soils by electrokinetics coupled with permeable reactive barriers

This paper presents the results of preliminary investigations into the potential application of a remediation system that couples the electrokinetic (EK) remediation with the permeable reactive barrier (PRB) concept. Atomizing slag was adopted as a PRB reactive material for freshing groundwater contaminated with either inorganic or organic substances. Laboratory experiments were performed with variable conditions including (i) type of pollutant, (ii) processing time, and (iii) the application of PRB system during the EK processing. From the results of the preliminary investigations, the coupled technology of EK with PRB system could effectively remediate contaminated groundwater in situ without extracting pollutants from subsurface through the effectiveness of the reactions between the reactive materials and contaminants.