选取三氯化铁和有机酸(柠檬酸、苹果酸、酒石酸)复合淋洗,采用土柱淋洗的方法对Cd、Pb污染土壤进行淋洗实验,研究了复合淋洗剂浓度配比、淋洗剂用量和淋洗次数对重金属去除效果的影响,并测定了土壤淋洗前后Cd、Pb形态的变化.结果表明:三氯化铁浓度为10 mmol/L,有机酸浓度为20 mmol/L时,淋洗率Cd为72.15％,Pb为30.26％,与使用单一淋洗剂相比均有大幅提升.复合淋洗剂能有效地去除交换态、碳酸盐结合态和氧化物结合态重金属,而对有机态和残余态部分重金属作用效果不明显;Cd比Pb容易去除是由于污染土壤中Cd的存在形态主要是可交换态、碳酸盐结合态和铁锰氧化物结合态,而Pb的存在形态主要是有机结合态和残渣态.淋洗后土壤中Cd和Pb均达到土壤环境质量标准.

Soil aggregates were prepared from a bulk soil collected from paddy soil in the Taihu Lake region and aluminum (Al) dissolution, solution pH changes during copper (Cu2+) sorption were investigated with static sorption and magnetic stirring. Kinetics of Cu2+ sorption and Al dissolution were also studied by magnetic stirring method. No Al dissolution was observed until Cu2+ sorption was greater than a certain value, which was 632, 450, 601 and 674mg/kg for sand, clay, silt, and coarse silt fractions, respectively. Aluminum dissolution increased with increasing Cu2+ sorption and decreasing solution pH. An amount of dissolved Al showed a significant positive correlation with non-specific sorption of Cu2+ (R2>0.97), and it was still good under different pH values (R2>0.95). Copper sorption significantly decreased solution pH. The magnitude of solution pH decline increased as Cu2+ sorption and Al dissolution increased. The sand and clay fraction had a less Al dissolution and pH drop due to the higher ferric oxide, Al oxide and organic matter contents. After sorption reaction for half an hour, the Cu2+ sorption progress reached more than 90% while the Al dissolution progress was only 40%, and lagged behind the Cu2+ sorption. It indicated that aluminum dissolution is associated with non-specific sorption.

The Taihu Lake region in East China has become prone to soil acidification, which changes heavy metals such as copper (Cu) in soil into water-soluble species and increases the mobility and contamination risks of heavy metals in the biological environment. In this study, the kinetics of Cu2+ sorption by the bulk soil and the aggregate size fractions of an acidic paddy soil collected from the Taihu Lake region, the effects of temperature on Cu2+ sorption, and the pH changes of the solution were investigated by static sorption and magnetic stirring. The aggregate size fractions were prepared by low-energy ultrasonic dispersing and freeze-drying. The total sorption amounts of the bulk soil and the aggregate size fractions for Cu2+ followed a descending order of clay > coarse sand > bulk soil > silt > sand, corresponding to those of organic matter content, free iron oxide content, free aluminum oxide content, and cation exchange capacity. The kinetic sorption curves of Cu2+ by the bulk soil and the aggregates, which were divided into two stages (rapid and slow sequentially), were well fitted by the first-order equation, the diffusion equation, and the Elovich equation, showing significant correlations (P < 0.05). Specific and non-specific sorption dominated in the fast and slow stages, respectively, and the former was predominant throughout the sorption process. The specific sorption accelerated and the non-specific sorption decelerated with rising temperature. The pH of the solution decreased significantly during the specific sorption and remained unchanged or increased slightly during the non-specific sorption. When the specific sorption terminated, the pH of the solution was minimized nearly simultaneously. The sorption progress of Cu2+ by the bulk soil significantly preceded that by the aggregates. Therefore, heavy metal contamination may be another factor reducing soil pH and metal sorption forms should be taken into consideration in studies of mitigating soil heavy metal pollution or determining environmental capacity of heavy metal in soil.

Arsenic contaminated soil is a serious worldwide problem nowadays, and soil washing technique is one of hottest topics in the area of remediating arsenic contaminated soils, while treatment of the washing effluent is still an urgent problem. In this study, in order to select the best washing extractants for arsenic contaminated soil of the Xiangxi Autonomous Prefecture, nine kinds of extractants (citric acid, oxalic acid, malic acid, tartaric acid, H3PO4, KH2PO4, KOH, NH4Ac and ultra-pure water) were studied. Innovatively, a new material (calcined Mn-Fe Layered double hydroxide) was firstly introduced and fully applied to the adsorption of arsenic washing effluents. Results showed citric acid, oxalic acid and KH2PO4 were the optimal extractants for arsenic contaminated soil, considering the extraction rate and environmental perspective. When the concentrations were 200, 300, 300 mmol/ L , solution soil ratios were 10, 10, 20 mL/g , extraction times were 12,12,12 h, the citric acid, oxalic acid and KH2PO4, respectively, achieved the maximum extraction rate of 39%, 65% and 29%. Calcined Mn-Fe LDH used in this work was characterized by SEM and FT-IR, indicating the unique structure and high phase purity of the synthetic samples. For the 28mg/L arsenic effluent washing by citric acid, calcined Mn-Fe LDH showed the most effective capacity as adsorbent under neutral or weak base condition as well as 2 h absorption time.

ortho-Nitrochlorobenzene (o-NCB) in soil poses significant health risks to human because of its persistence and high toxicity. The removal of o-NCB by both zero-valent iron (ZVI) and chemical oxidation (persulfate) was investigated by batch experiments. The o-NCB removal rate increases significantly from 15.1 to 97.3 % with an increase of iron dosage from 0.1 to 1.0 mmol g−1. The o-NCB removal rate increases with the decrease of the initial solution pH, and a removal efficiency of 90.3 % is obtained at an initial pH value of 6.8 in this combined system. It is found that temperature and soil moisture could also increase the o-NCB removal rate. The o-NCB degradation rate increases from 83.9 to 96.2 % and from 41.5 to 82.4 % with an increase of temperature (15 to 35 °C) and soil moisture (0.25 to 1.50 mL g−1), respectively. Compared to the persulfate oxidation system and ZVI system, the persulfate–iron system shows high o-NCB removal capacity. o-NCB removal rates of 41.5 and 62.4 % are obtained in both the persulfate oxidation system and the ZVI system, while the removal rate of o-NCB is 90.3 % in the persulfate–iron system.

The different particle size fractions of paddy soil were separated using the low-energy ultrasonic dispersion and siphon sedimentation methods, and the effects of different phosphate concentrations on the characteristics of the adsorption and the adsorption kinetics of cadmium and chromium4+ by aggregates in paddy soil were studied by the constant temperature oscillation method. The results show that the adsorption amount of Cd2+ is lower than that of the untreated soil when the adsorption capacities of phosphate by the sand, coarse silt, silt and clay are less than 50, 46, 50 and 97 mg·kg-1, respectively, and the adsorption amount of Cd2+ is more than that of the untreated soil when the adsorption amounts of phosphate are more than the above values, respectively, indicating that the low adsorption of phosphate inhibits the adsorption of Cd2+, while the high adsorption of phosphate favors the adsorption of Cd2+. With the increase of phosphate adsorption, the adsorption of Cd2+ changes in a trough shape variation. However, the aggregates inhibit the adsorption of Cr(Ⅵ)significantly after the adsorption of phosphate. The adsorption amounts of Cd2+ and Cr(Ⅵ) by the aggregates pretreated by phosphate are in the order: cosmid > sand > coarse silt > silt, which is the same as the order of the concentrations of organic matter and free iron oxide. The adsorption process of Cd2+ by the aggregates is divided into two stages, which are the fast period and the slow period. In the fast adsorption period, the adsorption is fitted best by first-order kinetic equation, while in the slow period, it is fitted best by the diffusion equation and the Elovich equation, suggesting that the adsorption process is controlled by the different adsorption factors, and the adsorption kinetic constant of Cd2+ increases when the aggregates adsorb phosphate. The adsorption process of Cr(Ⅵ) by the aggregates does not have the fast and slow periods, and the adsorption of Cr(Ⅵ) by the aggregates can be best described by the double constant rate equation and the Elovich equation, and the adsorption kinetic constant of Cr(Ⅵ) decreases after the aggregates adsorb phosphate. The effect of phosphate on the adsorption of heavy metals in the soil was related to the types of metal ions as well as the adsorption amount of phosphate. Therefore, the types of metal ions and application amount of phosphate fertilizer should be paid attention to during the restoration of the heavy metal contaminated soil using the phosphate fertilizer.