用酒石酸等有机酸清洗镉锌、镉镍复合污染土壤

针对受镉锌复合污染的A区土壤和受镉镍污染的B区土壤, 借鉴BCR分级提取的思路, 设计了用醋酸、柠檬酸、酒石酸及琥珀酸四种有机酸与草酸组合两步振荡清洗工艺, 去除土壤中环境风险较大的重金属形态, 并比较了单独用柠檬酸、酒石酸振荡清洗的效果, 探讨了超声波对酒石酸清洗的强化作用。结果表明:先用0.1 mol·L^-1柠檬酸或酒石酸振荡清洗16 h,再用0.2 mol·L^-1草酸振荡清洗16 h的两步清洗法对2种土壤目标重金属去除率最高;单独用0.1 mol·L^-1酒石酸振荡清洗2 h对A区Cd、Zn和Ca的清洗率分别为30.74%、25.59%和15.86%,对B区土壤Cd、Ni和Ca的清洗率分别为47.36%、6.89%和23.92%.酒石酸能有效去除目标重金属, 同时洗出的常量元素Ca较柠檬酸少, 是较理想的清洗剂。超声波(功率400 W,频率20 kHz)可以强化酒石酸对重金属的清洗效果, 超声30 min对2种土壤目标重金属的清洗率与单独用酒石酸振荡清洗2 h相当。

Remediation of Soils Co-contaminated with Cd-Zn and Cd-Ni by Washing with Oranic Acids

Soil flushing is one of remediation techniques for metals contaminated soils. Here an effective soil washing process was studied in two metal-contaminated sites, namely soil A, which was polluted by Cd and Zn, and soil B, which was polluted by Cd and Ni. A two-step washing method using oxalic acid combined with four different acids, such as acetic acid, citric acid, tartaric acid and succinic acid, was evaluated in terms of removal of bioavailable portion of heavy metals. In addition, soil washing with citric acid or tartaric acid alone was conducted. Enhancing effect of ultrasonic wave on metal washing by tartaric acid was also investigated. Results showed that the removal efficiencies of two-step washing process using citric acid or tartaric acid(0.1 mol·L^-1, for 16 h) and oxalic acid(0.2 mol·L^-1, for 16 h) sequentially were the highest. Under tartaric acid alone(0.1 mol·L^-1, t=2 h), the removal of Cd, Zn and Ca was respectively 30.74%, 25.59%, and 15.86% for soil A, while that of Cd, Ni and Ca was respectively 47.36%, 6.89%, and 23.92% for soil B. Tartaric acid was an efficient washing agent with high heavy metals removal capacity but low Ca leaching. The introduction of ultrasonic wave enhanced the removal efficiencies of heavy metals in tartaric acid washing system, which shortened the washing time from 2 h to 30 min. The findings show that it is possible to develop an environmentally friendly soil washing technique for heavy metals contaminated soils.