Washing using low-molecular-weight organic acid is an effective and eco-friendly technique to permanently remove heavy metals from soil. There is still lack of evaluation of the application modes and the recovery methods, as well as the variations of heavy metal and nutrients fractions on a pilot-scale during washing. Here, we developed a simple combined solubilization and eluent drainage system in a pilot-scale washing box using industrial grade citric acid with feasible waste eluent treatment method to remove cadmium (Cd) and copper (Cu) from agricultural soil. The removal rates of Cd and Cu after sequential two-stage citric acid-water washing reach up 68.9% and Cu 41.4%, which was 7.5% and 10.0% higher than single citric acid. The removed the heavy metals were mainly in exchangeable and reducible fractions. The heavy metals at different soil depth were dissolved more effectively by citric acid-water washing with wheat straw as underdrain filling material than that of crushed stone. The potential risks of Cd in soils all decreased by approximately 75% from considerable to low risk. The two-stage citric acid-water washing significantly mitigated the effect of soil acidification. The average contents of soil organic matter, available ammonium N-NH₄ and available phosphorus increased by 40.9%, 57.3%, 32.0% after citric acid-water washing under wheat straw filling. The waste eluent can be efficiently recovered by clam powder, which removed 78.7% of Cd and 57.5% of Cu. The regenerated citric acid showed similar removal efficiencies for Cd and Cu compared to the fresh citric acid. These results indicate that the combination of washing, drainage and flocculation can effectively remove Cd and Cu from contaminated agricultural soil and realize the recycling of waste eluent.

使用低分子量有机酸清洗是一种有效且环保的技术，可永久去除土壤中的重金属。尚缺乏对应用模式和回收方法的评估，以及洗涤过程中中试规模的重金属和营养成分的变化。在这里，我们使用工业级柠檬酸和可行的废物洗脱液处理方法在中试规模的洗涤箱中开发了一种简单的组合溶解和洗脱液排水系统，以去除农业土壤中的镉 (Cd) 和铜 (Cu)。连续两级柠檬酸-水洗后Cd和Cu的去除率分别达到68.9%和41.4%，比单一柠檬酸分别提高7.5%和10.0%。去除的重金属主要是可交换和可还原的部分。以麦秸为暗渠填充材料的柠檬酸-水洗比碎石更能有效溶解不同土壤深度的重金属。土壤中镉的潜在风险从高风险到低风险均降低了约 75%。两级柠檬酸-水洗显着减轻了土壤酸化的影响。土壤有机质、速效铵N-NH的平均含量₄、麦秆灌浆下柠檬酸-水洗后有效磷分别增加40.9%、57.3%、32.0%。蛤粉可有效回收废洗脱液，去除78.7%的Cd和57.5%的Cu。与新鲜柠檬酸相比，再生柠檬酸对 Cd 和 Cu 的去除效率相似。这些结果表明，洗涤、排水和絮凝相结合可以有效去除受污染农田土壤中的Cd和Cu，实现废弃淋洗液的回收利用。