Environmentally friendly remediation of lead/cadmium co-contaminated loess soil in northwestern China using a humificated straw solution

The remediation of heavy metal-contaminated soils is a great challenge and an important issue for global environmental sciences and engineering. Soil washing technology is popularly used for soil remediation, but there are issues that must be solved. These include selecting an environmentally friendly washing solution and preventing damage to the soil during the washing process. The aim of the present work is to reveal the effects of operational conditions on soil remediation contaminated by lead/cadmium, and the effects on soil physicochemical properties caused by the washing reaction. A loess soil sample was collected from northwestern China, and a humificated straw solution was used as the washing solution. The remediation efficiency was investigated using a small-scale experimental device. The remediation efficiency could be improved by optimizing the operational conditions, and we found that the Elovich equation fits better the reaction process compared to the double-constant equation and the first-order kinetics equation. The washing rate of cadmium was slightly faster than that of lead. Compared to the topsoil in the column, the concentration of lead/cadmium was higher in the bottom soil, and the content of lead/cadmium in the inner layer soil was lower than that in the outer layer soil. The washing process had little influence on the surface characteristics and functional groups of soil. The humificated straw solution could be used effectively to remove lead/cadmium and preserve nutrients in loess soil.