Possibility of using combined compost–attapulgite for remediation of Cd contaminated soil

Soil contamination by cadmium (Cd) is a critical global environmental issue that urgently needs to be solved. In this study, compost, attapulgite, and their combination were used for remediation of Cd-contaminated soil. Soil physicochemical properties, enzyme activities and plant uptake of Cd were investigated to evaluate the remediation effectiveness. Attapulgite and combined compost–attapulgite significantly increased the soil pH, while compost and combined compost–attapulgite induced the larger increase in soil organic matter (SOM) and available P and K. The catalase, urease, and sucrase activities in the soil had considerably improved, and those activities in the soil treated with compost–attapulgite increased by 2.04, 1.15 and 0.32 times, respectively, compared to untreated soil. The decrease of CaCl2–Cd content in the soil treated with combined compost–attapulgite was most pronounced, with a decline of 96.38% compared to untreated soil. Meanwhile, combined compost–attapulgite led to the decrease in exchangeable and reducible Cd from 0.70 to 0.64 mg kg−1 and from 0.47 to 0.43 mg kg−1, respectively, and an increase of residual Cd from 0.06 to 0.16 mg kg−1. The combination of compost and attapulgite promotes Cd immobilization through adsorption, complexation, coprecipitation, and ion exchange. The obvious Cd immobilization effectiveness of combined compost–attapulgite resulted in the lowest pakchoi (Brassica chinensis L.) uptake of Cd among treatments. These findings provided an alternative strategy for improving soil quality, reducing Cd bioavailability through combined use of compost and attapulgite as soil amendment in Cd contaminated soil.