Synergistic Remediation of Alkaline Cd-Contaminated Farmland Soil with Hydroxyapatite and Organic Fertilizer in a Combined Amendment

Highly effectively and economical method to immobilize cadmium from alkaline agriculture soil is urgently needed. Through kinetic and isotherm experiments of passivators adsorption, soil passivation experiment, and cadmium leaching, this study was to explore the applicability of hydroxylapatite-organic fertilizer compound repair agents (HO), individual hydroxylapatite (HA), individual organic fertilizer (OF), sepiolite (SP) and diatomite (DE) to passivate soil cadmium and its passivating effect. In the aqueous phase, HO successfully adsorbed Cd2+ on the surface and has superior potential Cd2+ adsorption capacity than OF, DE, and SP, with its adsorption capacity closely approach to that of HA, enabling its use as a passivator in real Cd-contaminated environments. In Cd-contaminated soil, HO effectively lower the pH from 9.22 to 8.59 at the addition of 5% and change the aggregate distribution. The increase in the amount of passivator also significantly increased soil aggregate size. Moreover, the addition of HO significantly improved the extractable contents of Cd in the soil. With the addition of 5% HO, the Cd extracted by TCLP decreased by 30.95%, 42.86%, 59.52% and 69.05%, respectively. Therefore, our findings demonstrated that HO is a highly efficient and low-cost organic-inorganic composite passivator for cadmium contaminated soils.