Facile one-step synthesis of attapulgite-hydrochar composite for in situ remediation of cadmium contaminated soils: Characterization, performance and mechanisms

Abstract A cost-efficient attapulgite-hydrochar composite (APHC) was prepared by a facile one-step hydrothermal treatment and evaluated for cadmium (Cd) immobilization in contaminated soils. The results showed that APHC could effectively reduce the leaching Cd content by 32.1%, and the immobilization efficiency was significantly improved by 70.2% compared to pristine hydrochar (HC). By the introduction of APHC, the contaminated soils showed the highest reduction rate of 91.0% for acid-soluble Cd, and the ecological risk of amended soils was remarkably reduced from high-risk polluted grade to low-risk rank compared to original contaminated soils. The pot experiments indicated that APHC could effectively decrease the adsorbed amount of Cd in paddy rice by 71.2% and reduce the inhibition effect of Cd on plant growth and biomass production. The mechanism study showed that surface complexation, cation exchange and electrostatic attraction played significant roles in immobilizing Cd in contaminated soils. The present study offered a potentially promising approach to prepare cost-effective and eco-friendly amendments from waste biomass for in situ immobilization of heavy metal contaminated soils.