Recyclable and reusable layered double hydroxide beads for soil remediation: Conveying belt recovery model, mechanism, bioavailability and microbial communities

Abstract

Soil heavy metal remediation has always been the focus of research. This work synthesized a recoverable, reusable, and efficient material for Cr(VI)-contaminated soil through a new strategy. The main structure is a bead that encapsulates the layered double hydroxides(LDHs) and magnetic particles into an alginate bead (LDHs-M). Varying applications in soil suggested LDHs-M showed high immobilization performance. Including LDHs interlayer ions, proportion of components, pH, dosage, and initial Cr(VI) concentration, many influence factors were systemically explored, suggesting that LDHs contained in the bead played a prominent role during the immobilization and LDHs-M with the interlayer anions of NO3- showed excellent immobilization efficiency. Different characterizations were used to investigate the immobilization mechanism, indicating that interlayer anion exchange and electrostatic adsorption were the main ways for soil Cr(VI) immobilization. The toxicity also decreased with the reduction of Cr(VI). Meanwhile, the simulation of natural aging processes, plant growth, and changes in the microbial community in the soil after remediation were also investigated, which verified the immobilizing stability and bioavailability of LDHs-M. Furthermore, the magnetic belt recovery system showed superior recovery performance in solid phase separation. Then, the separated beads were regenerated in an electrolyte solution and reused in soil remediation. The perfect immobility, instantaneous separation, and regenerability made it a promising material in heavy metal contaminated soil.