Super-stable mineralization of cadmium by calcium-aluminum layered double hydroxide and its large-scale application in agriculture soil remediation

Cadmium (Cd) contaminated cropland has posed severe risks to human health. While in-situ Cd immobilization by stabilizer has been widely adopted in practice, there is still a huge challenge to develop cost-effective stabilizers with strong and long-term immobilization ability. In this work, we report a CaAl-layered double hydroxide (CaAl-LDH) as an efficient stabilizer for Cd2+ in-situ immobilization both in lab scale and practice remediation. This material presents fast sorption rate (ca. 5 min) and high capture capacity (592 mg/g) towards Cd(2+ )in solution, and high immobilization efficiency (up to 96.9%) in soil remediation. Detailed investigations suggest that Cd2+ induces the reconstructing of CaAl-LDH to CdAl-LDH, with Cd being stabilized in a super stable state. In a large-scale and long-term application (in soil of 10 ha for continuous three years' test), we observe that the CaAl-LDH enables a low Cd content in wheat grain (0.06 mg/kg) that is below the national standard (0.1 mg/kg). By employing a scaling-up production in 3000 ton per year, we demonstrate the CaAl-LDH would be a promising competitive candidate for facile and cost-efficient remediation of Cd contaminated soil.