Employing dolomite as magnesium source to prepare calcined layered double hydroxides for chromium contaminated soil treatment: Exploring the influence of temperature, bioavailability, and microbial diversity.

Layered double hydroxides (LDH-D) and their calcined counterparts, using dolomite as a source of magnesium, were utilized for the immobilization of chromium (Cr(VI)) in soil. The results indicate that LDH-D, both with and without varying calcination temperatures, can effectively immobilize Cr(VI) in soil. Among the different calcination temperatures tested, LDH-D subjected to calcination at 500 °C (LDH-D-500) showed particularly high efficacy. Long-term TCLP experiments demonstrated the inhibition of soil-to-plant transmission of Cr(VI), thereby highlighting the long-lasting immobilization capacity of LDH-D and its calcined derivatives. Furthermore, the analysis of the microbial community's adaptation in post-remediation soil confirmed the durability and bioavailability of LDH-D-500 for Cr immobilization. Examination of the material's morphology and structure after immobilization shed light on the mechanism of immobilization in soil. The results revealed that interlayer anion exchange and surface adsorption were the main factors responsible for the effective immobilization of LDH-D and LDH-D-300. On the other hand, LDH-D-900, with a dominant spinel (MgAlO) structure, faced challenges in returning to its original layered configuration, making surface adsorption the primary mechanism for immobilization. LDH-D-500 primarily relied on the structure memory effects of LDHs to immobilize Cr(VI) through structural recovery processes, facilitated by electrostatic attraction and surface adsorption. It is also important to note that CaCO plays an important role in adsorption. Additionally, a portion of Cr(VI) was converted to Cr(III) through phenomena such as isomer substitution and complexation adsorption. The proficiency of LDH-D-500 in immobilizing Cr, its ability for instantaneous separation, and the potential for regeneration make it a promising material for remediation of heavy metal-contaminated soil. The investigations suggest that the use of dolomite to create hydrotalcite and calcining it at 500 °C could effectively render environmental Cr inactive, thereby optimizing resource utilization.