Vol. 12, Issue 7 (2023)

Author(s):
Soniya VP, Bhindhu PS and Rajalakshmi K

Abstract:
Layered double hydroxides (LDH) are hydrotalcite-type clays, consisting of stacked positive layers of brucite-like hydroxides that are separated and neutralized by exchangeable anions in inter-lamellar galleries. They exhibit colloidal properties and are characterized by small size (200-300 nm) and high surface area (50-200 m² g^-1). The zero-point charge of these minerals is usually in the pH range of 10-12. Positively charged surface provides high anion exchange capacity to these minerals, which ranges between 200-450 cmol (-) kg^-1. Delamination and memory effect are imperative properties pertaining to the commercial application of LDHs. Various direct (co-precipitation, hydrothermal synthesis, salt oxide method and sol-gel synthesis) and indirect (ion exchange and structural reconstruction method) techniques are available for the synthesis of LDH. Layered double hydroxides are used to immobilize heavy metals through precipitation and the anionic contaminants through adsorption and intercalation reactions. Fe-Al LDH was used to remediate chromium contaminated (1039.92 and 2080 mg kg^-1) soils, and recorded complete immobilization of the pre-adsorbed Cr (VI). A high immobilization efficiency of 96.9 percent could be achieved for in-situ decontamination of cadmium in soil with application of Ca-Al LDH through formation of stable Cd-Al LDH mineral.