Oxidative leaching of chromium from layered double hydroxides: Mechanistic studies

The layered double hydroxide (LDH) of Zn with Cr on treatment with a hypochlorite solution releases chromate ions as a result of oxidative leaching by a dissolution-reprecipitation mechanism. The residue is found to be epsilon-Zn(OH)(2). The LDH of Mg with Cr on the other hand is resistant to oxidative leaching. In contrast, a X-ray amorphous gel of the coprecipitated hydroxides of Mg and Cr yields chromate ions. These results suggest that the oxidation potential of Cr(III) in LDHs is determined by the nature of the divalent ion and the, crystallinity of the phase while being unaffected by the nature of the intercalated anions.