Adsorption and thermal desorption of Cr(VI) on Li/Al layered double hydroxide

Li/Al layered double hydroxide (Li/Al LDH), known as anionic clay, comprises positive charges, which are counter-balanced by interlayer anions. The material is capable of adsorbing anions through ion-exchange reaction. This property of LDH leads to its potential application in scavenging anionic contaminants, such as Cr(VI) in the waste streams. In this study, the adsorption of Cr(VI) by Li/Al LDH was investigated at 10 and 30 °C. The results showed that Cr(VI) adsorption was relatively rapid; however, a portion of adsorbed Cr(VI) was released over the reaction time and the releasing rate was dependent on reaction temperature. Particularly at 30 °C as high as 80.1% of adsorbed Cr(VI) was released after 24 h reaction. The release of adsorbed Cr(VI) is due to the deintercalation of Li+ from Li/Al LDH structures in aqueous solution and gibbsite, which was used as the precursor to synthesize Li/Al LDH, was the product of the deintercalation reaction. The Li deintercalation reaction of Li/Al LDH and its dependence on temperature of may be utilized to develop a method of treating Cr(VI)-containing wastes and recovering Cr(VI). That is, Li/Al LDH can be used as an adsorbent to remove Cr(VI) in wastewater. Then the Cr(VI)-bearing LDH particles are collected and re-suspended in hot water to enhance Li deintercalation and Cr(VI) desorption. Consequently Cr(VI) can be recovered from the solution and the solid product, i.e., gibbsite, can be recycled for further uses.