The Role of Mg Doping in Manipulating the Adsorption Mechanisms of CaAl-Layered Double Hydroxide: Investigating the Effects of Calcination Temperature and Borate Concentration Changes

Abstract

CaAl-layered double hydroxides (LDHs) exhibit different mechanisms of borate removal at varying calcination temperatures. The addition of Mg alters the structure and composition of the calcined products, ultimately impacting their adsorption process. To investigate this, CaAl-LDH and Mg-doped CaAl-LDH with and without different calcination temperatures (500 °C and 900 °C) were prepared to immobilize a wide concentration range of borate. XRD, SEM, FTIR, and EXAFS techniques were employed to study the influence of Mg doping. The results indicate that the doping of Mg increases the BET surface area and enhances the adsorption capacity of uncalcined LDHs, with the enhancement being more pronounced at high borate concentrations. For LDHs calcined at 500 °C, Mg-doped LDHs exhibited slightly better adsorption at any borate concentration due to its more favorable ettringite formation. However, for LDHs calcined at 900 °C, Mg-doped LDHs (LDO) had a slightly better adsorption effect at low borate concentrations. At high concentrations, the crystallinity and morphology of the regenerated CaMgAl-LDH deteriorated, resulting in poor adsorption effects. These findings provide valuable theoretical support for understanding the mechanisms of removing pollutants with different concentrations by different LDHs.