Treatment of hydrochloric acid using Mg-Al layered double hydroxide intercalated with carbonate

Mg-Al layered double hydroxide intercalated with CO32- (CO3 center dot Mg-Al LDH) was found to take up only low amounts of Cl- during the treatment of hydrochloric acid. Low pH promotes the removal of Cl-. HCl is considered to react with CO32- in the interlayers of Mg-Al LDH as a result of which Cl- is probably intercalated in the interlayers. High pH of the Mg-Al LDH suspension leads to a lower extent of reaction between HCl and Mg-Al LDH, owing to the neutralization of the acid. We can state that the adsorption of Cl- on Mg-Al LDH is best described by the Dubinin-Radushkevich adsorption isotherm. The maximum adsorption amounts were calculated to be 1.4 and 0.6 mmol/g for CO3 center dot Mg-Al LDH with Mg/Al molar ratios of 2 and 4, respectively, whereas the adsorption energies were calculated to be 82 and 124 kJ/molt respectively. In summary, the removal of Cl- is caused by both the reaction between hydrochloric acid and CO32- in the interlayers of Mg-Al LDH as well as anion exchange between the HCO3- produced and a different Cl- ion in hydrochloric acid. This explains why the adsorption is best expressed by the D-R adsorption isotherm, which assumes a heterogeneous surface and non-constant adsorption potential. (C) 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.