Sorption of humic acid from aqueous solutions by lanthana-alumina mixed oxide pillared bentonite

Abstract

This work aims to evaluate the sorbent power of pillared inter layer clay (PILC) for humic acid from aqueous solutions. PILC was prepared from natural bentonite clay with lanthana-alumina mixed oxide pillars and was found to be very effective in removing humic acid from water. Maximum adsorption of 97.3 and 88.8 % took place by PILC (pH 3.0) from an initial concentration of 15.0 and 30.0 mmol/l respectively. Lagergren first-order kinetic equation governed uptake process. Electrolyte (NaCl) compresses the diffuse double layer leading to the increased uptake of humic acid; this also showed that van der Waals attraction is an important part of the interactive forces between humic acid and PILC. According to Giles classification, adsorption isotherm may be classified as L-type. The applicability of Langmuir isotherm to PILC-humic acid system was tested. Adsorption capacity ‘<i style="">Q^o</i>’ (54.32 mmol/g) and binding constant ‘<i style="">b</i>’ (0.249 l/<img src='/image/spc_char/micro.gif'> mol) were maximum at 10^oC and pH 3.0. Experiments conducted at different temperatures allowed for the calculation of isosteric heat of adsorption, revealing that the adsorptionprocess was exothermic. About 94.6 % can be recovered from the spent clay using 0.01<i style=""> M</i> NaOH.