Application of agricultural wastes of rice to lead removal from aqueous solution, study of equilibriums and kinetics

Abstract

This study investigated the effect of organic base adsorbents derived from agricultural wastes; namely rice husk silica (RHS), raw rice husk (RRH), and rice bran (RB) on removing lead ions from aqueous solutions. RRH and RB are collected from the agricultural wastes of north of Iran farms and RHS prepared at 800ºC temperature after acid leaching. The adsorption rate examined in different contact times (CT from 5 to 90 min), initial pH (pH0 = 5, 6, 7, 8 and 9), adsorbents dosages (AD = 0.5, 1 and 1.5 mg/L) and initial concentration of lead (C0 = 1, 5, 10 and 15 mg/L). The optimum conditions for adsorption of lead were pH of 6, adsorbent dosage of 1 g/L and contact time of 60 min, and RHS showed maximum efficiency up to 96.4%. The results were admissibly confident with linear and non-linear Langmuir, Freundlich and pseudo first-order models. Langmuir isotherm indicated qm for the RHS up to 15.6 mg/L compared to RRH with 7.3 mg/g and RB with 4.8 mg/g. Adsorption process in this system was limited by mainly sorption process and bulk or boundary layer diffusion. The dominant reaction was estimated to be the ion-exchange according to the obtained energy values of sorption.