Removal of Pb(II) Ion from Aqueous Phase Under Uncontrolled and Controlled pH Conditions by Granular Activated Alumina

Abstract

AbstractAdsorption is a widely used technique for the removal of heavy metals from water/wastewater. Several published literature has ignored the impact of changes in solution pH during adsorption experiment and consequently the removal of metals by precipitation mechanism. The present work investigates the kinetics and equilibrium of Pb(II) ion removal under uncontrolled and controlled pH conditions using granular activated alumina (GAA). During the kinetic study, Pb(II) ion removal obtained under uncontrolled pH conditions (4.3804 mg/g) was higher compared to the same observed under controlled pH (3.6084 mg/g). Higher Pb(II) metal removal under uncontrolled pH conditions was attributed to precipitation mechanism due to the rise in solution pH during the adsorption process. The lower value for pseudo-second-order kinetic constant ‘k2’ [0.0173 (g/mg.min)] and higher value for Freundlich model adsorption capacity parameter ‘k’ [3.2479 (mg/g)/(mg/L)1/n] under uncontrolled pH conditions compared to controlled pH conditions [k2 = 0.0206, k = 0.8663] has further confirmed higher rate of Pb(II) removal under uncontrolled pH conditions due to rise in solution pH. As the solution pH increased during adsorption, the application of kinetic and adsorption isotherm models to represent the data obtained under uncontrolled pH conditions is not justifiable. Many published studies have only mentioned the initial pH of the solution and never monitored pH during the adsorption process, which eventually wrongly attributed the removal of metal by precipitation mechanism to the uptake by the adsorbent.KeywordsAdsorptionHeavy metalLead(II)Metal precipitationMetal uptake