Removal and recovery of lead from wastewater using an integrated system of adsorption and crystallization

Abstract

This study explores the feasibility of an integrated system comprising adsorption and crystallization in a pellet reactor to remove and recover lead from aquatic environment. The selective adsorption of Pb2+ over Ca2+ and Mg2+ was investigated using citric acid modified sugarcane bagasse (SCA) in batch and column systems. Selective separation of Pb2+ from the mixed solution was achieved at a molar ratio 3.22 <Co,batchCa+Mg/Co,batchPb < 4.49 in batch mode while in a packed bed column, lead was selectively adsorbed by SCA up to a capacity of 0.767 mmol/g with a bed height of 7 cm, a flow rate of 1.5 ml/min and an initial lead concentration of 0.482 mmol/L. The dynamic study shows a close agreement between the experimental results and the Thomas and Yoon-Nelson models. The desorption study of equilibrium biosorbent SCA in a column system demonstrates that sodium chloride is a promising desorption reagent, with a desorption capacity of 80% Pb2+. In addition, synthetic lead wastewater with characteristics simulating the concentrate from desorption of saturated SCA was further treated in a fluidized bed denoted as pellet reactor. Lead (II) was quantitatively recovered at optimized conditions of pH 10, molar ratio [CO32−]: [Pb2+] = 3:1, superficial velocity 9.55 m/h, and initial lead concentration 2.43 mM. The well-controlled crystallization process of cerussite on the surface of grain sand in the pellet reactor is comparable with the chemical equilibrium speciation data obtained by Visual MINTEQ. Overall, the developed system comprising adsorption combined with a pellet reactor was found sufficient to remove and recover lead as PbCO3 from wastewater.