Lead Adsorption on Rice Husk as a Function of pH Control

Abstract

The use of agro-based waste materials in treatment zones for removal of heavy metals from the aqueous phase by adsorption represents a low-cost and possibly effective remediation alternative. In this study, the adsorption of lead (Pb²⁺) on a rice-husk residue was tested in different experiments with initial 100 mg Pb²⁺/L, initial pH values of 3, 5, or 7, and solid:liquid ratio (mass basis) of 1:20. In some experiments pH was allowed to vary, whereas in other experiments pH was kept approximately fixed. For the experiments with variable pH, Pb²⁺ was most adsorbed (93%) in the test where pH increased from 3 to 5.1, and least adsorbed in the test where pH decreased from 7 to 6.4. The point of zero charge of the rice husk was determined to be pH 4.5. For the experiments with fixed pH, the optimum pH for Pb²⁺ adsorption (95%) was found to be pH 5, and the test at pH 3 removed 67% of the initial Pb²+. The results allowed to grasp the significant effect pH control plays on Pb²⁺ adsorption, and the relevance of studying the factors that control pH during Pb²⁺ adsorption in a field application (in-situ treatment zone).