Adsorption of Pb2+ from aqueous solution by modified melon (Citrullus lanatus) seed husk.

Abstract

The application of Modified Melon Seed Husk (MMH) an agricultural waste in the remediation of water contaminated with lead ions was investigated in the present study. Modification was done by soaking the melon seed husk in 0.5M NaOH solution. Batch kinetic and isotherm studies was performed to understand the ability of the adsorbents. Effect of some process variables were assessed viz: pH, initial metal ion concentration and sorbent dosage on the sorption process. The equilibrium sorption isotherm was studied using the Freundlich and Langmuir isotherm models. The results obtained showed that the process of the sorption fitted better with the Freundlich isotherm, implying that the sorption occurred on a heterogeneous surface of the MMH. The monolayer adsorptioncapacity determined from the Langmuir adsorption equation was found to be 52.08 mg/g which competes favourable with some other biosorbents. Data obtained from the kinetics of the sorption process via initial metal ion concentration were analyzed using pseudo second order, the pseudo first order model and intraparticle diffusion model. The sorption process obeyed the pseudo second order kinetic model better than the pseudo first order kinetic model, thus suggesting the role of chemisorption in the mechanisms of the sorption. The intraparticle diffusion model showed that intraparticle diffusion is not the singular rate limiting step in the sorption process. The kinetic parameters suggest that adsorption of lead ions by MMH was favourable. Overall, the present findings suggest that MMH, an environmentally friendly, efficient and low-cost biosorbent is useful for the removal of Pb²⁺ from aqueous media.

Key words: Adsorption, Isotherm, Kinetics, Lead, Melon seed Husk, Wastewater