Kinetics of Mercury and Nickel Adsorption Using Chemically Pretreated Cocoa (Theobroma cacao) Husks

Abstract

Abstract. Agroindustrial wastes have been widely used to prepare adsorbents for heavy metal removal because of their low cost, accessibility, and high efficiency. This work focuses on preparing a novel material from cocoa ( L.) husk residual biomass chemically modified with sodium hydroxide for used as a biosorbent for nickel and mercury uptake. The cocoa husk residual biomass was characterized by FT-IR analysis to test the diversification of functional groups. The effect of particle size on removal yield was evaluated through batch adsorption experiments. The experimental results were fitted to mathematical models to determine the adsorption kinetics and isotherms. Particle size significantly affected the adsorption process, and the highest removal yields (91.59% and 79.96%) were achieved using 0.36 mm and 0.5 mm particles for Hg (II) and Ni (II) ions, respectively. The adsorption kinetic model that best fit the experimental data corresponded to the Elovich model, with correlation coefficients (R2) above 0.89. The adsorption process of nickel and mercury onto cocoa husk biomass followed the Freundlich isotherm model. The results show that modification with sodium hydroxide improves the adsorption capacity of cocoa husk residual biomass, indicating that this novel material could be efficiently applied for nickel and mercury uptake. Keywords: Adsorption, Heavy metals, Removal yield.