Optimization of Heavy Metals Removal from Wastewater by Adsorption onto Theobroma cacao pod

Abstract

In this study, Theobroma cacao pod (TCP) adsorbent was prepared, characterized and tested for removal of Cd²⁺ and As³⁺ from synthetic wastewater. The TCP had a good cation exchange capacity, large surface area and small particle size. The optimization results from Central Composite Design (CCD) predicted the adsorption percentages of 98.72 and 92.48 for Cd²⁺ and As³⁺ respectively. The experimental results revealed the removal percentages of Cd²⁺ and As³⁺ by TCP as 98.80% and 92.46% respectively, which were in good correlation with the values predicted by the CCD for the respective metal ions at the optimum conditions of adsorption. The isotherm studies showed that the adsorption of Cd (II) and As (III) ions onto TCP best fitted the Langmuir isotherm model. The kinetic studies showed that rate of adsorption of Cd (II) and As (III) ions followed the pseudo second- order kinetic model. Thermodynamic studies revealed that metal adsorption onto TCP was feasible, spontaneous and endothermic for Cd (II) ions while the uptake of As (III) followed an exothermic process. The TCP, owing to its good cation exchange capacity, low-cost and eco-friendliness, has a good potential to be utilized as an alternative adsorbent in wastewater treatment.