Removal of Cr(VI) Using Citric Acid and Phosphoric Acid-Modified Groundnut Shells

The increasing industrialization leads to toxic pollutants in wastewater and it has a considerable impact on human health due to toxicity, accumulation, and persistence in nature. The study concentrated on the adsorption of chromium (VI) ions using groundnut shells modified with phosphoric (PA-GNS) and citric acid (CA-GNS) in aqueous solutions. Several factors were examined, encompassing contact time, pH, adsorbent dose, and initial chromium concentration, were systematically examined to understand their impact on the adsorption process. The findings revealed that, under optimized conditions of pH 2, stirring speed at 200 rpm, initial metal ion concentration of 50 mg/100 mL, adsorbent dose of 1500 mg/100 mL solution, a contact time of 120 minutes (45 minutes for PA-GNS) for stirring, and a temperature of 25°C, the maximum removal percentages for Cr(VI) were 96.95% and 93.69% for PA-GNS and CA-GNS, respectively. The biosorption of Cr(VI) ions by both PA-GNS and CA-GNS was found to conform to the Langmuir and Freundlich isotherm models. Regarding the kinetics of the adsorption process, it followed a pseudo-second-order model with rate constants of 3.25 and 3.311 (g/mg.min) for PA-GNS and CA-GNS, respectively.