Acid functionalization of activated carbon derived from coffee husks for the adsorption of lead in aqueous solution

This study is part of research into effective and less costly adsorbents for the removal of lead from aqueous solutions. Its objective is to functionalize activated carbon derived from coffee husks to improve its adsorption capacity. Activated carbon (AC) is obtained by chemical activation with a potassium hydroxide (KOH) solution. Functionalized carbon (AC-HNO₃) is obtained by impregnating AC with a 3N nitric acid solution followed by boiling at 120°C. The porosity of the activated carbons was studied by determining the iodine and methylene blue index. The surface chemistry of the activated carbons was evaluated by determining the pHzcp and surface functions. The performance of the carbons was evaluated for lead adsorption and studied as a function of contact time, carbon dose, solution pH and initial lead concentration. The elimination kinetics were monitored by atomic absorption spectrophotometry and then modelled according to pseudo-first and second order models. The iodine and methylene blue index were 482.3 and 18.56 mg/g and 336.1 and 35.8 mg/g, respectively, for CA and CA-HNO₃. The total acid and base site numbers are 2 and 2.5 meq/g and 6.21 and 1.51 meq/g, respectively, for CA and CA-HNO₃. The kinetic study of lead adsorption on these adsorbents follows the pseudo-second order model with a correlation coefficient of 0.99 and an equilibrium time of 75 min for both activated carbons. The quantities adsorbed at equilibrium are 6.64 and 7.35 mg/g for CA and CA-HNO₃, respectively.