ADSORPTION OF Zn2+ ONTO UNMODIFIED AND CITRIC ACID MODIFIED GROUNDNUT SEED SHELL FROM AQEOUS SOLUTION.

Abstract

This work studied the removal of Zn2+ from aqueous solution using unmodified and citric acid modified groundnut seed shell. Batch experiment was carried to ascertain the effects of adsorbent dose, particle size, and contact time on such adsorption with initial metal ions concentration of 100 mg/l at a temperature of 25 oC and pH of 7.5. It was deduced from the experiment that the amount of metal ion adsorbed increased as the adsorbent dose was increasing in both unmodified and citric acid modified ones; 97.27 mg/g at adsorbent dose of 4 g for the unmodified and 98.91 mg/g at adsorbent dose of 5 g for the modified. 250 µm and 354 µm were the optimum particle sizes for both unmodified and modified groundnut seed shell respectively, values given as 89.4 mg/g for the unmodified and 84.3 mg/g for the modified. Maximum adsorptions were all favoured at longer contact time; 90.31 mg/g at 120 minutes and 76.2 mg/g at 90 minutes for unmodified and modified, respectively. Generally, it was observed that the unmodified groundnut seed shell showed greater adsorption capacity than the modified groundnut seed shell. Lagergren’s first-order and Ho-McKay’s pseudo-second-order kinetics hypothesis were used to study the kinetic of metal ions adsorption onto unmodified and modified groundnut seed shell. It was observed that the removal of metal ions over the adsorbents showed a better fit with the pseudo-second-order process than the pseudo-first-order process with R2 values given as 0.957 and 0.967 for both unmodified and modified groundnut seed shell. Kinetics of Zn2+ adsorption obeyed the Pseudo-second order model which suggests chemisorption as the rate-determining step in adsorption process. Based on the results of the study, it was shown that the groundnut seed shell is capable of adsorbing Zn2+ from aqueous solutions especially when unmodified.