Adsorption Dynamics of Agricultural Waste Activated Carbon in Water Quality Improvement

Abstract

This study investigated the removal of Lead and Cadmium ions from aqueous solution using activated carbons from agricultural wastes. Activated carbons prepared by chemical activation using Phosphoric acid were characterized by Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. The influence of contact time, initial concentration and adsorbent dose which governed the efficiency of the process was ascertained through batch adsorption studies. Adsorption isotherms were determined by correlating with Langmuir and Freundlich isotherms and the kinetic studies were correlated with pseudo first order and pseudo second order equations. The results showed that the amount of Lead and Cadmium adsorbed decreased as the adsorbent dose increased while the adsorption capacity increased with increased in contact time and initial concentration. Activated carbons prepared from Coconut shell and palm kernel (shell and cake) competed favorably with the commercial activated carbon in percentage removal of the metal ions as all the activated carbons had over 90 % removal within 60 minutes when 1g of adsorbent was used. The equilibrium data fitted best into Freundlich isotherms for both metal ions. The rate of adsorption could be described by pseudo second order for all the adsorbents except Coconut shell activated carbon in the adsorption of Lead while intra-particle diffusion was the limiting step for Cadmium adsorption. Therefore, the agricultural by-products can be used as effective, low-cost, and environmentally friendly adsorbents for domestic water treatment in many parts of the world.