Metal ion sorption by alocally available natural polymineral adsorbent in Kenya.

Abstract

Two different samples of a micaceous mineral, herein referred to as MicaMA and MicaMB obtained from two separate sources here in Kenya, were utilized as inexpensive and effective adsorbents for the removal of heavy metal ions (Cu2+, Cr3+, Cd2+ and Pb21from aqueous solutions. The effects of contact time, pH, temperature, adsorbate and adsorbent concentration, acid- washing of mineral were investigated. Maximum removal of the metal ions took place over the pH range of 4.0 to 7.0. The adsorption of the metal ions increased with increase in the ratio of dose of mineral to concentration of metal ion and decreased with increasing adsorbent particle size. Temperature was found to have negligible effect on adsorption from 25°C to 60°C. Acid washing of the mineral samples showed drastic reduction in % adsorption for both Micalvl., and MicaMB. 20 minutes equilibration time was found to be adequate, yielding almost 100% adsorption at low concentration of metal ions (less than 100 ppm). Sonication was generally found to improve % adsorption and this was attributed to the possible deaggregation of the mineral particles, thereby exposing more adsorption sites. Isotherm studies showed that uptake of metal ions occurred by monolayer sorption with the eventual formation of a plateau at saturation. Freundlich adsorption isotherms showed higher adsorption capacity by micaMA than micaMB for all the metal ions investigated, with all adsorption isotherms yielding values for adsorption intensity, n, higher than 1.This indicated favourable adsorption.