Comparative Evaluation of Cadmium Ion Uptake byWastes Generated from Zea mays

Abstract

The removal of cadmium ions from aqueous solution by Zea mays husk (HK), stalk (SK), cob (CB) and seed chaff (SC) which are wastes generated after harvesting or processing this cereal were studied and compared. Batch adsorption studies were utilized to decide the impact of different parameters on the process. Cadmium ion uptake by the adsorbents increased with increase in pH from 3 – 6, with HK and CB showing a steady increase as pH changed. The removal efficiency of all the adsorbents increased with adsorbent dose. However, after 0.4 g load of adsorbent, the removal efficiency of SC became independent of adsorbent load. The maximum adsorption capacity of HK, SK and CB was attained in 12 minutes while SC reached this point in 9 minutes. The adsorption equilibrium data for all the adsorbents fitted well in the Freundlich isotherm model. The adsorption intensities of all the adsorbents from this model were greater than 1, and indicated that metal ion adsorption by these adsorbents were favourable physical processes. The rate of cadmium ion adsorption onto the adsorbents was better explained by the pseudo second-order kinetic model. The calculated equilibrium adsorption capacity of HK (16.36 mg/g) and SK (13.51 mg/g) showed that they had potentials for commercial application in the remediation of cadmium ion polluted water.