Locally-Sourced Beans Husk, a Potential Adsorbent for Cd(II), Pb(II), Hg(II) Ions in Aqueous Solution

Ground beans husk (GBH) was used to remove Cd (II), Pb (II) and Hg (II) ions from their aqueous solution. FTIR analysis showed the presence of functional groups that could serve as sites for adsorption. Adsorption was carried out with the variations of metal ion concentration, contact time, temperature and pH. Results obtained showed that adsorption in all cases was better described by pseudo second order kinetics with the R2 values of 0.999, 0.999 and 1.0 for Cd (II), Pb (II) and Hg (II) respectively. The experimental data for Cd (II) and Hg (II) were better described by Langmuir isotherm with the highest correlation co-efficient R2 values of0.935 and 0.990 and Pb (II) by Temkin isotherm model with R2 value of 0.870. Thermodynamic studies showed that the reaction was spontaneous and exothermic for Cd (II) and Pb (II) ions but endothermic for Hg (II) ion. pH studies revealed that the optimum pH value for better adsorption was pH of 6 for the three metal ions.