BIOSORPTION OF Cd2+, Cr3+, Pb2+, Hg2+, and Ni2+ FROM AQUEOUS SOLUTIONS USING BEANS HUSK (BH)

Abstract

The adsorption capacity of beans husk (Vigna Unguiculatae) towards metal ions such as Cd2+Pb2+, Hg2+, Cr3+, and Ni2+ were studied. The adsorption capacity was investigated using batch experiments under different experimental conditions such as pH, contact time, adsorbent dosage, adsorbent temperature and metal ion concentration to identify the optimum conditions. The effects of these parameters on the adsorption capacity were studied. The adsorption data were modeled using both the Langmuir and Freundlich adsorption isotherms. The results showed that the removal of ion percentages increased with increase in sorbent temperature (2980K-3430K). The effect of metal ion concentration was studied at six different concentrations (40 -140 ppm) and the results showed that the removal percentages increased as pH increased (pH 4-14). The fitness of experimental data to equilibrium isotherm models was tested and thermodynamic parameters were equally calculated. The values of the separation factor (RL) for beans husk were in the range of 0.463-0.373 which indicated favourable biosorption. The biosorption process of the metal ions onto BH was favoured by Freundlich model. Results showed that the Pseudo-Second order equation provided the best model for the biosorption process of the metal ions onto BH. Thermodynamics parameter evaluation for all the metal ions gave a positive value of ∆𝐻𝑜. ∆𝐻𝑜 for BH were 31.37KJ/mol, 38.63KJ/mol, 29.99KJ/mol, 12.06KJ/mol, 1.29KJ/mol for Cd2+, Pb2+, Hg2+, Cr3+, and Ni2+ respectively. The negative values of the Gibbs free energy at all the temperatures (298k-343k) showed that the adsorption process was spontaneous while the positive values of ∆𝑆𝑜 (0.105,0.141,0.129,0.042,0.009KJ/mol) for Cd2+, Pb2+, Hg2+, Cr3+, and Ni2+ respectively reflected good affinity of the metal ions towards the beans husk. The results have established that BH has a good potential to be used as biosorbent for the removal of cadmium, chromium, nickel, mercury and lead from waste water.