REMOVAL OF SOME HEAVY METAL IONS (Cd2+, Cr3+, Pb2+, Hg2+, and Ni2+) FROM AQUEOUS SOLUTIONS USING SOURSOP FRUIT BARK (SSB)

Abstract

The adsorption capacity of soursop fruit bark (SSB) (Annona Muricata L.) towards metal ions such as Cd2+, Pb2+, Hg2+, Cr3+, and Ni2+ were studied. The adsorption capacity was investigated by batch experiments using 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 classical adsorption isotherms. The results showed that the removal percentages increased as the sorbent temperature increased (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 calculated. The values of the separation factor (RL) for soursop fruit barks are in the range of 0.362-0.472 which indicated favourable biosorption. The biosorption process of the metal ions onto SSB was favoured by both Langmuir and Freundlich models. Results showed that the Pseudo-Second order equation provided the best model for the biosorption process of the metal ions onto SSB. Thermodynamics parameters evaluation for all the metal ions gave a positive value of ∆𝐻𝑜. ∆𝐻𝑜for SSB were 22.38KJ/mol, 42.38KJ/mol, 30.27KJ/mol, 42.19KJ/mol, 10.69KJ/mol for Cd2+, Pb2+, Hg2+, Cr3+, and Ni2+ respectively. The negative values of the Gibbs free energy at all the temperatures showed that the adsorption process was spontaneous and the positive values of ∆𝑆𝑜 for the SSB reflected good affinity of the metal ions towards the soursop fruit barks. The results confirmed that SSB had a good potential to be used as biosorbent for the removal of cadmium, chromium, nickel, mercury and lead from waste water.