Studies on Removal of Toxic Cd2+ and Pb2+ from Aqueous Solutions by Using Agro-waste (Cola nitida Pod)

Abstract

Industrial processes and used commercial (metallic) products generate large quantity of metallic waste products which are discharged into the water or land-dump sites. It has been estimated that the toxicity due to metallic discharge, into the environments far exceeds the combined total toxicity of all radioactive and organic wastes. The extent to which metals and their compounds are used in industrial operations cannot be overemphasized. Meanwhile, effluents from the industrial operations contain some heavy metal ions which are reported to be harmful to human and plant health when the effluents are discharged untreated into the environment. Therefore the need to remove heavy metal ions from industrial effluents before discharging becomes indispensable. The removal /adsorption of lead (II) ion and cadmium (II) ion from their aqueous solution by Cola nitida pod were investigated. The effects of contact time, initial metal ion concentration, initial pH, adsorbent dose and temperature on metal ions removal were studied, in contact time range of 15- 90 minutes, metal ions initial concentration range of 50- 200 mg/l. pH range of 5-8, adsorbent dose range of 0.1- 0.7 g and temperature range of 303-333 K. The equilibrium time was found to be of the order of 60 minutes. Percentage removal of both Pb2+ and Cd2+ from their aqueous solution by the adsorbent (Cola nitida pod) was found to be above 90%. The percentage removal of lead (II) ion and cadmium (II) ion by the test adsorbent was affected by changes in initial metal ion concentration, initial pH, adsorbent dose, and temperature. Langmuir and Freundlich adsorption isotherms were used to examine the adsorption mechanisms of the metal ions on the test adsorbent, and the adsorption of both Pb2+ and Cd2+ on Cola nitida pod fitted perfectly into the adsorption isotherms. The comparison of correlation coefficients values (R2) of the linearized form of both Langmuir and Freundlich models shows that the Langmuir model yields a better fit for the experimental adsorption equilibrium data and the most appropriate isotherm to describe the equilibrium data for lead and cadmium and hence Langmuir adsorption is recommended for the adsorption studies of Pb2+ and Cd2+. The comparison of correlation coefficients values (R2) of the linearized form of both Langmuir and Freundlich models shows that the Langmuir model yields a better fit for the experimental adsorption equilibrium data and the most appropriate isotherm to describe the equilibrium data for lead and cadmium.