Lead and cadmium removal from natural freshwater using mixed activated carbons from cashew and shea nut shells

Biomass wastes are potential low-cost and promising materials for removal of carcinogenic metals in contaminated waters. However, no information is available for cashew and shea nut shells that are abundantly grown in West Africa. We investigated lead and cadmium removal from aqueous solutions using activated carbons prepared from cashew and shea nut shells collected in Cote d'Ivoire, West Africa. The effects of contact time, initial concentration of cadmium(II) and lead(II), pH, and adsorbent mass were examined. The cashew and shea nut shells and their mixture were found to be good sorbents for cadmium and lead at an optimum mass dose of 12g/L and pH5.0 in synthetic solution. The adsorption rates varied between 94 and 99% for lead and between 86 and 94% for cadmium. The Langmuir model described isotherm of lead(II) ions adsorbed by shea nut shells, while lead adsorbed by cashew nut shells fitted the Freundlich model. The cadmium adsorption isotherms were described by Freundlich model. The Langmuir model best fitted lead and cadmium adsorptions by the mixture of the two activated carbons. Moreover, lead and cadmium adsorptions followed second-order kinetics. The cashew and shea nut shell activated carbons, and their mixture successfully removed cadmium and lead from natural freshwater.