Adsorption of Cd2+ and Ni2+ ions in coal fly ash

The single-component and bi-component adsorption properties of Cd2+ and Ni2+ ions in coal fly ash particles were investigated. The results showed that coal fly ash was very effective for the removal of Cd2+ and Ni2+ ions from aqueous solutions; the removal percent of metal ions increases with the solution pH value. The adsorption equilibrium is achieved in about 60min; the adsorption capacity of Ni2+ is higher than that of Cd2+. The single-component adsorption corresponds with the Freundlich and RedlichPeterson (RP) isotherms. A significant competitive adsorption effect was found between Cd2+ and Ni2+ ions in the bicomponent adsorption; this competitive effect increased with increasing the concentrations of interfering ions. Equilibrium isotherms for the bicomponent adsorption of Cd2+ and Ni2+ ions have been analyzed by different isotherm models, which suggested that the bicomponent adsorption equilibrium data can be fitted well by the Freundlich competitive adsorption model. The results of desorption tests revealed that Cd2+ desorption from ash was easier than Ni2+ desorption. The solutions of 0.1mol/L HCl, 0.1mol/L HNO3 and 0.05mol/L H2SO4 exhibit similar efficiencies for the desorption Cd2+ and Ni2+ from ash; the desorption rates are > 60% for Cd2+ and > 35% for Ni2+.