The removal of heavy metals (Cu2+, Zn2+ and Ni2+) from aqueous model solution has been studied using Tripoli (Microcrypto crystalline silica = MCCS) as adsorbent. The adsorption equilibrium studies are performed with a constant initial metal ion concentrations (namely 10 and 100 mg.L-1) and varying adsorbent weight. The adsorption percentages of Zn2+ and Cu2+ ions increase sharply by increasing adsorbent doses in the range of 0.5 g to 5 g (approx.) and then it slightly increases in the range of 5 g to 10 g of Tripoli, while the percentage removal of Ni2+ increases sharply in the whole range of 0.5 to 10 g of Tripoli. In this level, the maximum adsorption might be attained. The best pH value is at about 7 to achieve the maximum removal, otherwise the precipitation of sorbet and the hydrolysis of sorbent are occurred. The removal percentages at pH = 7 are high (Approx. above 92%), where the diluted Zn2+ is characterized as the highest removal efficiency. The obtained experimental data has successfully fitted to the Langmuir and Freundlich isotherm models. The Freundlich constant Kf for Zn2+ is greater than the other heavy metals for the initial concentration 100 mg.L-1. The negative value of DG° confirms the feasibility of the process and the spontaneous nature of adsorption with a high preference for metal ions (Zn2+, Cu2+ and Ni2+, respectively) to adsorb onto Tripoli
