Removal of Common Heavy Metals from Aqueous Solutions by Waste Salvadora persica L. Branches (Miswak)

The adsorption ability of miswak (Salvadora persica L.) waste was investigated for the removal of common heavy metals; Pb(II), Cu(II), Ni(II) and Cd(II), from aqueous systems. The miswak mainly consists of saponins, tannins, silica and resin, which are accounted for the removal of heavy metal ions from aqueous systems. The effects of various parameters, such as solution pH, contact time, initial concentration of the heavy metal ions and adsorbent dosage were examined. The linear correlation coefficients of Langmuir and Freundlich isotherms were obtained and the results revealed that the Freundlich isotherm fitted the experiment results better than Langmuir isotherm (r2=0.974–0.993). The maximum adsorption capacities of Pb(II), Cd(II), Cu(II) and Ni(II) for per g miswak waste were calculated as 6.84±0.23, 5.91±0.20, 4.56±0.17 and 3.73±0.15 mg, respectively. Five cycles of adsorption-desorption were carried out revealing the strong reuse potential of this low-cost adsorbent. The results indicate that the miswak waste, which has a very low economical value, could be used to effectively adsorb common heavy metals from aqueous systems for environmental cleaning purposes.