Use of Syrian natural zeolite for heavy metals removal from industrial waste water: Factors and mechanism

Abstract

Using static adsorption techniques, the adsorption of heavy metals of V+5,Ni+2,Zn+2,Pb+2 was investigated on natural zeolite (NZ) mined from southern Syria. This study was performed in order to determine the adsorption capacity of low- cost zeolite used to remove heavy metals from desalter wastewater of crude oil, many heavy metals are contained in this wastewater and threaten human life and fauna when discharged without treatment. The effects of the following factors on adsorption process were studied: contact time, initial concentration, size of adsorbent particles, the competing ions and hardness. The results showed that the adsorption rate accelerates at the beginning adsorption. The optimal removal efficiency was reached during 6 hours. The Langmuir adsorption isotherm model was able to give good fits to experimental data. An increase in the concentration of exchangeable cations (Ca+2) was noticed in solution at equilibrium. This finding reveals that ion exchange between zeolite and solution is responsible for the removal of heavy metal ions from the solution. It was found that precipitation affects the removal rate of Pb+2 from solution while it has negligible effect on other three ions. The highest pH of equilibrium was higher than the minimum pH necessary for complete precipitation of Pb+2 as hydroxides. The regeneration ability of the studied zeolite was examined using NaCl salt at concentration (20 g/L). The results also showed that the highest selectivity of (NZ) was for V+5 and Pb+2. Therefore their desorption efficiency is the lowest. The desorption series is a reversal of the adsorption series, desorption series Ni+2> Zn+2> Pb+2> V+5. So the locally - available NZ is considered a low - cost adsorption that can be applied to remove heavy metals.