Adsorption Performance Of Yemeni Natural And Modified Zeolite For Pb²⁺and Cd²⁺ In Water

Pb²⁺and Cd²⁺are a kind of toxic pollutants widely distributed in the environment.They can enter into the water environment in various ways,and they are highly toxic,difficult to be biodegraded,and easy to be accumulated in organisms.Therefore,it’s essential to find effective materials to remove Pb²⁺and Cd²⁺or minimize their concentration in the water to meet the standards before discharge or use.Zeolite is a low-cost material that exhibits a porous structure,excellent molecular sieving,and high ion-exchange abilities.Furthermore,the chemical treatments can modify the properties of zeolite to improve their adsorption and ion exchange capacities to pollutants.This work studies the removal performance of heavy metal ions from the water by Yemeni natural zeolites,which were used as low-cost adsorbents.Meanwhile,the natural samples were modified by a chemical solution（Na Cl or KCl）to improve their adsorption and ion exchange properties,the optimal conditions for the adsorption of natural and modified zeolites to Pb²⁺and Cd²⁺were also determined.Firstly,various analytical methods were used to characterize the physical and chemical properties of zeolites.The results showed that the clinoptilolite was the main phase in the composition of Yemeni natural zeolites.Furthermore,the natural zeolite maintained a high percentage of Si and Al.the modification of Na Cl or KCl solutions could remove impurities and volatiles on the surface of zeolites,and expand their pores,but had no significantly influences on the composition of zeolites.After modified by Na Cl or KCl solutions,the specific surface area of zeolites decreased,but their adsorption average pore diameter and total pore volume increased.The results of adsorption equilibrium studies indicated that natural zeolite is an excellent adsorbent for removing Pb²⁺and Cd²⁺from water solutions.The maximum adsorption capacities(q_max)of natural zeolite,Na Cl modified zeolite,and KCl modified zeolite were found to be 12.49,36.44,15.8 mg/g,for Pb²⁺ions and 18.03,33.05,25.37 mg/g for Cd²⁺ions,respectively.Also,the fitting results of isotherm models showed that the adsorption of Pb²⁺and Cd²⁺ions fit into the Langmuir model better than the Freundlich model,indicating that monolayer adsorption and ion exchange were the predominant processes in removing Pb²⁺and Cd²⁺ions by zeolites.The results of adsorption kinetics studies showed that the natural zeolite could rapidly remove Pb²⁺and Cd²⁺ions from water,and most heavy metal ions could be adsorbed by zeolite in 1 hour.Batch experiments were carried out to determine the influences of parameters on adsorption rate,including initial solution p H,reaction time,initial solution concentration,zeolite particle size,and reaction temperature.The results showed the optimum removal of Pb²⁺and Cd²⁺by natural zeolite reached at the p H of 5-6 and reaction temperature at 35°C.The kinetics studies also showed that the adsorption efficiency of heavy metal ions enhanced with the decrease in the size of the adsorbent particles while decreased with increasing initial concentration of the solution.Moreover,Na Cl and KCl chemical modification could improve the adsorption efficiency of natural zeolite.In comparison,the Na Cl modified zeolite showed higher adsorption efficiency for Pb²⁺and Cd²⁺ions in water than the KCl modified zeolite.