Studies Of Removing Cadmium(Ⅱ) With Modified Zeolite Powder From Micro-polluted Water

Modified zeolite powder,a new adsorbent,was prepared by natural zeolite powder,chitosan and sodium hydroxide,at different conditions,such as different modified time,different mixture ratio of zeolite powder and chitosan,and different sodium hydroxide concentration.And the optimum modified conditions of the zeoloite powders was determined by the cadmium(Ⅱ) removing rate in micro-polluted water after the treatment of adsorption-coagulation.The results show that modified time is not the longer the better,chitosan usage is not the larger the better, and sodium hydroxide concentration has not drastically influence over the cadmium(Ⅱ) removal. Considering material costs and meanwhile ensureing higher cadmium(Ⅱ) removing rate by modified zeolite powders,the optimum preparation technology is modified time 12 h,mixture ratio of chitosan and zeolite powder 1:40,sodium hydroxide concentration 2 mol·L^-1.Modified zeolite powder was analyzed by Fourier transform infrared spectrometer(FTIR), scanning electron microscope(SEM),surface measuring instrument and energy dispersive analysis of X-ray(EDAX).It was used to remove cadmium(Ⅱ) from micro-polluted source water, and the effects of contact time,pH,initial concentration of cadmium(Ⅱ) particle size and zeolite powder dosages on the removal of cadmium(Ⅱ) were investigated.The results show that cluster structure becomes pore structure of the modified zeolite powder,and chitosan is supported on it, forming porous material with bigger inner specific surface area.Nitrogen isotherms of natural and modified zeolite powders show that adsorption surfaces are multilayer,having similar mode of pore-size distribution.The tatal pore volume and average pore size of modified zeolite become larger,forming more regular mesoporous structure.Under the experimental conditions, longer contact time,higher pH,smaller particle size and larger zeolite powder dosages can make better removal efficiency of cadmium(Ⅱ) by natural and modified zeolite powder.The removal efficiency of cadmium(Ⅱ) by modified zeolite powder is better than that by natural zeolite powder.The cadmium(Ⅱ) saturation capacity of modified zeolite is 6.36 times as large as that of natural zeolite.When cadmium(Ⅱ) concentration is less than 60μg/L,sievemeshnumber 200 0.8g/L modified zeolite powder can make cadmium(Ⅱ) concentration after treatmentmeet the requirement of Sanitary Standard for Drinking Water(GB 5749-2006).Adsorption mechanism of cadmium(Ⅱ) on zeolite powders was discussed from the standpoint of sorption thermodynamic and sorption kinetics.The adsorption of cadmium(Ⅱ) on natural and modified zeolite indicated spontaneous natural of adsorption,regarding physical adsorption as main reason dedicating to micropore,and can be described by Langmuir, Freundlich,Dubinin-Kaganer-Radushkevich(DKR) isotherm models.Meanwhile,the adsorption of cadmium(Ⅱ) on modified zeolite was followed by chemical adsorption as the supported chitosan can chelate cadmium(Ⅱ) ions by chemical bond,and the cadmium(Ⅱ) removal effciency was improved obviously.The sorption kinetics can be well described by the pseudo-second-order kinetics,which can predict the influence of time on adsorption.The method is based on conventional water restriction technics,no need to adjust pH and add structures,and with very strong adaplability.It is of reference and guiding significance to the purification of cadmium(Ⅱ) pollution in drinking water.