Study On Removal Efficiency Of Modified Orange Peel For Perchlorate In Water

As a kind of persistent pollutant, perchlorate(Cl O4-) widely exists in the natural environment, which produced in the natural process and human activities. Perchlorate is harmful to the human body, which ascribed to the fact that perchlorate will interfere with the absorption of iodine ions, thus affecting the normal function of the human thyroid gland and resulting in the decrease of human metabolism and growth capabilities. Therefore, it is very valuable to find technical methods to remove perchlorate. The adsorption technology to remove contaminants has been extensively applied due to its following advantages: high removal efficiency, quick reaction rate and low economic cost. In this paper, orange peel was modified by appropriate method to prepare the adsorption materials with anion exchange function. The changes of physical and chemical properties of material before and after modification were investigated by various characteristic techniques. At the same time, the adsorption capacities of modified orange peel on perchlorate, the influence factors of perchlorate adsorption and the effects of coexisting anions on perchlorate adsorption were studied, respectively. In the end, the regeneration of adsorbent was explored preliminarily. The experimental results indicated that: the orange peel after modification, its surface became more clear and smooth; its surface potential changed from negative to positive; the large number of amino group was grafted to the cellulose structure of the orange peel. At the same time, a number of exchangeable chloride ions were introduced. Perchlorate adsorption capacity was increased with modified orange peel dose increasing, The adsorption of perchlorate had reached equilibrium when the adsorbent dosage exceeded 2000 mg/L; Perchlorate could be removed effectively at a wide range of p H(from 1.5 to 11). The Redlich-Peterson model was fitted to the adsorption isotherm very well. The pseudo-second-order equation(R2> 0.99) could describe well the perchlorate adsorption on modified orange peel under different temperature conditions, and the rate of adsorption reaction was accelerated with increasing temperature. The process of perchlorate adsorption on modified orange peel was spontaneous exothermic reaction. Ion exchange was primary mechanism for uptake of perchlorate onto modified orange peel. The experimental results of coexisting anions effect showed that: three anions had the effects in a different order for perchlorate adsorption in the different p H range. The order of competitive effect was SO42-> NO3-> PO43- at p H < 3; when 3 < p H < 10, the order was SO42-> PO43-> NO3-; the effects of three anions on perchlorate adsorption tended to be equal at p H > 10. The order of four anions adsorption capacities on modified orange peel was Cl O4- > NO3- > SO42- > PO43-in single-solute system; The competitive adsorption existed between coexisting anions in the order of PO43-> SO42-> NO3-. The equilibrium data fitted Freundlich isothermal model and pseudo second-order kinetic model well, and the chemisorption is the limit step for adsorption rate. The FTIR analysis results proved that NO3-、SO42-、PO43- had all involved in competitive adsorption in the process of Cl O4-adsorption by modified orange peels. The results of the adsorbent regeneration showed that: Using acid and salts as regeneration reagent, the regeneration rate still reached over 95% after the saturated adsorbent regerated twice.