Preparation Of The Adsorbent By Wheat Straw And The Study On Its Adsorption Properties For Phosphate In Aqueous Solution

Wheat straw was selected as the raw materials, which was made intocarbonaceous adsorbent through chemical modification, and the adsorption propertiesfor phosphate in aqueous solution were researched. Through the orthogonalexperiment, ratio of solution to straw, activation temperature, activation time, zincchloride solution concentration and other factors was detected in the biological carbonadsorbent preparation process, and the optimum modification process conditions wasdetermined. Through static and dynamic experiments, effects of a variety ofexogenous factors on phosphate adsorption by the prepared adsorbent were tested, andthe adsorption thermodynamics and dynamics were studied, which has provided ascientific basis for straw biomass scale and its application in water management. Themain research contents and results are as follows:Wheat straw was made into carbonaceous adsorbent through zinc chloridemodification, and the impact of solution concentration of zinc chloride, ratio ofsolution to straw, activation temperature and activation time on the product yield andadsorption properties were researched. The results showed that the yield of biologicalcarbon adsorbent from wheat straw and the removal rate of phosphate will beimproved when increasing the ratio of solution to straw and solution concentration ofzinc chloride. The removal rate of biological carbon adsorbent for phosphateincreased and adsorbent rate decreased gradually with the activation temperaturerising and activation time prolonging. The optimum technology was obtained throughorthogonal experiments and they were as follows: the solution concentration of zincchloride250g/L, the ratio of solution to straw2.2:1, the activation temperature600℃, activation time45min; the biological adsorbents rate is37.85%, and thephosphate removal rate is99.33%under the conditions above.The static adsorption of adsorbent for phosphorus wastewater prepared from themodified wheat straw was studied. The effect of straw dosage, solution pH, initialconcentration of solution, temperature and reaction time on the adsorption ofadsorbent for phosphate was researched with the method of equilibrium absorption.The results showed that the effect of modified wheat straw on phosphate adsorptionwith pH in neutral and alkaline range is good, and the removal rate is greater than95%; the maximum volume (Qmax) of adsorbent from the modified wheat straw forphosphate decreased gradually with the increase of temperature, the temperature from293K up to313K, the maximum adsorption capacity (Qmax) of the modified wheat straw for the phosphate (P) reduced from59.20mg/g to56.23mg/g.Langmuirisothermal model can describe the effect of isothermal absorption of the modifiedwheat straw for phosphate better; the modified wheat straw can achieve adsorptionequilibrium in20min; three kinds of temperature changes in Gibbs free energy andenthalpy changes are negative, which illustrate that the modified wheat straw forphosphate adsorption is an exothermic process, and can undergo spontaneously.The kinetic adsorption of adsorbent for phosphorus wastewater prepared from themodified wheat straw was studied. The results showed that the solution flow rate,initial concentration of phosphate, pH and other factors had a great influence on thedynamic adsorption. Flow rate increased, volume of penetration reduced, penetrationtime advanced, and equilibrium adsorption amount decreased; the equilibriumadsorption amount of straw increases, when increasing the concentration of phosphatesolution in the same velocity; the solution pH and temperature have little effect on theadsorption capacity. Increasing the amount of adsorbent is better for phosphateremoval but adsorbent dosage increasing too much will increase the flow resistanceand operating cost. The optimum operating conditions are as follow: the phosphatesolution flow rate is5mL/min, concentration is50mg/L and pH is7.