Study Of Arsenic Adsorption By Common Oxides In Soil & Desorption By Simulated Acid Rain

Manganese oxide,iron oxide,aluminum oxide as the adsorbent have been synthesized and the simulant acid rain is used as the desorption agent. The effect of pH value, ionic strength, temperature and time of the adsorption of As(Ⅲ) on manganese oxide,iron oxide and aluminum oxide have been studied. In the meantime,the acidity,ionic strength of simulant acid rain and the time of the desorption also have been studied.In addition the adsorption-desorption dynamics of oxides were analyzed and the practical application experiment of the manganese oxide and iron oxide were studied. The main research results are :1.The adsorption of As (Ⅲ) on Manganese oxide has been less affected by the the pH in the test range and the adsorption rate is more than 99%.The pH also has little influence on iron oxide in wide pH range(3.5～8.5),while pH<3.5 or pH>8.5, the adsorption rate decreased. The Maximum adsorption rate on iron oxide is 97.71% in the range of pH=3.5～8.5. The alumina oxide has lower adsorption capacity and the equilibrium adsorption rate is 32.03% between pH=5~9,the adsorption rate has been declined when pH<5 or pH>9;The result also shows that adsorption of As(Ⅲ) on manganese oxide and aluminum oxide is not affected by ionic strength. However when CKNO3<0.1 mol/L the adsorption of As(Ⅲ) on iron oxide is affected by ionic strength and adsorption equilibrium is reached when CKNO3>0.1 mol/L.Temperature has hardly influence on adsorption of As(Ⅲ) on manganese oxide and iron oxide.When T>40℃the adsorption of As(Ⅲ) on aluminum oxide has been declined;The result also shows that the adsorption reaction of As(Ⅲ) on three minerals is quick reaction. Under the optimized experimental conditions the saturated adsorption capacity for Manganese oxide,iron oxide,aluminum oxide are 48.38, 23.70, 1.38 mg/g, respectively.2.The main adsorption forms of As(Ⅲ) on manganese oxide and iron oxide are complex adsorption and the adsorbent of Manganese oxide and iron oxide were eluted difficultly by simulant acid rain while the adsorbent of aluminum oxide can be desorbed easlily.The desorption reaction also is quick reaction and the desorption balanced time of iron oxide and aluminum oxide is 30 minutes,while the balanced time for manganese oxide is 90 minutes.The research also show that both the ionic strength of simulant acid rain have little effect on desorption of As(Ⅲ) on three minerals. With the pH increase of simulated acid rain the desorption of As(Ⅲ) on iron oxide and aluminum oxide decreased and reached to balance. While the desorption of As(Ⅲ) on manganese oxide has been affected by the acidity of simulated acid rain. The Highest desorption point is at pH = 4 and the desorption would be down when pH<4 or pH>4.3.The adsorption dynamics of manganese oxide,iron oxide and aluminum oxide are correlated well with Lagergren second kinetic model,the Correlation coefficients are: 1,0.9998,0.9979;Desorption dynamics of manganese oxide can be fitted by several kinetic equations, different kinetic equation sequence are: Lagergren second kinetic model>the third order reaction>the second order reaction, all the linear correlation coefficient can reach more than 0.99.The data of iron oxide were fitted by Elovich equation and Lagergren second kinetic model,the linear correlation coefficient are greater than 0.99.The aluminum oxide kinetic data is correlated well with Lagergren second kinetic model and the correlation coefficient R is 0.9989.4.PO43-,SiO32- have strong compete against As(Ⅲ) adsorption, HPO42-,H2PO4- have less effect,Cl-,SO42- have little influnce on As(Ⅲ) adsorption, the competitive adsorption of ion were impacted by initial concentration of As(Ⅲ).5.Compare with the arsenic removal result of distilled water,the result of arsenic removal in natural water show that different adsorbents is used for removal of arsenic in the actual water sample have different results. Because of manganese oxide and iron oxide have great absorption capacity , difficult to elute , practical applications can be recycled hardly.The remove experimental results on manganese oxide are 2.00 mg/g for no.1 actual water and 1.33 mg/g for no.2 actual water.The result of iron oxide are 0.41 mg/g ,1.07 mg/g, respectively.