Adsorption Behaviors Of Halide And Bromate Anions On Calcined LDHs

Layered Double Hydroxides(LDHs)was a sort of magnesium material with double-layer structure。Because of their special structure , they had received a lot of attention , for example adsorption,anionic exchange and catalysis ,et al.Recently,the research work about LDHs was proceeding. LDHs were prepared hydrothermal by perfect mixed spraying reactor using industrialization equipment and the stuff was industrial magnesium sulfate , aluminium sulfate, sodium hydroxide ,sodium carbonate.Different instruments such as XRD and IR were used to characterize the chemical component ,crystal structure, thermal decomposition. Results indicated that the sample's crystal structure and character accord with Mg/Al layered double hydroxides ,there was carbonate in the middle of layered double hydroxides. TG-DTA characterized that there were two stages in the process of thermal decomposition and the lost weight was consistent with the theoretic value.This article explored the adsorption of fluoride,chloride,bromide,iodide and bromate anion behavior of CLDH-5 as the adsorbent,the results show that Halide and bromate anions have a very good adsorption on CLDH-5.The optimal condition for the adsorption of fluoride anion on CLDH-5 is : the initial concentration is 50mg/L,the dosage of CLDH-5 is 4.0g/L,the temperature of adsorption is 25℃,the adsorption time is 60min,the initial pH value is 7.The optimal condition for the adsorption of chloride anion on CLDH-5 is : the initial concentration is 40mg/L,the dosage of CLDH-5 is 4.0g/L,the temperature of adsorption is 25℃,the adsorption time is 3h,the initial pH value is 7.The optimal condition for the adsorption of bromide anion on CLDH-5 is : the initial concentration is 40mg/L,the dosage of CLDH-5 is 2.0g/L,the temperature of adsorption is 35℃,the adsorption time is 4.5h,the initial pH value is 7;The adsorption of bromide anion on CLDH-5 according with langmuir isotherm , the saturated adsorption amount is 133.33mg/g; CLDH-5 can be regenerated , the adsorption ratio of bromide anion reduced to 90% when they regenerated once , the mechanism is"structure memory effect"by contrasting the X-ray diffract grams of synthesized LDHs,CLDH-5 and CLDH-5 after adsorption.The optimal condition for the adsorption of iodide anion on CLDH-5 is : the initial concentration is 40mg/L,the dosage of CLDH-5 is 4.0g/L,the temperature of adsorption is 25℃,the adsorption time is 7h,the initial pH value is 7.The optimal condition for the adsorption of bromate anion on CLDH-5 is : the initial concentration is 40mg/L,the dosage of CLDH-5 is 5.0g/L,the temperature of adsorption is 25℃,the adsorption time is 4.5h,the initial pH value is 7. The adsorption of bromate anion on CLDH-5 according with Freundlich isotherm ,the adsorption process for bromate△rH is 7.5568KJ/mol,it shows that the adsorption is heat-absorbing reaction,△rS is 35.3J/s, shows that it is a entropy increasing process,△rGT﹤0,shows that the adsorption is a spontaneity reaction .The result of dynamics study shows that the energy of activation is 3.14KJ/mol,it shows that the primary reaction is physical adsorption.In this paper , we also studied the influence of pH value on the adsorption .The result shows that CLDH-5 has a good pH buffer action to the solution. Comparing with tradition sorbents , CLDH-5has lots of advantages , such as high amount of adsorption ,innocuity ,and can be recycled ,et al. This paper studied the adsorption of Halide and bromate anions .These studies develop the application of LDHs and magnesium salt.