EFFECTS OF CALCINATION TIME AND TEMPERATURE OF CO32--INTERCALATED Mg-Al LAYERED DOUBLE HYDROXIDE ON THE REMOVAL OF Cl- AND SO42- FROM SEAWATER

The effects of calcination time and temperature of CO32--intercalated Mg-Al layered double hydroxide (CO3 center dot Mg-Al LDH) on the removal of Cl- and SO42- from seawater were investigated. The degree of Cl- removal increased with the increase of calcination time from 2 to 8 h at 500 degrees C, suggesting increasing decarbonation of CO3 center dot Mg-Al LDH. However, the calcination time of CO3. Mg-Al LDH hardly affected the SO42- removal. The thermal decomposition of CO3. Mg-Al LDH at 500-800 degrees C for 2 h caused the production of Mg-Al oxide. However, MgO and MgAl2O4 were also obtained at 900-1000 degrees C. The degree of SO42- removal was over 90% at 500-800 degrees C. The product obtained by the calcination of CO3. Mg-Al LDH at 900-1000 degrees C could absorb SO42- from seawater. MgO and MgAl2O4 did not have any uptake ability, but the remaining Mg-Al oxide could take up SO42- from seawater. The degree of Clremoval was in the following order: 500 degrees C <600 degrees C < 700 degrees C < 800 degrees C < 900 degrees C. The increase in Cl- removal suggested the increasing decarbonation of CO3 -Mg-Al LDH with increasing temperature. The highest degree of Cl- removal at 900 degrees C was attributed to the high Mg/A1 molar ratio of the remaining Mg-Al oxide in the product.