Effects of calcination time and temperature of C0₃^2--intercalated mg-ai layered double hydroxide on the removal of CI^- and SO₄^2- from seawater

The effects of calcination time and temperature of C0₃^2-- intercalated Mg-AI layered double hydroxide (CO₃ Mg-Al LDH) on the removal of CI" and SO₄^2- from seawater were investigated. The degree of CI^- removal increased with the increase of calcination time from 2 to 8 h at 500 °C, suggesting increasing decarbonation of CCVMg-Al LDH. However, the calcination time of CO₃ • Mg-Al LDH hardly affected the SO₄^2- removal. The thermal decomposition of CO₃ Mg-Al LDH at 500-800 °C for 2 h caused the production of Mg-Al oxide. However, MgO and MgAk04 were also obtained at 900-1000 °C. The degree of SO₄^2- re-moval was over 90% at 500-800 °C. The product obtained by the calcination of C0₄- Mg-Al LDH at 900-1000 °C could absorb SO42" from seawater. MgO and MgAb04 did not have any uptake ability, but the remaining Mg-Al oxide could take up SO₄^2- from seawater. The degree of CI^- removal was in the following order: 500 °C < 600 °C < 700 °C < 800 °C < 900 °C. The increase in CI^- removal suggested the increasing decarbonation of CCV Mg-Al LDH with increasing temperature. The highest degree of CI^- removal at 900 °C was attributed to the high Mg/Al molar ratio of the remaining Mg-Al oxide in the product.