Synthesis of Hydrotalcite using Magnesium from Seawater and Dolomite

Abstract

Three methods of synthesizing hydrotalcite(HT) have been developed using magnesium from seawater and dolomite(MgCa(CO3)2). In the first process, 1.0M Na2CO3solution was added to calcium ion free artificial seawater containing AlCl3 with an initial Mg/Al molar ratio of 2.0∼3.7 until a pH of 10 was obtained. The solution was then continuously stirred for Ih at 60°C. CO3 2--HT was precipitated as a single phase, and the initial Mg/Al molar ratio, which each recovery of Mg2+and Al3+ from the solution was above 98%, was 2.0–2.3. In the second process, a Ca(OH)2 slurry was added to artificial seawater containing AlCl3 with an initial Mg/Al molar ratio of 1.0∼5.0 until a pH of 10.5 was obtained, and then was stirred for Ih at 60°C. HT was also precipitated as a single phase with initial Mg/Al molar ratio 2.0∼4.0. The initial Mg/Al molar ratio, which each recovery of Mg2+ and Al3+ from the solution was above 98%, was 2.2∼3.3, but SO4 2- and Cl− were contained in the precipitated HT. When HT was produced using initial Mg/Al molar ratio of 3.0 at 25°C, SO4 2- and Cl−in the HT were ion-exchanged with CO3 2- in a 0.05M Na2CO3solution for 24h at 25°C, and SO4 2- and Cl− content of the HT were decreased to 0.5 and 0.05wt%, respectively. In the third process, dolomite calcined at 1000°C was added to an AlCl3 solution with an initial Mg/Al molar ratio of 1.0∼2.0, and the solution was stirred for 1∼4h at 25∼90°C. HT was precipitated with the smallest amount of MgO and Mg(OH)2 when the initial Mg/Al molar ratio was 1.5 and the solution was stirred for 4h at 90°C.