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.