Study On Continuous Synthesizing Technology Of High Purity Magnesium Hydroxide Using Magnesium Chloride From Salt Lakes

The magnesium resource is very abundant in our country, especially in salt lakes. But at present the inadequate exploitation of the resource from salt lakes, to a certain extend, forms the "magnesium crisis". According to extensive applied prospect of high purity magnesium hydroxide, using magnesium chloride from salt lakes as magnesium material, high purity magnesium hydroxide is synthesized continuously by ammonia. So to extend and improve the development level for magnesium resource from salt lakes comes true, and turns the waste into a valuable product.Firstly it analyzes the synthesis of magnesium hydroxide using precipitation method in theory. Then, there are two stages to study on continuous synthesizing technology of high purity magnesium hydroxide using magnesium chloride from salt lakes, which include laboratory scale stage and pilot stage. Lastly various performances of specimen are tested by Laser particle size analyzer, Ion chromatograph, X-ray diffraction (XRD) and Scanning electron microscope (SEM).In the laboratory scale stage, the technical conditions, such as mixing speed, reaction temperature and inlet speed of ammonia, are considered. The optimum experimental conditions of synthesizing high purity magnesium hydroxide are obtained, which are 4.17 mol/L concentration of magnesium chloride, 300r/min mixing speed, 45℃～65℃reaction temperature, 300ml/min inlet speed of ammonia and 60min aging time. Dv50 of magnesium hydroxide is larger than 43μm, and the purity exceeds 99.9%.In the pilot stage, the amplificatory experiment proves that the optimum conditions would change little, when amplifying the scale of experiment. The best result is obtained on condition that 2.5 mol/L concentration of magnesium chloride, 44L/min ammonia flux and 60min aging time. the optimum conditions of synthesizing high purity magnesium hydroxide by ammonia liquid are 3.5 mol/L concentration of magnesium chloride, 65℃reaction temperature, 2.2:1 relation among mol ratio between ammonia and magnesium, 500r/min mixing speed, 60min reaction time, 60℃aging temperature, 90min aging time and 500r/min mixing speed. In this stage, Dv50 of magnesium hydroxide is larger than 39μm, and the purity exceeds 99.9%.To some extent, the study benefits to the synthesis of high purity magnesium hydroxide by exploiting magnesium resource in salt lakes.