Preparation of magnesium hydroxide

1. Magnesium hydroxide - preparation method brine lime method


It is prepared by the reaction of brine (MgCl2) and hydrated lime [Ca (OH) 2]. The lime milk made of brine and lime treated by digestion and slag removal is precipitated in the sedimentation tank. Flocculant is added into the slurry to be fully mixed, and then separated in the sedimentation tank. After filtration, washing, drying and grinding, the finished product of magnesium hydroxide is prepared.


MgCl2+Ca(OH)=2Mg(OH)2↓+CaCl2


2. Brine ammonia process


The brine which has been purified to remove sulfate, carbon dioxide, a small amount of boron and other impurities is used as the raw material, and ammonia water is used as the precipitant in the reactor for precipitation reaction. Before the reaction, a certain amount of crystal seeds are put in for full stirring. The ratio of brine to ammonia is 1: (0.9-0.93), and the temperature is controlled at 40 ℃. After the end of the reaction, flocculant was added, the precipitate was filtered, washed, dried and crushed to obtain the finished product of magnesium hydroxide.


MgC12+2NH3·H2O=Mg(OH)2↓+2NH4Cl


3. Method of magnesite hydrochloric acid ammonia water


Magnesite ore and anthracite or coke are calcined in shaft kiln to produce magnesium oxide and carbon dioxide. Magnesium chloride solution was prepared by the reaction of bitter soil powder with hydrochloric acid of specified concentration after being made into slurry with water. The magnesium chloride solution reacts with a certain concentration of ammonia in the reactor, and the product is washed, settled, filtered and separated, dried and crushed to obtain magnesium hydroxide product. Surface treatment agent can be added for surface treatment as required.


4. Extraction of concentrated seawater


In the process of extracting slurry magnesium hydroxide from concentrated seawater, the existence of Ca2 + is an important factor affecting the purity and quality of the product. The effects of the separation method, the amount of sodium carbonate, stirring speed, aging time and stirring time on the removal rate of calcium ion and the loss rate of magnesium ion in concentrated seawater were determined. Under the optimal operating conditions, the calcium removal rate is controlled above 60%. It can effectively reduce the calcium content in the process of extracting slurry magnesium hydroxide from concentrated seawater, and fully ensure the purity of subsequent synthetic magnesium hydroxide products. At the same time, it provides low impurity conditions for further utilization of mother liquor after extracting magnesium hydroxide.


CaCl2+Na2CO3=CaCO3↓+2NaCl


MgC12+2NH3·H2O=Mg(OH)2↓+2NH4Cl