In the salinization industry of sea salt, it is mainly used of bitter brine, heavy brine and high temperature salt as raw materials to produce light magnesium carbonate or light magnesium oxide. Industrialized production methods include soda ash method, lime and carbon ammonia.
(1) Soda ash process include: 1. Ingredients 2. Reaction 3. Washing 4. Pyrolysis 5. Filter 6.Roasting 7. Crushed packaging. Soda ash production of light magnesium carbonate or light magnesium oxide has mature technology, higher product quality. However, consumption of soda ash, fresh water consumption is also large.
(2) Lime method uses lime milk instead of soda ash. Its reaction with magnesium chloride in brine to generate magnesium hydroxide, followed by carbonation using carbon dioxide gas, generating magnesium bicarbonate. When using the lime method, the sulfate in the brine should be minimized, otherwise large deposits of calcium sulphate are formed and mixed in the product. The advantage of this method is the use of lime instead of soda ash, reducing costs. The disadvantage is that the process and equipment is more complicated than soda ash method, and by-produces large number of CaCl2 solution to be managed.
(3) Raw materials of carbon ammonia method are the high concentrations of bitter brine, brine or salt immersion thick solution. Carbon ammonia used is ammonia bicarbonate, carbonized ammonia or sending ammonia and carbon dioxide gas directly into the brine, with carbon ammonia instead of soda ash being reacted with the magnesium chloride or magnesium sulfate in the brine to generate the corresponding magnesium carbonate. The reaction is as follows:
1. Brine containing MgCl2 and MgSO4 reacts with NH4HCO3 solution: MgCl2 + 2NH4HCO3 = Mg (HCO3) 2 + 2NH4Cl MgSO4 + 2NH4HCO3 = Mg (HCO3) 2+ (NH4) 2SO4
2. Directly send ammonia and carbon dioxide to the brine.
3. The generated MgCO3 • 3H2O and Mg (HCO3) 2 are subject to pyrolysis to generate alkaline magnesium carbonate: Mg (HCO3) 2 + 2H2O = MgCO3 • 3H2O + CO2 ↑ 5 {MgCO3.3H2O} = 4MgCO3.Mg H2O + CO2 ↑ + 10H2O
4. Alkaline magnesium carbonate is roasted to generate light magnesium oxide: 4MgCO3.Mg (OH) 2.4H2O = 5MgO + 4CO2 ↑ + 5H2O
Control of carbon ammonia process: 1. Raw material concentration and reaction temperature 2. Pyrolysis temperature; 3. Dehydration, washing and drying; 4. Roasting; 5. Mother liquor treatment.
Compared with the soda ash method, the production of light magnesium carbonate and light magnesium oxide by the carbon ammonia process is simple, the product has a high specific volume, and the supply channel of the ammonium bicarbonate is more and the cost is lower. However, the mother liquor evaporation and concentration process is of high energy consumption.