GB339330A - Process and apparatus for the manufacture of alkali-metal carbonates and bi-carbonates and soluble magnesium salts - Google Patents

Abstract

339,330. Potts, H. E., (Soc. Anon. Alealina). Aug. 1, 1928. Alkali carbonates and bicarbonates are obtained by decomposition of a double carbonate of magnesium and potassium made by reacting nascent magnesium carbonate with a solution of a potassium salt, with or without a sodium salt, saturated with carbon dioxide at a pressure at least equal to the critical pressure at the temperature employed. Dolomite or magnesite is partially converted into oxides in a furnace B1, moistened and ground in B3, and re-carbonated in B4. The carbonates are suspended in a solution of say potassium chloride, containing 150-300 grams per litre, in B5, and forced by a pump B6 into an apparatus A1 in counter-current to carbon dioxide, which comprises 30-40 per cent of the roaster gases, fed by a compressor B2 at a pressure at least equal to the critical pressure. Magnesium carbonate dissolves, the pressure of the escaping gas and liquid is utilized in motors B7, B8, and the solution is filtered free from calcium carbonate in B9, a solution which may contain 100 grams or more of anhydrous magnesium carbonate being obtained. Excess carbon dioxide is removed in an agitator A2, or pressure reducer, the temperature being maintained at 18-27‹ C., say 22‹ C., when magnesium carbonate is precipitated and reacts in its nascent condition to form the double salt KHMg(CO3)2.4H2O. This precipitates, and is filtered in the apparatus A3, stage (1), dried in carbon dioxide under pressure, stage (2) and is decomposed, for example by steam, stage (3), into magnesium and potassium carbonates. The filtrate contains magnesium chloride, excess potassium chloride and other salts which may accompany this. Potassium carbonate is dissolved out from the magnesium carbonate, which may be returned to B5, while the potassium salt may react with sodium chloride and carbon dioxide in AH to produce sodium bicarbonates and from it, carbonate. The potassium chloride may be returned to B5. If sodium chloride replaces potassium chloride, sodium bicarbonate and magnesium chloride are formed by the reaction with carbon dioxide under high pressure in A1. By employing. a mixture of chlorides such as sylvine, part of the magnesium carbonate is converted into sodium bicarbonate which remains with the calcium carbonate in B9, while on reducing the pressure, the double salt is produced as previously described. Magnesium carbonate from any source may be used in the process, and alkali sulphates or nitrates may replace the chlorides. The process may be carried out concurrently with the known process described in Specification 184/81, in which the double salt is formed by treating magnesia, or magnesium hydrate with a potassium salt solution saturated with carbon dioxide at a low pressure of 2-4 kg./cm.<2>. The solid residue of this process can be used as a source of magnesium carbonate in the high pressure process, while the mother liquors from this latter process may be used as a source of potassium chloride in the low pressure process.