GB823215A - Method for recovering manganese compounds from manganese-containing materials - Google Patents

Abstract

Manganese sulphate and/or chloride are obtained by roasting material containing manganese compounds, e.g. ores and slags with ammonium chloride and ammonium sulphate, bisulphite, sulphite and/or bisulphite at above the decomposition temperature of manganese dithionate (200-250 DEG C.), e.g. at 900-1000 DEG F., leaching the roast with water and recovering the manganese compounds. To increase recovery of manganese compounds when silica, alumina or complex iron compounds are present, ammonium fluoride or bifluoride may also be added to the roast with the other ammonium salts. The ammonium salts may be mixed dry, or as a concentrated solution or slurry with an ore and introduced into a rotary kiln, retort or other device in which they are heated with continuous agitation until fuming ceases. The chloride and sulphate or sulphite salt is preferably used in an excess of 10-25% of the theoretical quantity, ammonium chloride may comprise 10-25% of the sulphate and sulphite salts and the fluoride may be in an excess of 10-35% of that theoretically necessary (equations are given). After reaction the roast is leached with the minimum quantity of water: neutralization to pH 4.5 with ammonia precipitates ferric hydroxide; by adding calcium hydroxide to attain a pH of 5.5 tricalcium phosphate is removed. Remaining iron is removed by increasing the pH to 6.8-7.2 with ammonia or ammonium hydroxide and thereafter the manganese can be precipitated as carbonate by addition of gaseous ammonia and carbon dioxide or ammonium carbonate. The manganese carbonate can be calcined in the absence of air to form MnO or in the presence of air to form MnO2. Byproducts may be utilized by recycling; the ammonium chloride fume is collected and the other gaseous products of roasting scrubbed with water to form aqueous ammonium sulphite, bisulphite, hydroxide and possibly fluoride; the fume and solution may be mixed with the filtrate remaining after removal of manganese carbonate and recycled after evaporation to dryness or to a saturated solution or slurry. Carbon dioxide from the calcination may be absorbed in water or preferably a portion of the above liquor containing ammonium hydroxide, and reused to precipitate the manganese.