GB380868A - Improvements in and relating to the decomposition of magnesium carbonate-containing ores - Google Patents

Abstract

Ores containing magnesium carbonate, such as dolomite and magnesite are decomposed at a temperature below that at which calcium carbonate present is decomposed, 400-550 DEG C. being specified, and in the presence of an inert gas such as steam or nitrogen. Carbon dioxide evolved is continuously removed by the inert gas. In carrying out the process, the ore is crushed in crusher A, Fig. 1, and decomposed under the above conditions in retorts in furnace B, heated by gases from a grate C and by those which have passed through a boiler D and superheater E. Steam from D is used partly to drive an engine F supplying the necessary motive power, and part is passed through superheater E to the retorts. Steam and carbon dioxide therefrom pass via the heat exchanger G to a condenser H. Carbon dioxide passes to a gas holder J. The calcined ore is passed via crusher M to washing apparatus N, and there treated with combustion gases which have passed through a heat exchanger K and cooling apparatus L, whereby a basic magnesium carbonate is produced. The suspension is treated in apparatus O with cooled carbon dioxide under pressure from gas holder J, soluble acid magnesium carbonate being produced. Calcium carbonate, silica, &c. are removed by a filter P2, and the solution is heated in a heat exchanger Q2 before being passed to a vessel R wherein it is treated with steam from the boiler and steam engine. Basic magnesium carbonate, Mg(OH)2.3MgCO3, is precipitated and steam and carbon dioxide evolved are passed via condenser S to a gas holder U for carbon dioxide. The contents of vessel R pass to a decanter V, drainer W, and finally to a drier X where the basic carbonate is dried indirectly by hot air from heat exchangers G, K, Y. By heating this product, the normal carbonate or magnesia may be obtained. The liquid from filter P2 may be evaporated in heat exchanger Q2 to give crystalline acid magnesium carbonate. This may be converted to normal magnesium carbonate by heating. The furnace B, Fig. 2, comprises retorts 2a heated by burners 2b, steam or other inert gas being passed therethrough by pipes 2c. Steam <PICT:0380868/III/1> <PICT:0380868/III/2> <PICT:0380868/III/3> is removed by a condenser 2f, the condensed water being employed in the chemical process proper, and for feeding the boiler. Carbon dioxide is washed in a scrubber 2m and passes to the gas holder via pipe 2n. The carbonating apparatus O, Fig. 3, consists of a vessel 3a rotating in a refrigerating medium in a vat 3d. It is charged with the basic carbonate through a funnel 3f, and carbon dioxide is supplied under pressure through a hollow trunnion 3h. Notched plates 3p are provided for mixing purposes. When reaction is complete, the vessel is emptied through a pipe 3r under action of the internal pressure.