GB876580A - Improvements in or relating to the treatment of spodumene - Google Patents

Abstract

<PICT:0876580/III/1> <PICT:0876580/III/2> Lithium carbonate is obtained from beta spodument by a cyclic process in which the spodument is treated at 175-500 DEG C. with a gas containing water vapour, sulphur trioxide, and oxygen or an inert gas, leaching the product with sodium carbonate solution to give a solution of lithium and sodium sulphates, and precipitating the lithium as lithium carbonate. The sulphur content of the solution is converted to sulphur trioxide, which is recycled, and the sodium content is converted to sodium carbonate, which is also recycled. In one embodiment, illustrated by Fig. 2, after the p beta spodument has been sulphated (3) it is leached with sodium carbonate solution (9) and filtered (10) to give a solution of lithium sulphate containing sodium sulphate. The lithium is precipitated as carbonate by the addition of sodium carbonate (14) and filtered off (15). The <PICT:0876580/III/3> <PICT:0876580/III/4> solution of sodium sulphate remaining is evaporated (16) and the solid is reduced to the sulphide (17) which is then treated with water and carbon dioxide (18) to give sodium carbonate, which is recycled, and hydrogen sulphide, which is burned with controlled amounts of air to give sulphur (11) and then sulphur dioxide (13) which is then catalytically converted, at least in part, to sulphur trioxide (7) which is recycled. In another embodiment (Fig. 3), the solution from filter 10 is evaporated (19) to give solid lithium and sodium sulphates, which are reduced to the corresponding sulphides (20) and then converted to the carbonates (21). These are leached with water (22) and the solution of sodium carbonate is recycled, whilst the lithium carbonate is left as solid. In a further embodiment (Fig. 4) the solution from filter 10 is treated with barium sulphide (24), the precipitated barium sulphate being removed (25), and reduced (26) to the sulphide, which is re-used. The solution of lithium and sodium sulphides is treated with carbon dioxide (27), liberating hydrogen sulphide and precipitating lithium carbonate, which is recovered. The solution of sodium carbonate remaining is treated with sulphur dioxide and air (29) in amount sufficient to convert the sodium from the spodument to the sulphate, and this solution is then cooled (30) to crystallise out as much of the sulphate as possible, after which the solution of carbonate, still containing some sulphate, is recycled. Fig. 1 is a flow sheet, illustrating prior practice, in which alpha spodument is heated in a decrepitator (1) to convert it to beta spodument, which is then sulphated (3) with sulphur trioxide and water vapour to form lithium sulphate, and a little sodium sulphate due to the presence of sodium. Impurities are converted to insoluble sulphides by means of hydrogen sulphides (8), and the lithium sulphate is leached out by means of water (9).