Patent GB-211536-A (GB)
Title: Improvements in and relating to the treatment of silicious metal bearing minerals
IPC: C22B1/14
Filed: 1922-10-24
Abstract: Iron ores are treated to obtain purified ferric oxide free from silica, suitable for the manufacture of iron and steel, and other oxides and salts by treating the ore with sulphuric acid, which may be of specific gravity 1.35-1.45 so as to dissolve the metal constituents and leave silica as a residue.  The solution is separated from the silica, evaporated to dryness and the residue of mixed sulphates heated for instance in a rotary kiln to expel sulphur trioxide which is absorbed in water or sulphuric acid. The heating may be such as to decompose all the sulphates or may be at about 650 DEG  C. which will decompose the sulphates of iron and aluminium, but not the sulphates of nickel and manganese.  On treating the residue with water, nickel and manganese sulphates dissolve, and the nickel is then separated as oxalate by adding oxalic acid.  The manganese sulphate is heated to produce the oxide and sulphur trioxide.  In a modification, when aluminium is an important constituent, the mixed anhydrous sulphates are digested rapidly in water, when the sulphates of iron and manganese dissolve, leaving most of the aluminium sulphate as a residue, which may be calcined to produce alumina and sulphur trioxide.  In another modification the aluminium sulphate may be separated from the solution of the mixed sulphates by adding potassium sulphate and crystallizing out the alum.  The separated alum, after dehydration, may be treated with strong sulphuric acid which dissolves the potassium sulphate leaving aluminium sulphate. This modification of the process may be employed when treating greensand or glanconite in which case it may be unnecessary to add potassium sulphate or to add only a small quantity of either potassium sulphate or aluminium sulphate to produce the alum.ALSO:Iron ores are treated to obtain purified ferric oxide free from silica, suitable for the manufacture of iron and steel and other oxides and salts by treating the ore with sulphuric acid, which may be of specific gravity 1.35-1.45 so as to dissolve the metal constituents and leave silica as a residue.  The solution is separated from the silica, evaporated to dryness and the residue of mixed sulphates heated for instance in a rotary kiln to expel sulphur trioxide which is absorbed in water or sulphuric acid. The heating may be such as to decompose all the sulphates, or may be at about 650 DEG  C. which will decompose the sulphates of iron and aluminium, but not the sulphates of nickel and manganese.  On treating the residue with water, nickel and manganese sulphates dissolve, and the nickel is then separated as oxalate by adding oxalic acid.  The manganese sulphate is heated to produce the oxide and sulphur trioxide.  The residue containing iron and aluminium oxides and some phosphoric acid is calcined with sodium carbonate and treated with water.  Iron oxide remains insoluble, while the remainder dissolves as sodium aluminate and phosphate. Carbonic acid is passed through the solution to precipitate the alumina, and the solution is then evaporated to obtain the sodium phosphate.  In a modification, when aluminium is an important constituent, the mixed anhydrous sulphates are digested rapidly in water, when the sulphates of iron and manganese dissolve, leaving most of the aluminium sulphate as a residue, which may be calcined to produce alumina and sulphur trioxide.  In another modification the aluminium sulphate may be separated from the solution of the mixed sulphates by adding potassium sulphate and crystallizing out the alum.  The separated alum, after dehydration, may be treated with strong sulphuric acid which dissolves the potassium sulphate leaving aluminium sulphate.  This modification of the process may be employed when treating green-sand or glauconite in which case it may be unnecessary to add potassium sulphate or to add only a small quantity of either potassium sulphate or aluminium sulphate to produce the alum.  Any zinc contained in the ore remains with the iron throughout the process, finally appearing as oxide mixed with the ferric oxide. On reducing the iron oxide, zinc oxide is recovered at a suitable cool spot in the furnace.  The iron oxide may be obtained in the form of a very fine powder or in sintered lumps.  The fine oxide may be reduced or partially reduced in a rotary kiln and then melted in an electric furnace, or it may be reduced and melted in an electric furnace, or it may be introduced into a cupola or blast furnace in which the draught is downwards, air, carbon monoxide, iron oxide and coke or other carbonaceous fuel being all introduced at the top.  Just above the melting zone additional air is blown in.  The iron may be collected at the bottom of the furnace or may be transferred to a separate steel-making furnace. This reduction in a blast furnace is preferably used when the iron oxide has not been produced in a pure form.