Improvements in or relating to processes for reducing iron impurities in ground calcite, dolomite, magnesite and cryolite

摘要

567,998. Purifying minerals. PILKINGTON BROS, Ltd., and SHERLOCK, A.. July 30, 1943, No. 12420. Addition to 555,241. [Class 1 (iii)] In a process for reducing iron impurities in ground calcite, dolomite, magnesite, and cryolite, the mineral is treated with an aqueous solution containing titanous sulphate or chloride and a fluorine compound, and then washed. The fluorine compound may be hydrofluoric acid, sodium fluoride, or sodium silicofluoride ; the latter compound may be added together with sodium hydroxide or sulphuric acid to form respectively sodium fluoride or hydrofluoric acid. A preliminary treatment with the titanous salt is necessary when sodium silicofluoride is used, and may also be given when using other fluorine compounds. The minerals are not too finely ground, except in the case of dolomite when this is necessary to expose the impurities. The washing water may be removed from the finely ground dolomite in settling pits, and the mineral dried in currents of warm air or by means of a centrifuge. The purification may be worked as a continuous process in a series of compartments. In an example, the iron content of calcite for use in the manufacture of glass, is reduced from 0.013 per to 0.006 per cent by grinding and grading the mineral, thoroughly mixing with 15 per cent titanous sulphate solution and sufficient water to give a flowable mass, adding hydrofluoric acid and mixing further, and finally washing.