GB514754A - Improvements in methods of adjusting the compositions of mineral mixtures - Google Patents

Abstract

514,754. Selective grinding of mineral mixtures. JORGENSEN, M. VOGEL-. May 14, 1938, No. 14485. [Class 59] A method of adjusting the composition of a mineral mixture consists in grinding together grains of a certain size of one component and similarly sized grains of another component, differing in hardness from the first component by means of grinding bodies of such a size that the softer grains are reduced whilst the harder grains are left substantially unaffected whereby the ratio of the average grain size of the hard and soft components is changed. Separation of part or all of the mixture is then effected in accordance with grain size and thereafter a composition of any desired proportions may be made up. As applied to the preparation of starting material for the manufacture of cement the rock contained 63 per cent. lime and the quartz grains embedded therein varied in size from .05 to .6 mm. The rock was then ground in a jaw crusher 1 to about 10 mm. and then further reduced to .06 mm. in a ball mill 2 working in a closed circuit with a separator 3. Balls of 30-40 mm..size were used in this mill and the quartz grains were ground only to a slight extent. Of the quartz in the original material 1¢ per cent. consisted of grains below .05 mm., whilst in the product resulting from. the closed circuit grinding 6 per cent. of the quartz was below .05 mm. As the fraction of the material below .05 mm. contained so little quartz and was rich enough in lime for use this fraction was removed in a second separator 4, and the balance ranging from .05 to .6 mm., was submitted to selective grinding in a mill 5 containing steel balls of 5 mm. The size of the balls was previously determined by experiment and were found to crush the lime and not the quartz between a grain size of .05-.6 mm. The material supplied to the mill contained 40 per cent. quartz and the output was divided in a further separator 6 into fractions above and below .05 mm. The fine fraction contained 75 per cent. calcium carbonate and 25 per cent.. quartz, and the coarse fraction 30 per cent. calcium carbonate and 70 per cent. quartz. The mixture of the two fine fractions (separated out respectively before and after the selective grinding) contained 80 per cent. calcium carbonate and 20 per cent. quartz. The calcium carbonate content is too high for the mixture to be used straight away for the manufacture of cement, but the adjustment of a mixture containing too much calcium carbonate is readily effected.