Biobeneficiation of mineral raw materials

A process for the combined chemico-biological removal of iron present as ox ide minerals in different mineral raw materials (quartz sands, kaolins, cla ys, etc.) was developed in the process, mineral raw materials are leached a t about 90 degrees C with lixiviant containing microbially produced oxalic and hydrochloric acids. The leaching is carried out in mechanically stirred acid-resistant reactors for periods of from I to 6 hours, depending on the iron content and the forms of iron in the raw materials being leached. The iron contents of some sands treated by this method were lowered from level s that were in the range of 0.035% to 0.088% Fe2O3 to less than 0.012% Fe2O 3, making them suitable for the preparation of high quality glass. The iron contents of different kaolins were lowered front levels that were in the I range of 0.65% to 1.49% Fe2O3 to levels in the range of 0.44% to 0.75% Fe2 O3. As a result, the whiteness was increased from values of 55% to 87% to v alues of 86% to 92%. The il on content of clay was lowered from 6.25% Fe2O3 to 1.85% Fe2O3, and this increased the "fireproofness" of the clay from 1, 670 degrees C to 1,750 degrees C. A similar process was used for the leaching of aluminum from aluminosilicat es, mainly clays and kaolins. However, in this case, the microbial fermenta tion fluid containing citric acid was acidified by means of sulfuric or hyd rochloric acid or by means of different mixtures of mineral acids. For enha ncing aluminum solubilization, the aluminosilicates were heated before leac hing at 600 degrees to 650 degrees C for 1 to 2 hours. Over 90% of the alum inum present in different clays and kaolins were leached within 3 to 6 hour s. "Silicate" bacteria I elated to the species Bacillus circulans were used to leach silicon from low-grade bauxite ores containing aluminosilicates as i mpurities. The bacterial action was connected with the degradation of the m ineral structures (by means of microbial metabolites such as organic acids and exopolysaccharides), as well as with the selective separation of the ri ch-in-aluminum fine fractions, which were retained by the mucilaginous caps ules of the bacteria, The solid residues after treatment were characterized by higher values of alumina and silicon module (Al2O3:SiO2 ratio), and the y were suitable for processing by means of the Bayer process for recovering aluminum. The bending strength and other ceramic properties of kaolins were improved by contact with well-developed cultures of "silicate" bacteria. The improve ment was caused mainly by bacterial metabolites (exopolysaccharides) that a cted as resins during drying. Pyritic sulfur and different metals (i.e., uranium, vanadium, molybdenum, a luminium, etc.) were removed from shales by means of acidophilic chemolitho trophic bacteria, which were able to use the shale pyrite as a source of en ergy for their growth. The desulfurization of the oil shales alms them into rich-in-kerogen concentrates suitable for producing petroleumlike oil. Conclusions concerning the prospects of applying the above biobeneficiation processes under commercial-scale conditions are presented.