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| Pietriková A., Búgel M., Buršák M., Neubauer M. |
| PREPARATION TECHNIQUE OF SILICONE DIOXIDE SIO2 FROM WASTE DUMP BASED ON SERPENTINE |
Abstract
The paper deals with a new, untraditional technology of obtaining high-purity nanosized SiO2 powder from secondary serpentine mineral raw material. This raw material is deposited in the form of waste dumps, where residues of carcinogenic chryzotile asbestos components also occur. Serpentine raw material is waste generated during processing primary serpentine raw material. SiO2 powder has found its application in a number of industrial branches. Its particular application is closely connected with its purity, granulometry and physical properties, such as the specific surface, the morphology and the crystal lattice. The finest fractions of SiO2 powder are basic raw material in production of silicate glass, silicon and certain types of optical fibres. SiO2 powder is used in production of dispersion paints and alkaline water glass, and also as an additive to synthetic masses, winter tyres, in production of grinding and polishing pastes, for grinding rare stones, for polishing and lapping, in civil engineering as an additive to concretes and special plasters, as a pigmentation substance and an additive in production of paper and plastics.
The work summarises the results of scientific research involving physical treatment and hydrometallurgical processing of mineral raw materials. Some factors influencing the chemical treatment of the raw material and the quality of one of products - SiO2 powder – are analysed. In article, the mechanism of the leaching process preparing SiO2 powder is analyzed. We discuss parameters such as specific surface, size, morphology of reactant, the ration of all reactants, etc.
After series of experiments, we successfully gained the high purity silica powder which diameter is about 200 nm. By analysing the granulometric composition of serpentine raw material, the ratio of the fraction below 1 mm to the fraction above 1 mm was determined as 85.2:14.8. The homogenisation and milling before the hydrometallurgical (chemical) processing of serpentine, which guarantees the top grain size level, the defined granulometry and the chemical homogeneity of treated material, significantly influence the reproducibility of the technological process of raw material processing.
The results of dry electromagnetic separation show that it is possible to remove 60-65 % iron from the input material using common means, while the material loss is ca 30 % by weight. By increasing the saturating current intensity, an increase of the weight recovery and the yield take place, as well as an unfavourable increase of the weight recovery. In wet magnetic separation, better results can be expected as regards the purity of products; however, the application of this method is debatable due to the formation of clusters of asbestos fibres. The uniform distribution of magnetite grains within the whole volume of serpentine is unfavourable from the practical point of view.
The chemical composition of the input material, the acid concentration and the leaching temperature and time are crucial factors of the leaching kinetics. The highest reaction efficiency was recorded in the action of 25 % HCl with the solid to liquid phase ratio of 1:4. The optimum leaching time is 1 hour. The reaction temperature must not fall below 105 °C. The efficiency of the chemical reaction after the leaching stage 1 is 78 to 84 %, after the leaching stage 2 the content increases by ca 6 %.
By implementing the proposed way of chemical treatment of serpentine mineral raw material it is possible to prepare powder with content of SiO2 more as 99 %. The mentioned technology of hydrometallurgical processing of secondary serpentine mineral raw material can be ranked among environmental technologies aimed at the disposal of a waste dump containing asbestos. Besides processing the environmentally unfriendly dump, this technology also results in obtaining lucrative raw materials based on Si and Mg. This technology can also be applied to other deposits with a similar chemical, mineralogical and grain composition.
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| Keywords: silicone dioxide|serpentine|asbestos|leaching| |
| No 1 (2004), p. 49-58 |
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