Advanced Materials Research Vols. 20-21 (2007) pp. 126-129 online at http://www.scientific.net © (2007) Trans Tech Publications, Switzerland
Biological purification of silicate minerals Iveta Štyriaková1,a and Michal Lovás1,b 1
Institute of Geotechnics SAS, Košice, Slovakia
a
email:
[email protected], bemail:
[email protected]
Keywords: bioleaching, kaolin, quartz sands, feldspars, Bacillus, iron
Abstract. Bioleaching is technology applicable to iron extraction from low-grade non-metallic raw materials. Bioleaching of quartz sands and feldspars involves the action of heterotrophic bacteria. Impurities include fine – grained limonite, goethite, hematite or mica were removed by the reductive dissolution of Fe3+ in linked with the silicate mineral destruction. Heterotrophic bacteria produced organic acids that are able to solubilize Fe oxide and silicates but require organic carbon as a source of energy. Molasses is a relatively inexpensive carbon source used for various industrial fermentations and contains also other nutrients that accounted for the enhancement of iron dissolution in this study. The admixture of pigments in molasses coloured the samples, but the discoloration could be removed by the addition of NaClO following the bioleaching step. The feasibility of the bioleaching treatment has to be tested specifically to each type of silicate raw materials. The Fe content in the quartz sands and feldspar samples by the biological leaching decreased as much as 60% and by subsequent using of electromagnetic separation of feldspars, the decrease of Fe content in 74% was achieved. However, the application of magnetic separation of quartz sands after bioleaching resulted in total iron removal of 93 % and in such combined way prepared product contained 0.024 % of Fe2O3. Achieved results on iron removal point to the fact that combination of leaching and magnetic separation enables to obtain product usable in glass and ceramic industry. Introduction Feldspar rocks and quartz sands are largely used as a raw material in the ceramic and the glass industry, however, are often associated with iron and titanium impurities that decrease their economic value and hinder their application. A froth flotation process is used for most feldspar ore benefication. Iron-bearing minerals can be floated away either using sulfonate or fatty acid type collectors in acid circuit [1]. However the iron-bearing minerals can be easily removed by magnetic separation, and ultra-fine iron particles are difficult to treat by conventional mineral processing methods, biochemical leaching appears to be the only alternative for the effective removal of iron minerals. Microorganisms can affect the mobility of iron as well as its accumulation. Both oxidative and reductive reactions of iron brought about by microorganisms play important roles in the iron cycle. Iron can even serve as an energy source for some bacteria [2]. Microbial production of organics by fermentation, or reductive dissolution of Fe – Mn mineral phases can greatly accelerate weathering rates of aluminosilicate minerals [3,4,5]. This alternative, eco-friendly and effective weathering process using bacterial leaching has been tested for removing of iron minerals and mica from feldspar samples and quartz sands in our study. The aim of this study was to determine the extent to which heterotrophic bacteria of Bacillus spp. may have influence Fe chemistry in these non-metalic raw materials. The feasibility of the bioleaching treatment has to be tested specifically to each type of silicate raw materials.
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 147.213.193.81-02/08/07,13:38:29)
Advanced Materials Research Vols. 20-21
127
Methods The iron – bearing minerals (goethite, mica, smectite) decrease the quality of non-metallic material. Its chemical characteristics are shown in Tables 1, 2, 3, 4, 5. Bioleaching of samples containing 50 g rocks and 500 ml medium containing NaH2PO4 – 0.5g/l, MgSO4 . 7H2O - 0.5g/l, (NH4)2 SO4 – 1.0g/l, NaCl – 0.2g/l, molasses – 0,3g/kg samples. However, medium was changed six times during bioleaching at 17 days intervals under aseptic conditions. The samples were inoculated with a mixture of both Bacillus cereus and Bacillus pumilus strains. The flasks were incubated statically for 3 or 4 months at 28oC. The abiotic controls were cultivated under the same conditions. After incubation, the culture solutions were separated from the biomass by means of membrane filtration. Dry electromagnetic separation has been realized by the laboratory separator with the induction of magnetic field 1.3 T.
Results and disscusion It was tested ability and activity of heterotrophic bacteria at Fe removal from various nonmetallics, from various deposits under laboratory conditions. The overall effect of batch bioleaching on Fe removal was different in individual samples. Particle size of iron minerals, mineralogical and chemical composition of non-metallics and iron bearing minerals are major factors in determining the rate and extent of any bioleaching effect of pretreament before elutriation or electromagnetic separation.
Table 1 Effect of bioleaching (BL) and elutriation on elements removal from quartz sands from Vyšný Petrovec deposit (VQ) Chemical composition w.t. % VQ (before BL) VQ (after BL) VQ (after BL and elutriation)
SiO2
TiO2 Al2O3 Fe2O3
FeO
MnO MgO
CaO
Na2O
K2O
96.10 96.22 95.82
0.45 0.39 0.9
0.19
