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Risultati sfruttabili
Techniques have been developed for removing traces of iron from quartz, kaolin and ilmenite.
The techniques presently used to remove iron from these minerals involve the use of mineral acids which are expensive, not always effective, and give rise to environmental problems.
Mineralogical investigations were carried out on the materials to determine the form and distribution of the iron and other major minerals.
Suitable microorganisms with affinity to ferric ion chelation and transport were selected and isolated.
Experiments on synthetic goethite identified 2 strains which produce acetic acid and butyric acid and a mixed acid. Leaching testwork has been carried out with chemically derived organic acids and with the fermentation broth (a molasses solution fermented by Aspergillus niger) and compared with the results of conventional processes.
Tests with chemically derived organic acids on quartz gave the highest iron removal rate of 37% and while this would appear to be low the highest removal rate achieved with concentrated hydrochloric acid and sulphuric acid has been 43%.
Tests on kaolin using a mixture of citric and oxalic acid enabled the removal of +/- 40% of iron from the kaolin samples.
Leaching of the ilmenite sample has been carried out using oxalic acid. After 12 days it was apparent that oxalic acid was effective at dissolving iron. After 35 days around 30% of the iron had been dissolved.
The organic acid produced by Aspergillus niger, contained citric and oxalic acids at a ratio of approximately 3:1. Testwork on the quartz sample at a range of temperatures and at pulp densities of up to 30% (weight for weight) gave a maximum iron removal of 36%.
Tests on the biological treatment of effluents showed that methanogenic bacteria in the sludge can decompose oxalates to carbon dioxide and methane (+/- 66% reduction). Heterotrophic sulphate reducing bacteria caused the reduction of sulphate to sulphide (between 20% and 80%) and the sulphides of iron and other metals were precipitated in the presence of the hydrogen sulphide anion.
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