EFFECTS OF VARIATIONS IN THE OPERATING CONDITIONS OF SOME PROCESS PARAMETERS ON THE BACTERIAL LEACHING OF A NIGERIAN IRON ORE SAMPLE
In this study, a bacterial isolate tentatively identified as Bacillus subtilis, obtained from a Nigerian iron ore sample was evaluated for its ability to beneficiate the ore under aerated (shake-flask) and static conditions with variations in inoculum sizes (0 ml, 0.5 ml, 2 ml, or 5 ml of standardized inoculum), ore grain sizes (0.2 mm, 0.4 mm, 0.6 mm, or 0.8 mm) and initial pH (2.5, 7, or 12). The iron ore which was obtained from Itakpe quarry site in Kogi State had the following composition: iron 36%, phosphorus 0.95 %, sulphur 0.03 % and other materials 62.02 %. The study was organized in two phases with each phase lasting for eight weeks. Phase one experiment was conducted in shake-flasks while phase two took place under static conditions. In each of these studies, the effects of varying levels of inoculum, ore grain size and medium pH on the ability of the organism to upgrade the iron metal (converting it from ferric sulphate to ferrous sulphate) as well as mobilize phosphorus and sulphur which are deleterious inclusions in the ore were assessed. A total of sixty-six (66) (33 for each phase) study samples containing both the controls and variations of the test parameters were used with each being conducted in triplicate. Results obtained showed that aeration significantly (p<0.05) enhanced the beneficiation process. Effect of inoculum under static condition was dose – dependent. Higher inoculum level produced higher percentage of iron and mobilized more phosphorus and sulphur. However, under aeration condition inoculum dose did not affect the beneficiation process. Medium pH significantly (p<0.05) affected iron leaching, as well as phosphorus and sulphur removal from the ore. Under static condition, alkaline pH (pH 12) enhanced iron leaching and sulphur removal but highest phosphorus removal was recorded at pH 2.5 in shake-flask condition; neutral pH (pH 7) gave optimum results for phosphorus (level reduced from 0.95 % to 0.0114 %) and sulphur (level reduced from 0.03 % to 0.0011 %). For leaching of iron, acidic pH (pH 2.5) produced optimum results, reducing the level of iron from the original 36 % to 35.5 %. Ore particle sizes also played a significant role in the leaching process in shake-flask and static conditions. Generally, the higher grain sizes (0.4 – 0.8 mm) produced better results in terms of the quantities of iron leached as well as phosphate and sulphate removed. The ranges of pH tolerance (pH 2.5 – 12), leaching efficiency and adaptation make B. subtilis good candidate for commercial bioleaching operation
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