Browsing by Subject "bioleaching"

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    The effect of As(III) and As(V) on the batch bioleaching of a pyrite-arsenopyrite concentrate
    (Elsevier, 1996) Breed, A W; Glatz, A; Hansford, G S; Harrison, S T L
    The bioleaching of arsenical gold-bearing sulphide ores and concentrates solubilises iron, arsenic and sulphur. Previous work has shown that high concentrations of iron and arsenic in solution inhibit bacterial growth, with As(III) reported to inhibit bacteria to a greater degree than As(V). Batch bioleaching experiments were carried out over periods of one month. Varying quantities of either 0.020–0.040 M As(III) or 0.107–0.220 M As(V), were added to a slurry, consisting of a pyrite-arsenopyrite concentrate (20% solids (m.v−1)) in a nutrient solution. The slurry was inoculated with a culture, consisting primarily of Leptospirillum ferrooxidans and Thiobacillus thiooxidans. The culture was obtained from a continuous bioleaching mini-plant treating the same concentrate. The results obtained were compared with those of a culture to which no arsenic was added. The effect of the added arsenic was determined by monitoring three parameters: the oxygen utilisation rate, rO2, of the culture, the rate at which the arsenic in the concentrate was solubilised and the speciation of the dissolved arsenic. The results suggest that the nature of the As(III) and As(V) toxicity is different. The addition of the culture to a slurry containing As(III) resulted in a reduced rate of bacterial oxidation. However, the addition of the culture to a slurry containing As(V) resulted in both a lag phase and a reduced rate of bacterial oxidation. At sufficiently high dosages of As(III) and As(V) the maximum oxygen utilisation rate, rO2max, of the culture was also affected. The results indicate that As(V) toxicity, and the relative toxicity of As(III) and As(V) to a mixed culture, appear to be affected by the availability of an energy source. Hence the toxicity of As(III) is not necessarily in the region of three times that of As(V). Furthermore, the results suggest that the mechanism of arsenic resistance may be attributed to the Pst+ Pit− mutations and an energy dependent efflux pump.
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    Particle effects in bioleaching of pyrite by acidophilic thermophile Sulfolobus metallicus
    (Springer Verlag, 2000) Nemati, M; Lowenadler, J; Harrison, S T L
    The effect of mineral particle size on the bioleaching of pyrite by the acidophilic thermophileSulfolobus metallicus was investigated in a batch bioreactor. Decreasing the particle size from a mean diameter of 202 micron (size fraction: 150–180 micron) to a mean diameter of 42.5 micron (size fraction: 25–45 micron) enhanced the bioleaching rate from 0.05 kg m−3 h−1 to 0.098 kg m−3 h−1. The particle size distribution of the mineral in this range did not influence the morphology and growth kinetics of the cells. The values of specific growth rate (μ) and yield factor (Y) were 0.018–0.025 h−1 and 0.67 × 1011–1.45 × 1011 cells (g iron)−1, respectively. Decreasing the particle size of the mineral to a mean diameter of 6.40 micron (size fraction <25 micron) adversely influenced the activity of the cells. The presence of fine particles apparently damaged the structure of the cells, resulting in their inability to oxidise pyrite.