Synergistic Competitive Inhibition of Ferrous Iron Oxidation by Thiobacillus ferrooxidans by Increasing Concentrations of Ferric Iron and Cells

Oxidation of ferrous iron by Thiobacillus ferrooxidans SM-4 was inhibited competitively by increasing concentrations of ferric iron or cells. A kinetic analysis showed that binding of one inhibitor did not exclude binding of the other and led to synergistic inhibition by the two inhibitors. Binding of one inhibitor, however, was affected by the other inhibitor, and the apparent inhibition constant increased with increasing concentrations of the other inhibitor.

Comparison of biooxidation with carbon dioxide assimilation during bacterial growth on ferrous ion or elemental sulfur

Biomass and oxygen uptake activity profiles of a mixed bioleaching culture were studied and compared at various temperatures. Bacteria were grown on ferrous ion or elemental sulfur in a Micro-Oxymax respirometer apparatus that allowed measurement of both oxygen consumption and carbon dioxide assimilation. Balanced growth was observed between 10 degrees C and 35 degrees C, with an optimum at 30 degrees C, on both energy sources. No significant growth was observed at the lowest temperature used, 5 degrees C, or at the highest temperature used, 40 degrees C. The oxygen to carbon dioxide molar yield was 50:1 when growing on ferrous ion but only 17:1 when growing on elemental sulfur. Upon transfer from a sulfide ore to a new energy source, greater numbers in the inoculum reduced the duration of the lag phase. Lag phase duration was also reduced by proximity to the optimum growth temperature. A longer lag phase decreased the achievable growth rate of the cells exponentially, significantly affecting biooxidation activity.

Effect of anions on selective solubilization of zinc and copper in bacterial leaching of sulfide ores

Bacterial leaching of sulfide ores using Thiobacillus ferrooxidans, Thiobacillus thiooxidans, or a combination of the two was studied at various concentrations of specific anions. Selective zinc and copper solubilization was obtained by inhibiting iron oxidation without affecting sulfur/sulfide oxidation. Phosphate reduced iron solubilization from a pyrite (FeS(2))-sphalerite (ZnS) mixture without significantly affecting zinc solubilization. Copper leaching from a chalcopyrite (CuFeS(2))-sphalerite mixture was stimulated by phosphate, whereas chloride accelerated zinc extraction. In a complex sulfide ore containing pyrite, chalcopyrite, and sphalerite, both phosphate and chloride reduced iron solubilization and increased copper extraction, whereas only chloride stimulated zinc extraction. Maximum leaching obtained was 100% zinc and 50% copper. Time-course studies of copper and zinc solubilization suggest the possibility of selective metal recovery following treatment with specific anions.

Selective inhibition of the oxidation of ferrous iron or sulfur in Thiobacillus ferrooxidans

The oxidation of either ferrous iron or sulfur by Thiobacillus ferrooxidans was selectively inhibited or controlled by various anions, inhibitors, and osmotic pressure. Iron oxidation was more sensitive than sulfur oxidation to inhibition by chloride, phosphate, and nitrate at low concentrations (below 0.1 M) and also to inhibition by azide and cyanide. Sulfur oxidation was more sensitive than iron oxidation to the inhibitory effect of high osmotic pressure. These differences were evident not only between iron oxidation by iron-grown cells and sulfur oxidation by sulfur-grown cells but also between the iron and sulfur oxidation activities of the same iron-grown cells. Growth experiments with ferrous iron or sulfur as an oxidizable substrate confirmed the higher sensitivity of iron oxidation to inhibition by phosphate, chloride, azide, and cyanide. Sulfur oxidation was actually stimulated by 50 mM phosphate or chloride. Leaching of Fe and Zn from pyrite (FeS(2)) and sphalerite (ZnS) by T. ferrooxidans was differentially affected by phosphate and chloride, which inhibited the solubilization of Fe without significantly affecting the solubilization of Zn.

Rate Equations and Kinetic Parameters of the Reactions Involved in Pyrite Oxidation by Thiobacillus ferrooxidans

Rate equations and kinetic parameters were obtained for various reactions involved in the bacterial oxidation of pyrite. The rate constants were 3.5 μM Fe 2+ per min per FeS 2 percent pulp density for the spontaneous pyrite dissolution, 10 μM Fe 2+ per min per mM Fe 3+ for the indirect leaching with Fe 3+ , 90 μM O 2 per min per mg of wet cells per ml for the Thiobacillus ferrooxidans oxidation of washed pyrite, and 250 μM O 2 per min per mg of wet cells per ml for the T. ferrooxidans oxidation of unwashed pyrite. The K m values for pyrite concentration were similar and were 1.9, 2.5, and 2.75% pulp density for indirect leaching, washed pyrite oxidation by T. ferrooxidans , and unwashed pyrite oxidation by T. ferrooxidans , respectively. The last reaction was competitively inhibited by increasing concentrations of cells, with a K i value of 0.13 mg of wet cells per ml. T. ferrooxidans cells also increased the rate of Fe 2+ production from Fe 3+ plus pyrite.

Competitive Inhibition of Ferrous Iron Oxidation by Thiobacillus ferrooxidans by Increasing Concentrations of Cells

The oxidation of ferrous iron (Fe 2+ ) to ferric iron (Fe 3+ ) with dioxygen (O 2 ) by various strains of Thiobacillus ferrooxidans was studied by measuring the rate of O 2 consumption at various Fe 2+ concentrations and cell concentrations. The apparent K m values for Fe 2+ remained constant at different cell concentrations of laboratory strains ATCC 13661 and ATCC 19859 but increased with increasing cell concentrations of mine isolates SM-4 and SM-5. The latter results are explained by the competitive inhibition of the Fe 2+ -binding site of a cell by other cells in the reaction mixture. Possible mechanisms involving cell surface properties are discussed.