N. V. Grigor’eva

Microbial degradation of cyanide and thiocyanate

The role played by a bacterial community composed ofPseudomonas putida, strain 21;Pseudomonas stutzeri, strain 18; andPseudomonas sp., strain 5, and by physical and chemical factors in the degradation of CN− and SCN− was studied. It was shown that the degradation of CN− is determined both by the action of bacteria and by abiotic physical and chemical factors (pH, O2, temperature, the medium agitation rate, etc.). The contribution of chemical degradation was found to increase drastically at pH below 9.0; when air was blown through the medium (irrespective of the pH value); under active agitation of the medium; and when the medium surface interfacing air was increased. Even at elevated pH values (9.0-9.2), suboptimal for bacterial growth, the microbial degradation could account for at most 20–25 mg/1 of CN−, regardless of its initial concentration. When CN− and SCN− were concurrently present in the medium, the former compound was the first to be degraded by microorganisms. The rate of bacterial degradation of SCN− under continuous cultivation in a chain of reactors was found to depend on its concentration, the medium flow rate, agitation rate, and the pattern of carbon source supply and could exceed 1 g/(l day). CN− and SCN− are utilized by bacteria solely as nitrogen sources. The mechanism of CN− and SCN− degradation by the microbial community is discussed.

Mechanism of cyanide and thiocyanate decomposition by an association of Pseudomonas putida and Pseudomonas stutzeri strains

The intermediate and terminal products of cyanide and thiocyanate decomposition by individual strains of the genus Pseudomonas, P. putida strain 21 and P. stutzeri strain 18, and by their association were analyzed. The activity of the enzymes of nitrogen and sulfur metabolism in these strains was compared with that of the collection strains P. putida VKM B-2187T and P. stutzeri VKM B-975T. Upon the introduction of CN− and SCN− into cell suspensions of strains 18 and 21 in phosphate buffer (pH 8.8), the production of NH4+ was observed. Due to the high rate of their utilization, NH3, NH4+, and CNO− were absent from the culture liquids of P. putida strain 21 and P. stutzeri strain 18 grown with CN− or SCN−. Both Pseudomonas strains decomposed SCN− via cyanate production. The cyanase activity was 0.75 µmol/(min mg protein) for P. putida strain 21 and 1.26 μmol/(min mg protein) for P. stutzeri strain 18. The cyanase activity was present in the cells grown with SCN− but absent in cells grown with NH4+. Strain 21 of P. putida was a more active CN− decomposer than strain 18 of P. stutzeri. Ammonium and CO2 were the terminal nitrogen and carbon products of CN− and SCN− decomposition. The terminal sulfur products of SCN− decomposition by P. stutzeri strain 18 and P. putida strain 21 were thiosulfate and tetrathionate, respectively. The strains utilized the toxic compounds in the anabolism only, as sources of nitrogen (CN− and SCN−) and sulfur (SCN−). The pathway of thiocyanate decomposition by the association of bacteria of the genus Pseudomonas is proposed based on the results obtained.

Isolation of an aboriginal bacterial community capable of utilizing cyanide, thiocyanate, and ammonia from metallurgical plant wastewater

An aboriginal bacterial community capable of degrading cyanide (10 mg/l) and thiocyanate (2 g/l) and eliminating ammonia (120 mg/l) had been isolated from recycled water samples after blast-furnace gas purification of a metallurgical plant wastewater. It was shown that the optimal conditions for this bacterial community were as follows: temperature, 34°C; pH, 8.8–9.0; available organic matter concentration (glucose equivalent), 5 g/l; and dissolved O2 concentration, 8–10 mg/l. This aboriginal community was formed by the bacteria belonging to the genus Pseudomonas.

Thiocyanate decomposition under aerobic and oxygen-free conditions by the aboriginal bacterial community isolated from the waste water of a metallurgical works

A mesophilic alkalitolerant aboriginal bacterial community capable of autotrophic thiocyanate decomposition under aerobic and oxygen-free conditions was isolated from reused water of a metallurgical works. The growth of the aboriginal bacterial community was optimal at pH 9.0. Ammonium and sulfate were the end products of thiocyanate decomposition under both aerobic and oxygen-free conditions. Under oxygen-free conditions, thiocyanate decomposition occurred in the presence of nitrate. Nitrite was accumulated as an intermediate product in the course of denitrification, and was subsequently used as an electron acceptor for thiocyanate oxidation. Dinitrogen was the end product of denitrification.

Thermoacidophilic microbial community oxidizing the gold-bearing flotation concentrate of a pyrite-arsenopyrite ore

An aboriginal community of thermophilic acidophilic chemolithotrophic microorganisms (ACM) was isolated from a sample of pyrite gold-bearing flotation concentrate at 45–47°C and pH 1.8–2.0. Compared to an experimental thermoacidophilic microbial consortium formed in the course of cultivation in parallel bioreactors, it had lower rates of iron leaching and oxidation, while its rate of sulfur oxidation was higher. A new thermophilic acidophilic microbial community was obtained by mutual enrichment with the microorganisms from the experimental and aboriginal communities during the oxidation of sulfide ore flotation concentrate at 47°C. The dominant bacteria of this new ACM community were Acidithiobacillus caldus (the most active sulfur oxidize) and Sulfobacillus thermotolerans (active oxidizer of both iron and sulfur), while iron-oxidizing archaea of the family Ferroplasmaceae and heterotrophic bacteria Alicyclobacillus tolerans were the minor components. The new ACM community showed promise for leaching/oxidation of sulfides from flotation concentrate at high pulp density (S : L = 1 : 4).

Biooxidation of a gold-containing sulfide concentrate in relation to changes in physical and chemical conditions

The growth of a microbial community and the oxidation of iron- and sulfur-containing substrates in batch culture during the leaching/oxidation of the flotation concentrate of refractory gold-arsenic sulfide ore were optimized with respect to the following medium parameters: temperature, pH, and requirement in organic substances. It was revealed that the optimum mode is (i) to maintain the pH at 1.6–1.7 and the temperature at 34–35 and 38°C and (ii) to add Corg in the form of yeast extract (0.02%). Mutually beneficial or competitive relationships among groups of microorganisms of the community were established, depending on the cultivation conditions.

Contribution of equilibrium vacancies to vanadium caloric properties

For the first time, data have been obtained on the parameters of the contribution of equilibrium vacancies to the caloric properties of vanadium: the vacancy formation energy, E = 1.22 eV, the vacancy formation entropy, S = 26.8 J/(mole K)−1, and the temperature dependence of the vacancy concentration (at the vanadium melting temperature, Tm = 2220 K, the concentration equals to c = 4.2%). These values are determined on the basis of experimental measurements of the average heat capacity of vanadium. From analysis of the interconnection between the vacancy contribution and the limit temperature of superheating of the beginning of melting, Tsh, we found that the most reliable vacancy-free straight line of the average heat capacity corresponds to (Tsh/Tm) ≈ 1.25 and may serve as a reliability criterion for calculation of the vacancy contribution in metals.

Optimization of bioleaching and oxidation of gold-bearing pyrite-arsnopyrite ore concentrate in batch mode

Biooxidation of refractory gold-bearing pyrite-arsenopyrite flotation concentrate was optimized and the abundance of predominant groups in the community of thermophilic acidophilic chemolithotrophic microorganisms at various stages of bioleaching was determined. The optimal parameters for growth and leaching/oxidation of the mineral components of the concentrate were pH 1.4–1.8; 47.5°C; and the following salt concentrations in the liquid phase (g/L): K2HPO4 · 3H2O − 0.53, (NH4)2SO4, 1.6 and MgSO4 · 7H2O, 2.5 (or (NH4)2SO4, 1.23; ammophos, 0.41; KOH, 0.1) with 0.03% yeast extract. The optimal conditions resulted in high growth rate, high levels of iron and arsenic leaching, of Fe2+ and S2−/S0 oxidation, and predominance of Acidithiobacillus caldus, Sulfobacillus spp., and Ferroplasma spp. in the community.

Leaching of pyrite-arsenopyrite concentrate in bioreactors during continuous cultivation of a thermoacidophilic microbial community

A community of thermoacidophilic chemolithotrophic microorganisms was shown to exhibit enhanced efficiency of leaching and biooxidation of the gold-bearing pyrite-arsenopyrite flotation concentrate in continuous mode of cultivation. Under the optimal values of growth parameters, the degree of oxidation of sulfide arsenic, iron, sulfur, and antimony in the line of three laboratory reactors (D = 0.004 h−1) was 99.55, 98.87, 99.65, and 97.08%, respectively, while gold recovery from the solid biooxidation residue was 97.4%.

Growth of acidophilic chemolithotrophic microbial communities and sulfur oxidation in the presence of coal ashes

Out of two communities of acidophilic chemolithotrophic microorganisms (ACM), a mesophilic and a thermophilic ones, the latter was selected due to its higher rate of sulfur oxidation and pH decrease to >1 in the presence of coal ashes (CA). The structure of ACM communities was retained. Sulfur-oxidizing activity of the microorganisms from the thermophilic community was observed at pH from 1.8 to 2.6 at sulfur concentrations of 0.6–1.0%. Efficient production of acidic solutions with pH 0.69–0.86 was observed after single CA introduction in the amount corresponding to 5–30% pulp density and in the course of pulp density increasing daily from 1 to 50%. Leaching of rare earth elements from 30% coal ash pulp (pH 0.76) was 15 to 30% of their initial content. No sorption of metals on the biomass was observed.