Importance of sulphate-reducing bacteria in environment

The sulphate-reducing bacteria represent the part of the biosphere, the active component in the cycle of elements in the biosphere and as shown by the existing knowledge they are becoming also the part of the environmental industrial technologies. The objective of this work was to give principal information concerning characteristics, the occurrence and the importance of sulphate-reducing bacteria in environment.

Towards the Biobeneficiation of PGMs: Reviewing the Opportunities

Conventional beneficiation of the Platinum Group of Metals (PGMs) relies on the use of inorganic chemicals. With the depreciation of high grade deposits, these conventional processes are becoming less economically viable. Furthermore, the use of chemicals has serious negative impacts on the environment. To address the challenges of conventional PGM beneficiation, biobeneficiation has been proposed. In conventional flotation, the flotation behavior of the associated sulphides determines overall PGM recovery. The same principle may also be applied for the bio-beneficiation of PGMs. Therefore, this paper discusses the biobeneficiation behavior of sulphides closely associated with PGMs with the aim of postulating the bio-beneficiation behavior of PGMs associated with the same base metal sulphides. Conventional PGM processes are briefly discussed, as bio-beneficiation of PGMs is governed by similar underlying principles. Potential microorganisms for the biobeneficiation of PGMs are highlighted, as well as the corresponding conditions for their effectiveness. The use of both single cultures and mixed cultures is discussed. Depending on conditions, PGMs associated with pyrite and/or chalcopyrite were projected to be biofloatable with B. polymyxa, P. polymyxa, A. ferrooxidans, L. ferrooxidans, B. pumilus, B. subtilis, halophilic bacteria, Alicyclobacillus ferrooxidans, sulphate reducing bacteria, and mixed cultures of A. ferrooxidans, A. thiooxidans and L. ferrooxidans. Pyrite-associated PGMsare expected to be generally prone to biodepression, whereas chalcopyrite-associated PGMs are expected to be generally recovered as the floatable phase. Sulphate-reducing bacteria were reported to have a dual role on the bioflotation of sulphide ores (flotation and depression), depending on the conditions. Therefore, this type of microorganism may serve as both a depressant or a collector in the recovery of PGMs. Based on the bioflotation response of pyrrhotite to L. ferrooxidans, it is anticipated that pyrrhotite-associated PGMS can be biodepressed using L. ferrooxidans. In terms of bioflocculation, PGMs associated with chalcopyrite may be recovered using L. ferrooxidans, whereas A. ferrooxidans, A. thiooxidans, B. polyxyma and B. subtilis can be used in the bioflocculation of pyrite-associated PGMs. M. phlei can be employed in the reverse bioflocculation of pyrite-associated PGMs. Although no information was found on the biobeneficiation of pentlandite, postulations were made based on other sulphide minerals. It was postulated that biobeneficiation (biodepression and bioflotation) with pentlandite-associated PGMs should be possible using A. ferrooxidans. It is also projected that sulphate-reducing bacteria will be suitable for the bioflotation of PGMs associated with pentlandite. The removal of gangue species such as silicates and chromites associated with PGM concentrates was also discussed. A. ferrooxidans, P. polymyxa and B. mucilaginous are candidates for the removal of gangue species. Furthermore, the need to control process conditions was highlighted. The most suitable conditions for biobeneficiation of the various base metal sulphide minerals associated with PGMs are presented in the paper. Most of the challenges associated with biobeneficiation of PGMs are already common to conventional methods, and the means of circumventing them are already well established. Developments in genetic engineering and the advent of new data science techniques are tools that could make the biobeneficiation of PGMs a possibility.

Positive and negative aspects of suplhate-reducing bacteria in environment and industry

The submitted work is oriented on the study of two aspects of the sulphate-reducing bacteria metabolism: the metals bioprecipitation and the concrete biodeterioration. The bioprecipitation of metals with the bacterially produced hydrogen sulphide by sulphate-reducing bacteria (SRB) represents the positive effect of the SRB existence in the environment. It allows the industrial exploitation in the area of the removal metals from industrial wastewaters. Referred method involves principal stages such as: hydrogen sulphide bacterial production, metals precipitation by biologically produced hydrogen sulphide, metal sulphides separation, setting pH of the filtrate from previous steps by 1M NaOH and metal hydroxides separation. The basis of the first stage i.e. the hydrogen sulphide bacterial production is the cultivation of SRB. In the laboratory conditions the sodium lactate is the energetic substrate for the growth of bacteria. Its price is not economic for the application in the practice and is needed investigate the alternative substitutes. Therefore was studied the cultivation of sulphate-reducing bacteria to using the selected energetic substrates such as: calcium lactate, glycerol and whey. Experimental studies confirm that all chosen substrates are suitable alternative substrates of sodium lactate for the bacterial sulphate-reduction. In the regard to the efficiency of bacterial sulphate reduction the calcium lactate is the best. The biodeterioration of the concrete presents the negative effect of the SRB existence in the environment. The research was oriented on the simulation of the biodeterioration of concrete samples under the simultaneous influence of the sulphur-oxidising bacteria genera Acidithiobacillus thiooxidans and sulphatereducing bacteria genera Desulfovibrio in the environs of the waste water, the acid mine drainage, the nutrient medium and the distilled water. The observation of the surface structure changes of concrete samples confirms the highest biodeterioration influences in the case of the acid mine drainage application.

Lifetimes of Used Nuclear Fuel Containers Affected by Sulphate-Reducing Bacteria Reactions inside the Canadian Deep Geological Repository

The present work aims at approximating the reduction of sulphate to sulphide caused by sulphate-reducing bacteria (SRB) inside the Canadian deep geological repository in order to calculate the expected lifetime of used nuclear fuel containers (UFCs). Previous studies have assumed a conservative constant concentration of sulphide at the host rock interface. The novelty of this study resides in the use of first-order kinetics to explicitly account for the SRB-induced sulphide production. This reaction term is developed following an empirical approach using published results on actual sulphate reduction by SRB and included in a coupled reaction-diffusion system. Lifetimes of UFCs are subsequently calculated following the conditions of two scenarios: having SRB active only at the region closest to the host rock and having SRB active at the host rock and throughout the bentonite clay. This study shows that the mean lifetimes of UFCs in both cases are above one million years. However, more accurate results would require the characterization of the host rock and groundwater of the prospective emplacement, as well as additional experiments on growth and sulphide production by the microbial communities from the site.

Advances and achievements of Academician D.L. Rakhmankulov’s scientific school in the field of applied and oilfield chemistry

This paper reviews the achievements of the scientific school of Academician of the Academy of Sciences of the Republic of Bashkortostan, Professor of the Ufa State Petroleum Technological University (USPTU) D.L. Rakhmankulov in the field of applied and oilfield chemistry. Having achieved fundamental results during theoretical and experimental research into the structure, properties and mechanisms of transformations of substituted cyclic acetals and heteroanalogues, D.L. Rakhmankulov and his colleagues proposed to apply this knowledge in various sectors of the national economy, in particular, in the oilfield chemistry. An analysis of copyright certificates obtained by the researchers from the 1970s to the 1990s, which were related to the development of reagents of the class of cyclic acetals intended for use in the oilfield chemistry, showed that the obtained reagents can be effectively used as components of drilling fluids, inhibitors of hydrogen sulphide corrosion of oilfield equipment, bactericidal reagents that inhibit the growth of sulphate-reducing bacteria. The efficiency of such reagents significantly exceeded that of well-known industrial reagents. It was noted that aqueous compositions containing 1,3-dioxacycloalkanes dissolve and keep in volume particles of resins and asphaltenes in the form of microemulsions, which makes it possible to increase oil recovery and use cyclic acetals as reagents-solvents of asphalt-resin-paraffin deposits. It was found that the use of cyclic acetals, e.g. 4,4-dimethyl-1,3-dioxane, in the composition of drilling fluids can significantly improve their lubricating, antiwear and anticorrosive properties. By-products of petrochemical industries were often used as a raw material for the production of compounds of the class of cyclic acetals, which at the same time solved the problem of their recycling. It was found that the bottom residue of industrial production of 4,4-dimethyl-1,3-dioxane, containing oxymethyl-1,3-dioxanes, can be successfully used for dissolving gypsum hydrocarbon fuels deposited in oil wells. In order to expand the range of reagents that inhibit the growth of sulphate-reducing bacteria, D.L. Rakhmankulov and his colleagues proposed to use aqueous solutions of 1,3-dioxacycloalkanes as bactericides.