Systematic studies were conducted at one of the uranium deposits in Kazakhstan. Native strains of Acidithiobacillus ferrooxidans bacteria were found in leaching solutions at the deposit. The modeling of iron species in the culturing medium was analyzed using Medusa software v.2.0.5. To intensify the process, the bacterial strains were propagated in laboratory conditions, and strains available in the laboratory were added. The ability of bacteria to oxidize divalent iron to trivalent iron at 8 °C in laboratory conditions was established, but the oxidation rate was low. It was found that the limiting stage of bioleaching use in deposit conditions is the temperature mode, the content of divalent iron, and oxygen. A biomass volume of 15 L was initially cultivated under laboratory conditions, and subsequently scaled up to 3 m³ in production using three 1 m³ pachucas with air aeration. In addition, pilot tests were carried out directly in production conditions and biomass in the volume of over 30 m³ was produced. The kinetics of the oxidation process of divalent iron to trivalent iron in 1 g/h under production conditions was established. The features of the bioleaching process at the field are shown as follows: since production, the solution contains the main microelements for the nutrition and reproduction of bacteria, and recommendations for the use of bioleaching are proposed. Research has established that under conditions of a shortage of divalent iron in the solution, sulfuric acid is formed due to sulfur-containing substances. It was observed that for the effective conversion of divalent iron to trivalent iron, bacteria of the provided strain and air (oxygen) supply are sufficient. The corresponding recommendations were issued during the work.

This study presents findings regarding the kinetics of ferrous iron oxidation in solution mediated by Acidithiobacillus ferrooxidans bacteria within a continuous-flow bioreactor employing diverse types of immobilizers. The objective is to augment the rate of ferrous iron oxidation in solutions utilizing an immobilizer for Acidithiobacillus ferrooxidans strains. Immobilization represents a promising avenue for enhancing the efficiency of Fe²⁺ oxidation via acidophilic ferrooxidizing bacteria, leading to a several-fold increase in oxidation rate. A comparative analysis was conducted to evaluate the efficacy of different types of immobilizer in facilitating iron oxidation within a continuous-flow bioreactor, including the application of wood chips coated with Fe(OH)₃. The results indicate that wood chips coated with iron hydroxide serve as effective type of immobilizer, facilitating the robust attachment of Acidithiobacillus ferrooxidans via electrostatic interactions between negatively charged bacteria and positively charged surfaces. Experimental investigations were conducted using novel immobilization matrices in pilot-scale tests simulating the underground borehole leaching (UBL) of uranium. The bioactivation of leaching solutions enhances the efficiency and environmental compatibility of UBL compared to conventional chemical oxidation methods. The relationships between redox potential and ferric iron content in bioactivated solutions during the UBL of uranium were delineated. The significance of this study lies in its elucidating the pivotal role of Fe²⁺ oxidation in uranium extraction processes, particularly in the context of UBL. By employing bioactivation mediated by Acidithiobacillus ferrooxidans, the study demonstrates not only enhanced uranium extraction efficiency, but also markedly improved environmental sustainability compared to traditional chemical oxidation methods. The findings reveal crucial correlations between redox potential and ferric iron concentration in bioactivated solutions.

Soil degradation in mining-affected regions – characterized by nutrient depletion, in-creased salinization, and heavy metal accumulation–poses serious risks to ecosystem stability and agricultural productivity. We conducted a comprehensive field study analyzing soil profiles using chemical, agrochemical, granulometric, and salinization assessments, along with heavy metal analysis. The aim of this work is to characterize the vertical distribution of nutrients and contaminants in these soils and to provide recommendations for effective remediation and sustainable land management. Our results show that the upper organic-rich layers exhibit significantly higher nutrient levels that sharply decline with depth, while heavy metals such as lead and copper are markedly elevated in certain profiles–especially in tailings soils, where contamination exceeds permissible limits by multiple folds. Additionally, granulometric analysis revealed a predominance of medium sand, which enhances permeability but limits water retention, and salinization increases with depth due to mineral weathering processes. Overall, our work provides critical insights necessary for developing targeted remediation strategies and sustainable practices to restore degraded ecosystems in mining regions.

A technology for bacterial iron oxidation in the process of in-situ leaching of uranium has been developed and proposed for industrial use. The technology was validated by the results of pilot tests conducted at a uranium deposit in Kazakhstan over a period of 12 months. The aim of the study was to develop a technology for bacterial iron oxidation in the process of in-situ uranium leaching using a new type of flow bioreactor. Two biotechnological installations with bioreactors of 20 m³ volume were created and installed in 40-foot containers. The bioreactors, equipped with piping, air compressors, a pumping station, and control and measuring instruments, were installed at the geotechnical site and connected to the main in-situ uranium leaching system through wells. The installations had a productivity of over 150,000 m³/year for the leaching solution. After passing through the bioreactors, the redox potential of the solution increased from 360 mV to 430-450 mV in flow mode. The concentration of ferric iron increased from 0.1 g/L to 1.5 g/L and higher. The bacterial iron oxidation process was carried out at a solution temperature of 10 to 12°C (optimal temperature — 25-35°C), which allowed eliminating the costs of heating the solution. The test results showed an increase in uranium content in the productive solution by 10-20% after the leaching solution passed through the ore-bearing layer for 1 month. This confirmed the prospects for using this technology for in-situ well uranium leaching. The economic costs of using the technology are 6-8 times lower compared to using chemical oxidants such as hydrogen peroxide. The obtained industrial results open new prospects for the application of biotechnological methods for in-situ well leaching of uranium and other metals for the first time.