# Development of Technology for the Boleaching of Uranium in a Solution of Bacterial Immobilization
###### Abstract
In this process, iron-oxidizing bacteria, such as Acidithobacillus, are involved. Ferrooxidants convert ferrous iron to ferric iron (from Fe\({}^{2+}\) to Fe\({}^{3+}\)). During underground in situ uranium leaching, ferric iron interacts with tetravalent uranium (insoluble) in the ore body, transforming it into soluble compounds. This method provides an efficient and, in some cases, economically advantageous alternative to traditional approaches to uranium extraction using expensive chemical oxidizers (hydrogen peroxide and others). To convert poorly soluble tetravalent uranium from ores into a soluble form in leaching solutions, various methods are employed, including chemical oxidizers and iron-oxidizing bacteria. The effectiveness of iron-oxidizing bacteria is associated with their increasing concentration in the bioreactor and their access to oxygen using immobilizers. Immobilizers contribute to the increase in bacterial concentration in the bioreactor by attaching bacteria to them and increasing their contact with oxygen. The surface modification of immobilizers, such as with iron hydroxide, enhances bacterial attachment, leading to the more efficient oxidation of ferrous iron. Thus, the hypothesis was proposed that modifying the surface of the immobilizer would allow bacteria to attach more effectively. Iron hydroxide was applied as a surface modification to the immobilizer. This substantial effect is due to the fact that the trivalent iron was formed biologically and will exhibit a higher affinity for bacteria. On the other hand, the influence of trivalent iron obtained through iron-oxidizing bacteria requires detailed investigation. Therefore, the task was to examine the effect of trivalent iron obtained in the bioreactor on the uranium content in the productive solution during UBL. It is known that tetravalent uranium is sparingly soluble in sulfuric acid solutions. Trivalent iron serves as an effective oxidizer of tetravalent uranium, converting it into the soluble hexavalent form, which is easily soluble in leaching solutions. Pilot trials were conducted to confirm the scientific hypothesis regarding the significant impact of biologically obtained trivalent iron on increasing the uranium content in the productive solution at the geotechnical field of a uranium mine. Extracting tetravalent, sparingly soluble uranium from the ore body may increase the recovery of uranium from the uranium deposit, leading to a more comprehensive development of the deposit. The main objectives of our research are as follows: (a) increase the rate of ferrous iron (Fe\({}^{2+}\)) oxidation in solutions using modified surface immobilizers for strains of _Acidithiobacillus ferrooxidans_ bacteria; (b) study the effect of the bioactivation of leaching solutions in a flow-through bioreactor with an immobilizer on the uranium content in the productive solution during the UBL of uranium. To achieve these goals, various types of immobilizers in a flow-through bioreactor were studied and compared to determine the most effective method for increasing the rate of Fe\({}^{2+}\) biooxidation. Pilot trials were also conducted to determine the effect of ferrous iron biooxidation on the uranium content in the productive solution. Although previous studies have focused on various aspects of these processes, ta critical gap trmsind in the understanding of the efficiency and stability of these biological systems, especially in dynamic environments such as flow-through bioreactors used for uranium extraction. This study aims to fill this gap by examining the effectiveness of different immobilizers in enhancing the stability and activity of _Acidithiobacillus ferrooxidans_ in flow-through bioreactors. Previous studies have established that in the presence of solid carriers [3] (immobilizers), a large portion of _Acidithiobacillus ferrooxidans_ attaches to the surface of the solid carrier.