MINERÍA la mejor puerta de acceso al sector minero MINERÍA / NOVIEMBRE 2024 / EDICIÓN 566 27 Abstract Biotechnological processes such as bioleaching are an appropriate alternative to solve critical issues affecting the developing world, for this reason, strategies must be sought for the manipulation of microorganisms, so that their application in industry is simple and economical. In this sense, the scientific contribution of this research is to encapsulate acidophilic bacteria with leaching capacity, establishing favorable conditions in the spray drying process, as well as determining the optimal wall material and ensuring the viability of microorganisms. In this context, the acidophilic bacterium acidithiobacillus thiooxidans (A.t) is potentially capable of leaching complex and low grade sulfide ores and has been applied in biohydrometallurgical processes. 20% of the world's copper production is carried out using this technology. However, there is still some distrust in the metallurgical industry, due to the cellular integrity, metabolic activities, genetic stability, and maintaining a continuous generation of microbial cultures and the prolonged time of the bioleaching process. A promising alternative to facilitate the handling and preservation process of this type of microorganisms is the microencapsulation process. In this work, a spray drying (SD) process was used to encapsulate acidithiobacillus thiooxidans, using different biopolymers as wall materials. The results were outstanding in comparison with other processes that encapsulate other types of microorganisms for other purposes. Among the results, we can summarize that the physicochemical properties of the microcapsules (powders) show a water activity (aw) of less than 0.55, a humidity of less than 10%, which ensures good stability of the powders during storage. The morphology by scanning electron microscopy (SEM) of spherical microparticles showing defined non-collapsed surfaces of uniform size, which in principle implies a mechanical stability to the flow of these microparticles. The calorimetric analysis shows that A. thiooxidans is encapsulated, since the exothermic peak that appears at 270 ºC corresponds to a crystallization of the exopolysaccharide (EPS) characteristic of this microorganism. In addition, by FT-IR the same response of the functional groups present in the biopolymers was observed after spray drying (SA), which is an indication of the encapsulation of the microorganism, this was corroborated by transmission electron microscopy (TEM). Finally, a high bacterial survival rate (1.4x10 9 Cells/mL) and a leaching capacity of 95% were achieved. It should also be noted that the bacteria remain viable after more than two years of encapsulation, which guarantees their long-term storage and availability for use in various biohydrometallurgical processes.
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