The study of bacterial metal leaching process from industrial waste
F.F. Nidzvedskiy, V.A. Snegirev, M.A. Bezmaternykh, M.N. Ivantsova, I.S. Selezneva
Section: Remediation and rehabilitation
The results of a study on the metals extraction from ash and slag waste of thermal power plants (TPP) by the bacterial leaching method are presented. Fly ash from the Troitskaya TPP was the study object. The phase-mineralogical composition of ash and slag from TPPs has been established. The composition includes burnt clay substance, glass phase, quartz, magnetite, and hematite. The mineral and chemical composition of fly ash from this thermal power plant
has been determined by X-ray phase and differential thermal analysis which showed the following results, in %: mullite (3Al2O3 · 2SiO2) up to 75, quartz (SiO2) – 7–8, hematite (Fe2O3 up to 65%) – 7–8, magnetite (Fe3O4 up to 72%) – 5–7. These data suggested the possibility of silicate destruction by Васillus mucilaginosus. Additionally, ash has sufficient energetic potential for the growth of chemolithoautotrophic microorganisms such as Acidithiobacillus ferrooxidans. Pure bacterial cultures of A. ferrooxidans, Thiobacillus thioparus and В. mucilaginosus were isolated by Drygalsky’s method from several native substrates. The composition optimization of the nutrient medium for the cultivation of A. ferrooxidansby Box-Wilson steep ascent method was carried out. Using this nutrient medium, it was possible to increase the A. ferrooxidans biomass yield by 1.5 times. Cell growth was viewed by the change in the protein concentration in the culture liquid by the Lowry method. It was found that the bioleaching of copper occurs to the greatest extent (46.9%) in comparison with zinc and manganese, and in addition, a more complete oxidation of iron occurs under the influence of A. ferrooxidans. Leaching in the same nutrient medium without bacteria was carried out as a control experiment. To determine the concentration of metals in the culture liquid that passed into solution from the ash after leaching, gravimetric and complexometric methods were used. In general, the data obtained indicate the effectiveness and prospects of the metals bioleaching application from the fuel, energy and metallurgical industries wastes. Using bacterial leaching method should help to reduce the negative impact on the ecological state of the region.