A Systematical Study On Bioleaching Of Realgar By Acidithiobacillus Ferrooxidans

Realgar is a naturally occurring arsenic sulfide. It contains over 90% tetra-arsenic tetra-sulfide (As4S4). In ancient Chinese and Indian medicine, realgar was commonly applied as a drug to treat various ailments. In recent years, realgar has been confirmed to be clinically effective for treatment of several forms of cancer in vitro and in vivo. Traditional means of preparing realgar include acid extraction, calcination, membrane dialysis, and mechanical milling. However, disadvantages such as low solubility in water, inadequate absorption of gastrointestinal, high toxicity, and poor bioavailability have seriously limited clinical applications of realgar. Bioleaching, a long-standing technology in hydrometallurgy, has recently been applied to preparation of realgar using indigenous acidophilic microorganisms in the field of pharmaceuticals. Recent studies have confirmed bioleaching solution with stronger antitumor activities, both in vitro and in vivo, of realgar extracted using A. ferrooxidans. It compared to the traditional methods mentioned above, bioleaching of realgar produces extraordinary increases in solubility and bioavailability and is efficient, ecologically safe, low cost and characterized by easy storage for realgar preparation. The characteristics of the bioleaching of realgar by Acidithiobacillus ferrooxidans BY-3(A. ferrooxidans) were investigated in this work. We examined the effects of using ferrous iron and elemental sulfur as the sole and mixed energy sources on the bioleaching of realgar. Under all experimental conditions, A. ferrooxidans BY-3 significantly enhanced the dissolution of realgar. Moreover, arsenic was more efficiently leached using A. ferrooxidans BY-3 in the presence of ferrous iron than in other culture conditions. A high concentration of arsenic was observed in the absence of alternative energy sources. This concentration was higher than that in cultures with sulfur only and lower than that in cultures with ferrous iron and sulfur. Linear or nonlinear models best fit the experimental data; the nonlinear model exhibited the dual effects of dissolution and removal on the bioleaching of realgar, whereas the linear model only applied to situations of slow bioleaching rather than removal.The characteristics of biochemical modification of realgar using A. ferrooxidans were investigated. SEM/EDS, XRD, and Raman observations were performed to elucidate the surface morphology of powder realgar and its interactions with A. ferrooxidans BY-3. The results show pararealgar was not found in after and before bioleaching. It suggested that the light-induced alteration of realgar to pararealgar that does not exist. The bioleaching of realgar can decrease toxicity by A. ferrooxidans BY-3. Moreover, modified realgar are more soluble than crude realgar in the solution. Therefore, it has been proven that the bioleaching of realgar can effectively solve the problem of partial oxidation and light-induced degradation products in traditional methods of preparing realgar. The effects of a range of operational parameters, including temperature, pH, bacteria population, ferrous iron concentration, and pulp density, on the efficiency of the bioleaching process were investigated. Experimental results demonstrated that optimum conditions in bioleaching of realgar were as follows:pH,1.5; 35℃; inoculum (v/v),20%; ferrous iron concentration,1.0 g/L; pulp density (w/v),1.5%. Surface chemical studies of A. ferrooxidans with reference to arsenic tolerance were studied. TEM observations were performed to elucidate the surface A. ferrooxidans BY-3. The results show that the existence of particulate matter on the surface of the A. ferrooxidans BY-3. The X-ray diffraction (XRD) assay indicated that the particulate matter contains Fe3+ compound [Fe3O4, KFe33+(SO4)2(OH)6,.etc] and arsenic-containing substances [KAsO3, Na2(H2As4O8)]. Fourier transform infrared spectroscopy (FTIR) analysis revealed the existence of different chemical groups (-OH or-NH,-CH,-CN,-CONH-,-CONH-,-COOH,-CN, C-O,-CH) on the surface of A. ferrooxidans BY-3. These chemical groups have a vital role to play in uptake of metals and metalloids by A. ferrooxidans BY-3. Under the guideline of systems biology, we had been preliminary built data integration system for bioleaching of A. ferrooxidans (DISBAf), which contains a series of dataset, the database of bioleaching substrates (DBS), the database of bioleaching metallic ion-related proteins (MIRP), the database of A. ferrooxidans bioinformation (Af-info), the database of Acidithiobacillus spp. (DAf) and the database for dynamics’s model of bioleaching (DDMB), respectively. DISBAf will be sever as a versatile database and analysis platform for bioleaching of realgar, and achievement simulation for computer simulation.