Study On The Bioleaching Of Marmatite By Iron-oxidizing And Sulfur-oxidizing Cultures

Abstract:When marmatite is treated by bioleaching technology, it can avoid generating SO2. It also has the advantages of simple process and low cost. While the element sulfur generated in the bioleaching process affects the further solution of marmatite. To eliminate or reduce this inhibition effect, it’s of great importance to study the bioleaching of marmatite by iron-oxidizing and sulfur-oxidizing cultures as well as how to add sulfur-oxidizing bacteria effectively.The bioleaching of marmatite by iron-oxidizing bacteria and sulfur-oxidizing bacteria was carried out by shake flask leaching experiments and orthogonal method, and the effects of temperatures, pH values, the inoculating times and concentrations of sulfur-oxidizing bacteria on the marmatite bioleaching by mixed culture composed of S.thermosulfidooxidans and A.caldus or L.ferriphilum and A.caldus were examined. The mechanism of marmatite bioleaching was discussed with the results of SEM、XRD and EDS.The bioleaching results showed that compared with the acid sterile condition iron-oxidizing L.ferriphilum and S.thermosulfidooxidans could accelerate leaching of marmatite, while sulfur-oxidizing A.caldus or A.thiooxidans cound not, or a little. In the system of inoculating pure L.ferriphilum and S.thermosulfidooxidans the leaching rates of zinc reached81.4%and54.8%, respectively.The addition of A.caldus was helpful to eliminate the surface cover of sulfur generated during the leaching process, so the leaching effect in mixed cultures composed of L.ferriphilum and A.caldus or S.thermosulfidooxidans and A.caldus was more effective than that in a pure culture.Marmatite bioleaching is an acid consuming process. The value of pH has a significant effect on marmatite bioleaching by mixed cultures. The leaching rate of zinc is higher when pH value is lower. The way of inoculating A.caldus also affects the leaching process. At the right time inoculating suitable concentration of A.caldus is more conducive to the leaching of marmatite. The statistical analysis on the orthogonal experimental results showed that the optimal condition during bioleaching by the mixed bacteria of S.thermosulfidooxidans and A.caldus is the pH value of1.8, inoculating A.caldus in the third day and inoculating A.caldus concentration of2.5x106/mL. The optimal condition during bioleaching by the mixed bacteria of L.ferriphilum and A.caldus is the pH value of1.6, inoculating A.caldus at the beginning and inoculating A.caldus concentration of2.5x106/mL. The primary and secondary order of the three factors that affect marmatite bioleaching is the pH value, the concentration of inoculating A.caldus, and the time of inoculating A.caldusThe results of SEM, XRD and EDS revealed that a product layer was formed on the particle surface; it reduced the dissolution rate of sulfide at the later leaching stage. The residues obtained were composed of elemental sulfur, jarosite and unreacted marmatite.