Study On Technology Of Bio-dephosphorization For High-Phosphorus Oolitic Hematite In Western Hubei

As the rapid development of the industry, the gap between the supply and requirement of the iron ore at home is increasing. And the available iron ore is inadequate although the resources are abundant in our country. Some of the ores are difficult to separate and some are refractory, including the high-phosphorus oolitic hematite, which takes up 9 percent of the total reserves and is considered as the most difficult one to be beneficiated through the traditional ways. As a new technology, biohydrometallurgy could be used to leach the phosphorus in this kind of ore because of the advantage of cheap and environmentally friendly.In this thesis, three kinds of microorganisms were investigated to bioleach the phosphorus from the high-phosphorus ores, which were Aspergillus niger, Acidthiobacillus ferrooxidans (At.f) and Acidithiobacillus thiooxidans (At.t), respectively. The experimental parameters were optimized and the mechanisms of one step and two-step bioleaching were discussed, which would underlie the industrialization.Through the experiments of breeding and leaching, several results could be showed as follows:(1)The most influential factor in the process of magnetizing roast was temperature. And the best condition was 850℃for 25 minutes, the ratio of the reductant and the ore was 5 percent, the strength of the magnetic field was 1500Oe. Finally, the ore concentrate mainly contained magnetite, maghemite(γ-Fe2O3) and quartz while theβ,εand phosphorus content were 54.92%,86.78% and 0.83%,respectively;(2) Among the five different kinds of acids,0.1 mol/L of sulfuric acid was the most effective one in the course of dephosphorization and increasing the grade of ore. The worst for removing phosphorus was citric acid while it could enhance the grade of ore; oxalic acid, as the most useful one for dephosphorization, could cause much loss of iron ore; however, the mixture of the above two was effective. Both 5 percent of raw ore pulp and 6 percent of ore concentrate pulp could be treated by sulfuric acid and the content of phosphorus in the leached ore could meet the requirements of industry;(3)Under 2 percent of pulp density, the result of leaching raw ore directly by Aspergillus niger was reasonable. In the process of two-step leaching, the optimum condition was PKO as the culture medium,4 percent of inoculum concentration, ammonium chloride as nitrogen source together with sucrose as carbon source. The effect of bioleaching raw ore was better than the ore concentrate. But the pulp density was always under 3 percent.(4) The main products of growing Atf were ammoniojarosite and jarosite; in the process of bioleaching directly, the minimum of dephosphorization rate was caused by non-stirring; within different rotating speeds of shaking table,140r/min was the best for leaching phosphorus, but meanwhile, the pulp density was only under 3 percent; to a certain extent, the addition of pyrite could improve the dephosphorization rate, nevertheless, the content of sulfur was beyond the standard; with the conditions of magnetic and mechanical stirring, the pulp density that could be treated effectively was under 4 percent. In the course of leaching by two steps, with sulfur as the energy source, the filtered fluid could treat the raw ore and ore concentrate that were under 6 percent of pulp density. However, the content of sulfur in the treated raw ore was over 1 percent whilst the content of phosphorus and sulfur in the treated ore concentrate could meet the requirements; with the increasing of pulp density, the dephosphorization rate was decreasing gradually.(5)Although the phosphorus content in the treated raw ore was up to the mustard, the sulfur content exceeded the standard. In the process of two-step bioleaching, the effects of dephosphorization were similar between the situations with and without the At.t. Meanwhile,18h was the best time for leaching and the phosphorus was up to 0.15 percent. Nonetheless, the treatment for raw ore failed in the area of sulfur although it could reduce the phosphorus content to 0.20 percent.(6) pH could be under 0.8 when the two kinds of thiobacteriua(At.t and At.f) were mixed and the filtered fluid could treat the ore concentrate under 6 percent pulp density. As a result, the content of phosphorus and sulfur content was 0.25 percent and 0.27 percent, respectively.(7) Ultrasonic wave was used to enhance the leaching process by sulfuric acid and filtered liquid of At.t. With the time extended, the phosphorus content, together with the recovery rate in the leached solid declined gently whist the grade of ore was enhanced slightly. Generally, in the field of sulfur content, it was under 0.25 percent no matter whether there was At.t or not.