Study On Preparation Of Ultra-pure Iron Concentrate By Bioleaching Iron-bearing Silicate

As an important new functional material,ultra-pure iron concentrate is widely used in the fields of powder metallurgy,magnetic materials,synthetic ammonia catalysts and iron oxide red.The technical challenge in the preparation of ultrapure iron concentrates is the removal of silicon from magnetically selected iron concentrates.Iron-containing silicate minerals and iron minerals in iron concentrates have a large number of structural iron ions,and the difference in physicochemical properties is small,which limits the efficiency of iron extraction and silicon reduction in iron concentrates.Although reverse flotation can remove partial silicon containing mineral,the conventional reverse flotation process has the problem of poor flotation process index,and it is difficult to obtain ultra-pure iron concentrate products.According to these problems above,the method of microbial leaching is used to desiliconize iron-containing silicate minerals(phlogopite,pyroxene,hornblende,red jasper)in iron concentrate to reduce silicon in iron concentrate,thus obtain the the high-grade ultra-pure iron concentrate.The contents was obtained as follows:(1)The strain was isolated and purified by the plate scribing method to obtained a single strain,which was identified as Aspergillus Niger by 18 SrDNA technology.In this paper,Aspergillus Niger was cultured on agar culture medium,and the effects of inoculum,carbon source and nitrogen source on the growth of Aspergillus Niger were explored.The results showed that the best carbon and nitrogen sources for the growth of Aspergillus Niger were mannitol and sodium nitrate,respectively.The optimum amount of bacteria was 7 mL.(2)The method of shake flask leaching was used to investigate the desiliconization effect of Aspergillus Niger on four iron-containing silicate minerals under the conditions of different inoculums,leaching times and pulp concentrations.The results show that Aspergillus Niger has different leaching effects on different structures of iron-containing silicate minerals.For the single-chain iron-containing silicate mineral pyroxene,the best leaching effect was achieved when the inoculum volume was 7 mL,the pulp concentration was 10% and the leaching time was 13 days,and the silicon content in the leaching solution reached 65.21 mg/L,140.74 mg/L and 125.47 mg/L respectively.Amphibole is a double-chain iron-containing silicate mineral,which achieves the best dip when the inoculum is 7 mL,the pulp concentration is 10%,and the leaching time is 17 days.The silicon content in the leachate was 42.84 mg/L,148.63 mg/L and 82.32 mg/L,respectively.Phlogopite is a layered iron-containing silicate mineral,the inoculum volume is 5mL,the pulp concentration is 12% and the optimum leaching effect was achieved at 11 days of leaching time.The silicon content in the leaching solution reached the maximum of 59.16 mg/L,301 mg/L and 113.11 mg/L respectively.Red jasper was a double-chain iron-containing silicate mineral.The amount of silicon in the leaching solution reached the maximum when the bacterial amount was 5 mL,the pulp concentration was 8%,and the leaching time was 11 days,which were 60.47 mg/L,250.74 mg/L and 126.37 mg/L,respectively.(3)Using XRD,SEM and FTIR to characterize the experimental ore samples before and after leaching of Aspergillus Niger,and the mechanism of action of Aspergillus Niger on four iron-containing silicates was investigated.The mode of action of Aspergillus Niger on different structural minerals is not identical because of the differences in the structure of the four iron-containing silicate minerals.After the action of Asbestos by Aspergillus Niger,the single-chain structure of the siloxane tetrahedral unit is broken,and the Si-O chemical bond changes.For the hornblende,two double-stranded structures formed by the mutual coupling of two single chains of silicon tetrahedrons are broken after the leaching,and the Si-O chemical bond and the OH chemical bond reduced.Phlogopite is a layered silicate mineral,which consists of an octahedral sheet sandwiched by two octahedral sheets.Under the action of organic acid acidolysis and extracellular polymer complexation of the metabolites of Aspergillus niger,the fragile surface of the phlogopite is eroded,and some metal ions in the trioctahedral layer are dissolved,which causes the partially eroded mineral particle lattice to deformation or disintegration.Besides,the mica layer collapses,and the silicon element is dissolved,the water peak between the phlogopite layers is weakened,the OH functional group is reduced,and the absorption peak of the Si-O-Si chemical bond is weakened.Red jasper is a framework silicate mineral.After the action of Aspergillus Niger,the intensity of quartz characteristic peak decreases,the crystallinity decreases,and the crystal structure is destroyed.With the increase of leaching time,its degree becomes more and more serious.After leaching,the absorption peak of Si-O chemical bond of quartz in Red Jasper decreases,the silica-oxygen bond at the corner-top junction is destroyed.