| Jinchuan Groop (JNMC) has about 400 Mt of low-grade nickel sulfide ore. The average grades of the ore are Ni 0.60%, Co 0.026%, Cu 0.30%, Fe 10.4%, S 2.2%, MgO 31%, CaO 0.80%, SiO2 39% and Al2O3 2.0%, it is typically a low-grade nickel-bearing sulfide ore containing high levels of magnesium. Due to the high cost of fuels and the implementation and enforcement of stricter environmental regulations, the existing process for high grade ores is not feasible for low-grade ores. Therefore choosing an economical recovery process for the low-grade ore is necessary. In addition, a large quantity of acid wastewater (dilute sulfuric acid solution; pH 0.0-0.3) is produced by off-gas treating during smelting. This effluent is costly to treat so that it meets the discharge standards, it is therefore important to utilize the acid wastewater comprehensively.In this paper, breeding a mixture of mesophiles composed of A. ferrooxidans (FJ427686 and FJ427687) named Jc-1, A. thiooxidans (FJ427688) named Jc-2 and L.f. numbered DSM2391 (Jc-1 and Jc-2 were collected from the tailings dam of JNMC and DSM2391 was purchased from DSMZ), a systematic experimental study on the bioleaching of Jinchuan low-grade nickel-bearing sulfide ore contaning high levels of magnesium was carried out and coclusions are drawn as follows:(1) The gangue minerals of Jinchuan ore are olivine, pyroxene, serpentine, chlorite, tremolite and carbonate and the content of MgO is high (30-35%); the sulfide minerals of the ore mainly are pyrrhotite, pentlandite and chalcopyrite.(2) Jinchuan tailings dam represents a highly specific artificial geochemical environment. The pulp is suitable for the bacterial growth due to a low quantity of sulfide minerals at pH 1-3; but it also has a great selection pressure on the bacteria due to high concentrations of inorganic salts and flotation reagent residue. Therefore only a simple bacterial community was achieved in the extreme environment, which includes A. ferrooxidans and A. thiooxidans.(3) The capacity of the ferrous oxidation has significantly increased when the wild strains of Jc-lwas treated by ultraviolet mutagenesis, but the mutation breeding is not suitable for improving the resistant of the bacteria to high levels of magnesium.(4) Magnesium is indispensable in the growth of bacteria. However Mg2+ beyond the range of bacteria regulation will lead to exorbitant osmotic pressure which is lethal to bacteria. Of all the ions in the Jinchuan bacterial leaching system, the greatest negative impact on the growth of mixed bacteria is Mg2+.Before adaptation, the mixed bacteria reproduce very slowly when the concentration of Mg2+ is 0.6 mol/L (14.6 g/L) and the mixed bacteria die out when the concentration of Mg2+ is 0.8 mol/L (19.4 g/L). Thereafter, the adaptation of the mixed bacteria to 15 g/L Mg2+ as the initial adaptation concentration in the medium is performed through serial sub-culturing and gradually the Mg2+ concentration in the medium is increased over nearly 2 years. After adaptation, The mixed bacteria are eugenic under 1.04 mol/L (25 g/L) Mg2+, reproduce very slowly under 1.25 mol/L (30 g/L) Mg2+ and die out at a concentration of Mg2+ (1.46 mmol/L or 35 g/L). With the upgrading of the adaptation concentration of Mg2+, adaptation time is prolonged markedly:only 8 weeks'acclimation time is needed at the concentration of 15 g/L but 37 weeks'acclimation time is needed at the concentration of 25 g/L, which indicates that the adapatation of the bacteria to magnesium is becoming increasingly difficult with the the upgrading of the adaptation concentration of Mg2+.(5) Using Jc-1, a serial of experimental studies on the bioleaching of the pure mineral of pentlandite and pyrrhotite were carried out. The results show that the contact leaching plays an important role in the bioleaching of pentlandite while the non-contact leaching plays an important role in the bioleaching of pyrrhotite at room temperature and pH 2.0. The effects on the dissolution of the minerals were significantly strengthened at the presence of bacteria.(6) Column bioleaching was performed to investigate the technical feasibility to process Jinchuan low-grade nickel-bearing sulfide ore containing high levels of magnesium using a mixture of mesophiles. The results show that an extraction of nickel (90.3%), cobalt (88.6%) and copper (22.5%) were achieved within a 300 days leaching process including a 55 days acid pre-leaching stage and a 245 days bioleaching stage at the room temperature. The results of the valuable metals extraction indicate that three effective means are effective to successfully reduce the disadvantages of magnesia in the ore. They were preleaching to remove most leachable magnesia, adaptation of the mixed mesophiles to improve the tolerance and periodic bleeds of a portion of the pregnant leaching solution to control the Mg2+ concentration based on the tolerance of the mixed microorganisms.(7) Based on the results of the column bioleaching,0.5 Kt heap bioleaching of the Jinchuan low-grade nickel sulfide ore was performed to test the economical feasibility of using heap bioleaching to process the Jinchuan low-grade nickel sulfide ore. A nickel (84.6%), cobalt (75.0%) and copper (32.6%) extraction was achieved after 350 days of heap leaching, including 80 days of acid pre-leaching and 270 days of bioleaching. The overall concentrated sulfuric acid consumption was 600 kg per ton of the ore and the acid wastewater produced by off-gas treating during the smelt process was utilized efficiently with consumption of 1.06 m3 per ton of the ore. The results of the valuable metals extraction indicate that the process of translation of the basic lab achievements into a cost-effective, reliable and robust plant-scale operation is successful.(8) The respective overall recoveries of nickel, cobalt and copper are not less than 96% after the iron removal, CCD thickening wash and co-precipitation of Ni, Co and Cu from the bioleaching solution.(9) Economical feasibility model and overall evaluation show that the bioleaching process is profitable and eco-friendly if the cheap acid is available on site.
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