Biometallurgy of nickel ore

1 leaching characteristics of pyrrhotite

Pyrrhotite is a major component of nickel-bearing sulfide ores and concentrates used for microbial leaching. Its chemical formula is Fe _1-x S, and x takes values ​​from 0 (Fes) to 0.125 (Fe ₇ S ₈ ). Belzile et al. reviewed the oxidation, acid consumption and heat production of pyrrhotite, which is prone to acid consumption in leaching environments. Acid consumption is a serious problem in both the agitation tank immersion of the concentrate and the microbial heap leaching. Addition of the acid in the leaching tank is relatively simple, but can lead to some non-essential metal ions. However, in the stacking process, the acidity is controlled by dripping, and the pH value changes greatly when the leachate is filtered through the heap. In addition, low acid has an effect on iron leaching, microbial activity and community dynamics. Some people think that it is possible to mix elemental sulfur in ore, and the acid production by sulfur microbial oxidation can effectively improve the low acid disadvantage caused by acid consumption of gangue.

Rosenblum and Spira studied a self-heating type of sulphurized waste rock pile in 1995, demonstrating that heat is derived from the oxidation of pyrrhotite, with temperatures up to 100 ° C in the reactor, and temperature profiles from two small nickel- copper sulphide test piles. The figure shows that the full oxidation of pyrrhotite causes the heap to heat up rapidly, but the excessive temperature rise will also accelerate the reaction of chemical Fe ²⁺ to Fe ³⁺ , and reduce the energy content of cell growth in heap leaching. In order to maintain the temperature range required for leaching microorganisms, it is usually controlled by dripping and/or ventilation to cool the heap. From the electrochemical point of view, the complex nickel-copper pyrrhotite symbiotic minerals are in the leaching process of sulfide ore. The dissolution of nickel is advantageous. Pyrrhotite (+120～+110mV vs.SHE) and pentlandite (+180～+100mV, vs.SHE) were leached prior to chalcopyrite (+250mV vs. SHE). Copper leaching occurs after most of the nickel leaching, as evidenced by data from two small nickel-copper sulfide ore test reactors. Microbial column leaching tests were carried out on the microbial leaching slag of the Sholl mine in Western Australia. It was also proved that the copper reaction on the surface of the pyrrhotite was the cause of copper leaching lag and low copper leaching rate.

2    Leaching characteristics of pentlandite

Synthetic minerals and concentrate leaching: Torma leaches synthetic NiS with A.ferroxidans , nickel and leaching rates of sterile and bacteriological conditions are 12% and 98%, respectively. Natarjan and Iwasaki nickel- accumulated A.ferroxidans leached nickel Pyrite and chalcopyrite concentrates, after 45 days, the immersion rate of domesticated nickel is 90%, and the leaching rate of unaccompanied bacteria is only 22%. Domestic scholars use A.ferroxidans and an unidentified thermophilic MLY) to leach nickel. Pyrite concentrate, its chemical composition is 32.72% nickel, 31.25% iron, 31.69% sulfur and 0.82% copper; nickel pyrite accounts for 95% in concentrate, ore size 38-74μm; the main impurity is brass ore and magnesium olivine. They concluded that A.ferroxidans adsorbed on the surface of the ore and contributed the most to the leaching; while the oxidation of Fe ²⁺ in the solution was mainly accomplished by bacteria that were free in solution. Santos et al. leached nickel pyrite, pyrrhotite and chalcopyrite concentrate using acid pit water containing mixed bacteria, and its chemical composition was nickel 5.9%, iron 28.1%, cobalt 0.4%, copper 0.l. % and sulfur 21.2%, the dissociation of androgenite and pyrrhotite in the concentrate is incomplete. The result was: leaching for 750 h, nickel leaching rate of 60%.

Thermophilic leaching of ferronickel concentrate: laboratory results show that it can effectively leaching, and its nickel leaching rate is above 85%. Mineral leaching practical terms, Finland Talvivaara ore containing pentlandite black shales, which is 25% mineral composition of quartz, potassium feldspar and plagioclase 38%, graphite 10%, 8% magnesium iron silicates, magnetic Pyrite 11%, pyrite 5%, needle nickel ore 3.2% and a small amount of pentlandite. Nickel (80.90%) mainly occurs in pentlandite and needle-nickel ore, and the rest is present in pyrite and pyrrhotite. A series of experimental results show that bacteria in the shake flask leaching the fine ore. Powder, leaching for 28 days, nickel and zinc leaching rate are 100%, cobalt is 73%, copper is 29%; bacterial column leaching experiment is loading 900kg, ore particle size is 70% is 0.5~2mm, leaching is about 300 days, nickel leaching The rate exceeded 90%, and the slag analysis indicated that the remaining nickel sulphide was not leached because it was surrounded by larger silica particles and the leaching solution could not be contacted. Puhakka and Tuovinen carried out a nickel pyrite bacterial column leaching experiment at a temperature range of 4 to 20 ° C. After 550 days of leaching, the nickel leaching rate was 62%, the temperature decreased, and the leaching rate was lower.

Nakazawa's research on Jinchuan Mine found that A.ferroxidans shake flask for 34 days, nickel leaching rate exceeds 90%, copper leaching rate does not exceed 30%, and pyrrhotite can be quickly dissolved by acid; copper leaching rate after silver catalysis Rise, but nickel leaching is inhibited. Chen and Fang used A.ferroxidans and A.thioxidans to carry out leaching of Jinchuan low-grade nickel sulfide ore in an airlift bioreactor with a slurry concentration of 15% and leaching for 20 days. The leaching rate was 95.4% nickel, 82.6% cobalt and copper. 48.6%.

3    Progress in microbial heap leaching test of nickel sulfide ore

In 2001, Hunter conducted a heap leaching test of nickel sulphide ore using BioHeapTM microbial heap leaching technology at Radio Hill, Western Australia. The technology is based on a proprietary medium-temperature thermophilic bacterium that preferentially oxidizes sulfur. The ore used for the heap leaching test is from the nickel sulphide mine of Mt Sho11. The ore grade is 0.92% copper, 0.67% nickel, 11.1% iron, 4.05% sulfur and 2.3% aluminum . The sulfide minerals account for 15% of the total ore volume. It is distributed in ore; pentlandite particles range from 30 to 2000 μm, chalcopyrite is 60.7% less than 100 μm, and more than 50% of chalcopyrite is distributed in unreacted silicate minerals. After nearly one year of microbial leaching, the nickel leaching rate is 90%, and copper leaching lags behind nickel, only 50%.

The Talvivaara mine in Finland is the largest nickel sulphide deposit in Europe. The average grade of the mine is 0.27% nickel, 0.56% zinc and 0.14% copper. Contains pyrrhotite, pyrite, sphalerite, pentlandite, sulphur nickel ore, chalcopyrite and graphite; nickel pyrite contains 80% nickel and the rest is mixed with pyrite (8 %) and pyrrhotite (21%); silicate minerals are quartz, mica , anorthite and micro-plagioclase. From laboratory research to column leaching tests to the current demonstration heap leaching tests, the Talvivaara mine bioleaching test has been conducted for 20 years. After 500 days of leaching, the leaching rate of valuable metals is 92% nickel, 82% zinc, 14% cobalt and 2% copper. The low leaching rate of copper is caused by the electrochemical properties of the mineral. The Talvivaara mine is currently the first commercialized nickel sulphide microbial heap leaching test site. From October 2008 to 2010, the mine will be flooded with a microbial heap at the Talvivaara mine, with an annual output of 33 kt nickel and 1.2 kt cobalt. , 60kt zinc and l0kt copper.

Domestic nickel-sulphide lean ore resources are mainly concentrated in Jinchuan, Gansu. Since 2000, Jinchuan has gradually introduced a series of microbial metallurgical experiments in the field of microbial metallurgy, and carried out microbial heap leaching of different grades of low-grade nickel sulfide ore. Experimental Research. Beijing Research Institute of Nonferrous Metal Wenjian Kang et al conducted a microorganism containing arsenic nickel sulfide ore heap leaching test MOJIANG. The ore grade is 0.6% nickel, 0.05% cobalt, 0.59% arsenic, 10.5% iron, 12.6% sulfur, A1 ₂ 0 ₃ 8.6% and Mg0 2.35%. The main arsenic sulfide nickel minerals are arsenic nickel ore and oblique. Square arsenic nickel ore. After one year of operation, the nickel leaching rate exceeds 60%, and the qualified leaching solution has Ni ²⁺ greater than 2g/L.

From the above-mentioned microbial heap test research practice of low-grade nickel sulfide ore, it can be seen that the microbial heap leaching of nickel sulfide ore is still in its infancy in research and industrial practice, and there is still a lot of work that needs long-term and meticulous work. Research to further promote the microbial metallurgical industrialization of nickel sulfide ore.

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