Microbial leaching of copper ore

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    Bacterial-assisted heap leaching
Australia Jili Lang collapse (Girilambone) mine [1] upper malachite and azurite ore, started in 1993 heap leaching oxide ores, copper annual 14000t. The sulphide ore in the lower part of the deposit is gradually increasing, accounting for 65% of the copper-bearing ore, mainly chalcopyrite, and the main part is chalcopyrite. In l 00mm The results of bacterial leaching in a small diameter column showed that the leaching rate of the chalcopyrite was 97% for 25 days, while the chalcopyrite only leached 27% to 42% at 710 days. Iron leaching is faster than copper, 42% for 25 days. The column immersion test also showed that Thiobacillus ferrooxidans gradually appeared in the leachate even if it was not inoculated, but it took a long time, so it was necessary to inoculate.
Further 6m High tested in large columns, leaching velocity depends on the initial start acidity, containing 8g Leaching of /L sulfuric acid raffinate, acid increased to 155~158 days 15g /L . The initial copper leaching rate was slower and the effect of the microorganisms began to be apparent at 99 days. At this time, the pH was 2.9 , and Fe ( II ) was oxidized to Fe ( III ) to precipitate. Starting acidity is 54g At /L , the leaching speed is very fast at first, and the copper leaching reaches 23% in 22 days, and the acidity is lowered. On day 74, the microorganisms began to function. However, in the later stage, iron still precipitates out of solution.
In designing heap leaching, the average leaching rate was set at 78% , taking into account the increasing proportion of chalcopyrite. A two-stage leaching process, ie a low copper solution from the old pile, is used for the new heap leaching. The ore contains an average of 2.5% copper, which is much higher than other mines. Ore crushed to -12mm , heap height 5~ 6m . The new pile at the beginning is built in the new yard and will be built on the old oxidized ore pile. Spray speed 13L /h·m 2 , the air in the pile, the designed stack temperature is 30 ° C . The acidity used when the new heap begins to leach is 50g /L, dropped to 35 days later 8g /L , average acid consumption 14kg /t Ore. However, according to the results of the column leaching, the iron ore is also partially leached to produce sulfuric acid. Therefore, the acid may be excessive, and a part of it is taken out for neutralization, so the neutralization tank is designed.
Although the design desired stack temperature is 30 ° C But the actual measurement result in winter is 12 ° C , the leaching liquid 8°C . The leaching speed dropped significantly and the stack cycle was longer than expected. The use of drip is better than the spray to reduce heat loss, but it is not used because of the blockage caused by salt precipitation.
Analysis of the typical copper leaching rate and leaching time curve in the operation of the Kirilan collapse can be divided into two regions. The first region rises steeply, mainly because the chemical leaching of the acid works, and the subsequent leaching speed becomes slow, and the bacteria are leaching the sulfide ore. Afterwards, changes in the conditions of the heap, such as ore pulverization, cause the pile resistance to increase, and the leaching speed is further reduced.
The results of one year's operation show that this mining sludge leaching treatment of high-grade mixed copper ore is successful, the leaching rate of oxidized ore is 84% , the sulphide is 78 %, and the annual processing ore is 7.5 million tons . The leachate contains copper . 8g /L , raffinate 0.3g /L .
Extremely thermophilic bacteria leaching chalcopyrite
The immersion of chalcopyrite by mesophilic bacteria also leads to passivation, ie the elemental sulphur produced prevents further leaching reactions. However, the results reported in recent years indicate that the passivation of mesophilic bacteria and extremely thermophilic bacteria in chalcopyrite is not obvious.
Factory-based bacterial leaching equipment is highly demanding and therefore requires a high investment. A company recently developed a method for the leaching of chalcopyrite, with low investment and production costs [2] . The core of this method is to spray the slurry of chalcopyrite concentrate on ordinary rock blocks, heap heap, and inoculate the seeds in the heap. They did not specify the name of the rock used, but it should be an acid-resistant rock that requires breaking to 6~ 25mm . Pulp stones outside the package thickness of about lmm, the quality of the rock and the concentrate is between 5 / 1-10 / 1.
When the stones flow down from the end of the belt conveyor, the slurry is sprayed from different directions to the stones through two nozzles and adheres to the stones. The stones covered with the slurry are directly piled up in a heap and are no longer moved. It is said that because the chalcopyrite is drowning, the concentrate adhered to the stone will not be washed away from the surface of the stone when it is sprayed with the leachate and when it rains. [next]
The sample used in a column immersion test contained 26.1 % copper, 29.7% iron, 29.0% sulfur and 0.5% calcium carbonate. The mineral analysis results were 75.4% for chalcopyrite and 14.5% for pyrite ( 63% of which were ferro-ferrite). mine). Among them, acid-soluble copper is 1.5% and acid-soluble iron is 2.1% . Column height 6m ,diameter 0.144m Underneath the air, test, and incorporate oxygen or carbon dioxide. They first inoculated medium-temperature bacteria at room temperature, leaching for 25 days , and the reaction rate decreased significantly. Warm up to 50 ° C The thermophilic bacteria were inoculated and immersed for 50 days . The leaching rate of copper reached 50% , and the reaction rate decreased again. Warm up again 70 ° C Inoculation of extremely thermophilic bacteria, the leaching rate continues to rise, to 150d , reaching more than 80% , will continue to rise. This test shows that there are large differences in the leaching abilities of different strains, as shown in the figure below. In another trial, warming up from the beginning 70 ° C And directly inoculated with extreme thermophilic bacteria, the leaching rate reached 97.5% at 140d . During the first two weeks, the bacteria are in the breeding phase and the leaching speed is very slow. Then leaching of copper per day to achieve 1.14% after 80d, with lower grade ore decreased, 150d daily average leach rate of 0.70%.

    The comparison of the results of several tests shows that the leaching rate of copper is linear with the oxidation of sulfur in the ore. In addition to the oxidation of the sulfide ore to elemental sulfur at the initial stage, the elemental sulfur gradually decreases. This helps to understand why there is no significant passivation when extracting chalcopyrite from extreme thermophiles, as shown in the following figure. [next]

    Recently Japanese scholars [3] studied 65 ° C Under extreme thermophiles Bray les acid bacteria (Acidianus Brierlay) [4] leach chalcopyrite, leaching demonstrate again its faster than other strains. The leaching mechanism is mainly based on the direct oxidation of ore by bacteria adsorbed on the surface of the ore, and the oxidation of high-iron ions only accounts for a small proportion. This finding can explain, on the other hand, the mechanism by which this bacterium overcomes the elemental sulfur block leaching reaction. They are also the result of small established test models, speculated in a stirred reactor, the optimum conditions for the continuous extraction of a bacterial concentration of 10 14 / m 3, the solid-liquid ratio of 5 ~ 10kg /m 3 .
References :
1. Nicholson HM, Smih GR, et al., conf. Proc. BIOMINE '94, Sep. 19-20, 1994, Perth, western Australia, Paper II
2. Harvey P et al, Conf. Proc. BIOMINE '99, 88-97
3. Konishi Y, et al., Hydrometallurgy, 2001, 59: 271-282
4.Brierlary , CL , Brans R. , Conf. Proc. BIOMINE'94 , Sep.19-20 , 1994 , Perth , Western Australia, Paper V

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