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2) oxidation of carbon argillaceous and iron ore roasting installation method Leaching of gold ore Changgiakou mainly occur in the native gold limonite, pyrite, white lead, galena, brass and quartz ore by flotation Produces refractory gold concentrates with high carbon, mud and alkaline minerals. For ore similar to this, various processes are taken before and after cyanidation to eliminate the effects of carbon and harmful impurities, but the cyanidation leaching rate is still not higher than 85%-90%, and directly or after decarbonization For thiourea immersion, the leaching rate of gold is only about 80%, and 135-180 kg of sulfuric acid per ton of concentrate is used, and thiourea is more than 5 kg. In order to improve the gold leaching rate of this concentrate, after the test, the concentrate is oxidized and calcined in advance to achieve the functions of removing carbon, decomposing carbonate and repelling the crystal water in limonite, and then immersing it with thiourea Set, obtained economic and technical indicators better than the cyanidation CCD process.
Fig. 6 is a flotation concentrate containing about 100g/t of gold, calcined at a temperature of about 680 ° C for about 20 minutes, and then finely ground to 94% - 0.043 mm (-325 mesh), and adjusted to pH by adding sulfuric acid. After 1.5-2, thiourea was added, and continuous thiourea iron immersion was carried out in six leaching tanks. Tests in 44 batches of 3 batches showed that the leaching rate of gold was 95.07%~96.40% with an average of 95.79%. The gold deposit recovery rate of gold mud on the iron plate is 98.45%-99.69%, with an average of 98.99%. The total recovery rate was 94.82% on average. Each ton of concentrate consumes 70kg of sulfuric acid, 1.5-2.2kg of thiourea, and the main material consumption is 42.42-52.48 yuan/t, which is 57%-47% lower than the cost of the same cyanide CCD process for processing the same ore of 98.66 yuan.
The process pulp does not need to be filtered, the equipment and infrastructure investment is low, the floor space is small, the operation is simple, the labor is saved, and the process is short. It is the first breakthrough of China's thiourea method for extracting gold from difficult-to-treat ore, and from research to industrial application, it has been successfully applied to the industrial production of Zhangjiakou gold mine. It lays a foundation for the research and popularization of thiourea iron slurry method in China.
3) Industrial test and popularization of the iron slurry method The raw material for the industrial test of the thiourea iron slurry method is a sulphur gold concentrate containing a small amount of oxidized mineral. The main mineral pyrite, chalcopyrite, galena, sphalerite, limonite, malachite, urea and natural gold minerals quartz, sericite, chlorite, kaolin, carbonates and the like. The concentrate component (gold/ silver is g/t, others are %) is Au 80.77, Ag 50, Cu 0.71, Pb 0.6, Zn 0.18, Fe 25.09, S 26.55, As 0.046, Bi 0.0063, Ni 0.038, SiO 2 22.44, CaO 4.08, MgO 11.80, Al 2 O 3 3.60. The natural gold particle size - 0.038 mm (400 mesh) accounts for more than 80%, of which 0.0067-0.0033 mm accounts for about 50%. [next]
The test was carried out in a continuous immersion operation with a scale of 1.5 t/d. The feeding mode 1 is mechanical continuous feeding, and the second is manual feeding. The flotation concentrate is dewatered by a thickener and then refined, and then milled into a closed loop composed of a cyclone and a classifier, and overflowed for leaching. The recovery of the leaching gold is to hang the iron plate in the tank and deposit gold while leaching.
The test was carried out continuously in seven tanks with a grinding particle size of 80%-85%-0.043 mm (325 mesh), a solid-liquid ratio of 1:2 thiourea initial mass fraction of 0.3%, pH 1-1.5, liquid temperature 25 °C, Insert iron plate 3m 2 ·m 3 · trough -1 , immersion time 35-40h, and automatically scrape the gold mud once every 2h by the crane.
After 12 days, the comparison of the two schemes showed that the leaching rates of gold were 94.50% and 95.21%, the sediment recovery rates were 99.35% and 99.64%, and the total recovery was 93.89% and 94.86%. The gold mud (an example) component (%) was: Au 3.05, Ag 1.73, Cu 13.57, Fe 15.66, S 20.36, SiO 2 19.42, CaO 0.33, MgO 0.35, A1 2 O 3 2.95. Among them (Au+Ag) is 4.78%. In order to improve the Au and Ag grades in the gold mud, the pyrite and fine-grained slime adhered to the surface of the iron plate were washed with high-pressure water before scraping, and the gold-containing gold content was increased to 5%.
The above industrial tests show that:
Compared with the cyanide countercurrent decantation washing process, the economic and technical indicators of the thiourea iron slurry method are comparable or slightly better (as shown in Table 3), mainly due to the fact that the gold content of the concentrate used in the thiourea method is lower than that of the cyanidation method. . If the thiourea iron slurry method is compared with the cyanidation carbon slurry method, the thiourea method costs more.
table 3 Â Comparison of economic and technical indicators between thiourea method and cyanidation method | ||||||||
method | Raw material containing gold / ( g·t -1 ) | Slag containing gold / ( g·t -1 ) | Leach rate /% | Lean liquid containing gold / ( g·m -3 ) | Replacement rate /% | Total recovery rate /% | Concentrate production fee / (yuan ·t ) | |
Cyanide CCD process | 101.15 | 4.06 | 95.1 | 0.07 | 99.56 | 93.53 | 165.13 | |
Thiourea method | Mechanical feeding | 80.77 | 4.44 | 94.5 | 0.25 | 99.35 | 93.89 | 147.7 |
Artificial feeding | 75.5 | 3.62 | 95.21 | 0.13 | 99.64 | 94.86 | ||
2 The initial leaching speed of thiourea leaching gold is very fast. When the slurry is adjusted to the thiourea tank by adding thiourea, the dissolution rate of gold has reached more than 50%, and the dissolution rate of each leaching tank gradually decreases. Table 4 is an indicator of the leaching and replacement operation of the concentrate in each tank. Because the gold leaching and iron displacement deposition in the slurry are synchronous, the metal ion concentration and the Au dissolved potential in the slurry are relatively stable. Therefore, the gold leaching rate and the replacement rate are steadily increasing. [next]
Table 4 Â Leaching and recovery index of thiourea iron slurry method | |||||||||
project | Acid tank | Sulfur | Dip tank | ||||||
Urea tank | 1 # | 2 # | 3 # | 4 # | 5 # | 6 # | 7 # | ||
Concentrate containing gold / ( g·t -1 ) | 75.5 | 34.5 | 16.5 | 12.5 | 8.85 | 6.75 | 6.4 | 4.5 | 4.05 |
Cumulative leaching rate /% | 　 | 54.31 | 78.15 | 83.45 | 88.28 | 91.06 | 91.53 | 94.04 | 94.64 |
Infusion containing gold / ( g · m -3 ) | 　 | 20.95 | 11.25 | 4.5 | 1.56 | 0.63 | 0.33 | 0.27 | 0.15 |
Cumulative replacement rate /% | 　 | 　 | 46.3 | 78.55 | 92.55 | 96.99 | 98.42 | 98.71 | 99.28 |
3 The test was carried out under conditions of high acid (pH 1-1.5) and high concentration of thiourea (0.3% by mass). The total dissolution rate of each impurity component in the concentrate was 25% on average. Table 5 shows the main components of the concentrate and the final leaching residue (taken from the 7# tank) and their dissolution rates (an example). It can be seen from the table that these impurities are dissolved into the solution in a large amount, which not only increases the consumption of the agent, but also causes a large amount of impurity ions or compounds to be sulfided or precipitated into the gold mud, so that the gold content of the gold mud is lowered. In the pulp with such high concentration of impurity ions and compounds, if it is not replaced by the iron slurry method while leaching, the surface of the gold particles is easily passivated to reduce the leaching rate, and a large amount of sulfide of the dissolved gold is precipitated. Reduce the recovery rate in the slag.
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