A carbonaceous gold deposit has large reserves and low grade, and the natural gold particle size is fine (mostly less than 0.005 mm), especially containing graphite and organic carbon, which makes gold recovery in the ore difficult. In the 1970s and early 1990s, the mine commissioned a research unit to conduct two trials and tests, all using flotation-gold concentrate roasting-cyanide gold extraction process, and the gold recovery rate was about 60%. This deposit has not been exploited for many years.
The study compared the options of the smelting process, and optimized the multi-factor process conditions for the presence of graphite, organic carbon and gold in the ore. The final study used a pretreatment-cyanide carbon leaching process. The gold recovery rate is 88.49%. According to the recommended gold extraction process and conditions, the mine is working on the design of a 500t/d smelting plant.
   I. Brief description of ore properties
(1) Chemical analysis of raw ore
The results of multi-element analysis of raw ore are shown in Table 1, and the results of gold phase analysis are shown in Table 2.
Table 1 Multi-element analysis results of raw ore
Component | ω B /% |
Au* Ag* Cu Pb Zn Ni Co Sb Mo Mn S TFe TC SiO 2 Al 2 O 3 V 2 O 5 As CaO MgO C graphite C organic Loss on ignition | 3.10 1.10 0.003 0.013 0.011 0.002 0.0006 0.0002 0.002 0.20 0.64 4.30 1.72 62.10 16.00 0.05 0.038 3.78 1.57 0.70 0.94 6.19 |
*ω(Au), ω(Ag)/10 -6
Table 2 Results of gold phase analysis in ore
Phase name | ω(Au)/10 -6 | Distribution rate /% |
Graphite and carbon minerals Bare gold and semi-naked gold Sulfide package gold Silicate package gold Carbonate package Red, brown iron ore wrapped in gold Total | 0.44 2.20 0.10 0.23 0.12 0.14 3.23 | 13.62 68.11 3.10 7.12 3.72 4.33 100.00 |
(2) Ore process types and mineral types
The gold ore process type is a small sulfide mineral thousand-shaped calcium, mud siliceous slate carbon-bearing fine-grained gold ore. Metallic minerals content of 4%, mainly pyrite, limonite red, yellow copper ore, arsenopyrite and the like; gangue minerals quartz, feldspar content of about 80%, about 8% of carbonate minerals, the balance being graphite, Carbonaceous, muddy minerals, etc.
The precious metal mineral is natural gold, which is the target mineral for this smelting test. Other minerals have no recycling value.
(3) The state of occurrence of gold
The natural gold has a fine particle size, and only three natural golds are observed under the microscope in the 48 light sheets, and the particle size is between 0.002 and 0.005 mm, which is microscopic and submicroscopic. Electron probe analysis showed that the pyrite, arsenopyrite, graphite, carbonaceous minerals, sphalerite, quartz components are gold, gold that part of the gold dispersion.
Natural gold is mainly embedded in ore in the form of horn-grain, and the others are linear and round. The embedding characteristics of gold are fissure gold, intergranular gold, and gold, which are present in rock fissures, intergranular, voids or wrapped in gangue. According to the gold phase analysis results, the distribution rate of gangue wrapped gold is about 10%, and this part of gold will be difficult to recover.
About 1.7% of the ore is present in graphite and carbonaceous minerals, complicating the gold recovery process and affecting gold recovery.
   2. Direct cyanidation carbon leaching and pretreatment-cyanide carbon leaching gold extraction process test
(1) Process plan determination
The study of ore properties shows that the valuable minerals recoverable in the ore are only natural gold, and other elements have no comprehensive recovery value. Because the gold carrier mineral pyrite, arsenopyrite, graphite, carbonaceous and other minerals have fine particle size, and the natural gold exists in microscopic, sub-microscopic and dispersed state, to improve the gold recovery rate, fine grinding is the primary condition. Carbonaceous minerals adsorb gold and gangue wrapped gold, and carbonaceous minerals have a phenomenon of gold robbing in the process of cyanidation. Solving this problem is the key to the technical research of this experiment. For gold ore containing sulfide and gold minerals, flotation-gold concentrate roasting-cyanide gold extraction process is used in China. Through exploratory experiments, the flotation gold concentrate grade is only about 15g/t when the grinding fineness is -200 mesh 90%, and the recovery rate is less than 80%. The gold concentrate roasting-cyanide leaching rate is about 85%, and the total gold yield is below 65%.
In view of the low content of impurities such as arsenic and antimony which affect cyanide leaching gold in addition to carbonaceous minerals in the ore, the direct cyanidation carbon leaching and pretreatment-cyanide carbon leaching gold extraction process is the preferred experimental scheme.
(II) Test results and discussion
1. Direct cyanidation carbon leaching process
In order to eliminate the influence of graphite and organic carbon on the gold recovery rate in the ore, the principle of using the activated carbon to competitively adsorb the dissolved gold is adopted, and the direct cyanide carbon leaching gold extraction process is adopted to improve the gold recovery rate. Under the condition of grinding fineness-200 mesh 90%, cyanide dosage 3000g/t and bottom carbon density 25g/L, the gold leaching rate is 82.26% after immersion in cyanide carbon for 24h, which is better than the total mud cyanide gold leaching rate. About 40%) increased by nearly 40%. It is obvious that cyanide carbon leaching is an effective process for extracting gold from the ore.
2. Carbon-cyanide carbon leaching process test
In order to further increase the recovery rate of cyanide carbon leaching gold, the ore is subjected to flotation and carbon removal and then cyanidation. In addition to carbon flotation, the carbonaceous material yield was 4.5%, the gold grade was 15g/t, and the gold recovery rate was 22%. In addition to carbon tailings (gold grade 2.4g / t) for cyanidation carbon leaching, gold grade of dipping slag 0.34g / t, leaching rate of 85.83%, better leachability. The total recovery rate of flotation-cyanide carbon leaching process is 88.95%. However, the gold content of the carbonaceous concentrate obtained by flotation is only 15g/t, which cannot be sold as the final product.
3. Pretreatment-Cyanide carbon leaching process test
To further improve the gold recovery rate, it is necessary to reduce the adsorption activity of carbonaceous minerals in the ore and eliminate the adsorption of dissolved gold by the carbonaceous minerals in the ore. The types of pretreatment agents were selected, and the organic and inorganic multi-agents were compared and eliminated. The YD-B and YD-A pretreatment agents were added for cyanidation carbon leaching, and the gold leaching rate was over 88%. This shows that the addition of pretreatment agent cyanide carbon leaching, the gold leaching rate can be increased by more than 5% than the direct cyanidation carbon leaching rate (83.55%). Considering the price and source of the two agents, the YD-B pretreatment agent was selected for the test. The test procedure is shown in Figure 1, and the test results are shown in Table 3.
Figure 1 Pretreatment-cyanide carbon leaching test procedure
Table 3 Pretreatment - Cyanide carbon leaching test results
Pretreatment agent dosage / (g · t -1 ) | Raw ore Au grade / (g·t -1 ) | Leaching Au grade / (g·t -1 ) | Au leaching rate /% |
YD-A 200 YD-B 200 No pretreatment agent added | 3.10 3.10 3.10 | 0.35 0.36 0.51 | 88.71 88.39 83.55 |
4. Influence of grinding fineness on gold recovery rate
Dissociation or exposure of gold monomer is a necessary condition for cyanide carbon leaching. Therefore, proper grinding fineness can increase the gold leaching rate, but over-grinding not only increases the grinding cost, but also increases the impact of impregnated impurities on gold cyanide. The possibility of leaching. Due to the fine grain size of the natural gold in the ore, the fineness of grinding is crucial. The fineness of grinding is -200 mesh, 80%, 90%, -400 mesh, 70%, and 85%, respectively, for pretreatment-cyanide carbon leaching. When the fineness is above -200 mesh and 90%, the leaching rate of gold is above 89%, indicating that it is necessary to finely grind the ore. The test results of the effect of grinding fineness on gold leaching rate are shown in Table 4.
Table 4 Grinding fineness test results
Grinding fineness | Raw ore Au grade / (g·t -1 ) | Leaching Au grade / (g·t -1 ) | Au leaching rate /% |
-200 mesh 80% -200 mesh 90% -400 mesh 70% -400 mesh 85% | 3.10 3.10 3.10 | 0.45 0.33 0.31 0.28 | 85.48 89.35 90.00 90.97 |
5. Effect of pretreatment agent YD-B dosage and pretreatment time on gold leaching rate
Pretreatment agent YD-B can reduce the adsorption activity of graphite and organic carbon in ore, inhibit the adsorption of dissolved gold by carbonaceous minerals, and thus increase the gold leaching rate. In order to determine the proper amount of YD-B before cyanide carbon leaching, the YD-B dosage test was carried out. The test results show that the amount of YD-B is in the range of 200-400g/t, and the leaching rate of gold is 87.42% and 87.41%, respectively. When the amount of YD-B is increased to 1200g/t, the leaching rate of gold is not improved.
When the pretreatment time is 1~2h, the leaching rate of gold is up to 87.74%, and the gold leaching rate of the pretreatment time is unchanged. The test results of the effect of pretreatment agent YD-B dosage and pretreatment time on gold leaching rate are shown in Fig. 2 and Fig. 3.
Figure 2 Effect of pretreatment agent YD-B dosage on gold leaching rate
Figure 3 Effect of pretreatment time on gold leaching rate
6. Effect of sodium cyanide dosage on gold leaching rate
In the cyanidation gold leaching process, the amount of cyanide and gold leaching rate are proportional to a certain range, but when the amount of cyanide is too high, not only the production cost is increased, but also the gold leaching rate is not improved. In order to reduce the amount of cyanide and the production cost, a sodium cyanide dosage test was carried out. The test results show that the gold leaching rate increases with the increase of sodium cyanide dosage; however, when the dosage increases above 1000g/t, the gold leaching rate does not increase much. The test results of the influence of the amount of cyanide on the gold leaching rate are shown in Fig. 4.
Figure 4 Test results of the influence of cyanide dosage on gold leaching rate
7. Effect of bottom carbon density and carbon leaching time on gold recovery rate
In the carbon leaching gold extraction process, the bottom carbon density, carbon leaching time and gold leaching rate, and adsorption rate are proportional to a certain range. For carbon-bearing ore, there must be sufficient amount of activated carbon to adsorb the dissolved gold to increase the gold leaching rate. The bottom carbon density is above 30g/L, the gold leaching rate is up to 88.5%, and the adsorption rate is 99.70%. Suitable carbon immersion time to reduce the wear of gold-loaded carbon and maintain a high gold recovery rate. The cyanide carbon immersion time was 20h, the gold leaching rate was 88.06%, and the adsorption rate was 99.63%. The effect of bottom carbon density and cyanide carbon immersion time on gold leaching rate is shown in Fig. 5 and Fig. 6.
Figure 5 Test results of the effect of bottom carbon density on gold leaching rate
Figure 6 Test results of the influence of cyanide carbon leaching time on gold leaching rate
   III. Pretreatment-Cyanide carbon leaching comprehensive condition test
In order to verify whether the pretreatment-cyanide carbon leaching process conditions are optimized, and the test results are reproducible, three sets of parallel tests were carried out. The test results are shown in Table 5. The test results in Table 5 show that the results of the parallel test of the pretreatment-cyanide carbon leaching process are reproducible and stable.
Table 5 Test results of pretreatment-cyanide carbon leaching comprehensive conditions
Raw ore Au grade / (g·t -1 ) | Leaching Au grade / (g·t -1 ) | Au leaching rate /% | Lean Au grade / (g·t -1 ) | Au adsorption rate /% |
3.10 3.10 3.10 average | 0.37 0.38 0.32 0.36 | 88.06 87.74 89.68 88.39 | 0.004 0.0035 0.004 0.004 | 99.71 99.74 99.71 99.71 |
   Fourth, the conclusion
(1) Due to the presence of graphite and organic carbonaceous minerals in the ore, natural gold has a fine particle size and is microscopically and sub-microscopically embedded. The leaching rate of whole mud cyanide gold is less than 50%. Flotation-gold The recovery rate of concentrate roasting-cyanide gold is about 60%, and the ore is a difficult ore smelting ore.
(2) Studying the principle of competitively adsorbing dissolved gold by adding activated carbon, the direct cyanidation carbon leaching process can make the gold leaching rate more than 80%. In order to further increase the gold leaching rate, pretreatment agent YD-B is added before cyanide carbon leaching to reduce the adsorption activity of graphite and organic carbon in ore and inhibit carbon.
The adsorption of the dissolved gold by the nucleus increases the gold leaching rate by more than 5% compared with the direct cyanide carbon leaching.
(3) After pretreatment, the cyanide carbon leaching process conditions are optimized, the grinding fineness is determined to be 90%-200 mesh, the pretreatment agent YD-B 200g/t is added, the pretreatment is 1h, and the sodium cyanide dosage is 1000g/t. The carbon density of 20g/L and carbonized cyanide for 20h can obtain the gold leaching rate of 88.49%, the gold adsorption rate of 99.73%, and the total gold recovery rate of 88.25%.
(4) The pretreatment agent YD-B is non-toxic, the market is easy to purchase, and the price is low. The cost of the ore ore agent is negligible, and the effect on improving the gold leaching rate is obvious.
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