Experiment on ore dressing method for refractory gold ore in a mine in Hami, Xinjiang

Hami gold ore metasomatic altered rock type gold deposit. The oxidized ore was - Semi oxide, iron ore magnet associated gold, copper ore. The industrial types are mainly gold-copper-magnetite type and gold-copper-pyrite. Because the gold in the ore is ultra-fine particles, the particles are micro-particle gold, and mainly exist in the pyrite in the form of a package, and secondly in the quartz , carbonate, limonite. The predecessors concluded that it was “difficult to choose gold ore”.

I. Study on ore properties

(1) The material composition of the ore

The main useful ingredients are gold, copper and iron. The gold grade is 2.54~4.33g/t; the highest grade of associated copper is 1.39%, generally 0.1%~0.2%. Metallic minerals mainly include magnetite, limonite, hematite, small and trace amounts of pyrite, chalcopyrite, copper orchid, malachite, natural gold and the like. Mainly carbonate gangue minerals, chlorite, epidote, quartz, kaolinite, sericite, tremolite, albite, jarosite, etc., a trace amount of organic carbon. Magnetite is up to 70%, typically greater than 10%. The chemical composition is shown in Table 1, in which the gold and silver content units are g/t.

Table 1 Results of chemical analysis of ore (%)

(2) The state of occurrence of gold

The natural gold in the ore is mainly present in pyrite in the state of ultramicroscopic (<0.001mm) and microparticulate gold (>0.002mm), and secondly in quartz, carbonate and limonite. Its embedding state in pyrite mainly includes crack gold, inclusion gold, hole gold and the like. The phase analysis results of gold are shown in Table 2.

Table 2 Gold phase analysis results

Second, the selection of mineral processing methods and processes

The mine is small in scale, the surface is mainly (semi) oxidized ore, and the useful minerals are mainly magnetite, sulfurized (iron) copper and its oxides and gold. However, iron ore is of little value because of its small amount. Copper is low in quality and is not easily recycled by secondary oxidation. Therefore, gold has become the main target element of Mining . According to the size of the deposit and the characteristics of the ore, it is better to use the heap leaching cyanidation method with less investment.

The presence of large amounts of acidic substances in the copper, iron sulfide minerals and gangues in the ore is detrimental to cyanidation. The conventional cyanidation method not only has a low leaching rate of gold, but also consumes a large amount of medicine and is not economical. Therefore, first, alkali, ammonia, oxygenation pretreatment, to eliminate or reduce the impact of harmful substances, and then cyanide leaching gold, is expected to receive good results. The process of "alkali dip-ammonia immersion-cyanide" was selected for testing and research.

Third, the whole mud cyanidation test

The whole mud cyanidation test is used as a baseline test to provide a basis for column leaching. The process is: alkali leaching - ammonia leaching - filtration - (leaching) cyanidation. The test results are shown in Table 3.

Table 3 Comparison of gold test results

By comparison it can be seen:

1. In the whole mud cyanidation test, only the alkali and ammonia prepreg are added, and the gold leaching rate is the highest.

2. The consumption of sodium cyanide is closely related to the amount of alkali and ammonium salt. Therefore, it is essential to strive for the best formulation of the infusion solution.

3. The leaching rate of the whole mud cyanide gold is high, respectively, which is 88.89% and 90.11%, and the column immersion test can be carried out.

(a) column dip

The results of the column leaching test are an important basis for semi-industrial testing and even development. The test is divided into two parts: pre-dip and cyanide. The process flow is shown in Figure 1. The column immersion test conditions are: ore particle size 30 ~ 0mm, sodium cyanide concentration initial 10 / 10,000, medium term 7 / 10,000, late 3 / 10,000; pharmaceutical system (kg / t): No. 1 column ammonium salt 6.10, lime 3.70, hydrogen Sodium oxide 9.32, sodium cyanide 2.00, column 2 ammonium salt 8.11, lime 5.2, sodium hydroxide 7.6, sodium cyanide 1.84, column 3 lime 6.00, sodium hydroxide 10.6, sodium cyanide 1.40. The leaching time does not include prepreg, and the temperature is 16 to 20 °C. The leaching results are shown in Table 4.

Figure 1 Column dip process

Table 4 Comparison results of gold leaching rate test

(two) pre-dip

From the reaction formula 4Au+8NaCN+O2+2H ₂ O→4NaAu(CN) ₂ +4 NaOH, the cyanide immersion gold must have three basic conditions: CN ^- , O ₂ , OH ^- . That is, in an alkaline medium, cyanide leaches gold from the ore and separates the gold in the solution, including absorption and dissolution of oxygen, diffusion of components thereof to the gold surface, adsorption, electrochemical reaction, and the like. The diffusion of O ₂ +CN ^- is crucial for the leaching rate of gold, while the alkali is the protection of the cyanidation process, and the three are indispensable. The large amount of acid and copper, iron, sulfur and other substances in the ore can consume a large amount of oxygen and cyanide, greatly slowing the cyanidation rate and even stopping the cyanidation process. Therefore, it is subjected to alkali leaching, ammonia leaching pretreatment, and sufficient oxygen is provided to eliminate the influence, thereby creating conditions for gold cyanide leaching.

1. Alkali dip. Large amounts of acidic substances in the ore and sulfur, pyrite (such as pyrite, pyrrhotite, etc.) strongly easily oxidized in moist air to generate a ferrous salt and an acid (such as _{FeSO 4, H 2 SO 3,} H ₂ SO _{4 ,} etc.) It is necessary to eliminate substances such as acidic and soluble metal ions before cyanide leaching. For example, the ferrous salt FeSO ₄ can rapidly change into a high iron salt Fe ₂ [SO ₄ ] ₃ under the action of alkali and oxygen, and finally a hydroxide Fe[OH] ₃ precipitate is formed. Repeat leaching with clear lime water and NaOH solution until pH = 8-9.

2. Ammonia leaching. Mainly used to eliminate copper. Before the cyanidation, an ammonia solution and a copper ion are used to form a stable ammonia copper complex ([Cu(NH3) ₄ ] ₂ ^{+ n} ), and the complex is easily dissolved in the ammonia solution, and the solubility is large. Copper in a basic copper carbonate mineral such as malachite and azurite is dissolved in an ammonia solution by forming a complex: CuCO ₃ ·Cu(OH) ₂ +6NH ₄ OH+(NH ₄ ) ₂ CO ₃ =2Cu(NH _{3 4} CO ₃ +8H ₂ O, sufficient ammonia concentration should be ensured in the immersion liquid to form a stable copper ammonia complex, neutralize the acid formed by ammonia immersion copper sulfide, and the like.

Columns 1 and 2 are leached with a solution of ammonium carbonate at a concentration of 7/10,000 to 8/10,000. The pH of the immersion liquid is 8 to 9; after the ammonia leaching, the ore is washed with water (containing copper solution and washing liquid) and then Cyanide. Column 3 was not pretreated with ammonia. In the ammonia leaching stage, the copper leaching rates of the No. 1 and No. 2 columns (in terms of liquid) were 20.2% and 19.2%, respectively, with little change. It can be seen from Table 4 that under the same conditions, when the amount of ammonium bicarbonate per ton of ore is increased from 6 kg to 8 kg, the leaching rate of gold increases from 79.9% to 80.75%, and the consumption of sodium cyanide decreases slightly. It can be seen that the amount of ammonium carbonate per ton of ore is about 7kg.

3. Ventilation. Both alkali leaching and ammonia leaching are based on the consumption of large amounts of oxygen. In particular, copper sulphide and iron sulphide need to be oxidized to become soluble copper and iron salts. The commonly used oxidants are air and oxygen. The oxidation of sulfur (S ^{2 -} 2 → S ^{6 +} ) consumes 16 times more oxygen than iron (Fe ^{2 +} → Fe ^{3 +} ). For example, the reaction of chalcopyrite with ammonia: CuFeS ₂ +41/4O ₂ +6NH ₃ +(n+1)H ₂ O→Cu(NH ₃ ) ^{2 +} ₄ +1/2Fe ₂ O ₃ ·2nH ₂ O+2NH ⁺ ₄ +2SO ^{2 -} ₄ , The role of oxygen is very obvious. Ventilation, that is, oxygenation work, runs through the entire process of the test. When immersed, the No.1 and No.3 columns are mechanically ventilated and the No.2 column is naturally ventilated. The result is the highest leaching rate on column 2.

(3) Cyanide

1. The cyanidation stage is a conventional method.

2. Leaching speed and leaching rate. It can be seen from Table 4 that the leaching rate and leaching rate of No.1 and No.2 columns pretreated by alkali and ammonia are better, especially the No.2 column has the fastest leaching rate and the highest leaching rate, that is, the leaching rate at the peak of 10d. It has reached 61.70%, its leaching period is 35d, and the final gold leaching rate is 80.75%. However, the leaching rate is only 48.1% when the leaching is carried out for 10 days after alkali leaching without ammonia pretreatment. The cycle is 50d, and the final gold leaching The rate is 70.57% and consumes a large amount of alkali and sodium cyanide without being economical.

Gold leaching rate: 80.91% in terms of slag; 80.75% in terms of liquid, 58.54% in silver, and 25% in copper.

(4) Determination of process conditions

According to the test results, determine the process conditions:

1. The ore particle size is 30~0mm.

2. The leaching period is 56d (including prepreg 21d). After summing up the experience, the pre-dip time can be 5~7d, and the ammonia immersion can be greatly reduced by 2~3d.

3, cloth liquid method: drip, drip strength is 29.4L / m2h, drip ratio: 1:1 ~ 1:3 (drip time is controlled daily 6 ~ 12h).

4. Pharmacy system: 7kg of ammonium bicarbonate and 1.8~2.0kg of sodium cyanide per ton of ore.

5. According to the test process and the pharmaceutical system, the ore beneficiation cost is about 113.09 yuan.

Fourth, the conclusion

1. For the characteristics of ore, learn from the previous experience of ore dressing, adopt the process of “original ore crushing-pre-dip (alkaline leaching, ammonia leaching)-washing (copper liquid and washing liquid separately to be stored and recovered)-cyanide-activated carbon adsorption process The process eliminates or weakens the effects of harmful substances and achieves better beneficiation indicators.

2, ammonia pre-dip should be "short, flat, fast", pH and ammonia concentration should not be too high, to avoid the possibility of ammonia leaching [Cu(NH ₃ ) ₄ ] ^{2 +} change and ammonium bicarbonate, alkali More consumption or waste.

3. If semi-industrial tests are carried out, natural ventilation facilities can be added during pile building. At the same time, further experiments and research should be carried out in order to apply to production as soon as possible.

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