Is selected from gold cyanide tailings containing enterprise using acidic, alkaline, toxic, radioactive or heavy metal content of waste produced by the process of gold cyanide, also often contain a certain amount of non-ferrous metals and non-metallic minerals, potentially using Value can be further recycled. However, at present, the cyanide tailings produced by most domestic gold enterprises have not been fully utilized. According to incomplete statistics, the tailings discharge of gold mines in China has reached more than 20 million tons. These tailings are usually only deposited by simple landfill. , causing potential impacts and harms to the environment. If these tailings can be recycled as secondary resources, it can bring huge economic and environmental benefits to enterprises and society.
Usually, gold concentrate is leached by cyanidation in the early stage, and most of the easily immersed gold has been recovered, but the taste of cyanide tailings gold is as high as 3 to 4 g/t, and most of the gold is wrapped in the form of fine grain gold. Among the pyrites , even after further fine grinding, the leaching rate of gold is still not high after conventional cyanidation. Potassium permanganate is a strong oxidizing agent, it can accelerate the speed of the leaching, the leaching rate of increase. In this paper, potassium permanganate was used as oxidant to study the oxidation pretreatment of cyanide tailings under acidic conditions.
1. Test materials and test methods
(1) Nature of the sample
The ore sample used is the high-sulfur and high- arsenic refractory metallurgical concentrate cyanide tailings provided by the Zhongyuan Gold Smelter in Sanmenxia, ​​Henan Province; the phase composition is shown in Figure 1. Tailings metallic minerals are mainly pyrite, quartz gangue minerals, followed by a small amount phlogopite and dickite. The sample was analyzed by secondary electron image analysis by JSM-5600 scanning electron microscope and Link spectrometer. It was found that in the dense distribution of Fe and S, Au had a dense distribution, indicating that gold is mainly distributed in pyrite. Pyrite is the main carrier of gold.
The main elemental composition of the cyanide tailings was measured by X-ray fluorescence as shown in Table 1.
Table 1 Elemental composition of cyanide tailings (mass fraction) /%
Au 1) | Ag 1) | Cu | Fe | Pb | S |
2.21 | 40.4 | 3.84 | 22.91 | 3.84 | 25.14 |
1) The unit is g/t.
(2) Test methods
The tailings used in the test have a small particle size after cyanidation, and most of them can pass through a 300 mesh (50 μm) sieve. There is no need to crush the fine grinding again, and it only needs to be dried and ready for use. The metered potassium permanganate powder is added to a certain amount of water to prepare a solution, and then the concentrated sulfuric acid is metered, stirred uniformly, and poured into a 500 mL three-necked flask, and the reactor is placed in a constant temperature oil bath heater with a stirring device. The magnetic constant heating and stirring method are used to achieve constant temperature and agitation during the reaction. When it is heated to about 20 ° C below the specified temperature, the ore powder is slowly added to carry out the reaction. After a certain period of time, the mixture is cooled and filtered to obtain a residue and a filtrate.
The chemical oxidation pretreatment can break the gold-wrapped minerals and make the gold-coated minerals dissolved in the solution, so that the gold becomes easy to be immersed and achieves enrichment. In this experiment, two indexes, the leaching rate of iron and the weight loss rate of the ore sample, were used as the evaluation indexes of the pretreatment effect. The higher the weight loss rate of the ore sample and the leaching rate of iron, the better the pretreatment effect and the subsequent cyanidation effect. The content of iron in the solution was determined by EDTA complexometric titration, and the residue was weighed after drying.
The weight loss rate X (WL) and the iron leaching rate E (Fe) are calculated using equations (1) and (2), respectively:
(1)
(2)
(three) reaction principle
Potassium permanganate has strong oxidizing properties under acidic conditions, and its strong oxidizing ability can oxidize various metals and sulfides. The reduction product of potassium permanganate under acidic conditions is usually stable Mn 2+ , (Mn0 4 - /Mn 2+ ) = 1.51V, higher than the redox potential of pyrite, theoretically can oxidize pyrite and break the pyrite encapsulation of gold. The possible redox reaction equation is:
16H + +6Mn0 4 - +2FeS 2 →2Fe 3+ +4S0 4 2- +6Mn 2+ +8H 2 0 (3)
24H + +3MnO 4 - +5FeS 2 →5Fe 3+ +lOS+3Mn 2+ +12H 2 0 (4)
Potassium permanganate solution will continuously form divalent manganese ions during the reaction with the ore sample. Under the condition of insufficient acidity, the generated divalent manganese ions may react with potassium permanganate to form a by-product manganese dioxide. .
2Mn0 4 - 3Mn 2+ +40H - →5Mn0 2 +2H 2 0 (5)
The formation of manganese dioxide is unfavorable for the reaction. It not only consumes potassium permanganate, but also wraps on the surface of the ore sample, which hinders the further oxidation of the ore sample by potassium permanganate. Therefore, the reaction process should maintain sufficient acidity. .
Second, the test results and discussion
(1) Effect of solid-liquid ratio on pretreatment effect
The reaction time is 5h, the stirring rate is 700r/min, the potassium permanganate dosage is 70g/L, the reaction temperature is 80°C, the initial concentration of sulfuric acid is 1.3mol/L, and the effect of solid-liquid ratio on the weight loss rate of iron sample and the leaching rate of iron is shown in Fig. 2. Show.
It can be seen from Fig. 2 that the solid-liquid ratio has a great influence on the pretreatment effect. With the decrease of solid-liquid ratio, the leaching rate of iron gradually increases, and the change of weight loss rate keeps the same trend as the leaching rate. When the solid-liquid ratio is less than 1..20, the iron leaching rate hardly changes, maintaining at about 88%, while the weight loss rate of the ore sample is greatly reduced. As the solid-liquid ratio decreases, the concentration of the ore sample decreases, the dispersion of the ore sample in the solution is better, and the potassium permanganate can react more fully, so the leaching rate of iron is gradually increased. After the ratio is reduced to a certain extent, potassium permanganate is excessive, and the divalent manganese formed in the reaction partially reacts with potassium permanganate to form a solid precipitated manganese dioxide, so that the weight loss rate of the ore sample is decreased. When the solid-liquid ratio is 1..20, the pretreatment effect is the best, and the fixed solid-liquid ratio in the subsequent experiments is 1..20.
(2) Effect of potassium permanganate dosage on pretreatment
The reaction time is 5h, the stirring rate is 700r/min, the solid-liquid ratio is 1..20, the reaction temperature is 80°C, the initial concentration of sulfuric acid is 1.3 mol/L, and the effect of potassium permanganate dosage on the weight loss rate of iron sample and the leaching rate of iron is shown in Fig. 3. Show.
As shown in Figure 3, with the increase of the amount of potassium permanganate, the iron leaching rate and the change of the weight loss rate of the ore sample remain the same. In the process of potassium permanganate dosage from 45g/L to 75g/L, iron The leaching rate and the weight loss rate of the ore sample were gradually increased. When the potassium permanganate dosage reached 75g/L, the pretreatment effect was the best, the iron leaching rate was 92.11%, and the weight loss rate also reached 47.6%. Further increasing the amount, the iron leaching rate and the weight loss rate of the ore sample are reduced, because the excessive production of manganese permanganate as a by-product of manganese dioxide, the formation of the by-product directly causes the weight loss rate to decrease, and is wrapped on the surface of the ore sample. It affects the oxidation of pyrite by potassium permanganate and reduces the treatment effect. Therefore, the optimum potassium permanganate dosage in this test is 75g/L.
(III) Effect of reaction time on pretreatment effect
The dosage of potassium permanganate is 75g/L, the stirring rate is 700r/min, the solid-liquid ratio is 1..20, the reaction temperature is 80°C, and the initial concentration of sulfuric acid is 1.3mol/L. The influence of reaction time on the leaching rate of iron is shown in Fig. 4.
Figure 4 shows that as the reaction time increases, the iron leaching rate also increases. Within 1~4h, the reaction leaching rate increased rapidly; when the reaction proceeded to 4~6h, the reaction leaching rate increased slowly; when the reaction progressed to 5h, the leaching rate basically did not change, and the iron leaching rate finally reached 92.56. %, the reaction is almost complete, it can be seen that under this condition, the reaction time should be controlled at 5h, and the following test reactions are controlled at 5h.
(4) Effect of reaction temperature on pretreatment effect
The reaction time is 5h, the stirring rate is 700r/min, the solid-liquid ratio is 1..20, the potassium permanganate dosage is 75g/L, the initial concentration of sulfuric acid is 1.3mol/L, and the effect of reaction temperature on the weight loss rate of iron sample and the leaching rate of iron is shown in Fig. 5. Shown.
It can be seen from Fig. 5 that with the increase of reaction temperature, the iron leaching rate and the change of the weight loss rate of the ore sample remain the same trend, and the reaction temperature has a great influence on the pretreatment effect. The elevated temperature can significantly improve the pretreatment effect. When the temperature is increased from 60 °C to 80 °C, the iron leaching rate and the weight loss rate of the ore sample are gradually increased, especially between 70 °C and 80 °C, the reaction rate is significantly increased, and the iron leaching rate is rapidly increased from 70.73% to 92.11%; When the temperature is increased from 80 °C to 100 °C, the leaching rate and weight loss rate are slightly reduced. It may be that potassium permanganate is decomposed at high temperature, and low-valent manganese inhibits the reaction. Observing the whole test process, it is found that the higher the temperature, the earlier the slurry enters the muddy state, and the more complete the reaction, indicating that the elevated temperature can increase the reactivity of the whole reaction and accelerate the reaction rate. In order to avoid excessive energy consumption, it is determined that a suitable reaction temperature is 80 °C.
(5) Effect of initial concentration of sulfuric acid on pretreatment
The reaction time is 5h, the stirring rate is 700r/min, the solid-liquid ratio is 1..20, the potassium permanganate dosage is 75g/L, the reaction temperature is 80°C, and the initial concentration of sulfuric acid has an effect on the weight loss rate of the ore sample and the leaching rate of iron. .
It can be seen from Fig. 6 that with the increase of the initial concentration of sulfuric acid, the iron leaching rate gradually increases. When the concentration is increased from 0.4mol/L to 1.0mol/L, the leaching rate of iron increases rapidly, and then the initial sulfuric acid is increased. The concentration has little effect on the leaching rate of iron, and the iron leaching rate tends to be stable. At the same time, it was found that the quality of the oxidized slag decreased with the increase of the initial concentration of sulfuric acid, but when the initial concentration was 0.4mol/L and 0.8mol/L, the quality of the oxidized slag increased compared with the original ore. The effect of enriching gold is because the acidity of the solution is too low, and the divalent manganese ions formed during the reaction react with the potassium permanganate to produce a large amount of insoluble manganese dioxide precipitate, which is wrapped on the surface of the ore sample and hindered. The reaction proceeds. The initial optimum concentration of sulfuric acid in this experiment was 1.3 mol/L.
Third, the test under the optimal pretreatment conditions
Through a series of experiments, the optimum pretreatment conditions for cyanide tailings were as follows: reaction time 5h, stirring rate 700r/min, solid-liquid ratio 1..20, potassium permanganate dosage 75g/L, reaction temperature 80°C, The initial concentration of sulfuric acid was 1.3 mol/L. Under these conditions, the iron leaching rate and the weight loss rate of the ore sample reached 92.82% and 47.94%, respectively. The pretreatment effect was ideal. The test results are shown in Table 2.
Table 2 Results of leaching test under optimal conditions
Test number | Iron leaching rate /% | Weight loss rate /% |
1 2 average | 92.11 93.52 92.82 | 47.60 48.27 47.94 |
The mineral phase analysis of the oxidized slag under optimal conditions was carried out by X-ray diffractometer, see Figure 7. Comparing Fig. 1 and Fig. 7, it can be seen that after pretreatment with potassium permanganate, the pyrite in the ore sample is almost undetectable in the X-ray diffraction pattern, indicating that the elemental iron in the tailings is effectively leached into the solution, thereby Breaking the gold-coated minerals and laying the foundation for subsequent cyanidation.
The content of iron in the tailings is high, and a large amount of iron ions are present in the reaction liquid, which is a secondary resource that can be utilized. The research team developed a new process using the cyanide tailings pretreatment and the resulting reaction solution to recover the iron ions in the reaction solution to prepare a high-performance iron pigment nano-iron oxide red, which is not only effective. It prevents the pollution of the waste liquid to the environment and brings huge economic benefits to the enterprise.
Fourth, the conclusion
   (1) The main mineral component of the cyanide tailings used in the test is pyrite. Gold is encapsulated in pyrite in the form of fine particles. Potassium permanganate is an effective oxidant that can break the pyrite to gold. package.
(2) Solid-liquid ratio, potassium permanganate dosage, reaction time, reaction temperature, and initial concentration of sulfuric acid have certain effects on the pretreatment effect of cyanide tailings. Under the experimental conditions studied, the optimal reaction conditions were: solid-liquid ratio 1..20, potassium permanganate dosage 75g/L, reaction time 5h, reaction temperature 80 °C, initial sulfuric acid concentration 1.3mol/L, corresponding iron The leaching rate and the weight loss rate of the ore samples were 92.82% and 47.94%, respectively, and the pretreatment effect was good.
(3) Pay attention to the dosage of potassium permanganate during operation to ensure that potassium permanganate is not excessive, otherwise it will easily produce by-product manganese dioxide, which will affect the pretreatment effect of cyanide tailings.
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