Recovery of gold from concentrate containing arsenic is the most complex problem. This is the root cause intractable concentrate: gold was present in a state disseminated sulphide (pyrite arsenic and pyrite) and, as well as capable of adsorbing gold cyanide solution in the presence of certain active concentrate Carbonaceous material.
Based on a large number of studies on the handling of such concentrates, the following methods are proposed:
(1) oxidative calcination (one-stage calcination or two-stage roasting), followed by cyanidation of the calcine (1.2);
(2) oxidizing roasting, and then smelting the calcine to make iron-containing ice steel or copper alloy;
(3) oxidizing roasting, and then recovering gold from the calcine by chlorination volatilization;
(4) directly smelting the original concentrate (unbaked) into iron-containing matte;
(5) Bacterial leaching, followed by cyanidation of the leaching residue.
A common disadvantage of all of these calcination processes is the large loss of gold in fine arsenic-containing soot. The difficulties encountered in recovering gold from the calcined calcine are even greater. For example, the gold recovery rate is not too high when the calcine is cyanidated. Smelting the calcine (eg, direct smelting of the concentrate) can only reduce the amount of material that is further processed to obtain the finished gold. The bacterial leaching method is relatively new, but at present, this method cannot obtain a high gold recovery rate, and it is also impossible to comprehensively utilize the sulfur contained in the concentrate.
The most promising method for dissociating fine-grained gold symbiotic with sulphide is the autoclaved oxidative leaching method. The gold is then further recovered from the insoluble autoclaved leaching residue by adsorption cyanidation or ordinary cyanidation.
In this paper, the kinetics and mechanism of autoclave leaching of arsenopyrite and pyrite are studied in order to select the optimum conditions for the full and rapid oxidation of sulfide. The results of these studies have been used in the process research of flotation concentrate samples for certain ores in the Soviet Union.
Gold-arsenic concentrates with a particle size of +10 to 100 microns were used as samples for kinetic studies. The original material contained 32.7% iron, 34.3% sulfur and 6.0% arsenic. According to X-ray structural analysis and mineralogy analysis, the sulfide fraction in this material is arsenopyrite and pyrite. At the same time, chemical phase analysis also proved that 14% of arsenic is present in the oxide state. They are formed during long-term storage, grinding and flotation of ores and concentrates.
In order to study the oxidation kinetics of the above sulfide products, a "Vini Nikowski, a titanium -based autoclave with a turbine stirrer" having a volume of 1 liter was used. In order to rule out the diffusion inhibition of the process that may occur, the solid-liquid ratio used in each test was 1:50. The temperature and pressure were kept constant in the autoclave (the accuracy was ± 2 ° C and 0.2 atmosphere 分别, respectively). After the test, the slurry was filtered, and the insoluble shallow slag was washed with water in a filter. Analyze the arsenic and iron in the filtrate. The insoluble autoclaved leaching residue (with the filter-up) was treated with a 4N hydrochloric acid solution at a temperature of 30 to 40 ° C for a treatment time of 2 hours. The content of arsenic phase iron in the filtrate was measured. The oxidized string of arsenopyrite is calculated based on the arsenic content in the autoclave and hydrochloric acid extract (taking into account that 14% of the arsenic in the original material is present as an oxide). The oxidation rate of pyrite was determined based on the analysis of iron in the above solution (excluding iron transferred to the solution due to the oxidation of yttrium pyrite).
The effect of temperature on the oxidation rate of arsenopyrite was studied under the condition that the partial pressure of oxygen was 2 atmospheres and the concentration of sulfur was 26.4 g/l (see Figure 1, a). Such a high acidity of the solution, on the one hand, meets the actual sulfuric acid concentration in the process solution for the oxidative leaching of the gold-containing concentrate, and on the other hand ensures that the acidity of the solution is constant throughout the test because of the hydrolysis of Fe(III) The possibility of acidifying the solution is small and negligible. The value of the activation energy was 13.4 kcal/gram. This indicates that the conditions of the autoclave leaching used ensure the smooth progress of the leaching process without complicating the leaching process due to diffusion.
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The oxidation kinetics of arsenopyrite at different oxygen pressures (temperature 130 ° C, sulfuric acid concentration 26.4 g / liter) are shown in Figures 1, 6. Treatment of these results indicates that the rate of the oxidation process is proportional to the oxygen partial pressure of 0.75. This is a supplementary argument that facilitates the oxidation process in the dynamics range.
The acidity of the solution is different from the temperature and oxygen partial pressure. It has little effect on the oxidation rate of arsenopyrite. It is known that Fe(III) ions are quite strong oxidants. During the autoclave leaching process, they can fundamentally change the oxidation rate of the sulfide. Therefore, it is important to study the effect of Fe(III) on the oxidation kinetics of arsenopyrite. To this end, a set of tests was conducted at a temperature of 130 ° C and an oxygen partial pressure of 2 atm. The acidic solution used for the test (26.4 g/L H 2 SO 4 contains iron sulfate (the concentrations are different). The test results (see Figure 1, a) show that Fe(III) ions can greatly increase the speed of the oxidation process. When the Fe(III) ion concentration is 5g/L, the oxidation rate of arsenopyrite is more than doubled. When the concentration of Fe(III) ion is increased to 20g/L, the oxidation process speed can be increased. three times.
Based on the results of these tests, two most probable mechanisms for the oxidation of arsenic pyrite are proposed: (1) direct oxidation under the action of oxygen; and (2) oxidation under the action of Fe(III) ions. At this time, the action of oxygen can convert Fe(II) into Fe(III).
In the absence of oxygen, the concentrations of CFe(III) and H 2 SO 4 in the acidic solution of ferric sulfate were 10 g/l and 26.4 g/l, respectively. The results of the original material leaching test (Fig. 2, a) show that under such conditions, the oxidation rate of arsenopyrite and arsenic pyrite are under oxygen pressure, but the oxidation rate is not increased when artificially adding Fe(III) ions. Poor up and down. This proves that oxidation according to the second mechanism is possible in principle. Anomalies in the oxidation process occurring at 120 ° C and 130 ° C may be related to the formation of a certain amount of elemental sulfur because they are rapidly oxidized at high temperatures.
The problem of the possibility of arsenic pyrite oxidizing according to the first mechanism is very complicated. Although this mechanism is possible in principle, it does not cause doubt (at least in the initial stage of oxidation, because the concentration of Fe(III) ions in the solution is extremely low), but it is evaluated by direct experiment. The role of this mechanism in the entire oxidation process is still relatively complicated. This is because there is an oxidation product of pyrite and arsenopyrite-Fe(III) ions in the solution itself. Therefore, the following method is utilized, that is, under the action of oxygen (the temperature is 100 ° C and the concentration of H 2 SO 4 is 26.4 g / liter and the concentration of Fe (III) is 10 g / liter), the fine in the acidic solution of ferric sulphate Ore oxidation. It can be concluded that in the case where the oxidation process is carried out according to the second mechanism, the influence of the partial pressure of oxygen on the oxidation rate is very small and can be ignored. This is because in the case of a significant excess of Fe(III) ions, the concentration can be considered to be fixed and equal to the original concentration, rather than the speed of their regeneration process.
The results of these tests (Figure 2.6) show that under the action of oxygen, the arsenic pyrite is oxidized faster in the ferric sulphate solution than in the absence of oxygen. Therefore, the results of these tests indicate that arsenic pyrite is oxidized simultaneously according to the above two mechanisms.
Industrially, when using an autoclave leaching process to treat arsenic-containing sulfide concentrates, the proportion of each of these two mechanisms will depend on the conditions under which the leaching process is specifically achieved. However, in all cases it should be expected that when the Fe(III) concentration in the solution is relatively high, the relative specific gravity of the second mechanism will increase as the leaching process proceeds. [next]
A number of studies have also been conducted on the oxidation kinetics of pyrite leaching processes. In these studies, the results of the studies by Maxxen and Xannep, TepnaxXene and nannexcll were the most detailed and reliable. Because the main conclusions of these studies are consistent with each other. In this paper, we strive to compare the oxidation kinetics of pure pyrite with the oxidation kinetics of similar products obtained by simultaneous oxidation of pyrite and arsenopyrite.
Figure 3, a is the oxidation kinetics of pyrite under different temperature conditions (acid concentration 26.4 g / liter, partial pressure of oxygen 2 atmosphere). The AppHHy equation illustrates the relationship between the velocity of the oxidation process and the temperature. The apparent activation energy is 11.5 kcal/gram and demonstrates that the oxidation process is carried out within the kinetic range. The effect of partial pressure of oxygen on the oxidation rate of pyrite is shown in Fig. 3, 6 (temperature is 130 ° C, solution acidity is 26.4 g / liter of sulfuric acid). Pyrite differs from arsenic pyrite in that its oxidation rate is proportional to oxygen pressure. This is in complete agreement with previous research data and is an important feature of pyrite unlike other sulfides. Increasing the acidity of the solution has less effect on accelerating the oxidation process.
Therefore, it should be noted that the presence of arsenopyrite does not change the basic regularity of pyrite oxidation.
From the technical point of view, the reaction rate of pyrite with oxygen is much slower than that of arsenite, and the reaction order is higher, which is very important. This allows us to draw important conclusions in the process: (1) When selecting the autoclave leaching parameters, we should first consider the possibility of rapidly and fully oxidizing pyrite, which is the most difficult to treat sulfide. 2) The loss of gold due to incomplete oxidation of sulfides is mainly due to the insufficient oxidation of pyrite, rather than the incomplete oxidation of arsenopyrite.
In the autoclave leaching process test, several gold-containing concentrate samples of the following composition were used. The concentrate sample contains 24.2~34.3% iron, 21.8~27.3% sulfur, 4.9~9.4% arsenic and 31.3~43.0g/ton gold. The gold in all samples was in a fine-grained state and was symbiotic with pyrite and arsenopyrite. Some samples also contain 4 to 5% carbon, which increases the impermeability of the process.
The autoclave leaching is carried out in a "Visnikovsky" type titanium autoclave with a volume of 1 liter and 5 liters. Water is used as the original liquid phase. 36~80% iron (mainly in Fe 3+ state), 80~98% sulfur and 12~40% arsenic are transferred into the autoclave leaching solution. The yield of the insoluble autoclaved leaching slag fluctuates between 54 and 80%. The autoclaved leaching residue is sent to adsorb cyanide (using an AM--26 anion exchanger) or subjected to ordinary cyanidation treatment after washing and lime treatment.
The results obtained prove that the temperature, oxygen partial pressure and leaching time during autoclave leaching are the main factors determining the gold recovery rate. After the autoclave leaching under the optimum conditions, the gold recovery rate for the adsorption cyanidation of the hot dip slag can be 90 to 95%. This is 2~3% higher than the conventional cyanidation of the hot dip slag.
The advantage of using the autoclave leaching method over the calcination process is that the gold recovery rate is higher.
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