Qianxinan minable reserves of gold ore 150t gold, but because of the high arsenic ore sulfur, low grade gold, mostly in 12g / t less, gold often microscopic or submicroscopic particles in toxic In the inclusion of fine particles impregnated in the sand, sulfide and silicate matrix. The leaching rate of gold is generally below 60%, and the leaching rate of typical refractory gold ore gold is about 20%. The use of direct immersion gold - the limited gold resources are wasted, on the other hand, the consumption of cyanide is too high, affecting the social and economic benefits of enterprises. To this end, a high-arsenic and high-sulfur refractory gold mine in a mine in southwestern Guizhou was pretreated by roasting arsenic and solid sulfur, and then oxidizing agent was used to strengthen cyanide, and an expansion test was carried out.
First, the test method
(1) Test materials
The test raw material is a mine refractory gold mine in southwest Guizhou, containing Au 11.8g/t, Ag 2.13g/t, other chemical components (%): S 15.22, As 3.54, Fe 37.65, Cu 0.032, Pb 0.022, C 1.37, Ca0 2.88, Si0 2 36.87, A1 2 0 3 3.45. The phase analysis showed that the gold ore was mainly sulfide (49.15%) and silicate (45.34%), and the free gold and carbonate inclusions accounted for a very small part.
(II) Expanding the test process and equipment
1, the process flow (Figure 1)
2, test equipment
The main test equipment is shown in Table 1.
Table 1 Main equipment
Serial number | name | specification | Quantity |
1 | Jaw crusher | 25 t/d | 1 set |
2 | roaster | Hearth area 8m 2 | 1 set |
3 | Ball mill | 50t/d, 50kW | 1 set |
4 | Intermediate slot | 10m 3 | 1 |
5 | Leaching tank | 35m 3 | 3 |
6 | Blender | P=7.5kW | 4 sets, including reducer |
7 | Complete electrical cabinet | 1 set | |
8 | Filter | Filtration area 60m 2 | 2 sets |
9 | Precious pool | 20m 3 | 3 |
10 | Lean pool | 20m 3 | 2 |
11 | Adsorption tower | 1m 3 | 3, used in series |
Second, the experimental theory analysis
(1) Thermodynamic analysis
Cyanide immersion gold In the absence of oxygen, the solubility of sodium cyanide in water is extremely slow, so an oxidant is required in the cyanidation gold leaching process. The reaction is as follows:
4Au+8NaCN+O 2 +2H 2 O→4NaAu(CN) 2 +4NaOH (1)
The reaction constant of the reaction is calculated by thermal calculation:
logK=16.935n(Φ 01 +0.54)
Wherein Φ 01 is the oxidant potential.
To make the cyanide reaction thermodynamically feasible, logK > 0 must be obtained, whereby the potential of the oxidant must satisfy Φ 01 >-0.54V.
Therefore, from a thermodynamic point of view, as long as the oxidation potential of an oxidant is greater than -0.54V, the cyanidation gold leaching process can be carried out spontaneously. The test uses H 2 O 2 instead of oxygen in the air, mainly because the oxygen in the air is in solution. The solubility is very low, and the potential of H 2 O 2 is 0.95V. The addition of H 2 O 2 enhances the dissolution process of cyanide, which can significantly increase the leaching rate of gold and save the amount of sodium cyanide. The reaction of H 2 O 2 as an oxidant is as follows:
2Au+4NaCN+H 2 O 2 →2NaAu(CN) 2 +2NaOH (2)
The reaction has a K = 10 50.5 , so the reaction can be carried out not only spontaneously but also completely.
(2) Dynamic analysis
The interaction of gold with sodium cyanide solution is a heterogeneous reaction in the lye at the solid-liquid two-phase interface. The whole process is mixed in the power zone and the diffusion zone. For the cyanidation reaction of gold, the equilibrium constant of the reaction has a large value, and the diffusion of the reactant into the solution generally proceeds relatively quickly, thus not limiting the speed of the leaching process. In the test, the calcination pretreatment is followed by wet grinding to -0.1 mm, and the mixture is vigorously stirred during leaching to make the solid-liquid contact sufficiently, and the reaction time can be shortened. The reaction is controlled by the rate of diffusion and the rate of chemical reaction. In the process of electrochemical dissolution of gold it is generally believed that the chemical reaction speed, rate of dissolution controlled by the diffusion, dissolution of gold cyanide solution velocity depends CN - and oxygen diffusion rate. According to Fick's law, when the dissolution rate of gold reaches equilibrium, the dissolution rate of gold reaches the maximum value. Simply increasing the concentration of cyanide or dissolved oxygen in the solution can not maximize the dissolution rate of gold. The concentration of cyanide leaching gold can reach the maximum value. The test proves that the concentration ratio of gold is the maximum at 4-6, which is consistent with the theory.
Third, test results and analysis
(1) Effect of calcination temperature on leaching rate
The amount of sodium cyanide added during the test leaching at different temperatures was 2 kg/t, the liquid-solid ratio was 3..1, and the hydrogen peroxide was 250 g/t. The test results are shown in Figure 2.
It can be seen from Fig. 2 that the leaching rate is 87% at the calcination temperature of 800 ° C, and the leaching rate is significantly lower when the temperature is lower than 650 ° C. This is because the sulphide-coated gold is not opened, resulting in the phase of the sulphide. Gold can not be leached; when the temperature is higher than 850 °C, the leaching rate is more obviously reduced. This is because the temperature is too high, the refractory gold ore is over-fired, the secondary package is re-formed, and the gold will be wrapped in the impervious material formed by roasting. In the end, the gold cannot be leached. Therefore, the most desirable baking temperature is 800 °C.
(2) Effect of calcination particle size on leaching rate
The amount of sodium cyanide added was 2 kg/t, the liquid-solid ratio was 3..1, the hydrogen peroxide was 250 g/t, and the calcination temperature was 800 °C. The leaching rates at different particle sizes were: -0.25 mm 86.42%, -10 mm 79.88%, 1-4 mm 64.51%, 5-9 mm 42.37%, 10-13 mm 36.76%.
It can be seen that the leaching rate of the leaching rate decreases remarkably with the increase of the grain size of the calcination. This is because the particle size is too large, the ore cannot be fully roasted, and the gold in the package cannot be completely opened, resulting in a decrease in the leaching rate of gold. Theoretically speaking, the finer the particle size, the more complete the calcination, the faster the leaching reaction, but the finer particle size increases the labor cost, equipment investment, energy consumption, and the oxygenation desulfurization during the roasting process. The fan pull will take away a part of the mineral powder, so that the roasting loss is large. The test combines various factors, and the choice of -0.1mm is more economical and reasonable in industrialization.
(3) Effect of oxidant on leaching rate
Thermodynamic analysis shows that as long as the oxidation potential of an oxidant is greater than -0.54V, the cyanidation gold leaching process can be carried out spontaneously. The amount of sodium cyanide added is 2kg/t, the liquid-solid ratio is 3..1, the hydrogen peroxide is 250g/t, and roasting. The test was carried out under the conditions of a particle size of -0.1 mm and a calcination temperature of 800 °C. The leaching rate of gold are different oxidants: hydrogen peroxide 87.64%, 68.43% potassium permanganate, sodium peroxide 49.00%, 42.83% air, permanganate + 82.79% calcium oxide, 83 weight chromium potassium 64%, lead nitrate 65.68%, calcium peroxide 73.42%, hydrogen peroxide lead nitrate 58.34%. It can be seen that the leaching rate of H 2 0 2 and K 2 Cr 2 O 7 , potassium permanganate + calcium peroxide as oxidant test gold is higher, but due to K 2 Cr 2 O 7 and potassium permanganate + peroxidation The calcium market is expensive, so the choice of H 2 O 2 as an oxidant in industrial production not only makes the gold leaching rate higher, but also reduces the cost.
(4) Effect of the amount of NaCN on the gold leaching rate
Test conditions: roasting desulfurization temperature 800 ° C, liquid-solid ratio 3.. 1, [CN - ] / [O 2 ] = 5, hydrogen peroxide 250 g / t, the test results are shown in Figure 3. Theoretically, it takes 0.49 grams of sodium cyanide to leach 1 gram of gold, but the actual need for sodium cyanide is much larger than the theoretical amount. This is because the ore contains a large amount of cyanide-depleting substances, and in order to accelerate the leaching rate of gold, the cyanide concentration should be 0.05% to 0.1%. It can be seen from Figure 3 that the optimum amount of sodium cyanide required to treat the gold ore of the mine per gram of gold is 200 grams.
Fourth, the conclusion
(1) After the refractory gold ore is pretreated by solid-arsenic solid-sulfur roasting, the oxidizing agent is used to strengthen the cyanide gold, and the leaching rate of gold reaches 85% or more, and the process flow is simple;
(2) The best process parameters for treating the mine refractory gold ore: sodium cyanide concentration 0.05% to 0.1%, sodium cyanide dosage 200g, liquid-solid ratio 3..1, [CN - ]/[O 2 ]=5, The baking temperature was 800 °C.
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