I. Introduction
When direct cyanidation gold ore containing copper, only add a lot of sodium cyanide in order to obtain a higher extraction rate. Since almost all copper minerals are dissolved in the cyanide solution, the composition and content of copper in the hot-pressed acid leaching residue has an important influence on the cyanidation of gold. According to reports, the dissolution rate of copper mineral in 0.1% NaCN solution is (23 ° C): chalcopyrite 5.6%, natural copper 90.0%, chalcopyrite 90.2%, porphyrite 70.0%, malachite 90.7%, red Copper mine 85.5% and so on. It can be seen that other copper minerals other than chalcopyrite have high solubility in cyanide solution. The Cu 2 + ion oxidized cyanide in the solution forms a very stable Cu(I) cyanide complex, which affects the cyanidation leaching of gold.
When treating copper-bearing gold ore with cyanide, an improved method of ammonia cyanide can be used, that is, adding NH 4 + during cyanidation improves the gold extraction performance. In this paper, the system of ammoniacal cyanide leaching showed a certain amount of ammonia under control conditions, leaching of copper-containing hot acid leaching residue can more effectively improve the leaching rate of gold and silver cyanide, and reduces cyanide consumption.
Second, the nature of the sample
The test ore sample was obtained from the leaching of the flotation copper-gold concentrate of Jilin Gan Mine after hot-pressed acid leaching pre-oxidation. The multi-element chemical analysis results of the leaching slag are shown in Table 1. The copper phase analysis results are shown in Table 2.
Table 1 Multi-element analysis results of leaching slag *Unit is g/t
element | Au* | Ag* | Cu | TFe | Ca | Mg | Na | K | TS | S 0 | SiO 2 |
wB/% | 45.25 | 63.2 | 0.57 | 33.04 | 0.68 | 0.10 | 1.45 | 0.46 | 29.89 | 18.03 | 17.89 |
Table 2 Analysis of copper phase in leaching
Free copper oxide% | Combined with copper oxide% | Secondary copper sulfide% | Primary copper sulfide% | Total copper% |
0.054 | 0.075 | 0.221 | 0.221 | 0.571 |
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Third, the experiment
(1) Basic principles
When cyanidation of copper minerals containing soluble sodium cyanide solution, only a large amount of sodium cyanide is added to obtain a higher recovery of gold, because cyanide is consumed by reaction with copper minerals, namely:
2Cu 2 + +8CN - =2Cu(CN) 3 2- +(CN) 2 (1)
(CN) 2 +2OH - =CN - +CNO - +H 2 O (2)
The total reaction formula can be written as:
2Cu 2 + +7CN - =2Cu(CN) 3 2- +CNO - +H 2 O (3)
The ammonia cyanide method is characterized by leaching with NH 3 -CN - mixed solvent, which can increase the leaching rate of gold and reduce the consumption of sodium cyanide. The role of NH3 in the cyanidation process is to change the inert [Cu(CN) 2 ] 2- , which becomes a complex ligand [Cu(CN) 3 (NH 3 ) 3 ] 2 - 2 capable of leaching gold, ie:
4Au 0 +4[Cu(CN) 2 ] 2- +O 2 +2H 2 O=4Au(CN) 2- +4CuCN+12NH 3 +4OH -
(Ii) Test Method
The copper slag and water are placed in a conical flask at a certain liquid-solid ratio, and after neutralizing the alkali to pH = 10 to 11 with lime, a certain amount of NaCN, NH 4 HCO 3 is added . The Erlenmeyer flask was placed on a HY-8 type adjustment shaker and shaken in a shake flask. After a certain period of time, the leaching residue is rinsed with water, and the slag sample and the liquid sample are sent together for testing.
Fourth, the results and discussion
Higher concentration of the leaching residue Ag, Cu in the pregnant solution cyanide, zinc cyanide suitable for all slime powder replacement process.
(1) Conventional cyanidation test
Cyanidation conditions: the concentration of the slurry is 35%, the amount of sodium cyanide is a variable, and the cyanide time is 24 hours. The test results are shown in Table 3.
Table 3 Direct cyanidation test results
Serial number | Sodium cyanide dosage (kg·t -1 ) | Cyanide residue position (g·t -1 ) | Leaching rate (%) | ||
Au | Ag | Au | Ag | ||
1 | 8 | 14.42 | 33.21 | 68.13 | 47.45 |
2 | 12 | 11.23 | 31.02 | 75.18 | 50.92 |
3 | 16 | 9.63 | 29.23 | 78.72 | 53.75 |
4 | 20 | 8.71 | 25.68 | 80.75 | 59.37 |
5 | 25 | 8.57 | 25.05 | 81.06 | 60.36 |
It can be seen from Table 3 that the leaching slag is directly cyanated by carbon slurry method. Even if the amount of sodium cyanide added is 25 kg/t, the leaching rate of Au and Ag is only about 81% and 60%. The solubility of copper ions in the cyanide residue can be analyzed to be 0.8 to 1.5 g/l. It is indicated that soluble copper cyanide complex ions are formed during the reaction. In order to increase the cyanidation leaching rate of gold, an ammonia cyanide method is employed.
(II) Effect of Cu grade on leaching rate
Cyanide conditions: the concentration of pulp is 35%, the amount of sodium cyanide is 10.0kg/t, the amount of ammonium bicarbonate is 100kg/t, and the cyanide time is 24 hours.
Fig.1 Effect of Cu grade on leaching rate of gold and silver
Figure 1 is a graph showing the effect of Cu grade on leaching rate. It can be seen from Fig. 1 that when the copper content in the copper slag is more than 2%, the gold leaching rate can only be maintained at about 80%; when the copper content in the copper slag is less than 2%, the gold leaching rate rises sharply. , reaching more than 95%, at which time the decrease in copper content has little effect on the leaching rate of gold. Since almost all copper minerals are dissolved in the cyanide solution, the composition and content of copper in the copper slag have an important influence on the cyanidation of gold and silver. Therefore, copper sulfide minerals should be used as much as possible during the hot-pressure acid leaching process. Oxidized thoroughly.
(III) Effect of sodium cyanide dosage on leaching rate
Cyanidation conditions: the slurry concentration is 35%, the ammonium bicarbonate dosage is 100kg/t, and the cyanidation time is 24h.
Figure 2 Effect of sodium cyanide dosage on leaching rate of gold and silver
Figure 2 is a graph showing the effect of the amount of sodium cyanide on the leaching rate. It can be seen from Fig. 2 that increasing the amount of sodium cyanide can increase the cyanide leaching rate of gold and silver, but the increase of sodium cyanide also causes an increase in its consumption. Considering the leaching rate and cost, the amount of sodium cyanide is preferably 8.0 kg/t.
(4) Effect of ammonium bicarbonate dosage on leaching rate
Cyanide conditions: pulp concentration of 35%, sodium cyanide dosage of 8.0kg / t, cyanide time of 24h.
Figure 3 Effect of ammonium bicarbonate dosage on leaching rate of gold and silver
Figure 3 is a graph showing the effect of the amount of ammonium bicarbonate on the leaching rate. It can be seen from Fig. 3 that increasing the amount of ammonium bicarbonate can increase the cyanidation rate of Au, but has no significant effect on the leaching rate of Ag. When the amount of ammonium bicarbonate reaches 75kg/t, the amount of ammonium bicarbonate is increased, and the leaching rate of Au is not significantly improved, taking into account the leaching rate and cost, and the amount of ammonium bicarbonate is preferably 75 kg/t.
Figure 4 Effect of slurry concentration on gold and silver leaching rate
(5) Effect of slurry concentration on leaching rate
Cyanidation conditions: sodium cyanide dosage 8.0 kg / t, ammonium bicarbonate dosage 75 kg / t, cyanidation time 24 hours.
Figure 4 is a graph showing the effect of slurry concentration on leaching rate. As can be seen from Figure 4, better indicators can be obtained in the range of 25% to 45%. The concentration of the slurry is not the main factor affecting the leaching. Therefore, the concentration of the slurry can be selected to be more suitable for about 40% of industrial applications.
Figure 5 Effect of cyanide time on the leaching rate of gold and silver
(6) Effect of cyanide time on leaching rate
Cyanide conditions: slurry concentration of 40%, sodium cyanide dosage of 8.0kg / t, ammonium bicarbonate dosage of 75kg / t.
Figure 5 is a graph showing the effect of cyanide time on the leaching rate. It can be seen from Fig. 5 that the leaching rate of gold increases remarkably with the increase of leaching time. After 14 hours, the leaching rate of gold has no obvious change, and the leaching rate of silver has an optimum value at 16h. Considering the recovery rate of gold and silver, the cyanidation time was chosen to be 16h.
(7) Comprehensive condition test
On the basis of the above single factor test, the following comprehensive condition tests were carried out: the slurry concentration was 40%, the NaCN dosage was 8.0 kg/t, the carbonic acid competition was 75 kg/t, and the cyanidation time was 16 h. At this time, the leaching rates of gold and silver were 98.3% and 82.7%, respectively.
V. Conclusion
(1) The copper in the ore is leached by sodium cyanide, which consumes sodium cyanide and greatly reduces the free CN - concentration, which is the main reason for copper cyanidation in conventional cyanide.
(B) adding ammonia to provide a compound of boiling soluble ligand bonded gold [Cu (CN) 3 (NH 3) 3] 2-, without depending on the gold leaching solution free CN - concentration, thereby greatly Improved the cyanidation process of gold in the presence of copper.
(3) Using the ammonia cyanide method, the cyanidation leaching rate of gold less than 70% in conventional cyanidation can be increased to 98.3% under the same amount of sodium cyanide.
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