Sulfuric acid production process, after roasting pyrite cinder produced, containing iron oxide and residual iron sulfide and small amounts of copper, lead, zinc, arsenic and trace elements cobalt, selenium, germanium, silver, gold, group Minute. According to statistics, the amount of slag discharged in China in the past few years is about 20 million tons, and the utilization rate is only 30%. The remaining large amount of slag not only occupies land, pollutes the environment, and this trend is increasing year by year [1] . Therefore, it has become a top priority to comprehensively utilize sulfuric acid slag to extract valuable components and reduce waste slag emissions. This experiment takes a high-grade sulfur concentrate as the research object, and studies the optimum process conditions of sulfur concentrate roasting and slag leaching gold to achieve the purpose of comprehensively recovering iron and gold in the slag and reducing waste slag discharge.
First, the nature of the sample
The chemical multi-element analysis of a high-grade sulfur concentrate is shown in Table 1. The sulfur concentrate has a high sulfur content of 51.6%, and also contains low-grade gold, silver, and elements such as copper, lead, and zinc. The content of copper, lead and zinc is low and cannot be comprehensively recovered. The gold grade is 0.98g/t, which can be comprehensively recovered.
Table 1 Results of multi-element analysis of sulfur concentrate
ingredient | w/% |
S | 51.60 |
Cu | 0.22 |
Pb | 0.01 |
Zn | 0.28 |
Au* | 0.98 |
*w(Au)/10 -6
According to the results of the process mineralogy of the sulfur concentrate, the mineral composition of the sulfur concentrate is complex, mainly sulfide minerals, and the sulfide minerals are mainly pyrite, a small amount of pyrite and colloidal pyrite; the gangue mineral has calcite , Garnet, quartz , mica, etc. The degree of dissociation of sulfur mineral monomers is relatively high, and the size of yellow (white) iron ore in the continuous body is fine. Gold in the sulfur concentrate is encapsulated in pyrite by ultrafine particles, which must be treated to dissociate and expose it, which is beneficial to gold leaching. The sulfur concentrate is oxidized and calcined, and then gold is extracted to achieve the purpose of comprehensive recovery.
Second, the process test
(1) Sulfur concentrate roasting test
1. Different baking heat preservation time experiments
The calcination holding time was 6, 7, 8, 9 h, and the calcination temperature was 850 ° C. The test results are shown in Table 2.
Table 2 Results of sulfur concentrate roasting test at different holding times
Holding time / h | Slag yield /% | Iron taste /% | Au grade /g·t -1 | S grade /% |
6 | 68.5 | 60.19 | 1.01 | 2.08 |
7 | 67.7 | 62.62 | 1.13 | 1.20 |
8 | 67.3 | 66.81 | 1.31 | 0.31 |
9 | 66.7 | 66.18 | 1.35 | 0.25 |
It can be seen from Table 2 that under the condition of calcination temperature of 850 °C, the yield of slag decreases with the increase of holding time, but the grade of iron and gold in the slag is continuously increased, while the sulfur content decreases rapidly. . When the holding time is 8h, the sulfur mass fraction is reduced to 0.31%. Continue to increase the holding time, the iron and sulfur and sulfur content changes little, so choose the best holding time is 8h.
2, roasting temperature test
The calcination test results are shown in Table 3 at a holding time of 8 h and at a calcination temperature of 750 ° C, 850 ° C, and 950 ° C, respectively.
Table 3 Results of roasting test of sulfur concentrate at different temperatures
Calcination temperature / °C | Slag yield /% | Iron taste /% | Au grade /g·t -1 | S grade /% |
750 | 69.0 | 70.90 | 1.09 | 0.97 |
850 | 68.3 | 66.81 | 1.31 | 0.31 |
950 | 67.8 | 65.82 | 1.37 | 0.30 |
The test results and the chemical multi-element analysis of the slag show that the roasting temperature is 850 ° C, the holding time is 8 h, the iron content in the slag is the highest, reaching 66.81%, the gold grade is 1.31 g / t, the sulfur content is 0.31%, and the baking slag has reached The requirements for qualified iron concentrates, and the temperature is just within the temperature range of industrial pyrite roasting to sulfuric acid, so the calcination temperature is determined to be 850 °C.
(II) Study on gold leaching process of slag
1. Sulphur leaching and sulfur removal test
In order to comprehensively recover the gold in the slag, an immersion gold experiment was conducted. There is residual sulfur in the calcined slag after calcination. In order to remove this part of sulfur, the slag is subjected to water immersion. The experimental conditions of water immersion slag: the ratio of water immersion liquid to solid is 2:1, and the water immersion time is 15min, 45min, 60min, 90min, 120min respectively. The test results are shown in Table 4.
It can be seen from Table 4 that as the immersion time increases, the sulphur content in the slag is less and less. When the immersion time is 45 min, the sulphur content does not change significantly, so the immersion time is 45 min.
Table 4 Experimental results of slag immersion time
Immersion time / min | w(S)/% |
0 | 0.31 |
15 | 0.27 |
45 | 0.18 |
60 | 0.16 |
90 | 0.15 |
120 | 0.15 |
For the convenience of the test, all the slag samples were first immersed in water for 45 minutes, and dried for immersion gold test. Therefore, the following samples for immersion gold are samples after 45 minutes of water immersion.
2. Cyanide immersion gold test after lead nitrate pretreatment
According to the chemical analysis results of the sulfur concentrate slag, the gold grade in the slag is 1.31, which contains harmful elements such as S, Cu and As which affect cyanide leaching. These elements can interact with cyanide, consume cyanide, and some consume dissolved oxygen, thereby reducing the cyanide leaching rate of gold, but the presence of a small amount of Pb salt can accelerate the rapid dissolution of gold. To this end, the cyanide immersion gold test after pretreatment of lead nitrate was carried out on the slag after water immersion. The slag slurry after water immersion is repeatedly filtered and washed, and the gold grade of the slag before and after leaching is measured. Conditional tests include: fineness of grinding, amount of lead nitrate, pretreatment time, cyanide leaching pulp concentration, cyanide leaching pH, sodium cyanide dosage, cyanide leaching time, etc. The test process and conditions are shown in Figure 1.
Figure 1 Cyanide leaching process
(1) Grinding fineness test
Change the grinding time, obtain different grinding fineness, carry out cyanide immersion gold test, the results are shown in Figure 2. It is known from Fig. 2 that as the grinding time increases, the leaching rate of gold decreases. This indicates that the porosity of the slag is increased, and the gold particles have been exposed. The fine grinding causes the slurry to be muddy, so that the mud covers the exposed gold particles, which is not conducive to the cyanide leaching of gold. Therefore, the slag is selected without grinding. Direct immersion gold.
Figure 2 Effect of grinding fineness on gold leaching rate
(2) Lead nitrate test
The results of the test for lead nitrate are shown in Figure 3. It can be seen from Fig. 3 that the leaching rate of gold is only 37.8% without the addition of lead nitrate; as the amount of lead nitrate increases, the leaching rate of gold also increases. When the amount of lead nitrate reaches 300g/t, the leaching rate of gold reaches 52.3%; when the amount of lead nitrate is 400g/t, the leaching rate of gold is 53.5%, which is slightly better than the dosage of 300g/t. Considering comprehensively, 300g/t is selected as the optimum amount of lead nitrate.
Figure 3 Effect of lead nitrate dosage on gold leaching rate
(3) Pretreatment time test
The amount of lead nitrate was fixed at 300g/t, the pretreatment time was changed, and other conditions were fixed. The test results are shown in Fig. 4. It is known from Fig. 4 that the leaching rate of gold increases with the increase of pretreatment time; when the pretreatment time reaches 4h, the leaching rate of gold changes slowly, the effect of leaching is not improved, and the pretreatment time is determined. It is 4h.
Figure 4 Effect of pretreatment time on gold leaching rate
(4) Cyanide pulp concentration test
The amount of lead nitrate was 300 g/t and the pretreatment time was 4 h. The slurry concentration (expressed as liquid-solid ratio) is shown in Figure 5. It is known from Fig. 5 that the leaching rate of gold is 46.3% when the liquid-solid ratio is 1.5:1. The liquid-solid ratio has little effect on the leaching rate of gold.
Figure 5 Effect of slurry concentration on gold leaching rate
(5) pH condition test
The amount of lead nitrate was 300g/t, the pretreatment time was 4h, the cyanide leaching solution was 2:1, and other conditions were fixed. The pH condition test results are shown in Fig. 6. Lime is used to adjust the pH of the slurry. The effect of adding lime: First, lime can clean the surface of monomer gold and continuous gold, making gold particles easier to cyanide leaching; second, lime can adjust the pH value of the pulp during cyanidation, so that the slurry can maintain high enough The ph value, so that the cyanide leaching proceeds smoothly; in addition, the lime is cheap and easy to obtain, and the slurry can be agglomerated, which is beneficial to the washing of the cyanide pulp.
It can be seen from Fig. 6 that as the pH value of the slurry increases, the leaching rate of gold changes significantly. At low pH (pH=9), the leaching rate of gold is very low, only 8.4%; when the pulp pH is increased, the leaching rate of gold increases; when the pH reaches 11, the leaching rate of gold is the largest. , 55.9%; the pH continues to rise, and the gold leaching rate decreases slightly. This may be due to the fact that excess Ca(OH) 2 will cause the film to cover the surface of the gold, affecting the action of gold and cyanide, resulting in a decrease in the leaching rate. The pH of the slurry is controlled to about 11 at the time of leaching.
Figure 6 Effect of cyanide leaching ph on gold leaching rate
(6) sodium cyanide dosage test
The amount of lead nitrate was 300g/t, the pretreatment time was 4h, the cyanide leaching solution was 2:1, the slurry pH was 11, the leaching time was 24h, and the sodium cyanide dosage test results are shown in Figure 7. It can be seen from Fig. 7 that as the amount of sodium cyanide increases, the leaching rate of gold also increases. The leaching rate of gold is low at low dosages. Only 19.3%; when the amount of sodium cyanide reached 5g / t, the gold leaching rate reached 53.8%; continue to increase the amount of sodium cyanide, the gold leaching rate does not change much.
Figure 7 Effect of sodium cyanide dosage on gold leaching rate
(7) Cyanide leaching time condition test
The cyanide leaching time test results are shown in Fig. 8. As can be seen from Fig. 8, as the cyanide leaching time increases, the leaching rate of gold also increases. When the cyanide leaching time is 24h, the leaching rate of gold reaches 52.3%; while the cyanide leaching time continues to increase, the leaching rate of gold does not change much. Considering comprehensively, the cyanide leaching time is selected for 24h.
Figure 8 Effect of cyanide leaching time on gold leaching rate
(8) Comprehensive condition test
The comprehensive condition test was carried out according to the conditions determined above. The dosage of lead nitrate is 300g/t, the pretreatment time is 4h, the solid ratio of cyanide leaching solution is 2:1, the pH value of slurry is 11, the dosage of sodium cyanide is 5kg/t, and the time of cyanide leaching is 24h. table 5. The multi-element analysis of the leaching residue after cyanide leaching gold is shown in Table 6. The test results show that the leaching rate of cyanide cyanide gold is 51.9%, the iron taste in the slag is 66.63%, and the contents of Cu, S, Pb, As and other elements in the slag are in line with the iron smelting standard.
Table 5 Results of comprehensive conditions for cyanide leaching
Serial number | Slag Au grade / (g·t -1 ) | Leaching Au grade / (g·t -1 ) | Au leaching rate /% |
1 | 1.32 | 0.65 | 50.8 |
2 | 1.32 | 0.62 | 53.0 |
average value | 51.9 | ||
Table 6 Chemical multi-element analysis of cyanide leaching residue
ingredient | w/% |
Fe | 66.63 |
Cu | 0.258 |
S | 0.16 |
Pb | 0.022 |
As | 0.12 |
Au* | 0.61 |
w(Au)/10 -6
Third, the conclusion
(1) The calcination conditions of sulfur concentrate with sulfur content of 51.6% and gold of 0.98 g/t were tested. The calcination temperature was determined to be 850 °C, the holding time was 8 h, the iron content in the slag was 66.81%, and the gold grade was 1.31. g/t, while the mass fraction of sulfur in the slag is 0.31%.
(2) Residual sulfur in the slag can be effectively removed by using water immersion for 45 minutes, so that the sulphur mass fraction in the slag is reduced to 0.18%, which is in line with the sulfur requirement of iron concentrate smelting.
(3) After the water immersion, the slag was pretreated with cyanide leaching gold, and the gold leaching rate was 51.9%, the iron taste in cyanide leaching slag was 66.63%, and the content of impurity elements were in line with iron concentrate smelting. Standard.
(4) The sulfur ore concentrate is treated by the process and conditions determined by the test, and iron and gold can be comprehensively recovered to reduce the discharge of waste residue.
ã€references】
[1] Luo Wen, Xu Chengfeng.A new way to comprehensive utilization of sulfuric acid slag[J].Anhui Chemical Industry,2004,31(6):42-43.
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