Experimental study on roasting-cyanide leaching of gold and silver from arsenic-bearing gold concentrate

In the gold concentrate roasting-cyanide process, arsenic is the main factor affecting the leaching rate of gold and silver cyanide. For this reason, the content of arsenic in the process of roasting-cyanide leaching gold and silver is strict, and the content of arsenic in gold concentrate is usually controlled below 0.1%. With the increase of arsenic content, cyanidation of gold and silver The leaching rate is gradually reduced. The author has studied the recovery rate of gold, silver and copper in the roasting-cyanide leaching process of arsenic-containing gold concentrate. Based on this, the paper studied the addition of sodium sulfate in the calcined gold concentrate to improve the leaching rate of gold and silver in the roasting-cyanide leaching process of arsenic-containing gold concentrate. The test results show that for the arsenic mass fraction of 0.45% gold concentrate, the addition of 4% to 5% sodium sulfate in the calcination can increase the cyanidation leaching rate of gold and silver by 5.0% and the original process. 40% or more. This not only makes full use of national resources, broadens the source of raw materials, but also improves the economic and social benefits of enterprises, and has the value of promotion.

First, the nature of the sample

The ore sample used in this test is provided by a gold mine. Mineral composition mainly pyrite, arsenopyrite, chalcopyrite, galena, sphalerite and other sulfide minerals, gold, silver places sulfide fine particle is wrapped state. The main chemical components of the ore samples are shown in Table 1.

Table 1 Chemical composition of the ore sample

^* (Au), (Ag)/10 ^-6

It can be seen from Table 1 that in addition to the higher Au and Ag, the contents of Cu, Pb, As, and S are relatively high. The ore sample belongs to the type of arsenic- and copper-refractory gold concentrate. With the current roasting-cyanide leaching process, it is difficult to obtain a high gold and silver cyanide leaching rate.

Second, direct cyanidation leaching test

The ore sample was tested using a direct cyanidation leaching process. The test leaching conditions were: NaCN mass fraction 0.5%, liquid-solid ratio 2:1, leachate pH>11 (lime adjustment), and leaching time 42 h. The results of the leaching test are shown in Table 2.

Table 2 Direct cyanidation leaching test

It can be seen from Table 2 that the cyanidation leaching rate of gold and silver is very low under normal conditions, especially the cyanidation leaching rate of silver is lower, only 7.2%. The main reason is that the content of copper and arsenic is high, which affects the cyanide leaching of gold and silver. In addition, the presence of a large amount of sulfides, the gold and silver coating of fine particles, makes the cyanide leaching reaction of gold and silver difficult.

Third, roasting-cyanide leaching test

The ore sample was subjected to a leaching test by a roasting-cyanide leaching process. Calcination conditions: temperature 63 ° C, calcination time 60 min. Copper sulphate leaching conditions: sulfuric acid mass fraction 2%, liquid-solid ratio 3: 1, leaching temperature 70 ° C ~ 80 ° C, time 2 h. After acid leaching of copper, the liquid-solid separation, the leaching residue is washed to neutral, cyanide leaching. Cyanide leaching conditions: NaCN mass fraction 0.2%, liquid-solid ratio 2:1, leachate pH ≈9.5 (NH ₄ HCO ₃ + NaOH adjustment), leaching time 36 h. The test results are shown in Table 3.

Table 3 Roasting-Cyanide Leaching Test Results

It can be seen from Table 3 that the arsenic-containing gold concentrate is treated by the roasting-cyanide process, which can increase the cyanide leaching rate of gold and silver, but the gold and silver content in the cyanide residue is still high, especially silver, and the leaching rate is only At 26.28%, most of the silver is still not leached.

Fourth, sodium sulfate roasting-cyanide leaching test

Sodium sulfate is a neutral compound that is chemically stable and inexpensive, making it easy to purchase. The author has added 1% Na ₂ SO ₄ to the copper-bearing gold concentrate for calcination-cyanation test. The results show that the addition of sodium sulfate has a significant effect on increasing the leaching rate of copper, but under the same amount of conditions. To increase the cyanidation leaching rate of silver, the effect is not as good as adding NaOH, Na ₂ SO ₃ and Na ₂ S. It has been found that increasing the amount of Na ₂ SO ₄ during calcination can not only greatly increase the cyanide leaching rate of silver, but also have a certain effect on the cyanidation leaching of gold, and it has certain adaptation to arsenic-containing gold concentrate. Sex. The test results are shown in Table 4.

Table 4 sodium sulfate dosage test

It can be seen from Table 4 that as the amount of sodium sulfate increases, the cyanidation leaching rate of gold and silver gradually increases. Considering the production cost, in the production practice, depending on the content of gold and silver, an addition amount of 4% to 5% can be selected.

5. Adding mixed additive (Na ₂ SO ₄ + NaOH) roasting-cyanide test

The use of sodium hydroxide as an additive for calcination cyanidation leaching can greatly increase the cyanide leaching rate of silver. To this end, a calcination-cyanide leaching test was carried out using a sodium sulfate + sodium hydroxide mixed additive. The test results are shown in Table 5.

Table 5 Addition of additive additives roasting - oliveization results

It can be seen from Table 5 that roasting-cyanide using NaOH and Na ₂ SO ₄ as additives has a certain effect on increasing the cyanidation leaching rate of silver, and the effect of roasting by adding NaOH is better. If the mixed additive is used for the calcination pretreatment, the effect is better. This is because sodium hydroxide is added during calcination to form arsenic in the ore sample to form soluble sodium arsenate, which is removed when the sulfuric acid is immersed in copper, which reduces the influence of arsenic on cyanide leaching; The fluidity of the ore sample makes the calcination more porous and porous, and the roasting of the ore sample is more complete, which is beneficial to the cyanide leaching of gold and silver.

Conclusion

(1) The test results show that the addition of 4% to 5% of the mineral amount of sodium sulfate during calcination is effective for increasing the gold and silver cyanide leaching rate of the arsenic-containing gold concentrate, and the current roasting-cyanide Compared with the process, the cyanidation leaching rates of gold and silver increased by 5% and 40%, respectively.