4. Two-stage cyanidation-adsorption process
Not long ago, cyanide - adsorption process plant mainly containing gold as a primary ore, a silver ore recovery and gold. In recent years, this method has also been used to treat ore containing high silver, and a cyanide adsorption method is used in the treatment. The recovery rate of silver is not high, causing a large loss. For this purpose, a two-stage cyanidation-adsorption method was used.
Silver forms a silver cyanide complex [Ag(CN) 2 ] - like gold when it is sailed. However, under normal conditions, Ag(CN) 2 - is mainly composed of gold and silver ore and natural silver. Other silver minerals, especially silver sulfide minerals, are difficult to form Ag(CN) 2 - . In the solution, the dissolution reaction of silver sulfide is:
Ag 2 S+4NaCN=====2NaAg(CN) 2 +Na 2 S
The direction of the reaction in the formula depends on the ratio of the amount of cyanide to soluble sulfide in the solution. When the sodium sulfide formed during the reaction accumulates in the slurry until the equilibrium is gradually established, the dissolution reaction of the silver stops. In order to carry the reaction to the right, it is necessary to increase the cyanide concentration in the slurry and enhance the slurry aeration. At this time, the sodium sulfide is first oxidized to sodium thiosulfate in the presence of oxygen, and then oxidized to sodium sulfate:
2Na 2 S+2O 2 +H 2 O→Na 2 S 2 O 3 +2NaOH
Na 2 S 2 O 3 +2NaOH + 2O 2 → 2Na 2 SO 4 + H 2 O
Therefore, in the high concentration cyanide solution in the presence of oxygen, the total reaction formula for the decomposition of silver sulfide is:
Ag 2 S+4NaCN+2O 2 →2NaAg(CN) 2 +Na 2 SO 4
It can be seen from the above that in order for the silver sulfide to be effectively decomposed in the cyanide pulp, the slurry must contain a high concentration of cyanide and oxygen.
The gold and silver cyanide kinetic curves of a gold-silver deposit in the former Soviet Union are shown in Fig. 5. It can be seen from the figure that: 1 When the cyanide concentration is between 0.1% and 0.4%, the dissolution rate and dissolution rate of gold and silver are the largest; 2 at the above cyanide concentration, the gold cyanide is almost completely dissolved after 12h; Even after 42h, the dissolution rate is only close to 80%; 3 within 2~3h of the start of cyanidation, the dissolution rate of silver is almost 50%. At the beginning, the dissolution rate of silver is fast, because the gold and silver ore in the ore are dissolved first; 4 the time required for silver to reach the maximum dissolution rate is 4 times longer than that of gold, which is due to the slow dissolution of silver sulfide minerals in the ore. The reason. Therefore, the high cyanide concentration and long cyanide time are the main features of the cyanide-containing cyanide operation. [next]
The kinetic study of the adsorption of silver on the resin is considered. When the solution containing only a small amount of silver and CN - pure cyanide solution, the resin will strongly adsorbed silver. If the solution contains a gold complex anion in addition to the silver complex anion, the resin is first saturated with silver and then saturated with gold. This is because after the resin is saturated with silver and gold during the adsorption process, the silver complex anion adsorbed by the resin is replaced by the ruthenium anion. In the solution in which gold, silver and impurity metal anions coexist, the mutual order of adsorption of anions of AM-2Б anion exchange resin is arranged in the following adsorption selection order: [Au(CN) 2 ] - >[Zn(CN) 4 ] 2- >[Ni(CN) 4 ] 2- >[Ag(CN) 3 ] 2- >[Cu(CN) 4 ] 3- >[Fe(CN) 6 ] 4- . This indicates that when the resin is saturated, the latter anion is replaced by the former anion from the resin. This is the principle of two-stage cyanidation-adsorption process for selective adsorption of gold and silver by AM-2Б anion exchange resin.
The two-stage cyanidation-removing process for recovering gold and silver from ore (Fig. 6) absorbs gold in the first stage and recovers silver in the second stage. That is, the ore slurry is cyanated for 12 hours under the condition of NaCN with a mass fraction of 0.1%~0.15% and CaO of 0.2%~0.3%. During this process, the gold is almost completely dissolved, and the silver is about 50% (mainly in the gold and silver mine). Silver) is dissolved. [next]
The slurry is sent to the first stage for adsorption, and the resin is added to the last Pachuca adsorption tank (the resin in the tank adsorbs gold, silver or silver), and after 2~3 adsorption, the resin is silver. saturation. However, when the resin and the slurry are reversely moved to the subsequent adsorption tanks, the silver adsorbed by the resin is gradually replaced by gold ions and is rich in gold. The adsorption recovery rate of gold in the first stage of adsorption is 98%~99%. After the first stage of adsorption, the cyanide concentration in the slurry (maintained at 0.15% or more) is increased to cyanide again, and the silver sulfide is decomposed. After the secondary cyanidation, the slurry is sent to the second stage of adsorption, and the silver is mainly adsorbed and recovered from the slurry, and the residual and redissolved gold is recovered. Therefore, the second segment of the resin adsorbs more silver and less gold.
The authors have also studied the existence of silver cyanide ions in the adsorption process. It is proved that the resin adsorbs a multi-charged silver cyanide ion [Ag(CN) 3 ] 2- , [Ag(CN) 4 ] 3- . It has been found that when the silver anion is adsorbed by the resin, a multi-charged silver cyanide ion is generated due to the adsorption of CN- ions in the resin, which affects the amount of silver adsorbed, because a multi-charged complex anion occupies a few of the resin. One reactive group. This is also the reason why the exchange capacity and selectivity of the AM-2Б anion exchange resin for adsorbing silver under such conditions are relatively low.
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