Production examples for processing high copper and lead silver anodes

In the traditional silver electrolysis process, the quality of the silver anode is relatively high, generally as follows: (Au + Ag) > 95%, Cu < 1.5%, Pb < 3%. Only in this way can the process conditions be well controlled and high-purity electro-silver can be produced. Therefore, in the production process of the anode, the oxidation and impurity removal process must be strengthened. And due to the nature of the ore I changeable, the processing capabilities of small, containing copper anode lead plate is very unstable, the general composition (%) :( Au + Ag) 44.89 ~ 80.83, Cu 1.5 ~ 31.21, Pb 5.18 ~ 41.31, for such a high The anode of the impurity, we have determined the following production process through production and exploration, the main process flow is shown in the figure below.

1. Primary electrolysis of high copper lead anode

According to the electrochemical principle, in the electrolysis process, the impurity potential is negative compared to silver, and preferential oxidation occurs. Copper enters the electrolyte in ionic form, with a portion of the lead entering the electrolyte in ionic form and another portion entering the anode mud in the form of PbO ₂ . Since the anode impurities are high, in order to prevent the depletion of Ag ^{+ in the} electrolyte and the precipitation of impurities at the cathode, it is necessary to increase the Ag ⁺ concentration and the HNO ₃ concentration. Meanwhile, in order to prevent the metal backlog, high current density rapid separation of gold and silver. In operation, we use the following process conditions: current 550 ~ 600A, bath temperature > 40 ° C, electrolyte composition (g / L) Ag ⁺ 110 ~ 130, Cu ^{2 +} > 3.0, HNO ₃ > 15.0, one electrolysis is obtained as follows Products: high lead anode mud, high lead copper electrolyte, national standard 3 ^# electrolytic silver powder (primary electrolytic silver powder). According to the production practice, 1000kg anode plate is treated and three-tank electrolysis is used. This process only takes 4 to 5 days.

Second, the treatment of high lead anode mud

The high-lead anode mud is pretreated with dilute nitric acid to obtain high-lead black gold powder (Au 40% to 83%, Pb 10% to 30%, Ag 1.3% to 4.5%). If the gold powder adopts the pyrometallurgical smelting technology, the effect of the 67,!" is not good, it will affect the production of the gold electrolysis process, and the slag contains gold, silver and lead, and the closed process will form a closed loop of lead.

To this end, we use a full wet process to process high-lead gold powder for a few hours. In addition to lead 0.007g/L and Ag 0.2g/L, the lead silver waste liquid can be discharged into the cyanide wastewater treatment system after simple lead removal. After the lead removal, the gold powder composition (%): Au 96.8～99.43, Pb 0.03 to 0.99 and Ag 0.3 to 1.24. The gold anode plate is cast with the gold powder, and the asymmetric gold power source is used for the electric gold production, which can produce better than the national standard 1 ^#金, and the 1 ^# grade rate reaches 100%. The electro-gold composition (%) produced by our company: Au>99.996; Ag<0.0005; Cu<0.0005; Pb<0.0005; Fe 0.0005-0.00015; Bi<0.0005; Sb<0.0005.

Third, the treatment of high copper lead electrolyte

After a certain period of electrolysis, Ag ⁺ in the electrolyte drops, and Cu ^{2 +} and 671# accumulate to a considerable concentration. At this time, it is necessary to carry out treatment to regenerate the electrolytic solution. According to theoretical calculations, for an electrolyte containing Ag ⁺ 100 g/L, only when Pb is lowered to 0.2 g/L, silver forms Ag ₂ SO ₄ precipitate. Therefore, we use the dilute sulfuric acid method to regenerate the electrolyte. The composition of the electrolyte before and after the lead is shown in the following table (g/L)

The electrolyte after sinking lead contains too much acid, and it is necessary to properly heat up the nitrate, and the filtered part can be returned to the electrolysis system. Part of the industrial salt replacement is used to recover silver to reduce the concentration of Cu ^{2 + in the} electrolyte. The precipitated lead powder was washed (%): Ag 0.025 to 0.70, Pb 66.51 to 86.12. We sell it as slag.

Fourth, the treatment of electrolytic silver powder

The quality of the silver powder separated by one electrolysis is very poor. The composition (%): Cu 0.0018 to 0.025, Pb 0.016 to 0.61; Fe 0.0005 to 0.003. For these silver powders, a re-cast anode plate is used to carry out secondary electrolysis. The equipment adopts the electrolysis cell of the original primary electrolysis, but it must be fully cleaned before. The secondary electrolysis adopts the following process conditions: Ag 75～130g/L, Cu<60g/L, HNO ₃ >8g/L, temperature>35°C, current 450 ~ 480A, the production of the national standard 1 # silver powder once qualified rate of more than 90%.

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