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What are the precious metal refining processes?
- Refining process of precious metals in anode mud from waste copper refining
NaOH roasting – water leaching – coordinated acid leaching process
First, mix NaOH and anode mud in a mass ratio of 1:1 and roast at a roasting temperature of 700℃ for 2.0 hours. This step allows Cu, Ag₃SbS₃, and Ag₂SO₄ in the anode mud to proceed in the direction of phase transformation reaction of Cu₉Sb₄O₁₉ and Ag, laying the foundation for the subsequent efficient leaching of Cu and Sb and high retention of Ag.
Then water leaching is carried out.
Then coordinated acid leaching is carried out, and leaching is carried out for 30 minutes under the conditions of H₂SO₄ concentration of 2.00 mol/L, tartaric acid concentration of 0.33 mol/L, H₂O₂ concentration of 0.44 mol/L, solid-liquid ratio of 25 g/L, and temperature of 80℃. During this process, the removal rates of Cu, Ni, Sb, Pb, Sn, As and S reached 99.68%, 81.99%, 99.94%, 76.39%, 79.29%, 95.20% and 87.72%, respectively. The retention rate and enrichment multiples of rare metals Ag, Au and Pd were as high as 99.98% and 5.17 times, 99.50% and 3.31 times, 91.00% and 4.00 times, respectively.
Finally, the valuable metals in the leaching solution were recovered by electrodeposition-chemical precipitation method, and the total recovery rates of Cu, Sb, Ni, As, Pb and Sn reached 80.3%, 94.0%, 66.1%, 81.0%, 64.7% and 67.4%, respectively.
Process for recovering Ag, Pd and Au from precious metal-enriched slag of anode mud from waste copper refining
Nitric acid-citric acid synergistically leaches Ag and Pd. In this process, the H⁺ released by the continuous ionization of citric acid greatly enhances the leaching power of the system, and the complexation of citric acid promotes the ionization of citric acid and the leaching of Ag and Pd.
After Ag is precipitated with sodium chloride, it is reduced with glucose to obtain high-purity silver powder.
Pd is recovered by reducing the palladium-containing solution after Ag separation with copper powder or recovered cathode copper.
Au in the leaching slag solution in which Ag and Pd are dissolved by hydrochloric acid-potassium chlorate is reduced with copper powder or recovered cathode copper. Under the optimal process conditions of each unit, the process recovers 99.69% of Ag (purity 99.99%), 98.55% of Pd and 97.97% of Au. In addition, Ni in the gold leaching slag is fully enriched, and its high content of 65.19% is much higher than that of ordinary nickel ore, which can be used as an ideal raw material for smelting nickel. - Silver refining process
Methanesulfonic acid leaching – electrowinning process
Based on methanesulfonic acid (MSA) as the basic chemical, an efficient refining method is designed to first leach silver particles containing about 94% silver, using hydrogen peroxide as an oxidant. In a laboratory-scale stirred leaching experiment, the effects of leaching parameters such as solid concentration, hydrogen peroxide dosage and temperature were studied.
The results show that the leaching rate of silver can reach more than 90% under the conditions of elevated temperature of 65℃ or 80℃, solid concentration of 500 g/L, and stoichiometric ratio of H₂O₂:Ag of 3:1. Increasing the solid concentration to more than 500 g/L and raising the temperature to 65℃ or 80℃ can also improve the selectivity of the process for Pd leaching. - Process of gold purification and refining
The gold is purified by aqua regia dissolution-reduction, but the gold powder obtained has a high content of impurity silver. To solve this problem, the influencing factors such as hydrochloric acid concentration and temperature are investigated to determine better process conditions and improve the precipitation efficiency and degree of silver chloride.
The gold powder obtained by reduction is washed with hot water and nitric acid to obtain product gold powder with a quality reaching the national standard IC-99.99. - Process of iridium recovery and refining in iridium-containing waste
The precious metal iridium is recovered from the titanium anode stripping material solution through oxidation precipitation, reduction dissolution and other processes. The optimal process conditions were determined in the experiment. When the redox potential is greater than 900 mV and the amount of ammonium chloride is more than 1 times that of iridium, the precipitation rate of iridium is greater than 98%. When the reduction pH value is 3, a small amount of platinum, palladium, rhodium and ruthenium impurities in iridium can be separated well.
This method is suitable for the treatment of iridium-containing waste with iridium as the main body and low content of precious metal impurities. It is easy to operate and the product purity can meet the national standard requirements. - Separation and purification process of precious metals in copper anode mud
Traditional process
The separation and purification technology of precious metals in traditional copper anode mud usually includes multiple steps, such as leaching, separation, reduction, etc.
Optimized process
Combined with modern production processes and production examples, two optimized separation and purification technologies are introduced to help manufacturing companies improve the efficiency of precious metal recovery. - Process for recovering precious metals from silver-rich lead anode mud
An innovative directional vacuum volatilization process of silver-rich lead anode mud is proposed for enriching Ag and Au. The results show that Ag and Au are successfully enriched in the residue, while impurities such as As₂O₃, Sb₂O₃, etc. are collected in the volatiles. The direct recovery rate of Ag and Au reaches 99.0%. The vacuum strategy not only effectively extracts Ag and Au, but also avoids arsenic contamination.