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Taiwan Institute of Nuclear Energy (INER) study of a new method for recovering precious metals from copper anode mud, known as "INER" method. This process includes four leaching, five extraction systems, and two reduction processes. A production plant with an annual processing capacity of 300t anode mud has been built. The process is shown in Figure 1.
Figure 1 Flow chart of the INER for recovering precious metals from copper anode mud
First, acetate leaching
A large amount of lead is present in the anode slime, making it difficult to recover valuable metals in the anode. Studies have shown that lead leaching with acetate solution leads to an increase in lead leaching rate with increasing acetate concentration and temperature. Use 5~7mol/L acetate solution as leaching agent, leaching at 20～70°C, and extracting by LLX34 or LLX64.
Second, nitric acid leaching
The silver and selenium in the acetate leaching residue were dissolved in nitric acid, and the leaching temperature was 100-150 ° C in a stainless steel tank having a volume of 300 L. The leaching rates of silver, copper, selenium and tellurium were respectively 96.13%. >99%, 98.8% and 70%. Chlorine gas was passed into the leachate to precipitate silver in the form of AgCl, and the purity of AgCl was >99%, and the recovery was >96%.
After separating AgCl, the filtrate contains Cu, Pb, Se, and Te for denitration and extraction. With 75% TBP and 25% kerosene as the extractant, the extracted eight denitration composition, acid recovery also with eight or elution. The mixing clarifier is made of FRP and has a size of 330 cm to 80 cm x 40 cm. This equipment is equivalent to one-fifth of the production scale. The intermediate test flow is shown in Figure 2.
Figure 2 Schematic diagram of denitration and acid recovery process
Concentrate the chloride solution containing copper, lead, selenium and tellurium to 4~5mol/L with free hydrochloric acid, then extract and separate the selenium bismuth with 30% TBP and 70% kerosene, adopt four-stage extraction, two-stage washing and four-stage washing. As shown in Figure 3, the selenium and other impurities are well separated in the mixing and clarification equipment.
Figure 3 Selenium separation
Selenium and selenic acid are reduced to obtain selenium by using sulfur to obtain SO 2 . The sulfur combustion chamber area is 0.2m 2 , the sulfur consumption is 2～4kg/h, the air input is 600L/min, and the SO 2 concentration at the burner outlet is 4%～8%. After purification, it is introduced into the reduction cylinder, and the elemental selenium is reduced at room temperature. After filtration, washing and drying, the purity is >99.5%. In the same manner, hydrazine can be precipitated from a hydrazine chloride solution.
Third, the dissolution of aqua regia, gold extraction and reduction
The residue was leached with aqua regia to remove the residue, so that 99% of the gold in the slag entered the leachate, and then the gold was extracted by dibutyl carbitol (DBC). The gold-loaded organic phase was reduced and stripped with oxalic acid to obtain gold powder and the filtration performance was good. The recovery of gold was 99%, and the purity of gold was >99.5%.
Fourth, the recycling of tin
After the copper anode mud was treated as described above, the tin content in the residue increased from 11.2% to 35%. The presence of tin in this form of SnO 2 tin concentrate after mixing CaO carbon, and iron powder, the melting temperature at 1350 ℃ 1h, easily separated from the slag crude tin. The crude tin was refined twice, the first time at a temperature of 350 ° C, and the second temperature was 230 ° C, to a high purity metal tin, the recovery of tin was 95%.
Five or three waste treatment
The waste liquid in the "INER" process is treated by a combined precipitation method of sulfide and hydroxide, that is, by neutralizing, reducing, precipitating, filtering, etc. with NaHSO 3 , Ca(OH) 2 , FeS, the heavy metal in the waste liquid can be Meet the wastewater quality control standards. "INER" process a small amount of NO x gas generated after washed by water and alkali absorption into the atmosphere.
The “INER†process plant, which handles 300t copper anode slime, is estimated to require an investment of US$3.99 million. Compared with the traditional method, this method has the advantages of low energy consumption, less emissions, high recovery rate of precious metals (more than 99% of gold, 98% of silver), convenient operation for extraction, and suitable for continuous production.