Rich mineral resources extracted precious metal concentrate, containing all precious metals, they must first be roughly separated from each other, then the metal refining, yielding pure metal. Due to the similar physical and chemical properties of the precious metals, there is always me in the separation process. I have you, deep separation is difficult, and the separation and refining processes are more complicated. At present, there are two main methods of selective precipitation and solvent extraction. However, the precious metal concentrate must be dissolved before separation.
(A) dissolving a noble metal a noble metal technique secondary resources are recycled into the solvent extraction separation and refining of precious metals and precious metals are carried out in solution, and a noble metal, particularly platinum group metals sub-element is chemically inert, which has been effectively dissolved The problem in precious metallurgy. The main methods used in metallurgy include sodium peroxide melting method, aluminothermic reduction method, and bismuth melting aluminum thermal reduction method.
1. Sodium Peroxide Melting Method This method is suitable for treating high-grade concentrates mainly composed of para-platinum group metals, such as (%): Pt 28.74, Pd 33.43, Rh 3.57, Ru 2.98, Ir 1.36, Au 5.55, Ag 7.70. The total of 7 precious metals is 83.33%, and the rest is mainly SiO 2 and a small amount of base metal.
The process first leaches the concentrate with HC1/C1 2 at 95 ° C for 5-10 h to dissolve most of the platinum palladium gold. Taking platinum as an example, the leaching reaction is:
Pt+2HC1+2Cl 2 ====H 2 PtCl 6
After the filter cake twice with Na 2 O 2 in the melt at 550 ℃ 1-2h, cooled frit flooding, formic acid was added to the solution to dissolve the ruthenium sodium again reduced to ruthenium, the alkaline solution was filtered free of noble metals The residue was hydrolyzed with the first leachate and then subjected to a second chlorine gas leaching. The leaching index and material composition of each section are shown in Table 1.
Table 1 Â Leaching index and material composition table | |||||||
project | Pt | Pd | Au | Rh | Ir | Ru | Ag |
First stage HCl/Cl 2 leaching rate /% | 98 | 98 | 90 | 39.2 | 43.7 | 25.4 | |
First stage leaching slag composition /% | 2.44 | 3.02 | 2.1 | 9.13 | 3.53 | 8.8 | |
One-stage plus two-stage total leaching rate /% | >99.9 | >99.9 | >99.9 | 97.2 | 97.9 | 98.1 | |
Final precious metal solution concentration / ( g / t ) | 25.6 | 31 | 4 | 2.78 | 1.21 | 2.42 | 3.97 |
Final insoluble slag component /% | <0.2 | <0.02 | <0.02 | 1 | 0.35 | 0.56 | 　 |
Finally, the insoluble residue returns to alkali fusion. A disadvantage of this method is that the formation of silica gel upon silica alkali immersion in water sometimes affects filtration.
2. Aluminothermic reduction smelting iron alloying process leach into three sections, namely: â‘ noble metal concentrate with the melting temperature of aluminum and iron, aluminum and noble metal, iron alloy of the concentrate; â‘¡ with an acid to dissolve aluminum and iron base The metal causes the precious metal to fall out of the alloy solid solution into a state of high dispersion active metal powder; 3 finally dissolves with HCl/Cl 2 to obtain a high concentration precious metal solution. Different smelting methods and operating conditions are used for concentrates of different grades and compositions.
(1) Dissolution of high-grade precious metal concentrates. If the lead in the traditional process is dissolved in lead and silver by nitric acid, the concentrates mainly composed of para-platinum metals are typical (%): Pt 5.5, Pd 3.8. , Au 0.8, Rh 9.8, Ru 17.1, Ir 2.9, Os 1.9, Ag 1.4, total precious metal) 40%, in addition to Cu, Fe, Ni, Pb, totaling about 35%. When the concentrate is directly dissolved by aqua regia, dissolved in aqua regia after high-temperature hydrogen reduction, and dissolved in aqua regia after aluminothermic smelting, the dissolution efficiency of the noble metal is not high. However, after activation by aluminum melting, the dissolution rate of all precious metals is high. The process is as follows: concentrate and equal-quality aluminum are directly smelted into aluminum alloy in an inert atmosphere above 1000 ° C. The aluminum alloy is dissolved in 4 mol of hydrochloric acid to remove the ruthenium metal, and finally the noble metal is oxidized to dissolve the noble metal. The efficiency of various precious metals in dissolving precious metals is shown in Table 2.
Table 2 Â Comparison of the efficiency of various methods for dissolving precious metals | |||||||
project | Pt | Pd | Au | Ru | Rh | Ir | Os |
King water directly dissolved at 90 °C for 5h | 89.3 | 76.2 | 92.9 | 2 | 8.5 | 2.5 | 2 |
HCl/Cl 2 dissolves at 80 °C for 5h | 86.3 | 74.5 | 90.2 | 2.5 | 7.6 | 2 | 2.1 |
Hydrogen reduction at 900 °C for 1 h , aqua regia at 90 °C for 5 h | 96.3 | 97.4 | 98.5 | 4.5 | 14.6 | 8.3 | 5 |
Aluminum melting - dip metal - aqua regia at 90 ° C for 2h | 99.5 | 99.2 | 99.6 | 98 | 98.5 | 98.3 | 97.6 |
Aluminum melted bismuth metal -HCl/Cl 2 dissolves at 80 °C for 1 h | 99.1 | 99.8 | 99.8 | 97.1 | 98.9 | 97.4 | 98.6 |
(3) Dissolution of low-grade precious metal concentrates This method is used to treat coarse concentrates containing <20% of precious metals. The concentrate also contains about 14% FeO, about 16% SiO 2 and other base metals. Firstly, the concentrate and carbon powder and lime are mixed and granulated, and calcined at 800 ° C. The calcined sand and iron chips are smelted into iron alloy at 1600 ° C in an electric furnace. After separating the slag, aluminum flakes are added to the melt according to aluminum: precious metal = 0.4:1. Produce aluminum-iron alloy. The amount of slag produced is large, and the amount of precious metal entrained can reach 2%-3%. The content of base metal in the alloy is 90%, and a large amount of hydrochloric acid is consumed to dissolve the base metal, but the efficiency of dissolution of the produced precious metal concentrate with HCl/Cl 2 is still high.
When the method of treating low-grade variety of staple-rich Rh, Ir residue was dissolved 3 Table 3 metal.
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