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INVENTION
Russian Federation Patent RU2090638
METHOD FOR PROCESSING WASTE CONTAINING PRECIOUS METALS
Name of the inventor: Ermakov AV .; Sivkov MN .; Nikiforov SV .; Mazaletsky AG .; Gorbatova LD .; Dmitriev VA .; Matyuhin PA .; O. Afanasiev
The name of the patentee: Open Joint Stock Company "Ekaterinburg plant for processing non-ferrous metals"
Address for correspondence:
Starting date of the patent: 1995.06.14
Usage: As for the pyrometallurgical methods of processing gold and silver waste. The inventive method comprises melting raw material with the addition of a copper component in an amount to increase the partial pressure of steam evaporated harmful impurities above the melt, the melt evacuation at 10 -1 - 10 -2 mmHg and holding at a temperature of 1100-1200 o C with stirring for 20-30 min. The process is carried out in a protective atmosphere. The method allows to increase the degree of purification of the melt precious metals from hazardous impurities, reduce the duration of the processing cycle and does not require substantial economic costs.
DESCRIPTION OF THE INVENTION
The invention relates to metallurgy of precious metals, particularly pyrometallurgical processes to gold and silver processing waste, in particular waste jewelry alloys of different fabrication techniques. This material has significant impurities on elements related to soldering technology, especially cadmium, but also zinc, lead, bismuth and antimony. These impurities greatly reduce the physicochemical and mechanical properties of the alloy, which makes it impossible to use them for the manufacture of jewelry without pretreatment of the feedstock impurities.
Known classic precious metal refining complete dissolution, precipitation separation of solutions, melting of pure metals, followed by smelting alloy [1] The method allows to obtain the impurity conditioning alloys, but requires substantial economic costs and long processing cycle up to 3 months. Moreover, the dissolution of noble metals in acids is carried out with a high concentration, which makes the process environmentally messy and requires special hardware design.
There are known methods for refining and purification of alloys of non-ferrous and precious metals.
A method is known for refining molten metals and alloys [2] The process comprises refining the liquid metal melt by electric vacuum processing. Pretreatment melt electric current destroys active ionic bonds free of oxides and ionizes the oxygen atoms that when creating vacuum above the melt promotes removal of nonmetallic inclusions from the melt.
Known method of vacuum processing of aluminum alloys [3] In order to increase the degree of purification from impurities the alloy, particularly zinc, the alloy is heated to a temperature of 850 900 o C, evacuated and sparged with inert gas.
However, the above methods can not be utilized with sufficient effectiveness for cleaning precious metals, as based on the properties of the impurity main components of the alloy and known modes do not provide the required quality of the finished product.
Technical essence closer to the proposed object of the invention is a method for silver treatment [4] The method relates to metallurgy noble metals include silver removal of impurities such as iron, magnesium, copper, lead, manganese, silicon, aluminum and nickel, by melting starting material at 1000 o C and evacuating at a pressure of 5 × 10 -2 10 -3 T in the presence of silver chloride. The content of impurities thus reduced by 1 3 orders.
However, said cleaning mode removes from the melt the above elements only and do not provide sufficient depth cleaning of other impurities, and an item such as cadmium, which is the most harmful and difficult to remove impurity inclusion in alloys of noble metals, by a known technology generally is not removed.
The object of which was sent to the proposed invention is to enable the processing of precious metals with high efficiency by reducing the duration of the processing cycle, improve the degree of purification from impurities and obtaining a finished product of high quality.
The task is achieved by a method for processing waste containing precious metals by purification from impurities comprising melting and evacuation of the invention smelting lead from the addition of the copper component in an amount to increase the partial pressure of steam evaporated harmful impurities above the melt, and the mass ratio of recycled wastes containing precious metals and copper component added is maintained at 1 (0.21 0.60), then the melt is evacuated at a pressure of 10 -1 to 10 -2 mmHg and maintained at a temperature of 1100 1200 o C with stirring for 20 30 min. The process is carried out in a protective atmosphere.
These features that characterize the proposed regime of processing are significant and together provide the high quality of the alloy of precious metals to make jewelry.
Adding the copper component in the melt allows to increase the thermodynamic activity of trace elements, in particular cadmium, which contributes to their intense evaporation and separation of the noble metals. This is achieved by increasing the partial vapor pressure of impurity elements, which when exposed to high temperatures will exceed the residual pressure in the system, by changing the ratio between the forces of attraction of the atoms in the melt. The amount of copper added to the melt component in a ratio of 1 (0.21 0.60) is optimum since increasing rate of copper alloy is not obtained, corresponding to GOST noble metal content (due to dilution), and decreased with a decrease in the activity of evaporation of impurity elements due to the reduction ratio of the activity coefficient of impurities and precious metals.
Using the processing reception vacuum provides a melt flow acceleration and completeness it physico-chemical processes leading to a significant reduction in process time and improve the purity of the product.
Selection of parameters method of cleaning gold and silver waste is justified as follows. When the value of applying a vacuum of less than 10 -1 mm Hg. Art. reduced the rate of evaporation of impurities and increases the duration of the process; vacuum value is more than 10 -2 Torr impractical, since in this case the removal rate of impurities is not significantly increased, but there is a need to use more expensive equipment, which reduces the efficiency of the process. The duration of the isothermal hold temperature of the melt in the claimed range provides the highest degree of purification from its impurities. With an increase in melt temperature over 1200 o C increases the partial vapor pressure of impurity elements, particularly cadmium, and thus their volatility. At the same time increases evaporation main component silver melt, which leads to a loss of it sublimates. The lower limit temperature of 1100 o C is dictated by the need to obtain a melt processed material. Extract with melt mixing in the claimed temperature range provides the greatest possible degree of surface renewal and evaporation decreases the inhibition limiting diffusion process, which increases the rate of sublimation of impurities and leads to higher quality finished product. At this residence time less than 20 min reduces the degree of removal of impurities, an increase in exposure duration of 30 minutes did not increase the degree of purification due to the onset of dynamic equilibrium in the system. An important condition is conducting the process in a protective atmosphere to prevent oxidation of the copper component to be added and melt saturated with gaseous impurities.
The method was performed as follows. Waste and scrap noble metals in an amount of 20 kg, containing gold and silver, and contaminated with impurities Cadmium 0.3 0.02 Zinc, Lead 0.008, 0.007 antimony, bismuth of 0.009 was charged into a graphite crucible, chamotte added copper component and melted protected propane-butane. As the copper component used metallic copper, copper shavings, copper powder. The melt was evacuated and kept under vigorous stirring. The compositions of the initial melt, the content of impurities in the recycling process were determined by X-ray phase, emission spectral and chemical analysis. Results of removal of impurities at various parameters are presented in Tables 1, 2. For comparative data the same batch of raw material was processed under optimum conditions and existing claimed method (Table 3).
The test results show that the proposed method provides a higher degree of melt purification from impurities. Conditioned get high quality alloy of precious metals for the jewelry. The proposed method over known not require substantial economic costs considerably shortens the processing cycle.
CLAIM
Method for processing waste containing precious metals, comprising the purification of waste impurities by melting and degassing the resulting melt, characterized in that the melting is carried out in a protective atmosphere with the addition of a copper component, while maintaining the mass ratio of copper waste component 1 0.21 0.60 with increasing partial vapor pressure over the melt of evaporated impurities and evacuation is carried out at from 10 -1 - 10 -2 torr. Art. delayed melt at 1100 1200 o C and stirred for 20 30 min.
print version
Publication date 14.03.2007gg
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