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DEVICES AND METHODS OF EXTRACTING COLORFUL AND NOBLE METALS
INVENTION
Patent of the Russian Federation RU2086685

METHOD OF PYROMETALLURGICAL REFINING OF GOLD AND SILVER-CONTAINING WASTES

METHOD OF PYROMETALLURGICAL REFINING
GOLD AND SILVER CONTAINING WASTE

The name of the inventor: Ermakov AV; Sivkov M.N .; S. Nikiforov; Mazaletsky AG; Gorbatova LD; Dmitriev VA; Matyukhin PA; Afanasiev O.Yu .; Maslennikov VS
The name of the patent holder: Joint-stock company of open type "Ekaterinburg plant for processing non-ferrous metals"
Address for correspondence:
Date of commencement of the patent: 1995.12.14

Use: refers to the methods of pyrometallurgical refining of noble metals or their alloys. Essence: the method includes melting the starting material and performing the melting in two stages at 1100-1200 ° C. In the first stage, oxidative smelting is carried out with the supply of oxygen-containing gas to the melt for 20-25 minutes, and in the second stage, smelting reducing melt Reducing gas and simultaneously mixing the melt for 30 minutes, while the ratio of the area of ​​the metal mirror to the melt mass is maintained in the range of 0.06 to 0.07. The method provides a high degree of melt refining from impurities and an increase in the mechanical properties of the precious metal alloy.

DESCRIPTION OF THE INVENTION

The invention relates to metallurgy, in particular to methods for pyrometallurgical refining of noble metals or their alloys.

At present, the raw materials of non-ferrous metals processing plants are mainly scraps of jewelry alloys (gold, silver) and scrap of jewelry production, containing a large number of impurities, including iron, nickel, lead6 zinc, etc. In addition to contamination of the alloy, these impurities due to High affinity for oxygen increase its content in the alloy (to a concentration of 0.06 mass%), which sharply negatively affects the mechanical and physico-chemical properties of the alloy: plasticity, fluidity, elongation decreases, etc. This makes it impossible to obtain from these Alloys of jewelry and other products without preliminary waste refining.

Existing methods for processing metal wastes containing gold and silver are predominantly based on hydrometallurgical schemes focused on the extraction of gold or silver separately in the first stage of the process.

The classical refining of noble metals is known for complete dissolution, separate precipitation from solutions, smelting of pure metals, and then subsequent alloying of the components in an alloy (Plaksin, IN "Metallurgy of precious metals", M.1958 p.333). The method makes it possible to obtain alloys that are conditioned by impurities, but it requires significant economic costs and a long processing cycle of up to 3 months. In addition, the dissolution of precious metals is carried out in concentrated acids, which makes the method environmentally dirty and requires special instrumentation.

Refining is known for chlorination by remelting during purging through a chlorine melt. Chlorination is used to separate non-noble metals from the alloy, but it can also be used for complete refining with the transfer of noble metals to chlorides, with zinc, lead, iron, copper, silver and gold sequentially removed from the alloy composition (Plaksin IN Metallurgy Noble metals ", M.1958, p.332). However, the method of chloridation can be applied at significant costs for environmental protection measures, Chlorine poison the atmosphere of the shop. In addition, in the process of chlorination a large amount of chloride gold is lost, refining by chlorination involves an additional technological operation - separation and treatment of chlorides to separate precious metals from them.

Other methods for refining and purifying alloys of non-ferrous and precious metals are known.

A method is known for refining metals and alloys with gases, which involves purging the melt with inert gases. [1] The method is carried out in a hermetic volume containing the getter, as the melt rotates relative to the vertical axis in the pulsating regime. The proposed technology allows to reduce gas consumption, but when using inert gas as a refining melt, not all impurity elements are removed.

A method for refining a silver alloy is known. [2] Including purging the silver alloy with air or oxygen, while the metals contained in silver are converted to oxides, which are then separated by the densities of the metal and oxides. The disadvantage of the process is that it does not provide deoxidation of the melt, and the oxygen content of the proaffined metal remains above the allowable, which reduces the mechanical properties of the alloy.

According to the technical essence, the method closest to the proposed object of the invention is a method for refining silver. [3] The method relates to the field of metallurgy of noble metals and includes melting the metal with flux introduction and performing the melting in two stages: in the first stage in the air atmosphere and on the second stage when the oxygen-containing gas is injected into the melt.

The disadvantage of the known method is that by the proposed technology only pure metals can be refined, and not alloys. In addition, because of the high saturation of the melt with oxygen, the mechanical properties of the finished alloy are reduced. The drawbacks of the method include the introduction of fluxing additives into the melt, which leads to an increase in the losses of precious metals with the resulting slags or requires additional technological operations to extract them from slags.

The objective of the invention is to increase the degree of purification of the melt from impurities, including oxygen, and to increase the mechanical properties of the resulting alloy of precious metals, to shorten the processing cycle, and to reduce losses of precious metals.

The objective is achieved in that in the method for refining gold- and silver-containing materials, including melting the starting material in a refractory crucible and carrying out a two-stage smelting with the supply of refining gases to the melt, oxidative smelting is carried out in the first stage, and the oxygen-containing gas is fed into the melt at 110-1200 ° C for 20-25 minutes with correction of the melt for the main components by impregnating it with pure metal, and in the second stage, reductant melting is carried out by feeding the reducing gas into the melt and simultaneously mixing the melt for at least 30 minutes. The refining process is carried out while maintaining the ratio of the area of ​​the melt mirror to the melt mass in the range of 0.06-0.07.

The essence of the invention is as follows. Zinc, which has a high partial pressure at the process temperature of 1100-1200 ° C, transforms as a metal into a gas phase and, when creating an oxidizing environment, subsequently forms a stable zinc oxide ZnO. Apparently, the purification from impurities of a noble alloy has the following mechanism: transition to a gas phase of metallic zinc and further oxidation to ZnO; The formation of condensed PbO oxide and its transition from condensed to gaseous state; The formation of stable condensed oxides of nickel and iron and their transition into slag.

In order to create the conditions for the above reactions to proceed in the melt, oxidative melting is carried out in the first stage, as a result of which zinc distillation occurs followed by its oxidation and complete oxidation of the melt due to the formation of copper oxides and further reduction of copper oxides by impurity elements of iron, nickel and lead. Then, insoluble oxides of iron, nickel and PbO float to the melt mirror, go into the slag phase of iron and nickel oxides, and into the lead gas. All this occurs against the background of an increase in the oxygen content, its maximum content can reach 0.3% due to the process of dissolution of cuprous oxide in liquid copper. Such an amount of oxygen at 110-1200 ° C ensures almost complete oxidation of all impurity elements.

Reducing melting, carried out in the second stage of the refining process, is necessary to remove oxygen from the melt to the required concentration, which provides the necessary mechanical and physical properties of the jewelry alloy. Stirring of the melt at this stage creates a constantly renewed reaction surface, which intensifies the process of deoxidation of the melt. Stirring of less than 30 minutes is not enough to obtain the required oxygen concentration in the melt (less than 0.0065 wt.), And an increase of more than 30 minutes is impractical since It does not increase the purification indexes, but leads to an increase in losses of precious metals.

The claimed ratio of the area of ​​the melt mirror to its mass is optimal with respect to loss of noble metals due to evaporation: if this ratio is more than 0.07, there are significant losses of gold and silver (up to 9%), and with a smaller 0.06, the refining time Melt (Table 1).

The process of refining with the supply of gases in the declared temperature range is dictated by the necessity to obtain a melt of the processed material (1100 ° C) and to create conditions for the formation of oxides (1200 ° C). At a temperature of more than 1200 ° C, the degree of purification does not increase, but the loss of precious metals increases.

The duration of oxidizing melting during 20-25 min is a necessary and sufficient period of saturation of the melt with oxygen, which is required for the oxidation of copper and impurity elements. Duration of less than 20 minutes does not ensure complete removal of iron and nickel from the melt, because They oxidize through copper oxide followed by a transition to the slag phase, and with a duration of more than 25 minutes there is a significant increase in the content of oxygen in the melt, which leads to an increase in the duration of the reducing stage and leads to losses of precious metals.

Due to the two stages of refining in one unit, the problem of obtaining an alloy in accordance with GOST without additional technological operations is solved due to the possibility, in the case of deviation from the GOST, of the correction of the melt by simple addition of pure metal carried out in the oxidation stage after removing impurities.

The invention corresponds to the inventive step. Considering the totality of its essential features, it can be noted that they do not follow explicitly from the prior art. When it is revealed from the totality of the functionally separate features of the invention that are distinct from the closest analogue, it is found that all the distinctive features do not show any independent function (regime conditions and sequence of carrying out the method actions), therefore such signs can not be considered in isolation from the feature to which they And, in isolation from the object as a whole. Taking this into account, it should be noted that among the objects of the same purpose, the known technology with the same set of characteristics was not found. Regularities in terms of a certain sequence of operations, including Mechanism for removing impurities under the stated conditions, was not found. The sequence of operations indicated in the claimed method, in combination with the operation mode, provides the necessary interrelation and mutual influence of the features of the method, due to which a new technical result is achieved with a higher degree of purification of the melt from impurities and oxygen, which provides high mechanical properties of jewelry obtained from waste , Containing noble metals.

In order to confirm the possibility of implementing the invention, we give examples of the implementation of the method.

The method was carried out as follows. A lot of jewelery alloys waste and scrap containing gold, silver and copper and contaminated with impurities, wt. Iron 0.08; Nickel 0.06; Lead 0.04; Zinc 0.10 was melted in a crucible at a PGM-100 unit. The wastes were loaded in such a quantity that the ratio of the area of ​​the melt mirror to its mass was in the range 0.06-0.07. After reaching the set temperature, the melt was blown with air and at the same time, fumigated samples were taken for analysis for the content of impurities, oxygen and basic components. The content of impurities decreased and simultaneously there was an increase in the oxygen content. Air blasting was carried out for 20-25 minutes, while the oxygen content in the melt was reached to 0.06% and the content of impurities was minimal (Table 2). After 20-25 minutes, the blast was stopped. In case of inconsistency with GOST on the main components, the necessary pure metal was added to the melt.

After obtaining the oxidized melt, a smelting reduction was carried out in order to remove oxygen dissolved in the melt and to reduce the copper oxide. For this purpose, natural gas was supplied to the melt as a reducing agent. The recovery was carried out both by hydrogen and carbon monoxide. The reducing gas was fed into the melt for 30 minutes. During this period, the oxygen concentration in the melt was reduced to the required not more than 0.0065 wt. The smelting reduction step was carried out while stirring the melt. Analysis of samples for the oxygen content was carried out on the gas analyzer OMAT-3500 of the firm "Strochlien". The alloy obtained from impurities is tested for mechanical properties (Table 3). Comparative parameters of melt purification from impurities by the known and proposed methods are given in Table 4.

Thus, the proposed method provides for selective removal of impurity elements from metal waste containing noble metals, without dissolving the metal substrate and obtaining an alloy corresponding to GOST for manufacturing jewelry.

In comparison with the known methods, the method has the following advantages:

  • An increase in the degree of removal of impurities and the quality of the finished alloy is achieved;
  • The number of technological stages is reduced;
  • The processing cycle is significantly shortened;
  • Decreases the amount of irreversible losses of precious metals;
  • The ecological situation of the enterprise is improved due to exclusion of nitrogen oxides, hydrochloric acid, etc.

In Table 1, these results are given under the condition of purification from impurities, including oxygen, to the required level.

CLAIM

A method for pyrometallurgical refining of gold- and silver-containing wastes, comprising melting the starting material in a refractory crucible and two-stage smelting with the supply of refining gases to the melt, characterized in that in the first step, oxidative smelting is carried out by feeding into the melt an oxygen-containing gas at 1100-1200 ° C for 20 25 minutes when the melt is corrected for the main components by impregnating it with pure metal, and in the second stage, reduction melting is carried out by feeding the reducing gas to the melt and simultaneously mixing the melt for at least 30 minutes, the refining being carried out while maintaining the ratio of the melt-to-mass mirror area Melt 0.06 0.07.

print version
Date of publication 14.03.2007gg