RU2730331C1 - Method of electrochemical extraction of noble metals from secondary raw materials - Google Patents

Abstract

FIELD: electrochemistry.

SUBSTANCE: invention relates to electrochemistry of noble metals, particularly electrochlorination, and can be used in processing secondary platinum group metals (PGM). Method involves treatment of a catalyst in electrochlorination electrolyte with application of direct and alternating currents with preliminary activation of noble metals and their subsequent electrodeposition at the cathode in conditions of reduction of electrolyte volume. Preliminary activation of noble metals in catalyst is carried out in medium of gaseous products of electrolysis with gradual filling of catalyst charge with electrolyte based on hydrochloric acid. After filling with electrolyte – in inert gas at pressure of 5–10 atm. Decrease of electrolyte volume in process is carried out and controlled due to its recondensation into separate accumulating capacity by means of periodic depressurisation of gases into condensation system till moment of accumulation of electrolyte in accumulating capacity. Fresh electrolyte is added to initial volume, pressure of inert gas is increased to initial value of 5–10 atm, and cycle of electrodeposition is repeated with periodic depressurisation.

EFFECT: invention simplifies and increases efficiency of the process while ensuring high percentage extraction of noble metals.

1 cl, 2 ex

Description

The invention relates to the electrochemistry of noble metals, in particular, electrochlorination and can be used in the processing of secondary metals of the platinum group (PGM), including catalysts, as well as their concentrates and refined metals.

A known method of extracting precious metals from spent catalysts, in which the processed material, in the form of backfill, is placed in the interelectrode space of the electrolyzer. Electrochemical leaching of noble metals is activated by preliminary polarity reversal of the electrodes in statics to convert it into a multipolar bulk electrode, which ensures anodic dissolution of the metal in the entire volume of the material. And the circulation of the electrolyte through the backfill from the anode to the cathode is carried out at a rate determined from the conditions for preventing the drift of hydrated anionic complexes of chloride complexes of noble metals to the cathode, formed during leaching in the volume of the backfill by controlling the formation of a brown cloud at the anode at the beginning [1].

The existing method has the following disadvantages. The process of depassivation of PGMs under conditions of only alternating current is ineffective due to insufficient release of chlorine on variable electrodes and the impossibility of converting the noble metal into a water-soluble form. Therefore, a high extraction of noble metals is achieved during the subsequent long-term chlorination process in direct current with its simultaneous deposition. The time for the subsequent stage of the electrochemical extraction of noble metals under conditions of constant depletion of the concentration of noble metals in the electrolyte also increases. As a result, the productivity of the extraction process as a whole is significantly reduced.

Closest to the claimed method is a method for the electrochemical extraction of precious metals from secondary raw materials, mainly in the form of spent catalysts and concentrates, adopted as a prototype, in which the preliminary activation of precious metals and their subsequent electrodeposition from the electrolyte to the cathode is carried out at a temperature of 90-160 ° C when alternating and direct currents are applied, the electrodeposition of noble metals on the cathode is carried out cyclically with a decrease in the volume of the electrolyte until the passage of current stops, then fresh electrolyte is added to the initial volume and the electrodeposition cycle is repeated. The number of cycles of electrodeposition of noble metals on the cathode is 1-3 [2].

The main disadvantage of this method is the duration of the stage of reducing the volume of the electrolyte until the moment the passage of current stops. Under conditions when the processed material has pores saturated with electrolyte, the moment of stopping the passage of current can be achieved only under conditions of a long stage of electrolyte evacuation from the pores, for example, due to additional external heating of the filling and electrolyte evaporation. In this case, the dispersed material is sintered and its subsequent extraction from the installation is difficult, the efficiency of the process decreases. Moreover, under conditions of a significant sulfur content in the spent catalyst, passive forms of the noble metal are formed, which are not fully revealed during activation due to the superposition of alternating and direct current. These forms are located in fine pores, which complicates and lengthens the time process of washing and extracting the noble metal.

From the existing level of technology, no objects have been identified that contain a combination of the claimed essential features. This allows us to consider the proposed method as new. The existing state of the art also does not know the set of features that differ from the features of the method according to the closest analogue. This allows us to consider the proposed method as having an inventive step.

The objective of the present invention is to increase the efficiency of the process of extracting noble materials with obtaining a technical result consisting in simplifying and increasing the productivity of the process, while ensuring a high percentage of extraction of noble metals.

The essence of the way

The technical result is achieved by the fact that in the known method of electrochemical extraction of precious metals from secondary raw materials, including the processing of the material in an electrolyte by electrochlorination with the imposition of direct and alternating currents with preliminary activation of noble metals and their subsequent electrodeposition on the cathode in conditions of a decrease in the volume of electrolyte, preliminary activation of noble metals the catalyst is carried out in an environment of gaseous electrolysis products during the gradual filling of the catalyst backfill with electrolyte, and after filling with electrolyte - in an inert gas at a pressure of 5-10 atm. A decrease in the volume of electrolyte in the process of electrodeposition of noble metals is carried out and controlled by its recondensation into a separate container by periodic release of the gas pressure into the condensation system until the end of the accumulation of electrolyte in the storage container. Then add fresh electrolyte to the initial volume, increase the pressure of the inert gas to 5-10 atm and repeat the electrodeposition cycle with periodic pressure release.

The essence of the proposed method is as follows. During preliminary treatment (activation) of the initial catalyst in the gas phase with the active products of hydrochloric acid electrolysis, gaseous active reagents (chlorine and hydrogen) penetrate into the pores of the catalyst, which contribute to the depassivation of the noble metal. Subsequently, when filling the backfill with electrolyte, the supply of an external pressure of an inert gas promotes the penetration of the liquid electrolyte into the small pores of the material. Further processing of the catalyst at temperature and pressure makes it possible to achieve a more complete opening of the passive phases of the noble metal located in narrow pores. The release of external pressure allows, due to the effect of the expanding gas piston in the pores, to push the electrolyte out of them together with the dissolved reaction products into the total volume of the electrolyte. This effectively flushes the catalyst pores.

Examples of implementation of the method

Example 1

Spent autocatalyst with platinum content - 0.1 wt. %, palladium - 0.04 wt. %, rhodium - 0.012 wt. % after grinding was loaded into an autoclave-electrolyzer in an amount of 20 kg. An electrolyte based on hydrochloric acid was fed into the lower free interelectrode space of the autoclave-electrolyzer. Further, its electrochemical decomposition was carried out for 0.5 hour, treating the catalyst with active chlorine and hydrogen in the gas phase.

Then, electrolyte was fed from the bottom of the catalyst backfill with the lower pair of DC electrodes turned on for 1 hour, gradually filling the backfill with electrolyte to the final volumetric ratio T / L = 1 / (1-2). Then, an inert gas was fed into the autoclave-electrolyzer at a pressure of 5 atm, and the charge was heated by alternating current to a temperature of 150 ° C. When a temperature of 90 ° C was reached, the electrochlorination of the material was started in alternating current with a frequency of 1-100 Hz and direct current of 20-30 A. Exposure at a temperature of 150 ° C and a pressure of 10 atm was 1 hour. Then the alternating current was turned off and the pressure was gradually reduced by lowering the temperature. During the electrodeposition of dissolved noble metals on the cathode, the vapor pressure was periodically depressurized by an automatic valve into the condensation system, thereby partially lowering the electrolyte level in the backfill. Further purging with an inert gas made it possible to reduce the time of the electrodeposition stage until the end of the accumulation of electrolyte in the storage tank to 8 hours. For a more complete extraction of noble metals, fresh electrolyte was again poured into the electrolyzer, and the electrodeposition of noble metals was carried out without heating under conditions of pumping an inert gas pressure of 5 atm and its periodic discharge with electrolysis vapors. At the end of the process, the remaining electrolyte was drained and combined with condensate for reuse. This process took 4 hours. The total extraction for platinum was 97 wt. %, palladium - 99 wt. %. rhodium -84 mass. %.

Example 2

Spent petrochemical catalyst based on gamma alumina in the form of granules in an amount of 20 kg with a platinum content of 0.23 wt. % was poured into an autoclave electrolyzer. An electrolyte based on hydrochloric acid was fed into the lower free interelectrode space of the electrolyzer and its electrochemical decomposition was carried out for 1 hour. Then, the electrolyte was fed gradually from the bottom of the catalyst backfill with the lower pair of DC electrodes turned on for 1 hour, filling the backfill with electrolyte in the final volumetric ratio T / L = 1 / (1-2). Next, an inert gas was fed into the autoclave-electrolyzer at a pressure of 10 atm, and the charge was heated with an alternating current to a temperature of 180 ° C. Upon reaching a temperature of 60 ° C, the electrochlorination of the material was started in an alternating current with a frequency of 1-100 Hz and a direct current of 20-30 A. Exposure at a temperature of 180 ° C and a pressure of 15 atm was 1 hour. Then the alternating current was turned off and the pressure was gradually reduced by lowering the temperature. During the electrodeposition of dissolved noble metals on the cathode, the vapor pressure was periodically depressurized by an automatic valve into the condensation system, thereby partially lowering the electrolyte level in the backfill. Further purging with an inert gas made it possible to reduce the time of the electrodeposition stage until the end of electrolyte accumulation in the storage tank to 7 hours. For a more complete extraction of noble metals, fresh electrolyte was again poured into the electrolyzer, and electrodeposition of noble metals was carried out without heating under conditions of pumping an inert gas pressure of 10 atm and its periodic discharge with electrolysis vapors. At the end of the process, the remaining electrolyte was drained and combined with condensate for reuse. This process took 4 hours, the total extraction for platinum was 97 wt. %.

Thus, the proposed method allows you to increase productivity while ensuring a high percentage of extraction of noble metals in comparison with the prototype.

List of literary sources

1. Patent 2198947 Russian Federation, IPC С22В 11/00, С22В 3/04, С22В 7/00. Method of extraction of noble metals / Antonov A.A., Morozov A.V., Kryshchenko K.I. - Application: 2000123379/02, 12.09.2000, publ .: 10.08.2002 Bul. No. 22.

2. Patent 254025 Russian Federation, IPC С22В 11/00, С25С 1/20, С22В 7/00. Method of electrochemical extraction of noble metals / Antonov A.A., Morozov A.V., Novikov A.A., Sapelkin V.S. - Application: 2014107078/02, 26.02.2014, publ .: 10.02.2015 Byull. No. 4.

Claims (1)

A method for the electrochemical extraction of noble metals from spent catalysts, including the treatment of the catalyst in an electrolyte of electrochlorination when direct and alternating currents are applied with preliminary activation of noble metals and their subsequent electrodeposition on the cathode under conditions of decreasing electrolyte volume, characterized in that the preliminary activation of noble metals in the catalyst is carried out in environment of gaseous electrolysis products with gradual filling of the catalyst backfill with an electrolyte based on hydrochloric acid, and after filling with electrolyte - in an inert gas at a pressure of 5-10 atm, while a decrease in the volume of electrolyte during the electrodeposition of noble metals is carried out and controlled by its recondensation into a separate storage a container by periodically releasing the pressure of gases into the condensation system until the end of the accumulation of electrolyte in the specified storage container, after which fresh electrolyte is added before starting volume, increase the inert gas pressure to the initial 5-10 atm and repeat the electrodeposition cycle with periodic pressure release.