RU2090633C1 - Method of processing electronics scrap containing precious metals - Google Patents

Abstract

FIELD: hydrometallurgy of nonferrous and precious metals. SUBSTANCE: electronics scrap is fused in presence of fusion agents to produce ingots. The latter are placed into nitric acid bath to serve as electrodes. Industrial-frequency alternate current with predetermined voltage and density is passed through electrolyte accompanied with fall of gold and tin-containing sludge from ingots onto bath bottom, whereas nonferrous metals, silver, and palladium are accumulated in solution. Sludge is calcined at 500-550 C to transfer tin compounds into inert state and then leached in aqua regia. EFFECT: enabled one-cycle scrap processing, reduced power consumption, and isolation of precious metals is increased by 1-4%.

Description

 The invention relates to the field of hydrometallurgy of precious and non-ferrous metals and can be used when moving secondary materials, in particular electronic scrap, to extract gold, silver, palladium, non-ferrous and small metals.

 A known method of processing raw materials containing noble metals, including melting raw materials to obtain an alloy, forming an anode from it, dissolving the alloy in acid with the application of direct electric current. A gold-containing solution and a slurry containing silver are obtained (Metallurgy of precious metals. Edited by L. V. Chugaev, M. Metallurgy, 1987, pp. 336-338). The disadvantage of this method is the duration of the process, the inability to process this method of multicomponent materials.

 A known method of processing precious metal alloys with hot nitric acid, in which silver, copper, platinum, palladium pass into solution, and gold remains as a residue (ibid., Pp. 338-339). The process proceeds violently, accompanied by emissions of nitrogen dioxide with the capture of electrolyte, therefore, special cleaning of the gas-vapor phase is required. In addition, the disadvantage of this method is the need for preliminary adjustment of the composition according to the ratio of gold and silver, as well as the removal of tin, antimony, arsenic, since these elements, in particular tin, are further distributed among the processed products and are difficult to separate.

 The closest in technological essence and the achieved result is a method of processing scrap of electronic devices, including sorting, melting under a flux layer to obtain an alloy containing noble metals, non-ferrous and small metals, in particular tin, melting of the alloy, electrochemical dissolution of copper to produce sludge, containing gold and silver, and electrolyte. Sludge and solution are further processed (Williams D. P. Drekc P. Recovery of ptecious metals from electronic scrap // Proc. 6th Int. Precious Metals Conf. Newport Beach, Calif June 1982. Toronto, Pergamon Press. 1983. P 555-565).

 The disadvantage of this method is the duration of the process, high energy consumption. Due to the multi-stage method, gold has been in the process for a long time and is not output into the marketable product, which significantly reduces the economic efficiency of the process and increases the loss of precious metals. Small metals, in particular tin, are spread between processed products. Palladium, if present, also passes into the sludge, and the separation of the palladium-gold pair is a separate task.

 The technical result that the applicant seeks to achieve in this invention is to intensify and simplify the process of processing electronic scrap, reduce energy consumption, the possibility of separate production of silver-palladium and gold-tin products, which greatly simplifies the further scheme of the allocation of individual metals, accelerating the separation of gold from process.

To this end, in a method including fusion of electronic scrap to obtain an alloy, casting ingots from an alloy, subsequent electrochemical dissolution of the alloys in acid with the application of current and obtaining a copper-containing electrolyte and sludge containing gold, and processing of the obtained products, electrochemical dissolution is carried out in nitric acid when applied alternating electric current of industrial frequency and the process is carried out at a nitric acid density of 1.1-1.15 g / cm ³ , a voltage of 5-10 V and a current density of 0.02-0.2 A / m ² to obtain ctrolite containing silver, palladium and non-ferrous metals, and scrap containing gold and tin, and the processing of sludge is carried out by calcining it at 500-550 ^o C to obtain a cake, followed by processing cake with aqua regia to obtain a solution of gold and a tin-containing residue.

 The essence of the method is as follows. Remelted scrap of electronic products with a complex composition is cast into ingots that serve as an electrode in the process of electrochemical dissolution. The combined action of nitric acid and alternating electric current creates a certain oxidation-reduction potential in the system, which makes it possible to efficiently transfer silver, palladium and non-ferrous metals (copper, zinc, lead, etc.) into the solution and separate gold and tin into the sludge. The result is products of this composition, the further processing of which can be carried out according to a simplified scheme. In this case, the dissolution process proceeds at lower current loads compared with acid leaching.

At the selected concentration characteristics, the dissolution proceeds quickly, but evenly, without overheating and emissions of the vapor-gas phase. When the acid density is less than 1.1 g / cm ^{3 the} process is slow even when AC is applied. The use of more concentrated acid (with a density of more than 1.5 g / cm ³ ) leads to the release of nitrogen oxides, deterioration of the sanitary situation in the workshop and an increase in the consumption of nitric acid.

The increase in current density of more than 0.2 A / cm ² and voltage of more than 10 V leads to overheating of the system, unjustified energy consumption. A decrease in the current density of less than 0.02 A / cm ² and the voltage of less than 5 V causes a slowdown of the transition of silver into solution due to the inhibition of the dissolution process due to the formation of a stable film of complex composition on the alloy surface.

The solution (electrolyte) is directed to the selective separation of silver, palladium, copper, and the sludge is calcined at 500-550 ^o C, which ensures the decomposition of tin acid to oxides, which are inert upon further leaching of cake with aqua regia and remain completely in the insoluble residue.

Example. 100 kg of scrap electronic products (dimensions, contacts, wire) are melted in the presence of flux at a temperature of 1250 ^o C to obtain a melt. The melt is poured into the molds and ingots are obtained. In total, 84 kg of ingots of the composition, 2.1 gold, 5.2 silver, 0.4 palladium, 12.3 tin, were obtained, the rest - copper, zinc, lead, nickel.

The ingots are loaded into the bath, an electrode is supplied to them. The other electrode is a titanium plate. Nitric acid with a density of 1.12 g / cm ^{3 is} poured into the bath and an alternating electric current with a frequency of 50 Hz, a voltage of 8 V, and a density of 0.08 A / cm ^{2 is} passed through the electrodes. After 10 minutes, the gradual dissolution of the ingots begins, the temperature of the solution rises to 50 ^o C.

 Sludge from ingots falls to the bottom of the bath, non-ferrous metals accumulate in the solution and do not deposit on the electrodes.

After 63 hours of dissolution, a 320 L solution was obtained containing 13 g / dm ³ silver with a degree of recovery of 98.5% and 1 g / dm ^{3 of} palladium with a recovery of 90%
The sludge containing gold and the main mass of tin (recovery, respectively, 99.6% and 91.2%) is separated from the solution, washed, dried and calcined at 530 ± 10 ^o C. Calcined sludge is leached in a mixture of nitric and hydrochloric acids (1 : 3). The degree of leaching of gold is 99%. Tin remains at 94.3% in the leachate.

99.5% pure gold is isolated from the filtrate by known methods.
Thus, the method allows to simplify the process of processing electronic scrap of a multicomponent composition containing noble metals due to the acceleration of the leaching stage, the effective separation of silver, palladium, gold and non-ferrous metals during processing. The proposed method makes it possible to carry out the entire process of scrap processing in a single cycle at one enterprise, while the consumption of nitric acid is reduced by 15-20%, and electricity consumption by 20-30%. The recovery of precious metals increases by 1-4%. The method is environmentally friendly by reducing the amount of nitrogen oxides entering the environment.

Claims (1)

A method of processing electronic scrap containing precious metals, including melting the starting material to obtain an alloy, electrochemical dissolution of the alloy in acid to obtain a solution and sludge containing gold, processing of the obtained products, characterized in that the electrochemical dissolution of the alloy is carried out in a solution of nitric acid with a density of 1 1 1.15 g / cm ^2, with alternating current of industrial frequency, voltage of 5 to 10 V, at a current density of 0.02 0.2 a / cm ² to obtain a solution containing silver, palladium minutes and nonferrous metals, and sludge containing gold and tin, wherein the sludge processing performed by his propalivaniya at 500 550 ^o C and calcining the product of leaching with aqua regia.