DE1808471C3 - Process for the recovery of gold from galvanic washing water - Google Patents

Description

20th

The invention relates to a method for the recovery of gold from acidic and / or neutral Discharge of electroplating baths, possibly in combination with the discharge of cyanidic electroplating baths.

Since the discharge losses in the galvanic Gold deposition is of particular concern because of the high metal cost, a need exists for economic recovery of the gold from the washing solutions.

In an effort to reclaim gold, it has been a common practice in the industry to galvanize the workpiece to wash in a standing rinse. The gold concentration in the rinsing bath increases progressively, so that depending on de. Operating load according to a known method the flushing solution on Bottled once a month at the end of each individual electroplating line and used for recovery of the Gold is sent to the refinery.

From the rinse water is according to a well-known Process the gold is deposited electrolytically on the anode after adding potassium and sodium cyanide.

According to another method, the rinsing solution is passed through an ion exchange cartridge, which is then inserted into the refinery is burned to recover the gold. These are two recovery methods cumbersome and expensive and involve a considerable amount of work. Although it was found that Gold can be electrodeposited when the gold concentration is around 500 to 600 milligrams each Liters, gold recovery by electrolysis has not been used because the gold only available as a powder The possibility of filtering out this powder was investigated; was doing it However, it was found that the quantities in question were due to the filter surfaces to be provided and the need to burn the filter paper is uneconomical, the small amount of gold dust to win back.

The electronic gold recovery from a neutral or acidic gold solution is even more difficult and the efficiency reaches a gold concentration of about 200 milligrams per liter or less is zero. It has also been found that acidic <" Gold solutions counteract such a recovery process in particular, since the gold is in there trivalent form is present.

A number of standing rinse baths have been analyzed and found that the gold concentration is about 1 g per Liters. The normal discharge was found to be 2 to 4 g of gold per hour. Now it is also common to carry three, to keep four or more parallel electroplating lines in operation, especially in the field of Electronics.

The invention is therefore based on the object of providing a method for recovering gold from cyanidic, To propose neutral or acidic galvanic washing water that is economical and without risk can be carried out for people operating such a system.

The invention is also based on the object of providing a process for the recovery of gold from cyanidic, neutral and / or acidic discharges from such electroplating baths by means of washing water to propose the economic and ohive danger for the persons operating such a system can be carried out. This object is achieved in that the discharges from the rinsing baths in alkaline cyanide solutions are added, from which after adding alkali hydroxide and / or Alkali cyanide for the production and maintenance of a pH value of 10 to 12 and a minimum content of 3.75 g / l cyanide, the gold is electrolytically deposited in a known manner, whereupon the Solution is returned to the rinsing baths in the circuit.

The current density is expediently increased with a low gold concentration and with a higher gold concentration This means that even recovery is achieved even if the gold concentration fluctuates achieved.

Sodium and potassium cyanides and hydroxides are preferably added.

The method according to the invention makes it possible to obtain gold ions with a low valence treat. This is important for recovering gold from production lines that have various types of Use electroplating solutions.

The electrolytically treated washing solution is pumped around for reuse, so that even minimal Gold content (below a concentration of around 5 to 6 mg per liter) is not lost.

With optimal adaptation, the claimed method works with an efficiency of about 20%, the average current density being about 034 A / dm ² and a deposition up to a gold concentration of 5 to 6 mg / liter.

About 3.75 g per liter of cyanide are sufficient to start the recovery process. in the further operation, the cyanide level increases automatically. It is preferred to initially incorporate Cyanide in an amount of about 15 g per liter, the upper limit only for economic reasons is determined.

Since with a current efficiency of about 100% 5.15 A per hour were required, enough for one Cathode efficiency of 20% about 25 A per hour from 38 g of gold per hour in a plant recovering which works with two gold electroplating lines. In this example, one was acidic Gold electroplating line, which contained about 7.5 g per liter of gold and the other a cyanide electroplating line, which contained about 2.5 g per liter of gold in its plating solution. If there is a discharge on every electroplating line Assuming 3.79 liters per hour, this would be

28.4 g per hour of the acidic gold solution and about 9.5 g per hour of the cyanide gold solution. By setting up an electrolytic recovery system using a cathode area of 4.65 to 5.57 m ² , it is possible to recover the gold effluent in the same rate that it was introduced into the electrolyte and an electrolytic recovery solution with a residual gold content of about 5 to get 6 mg per liter. Any loss of gold from such a solution is negligible, since 7.57 liters of this solution contain only about 100 mg of gold on average, so that a gain of 37.9 g per hour is offset by a loss of only 100 mg.

As the cathode material for the recovery cell, stainless steel sheet is preferred because gold precipitates let it peel off a few millimeters thick.

The invention is explained in more detail below with reference to an exemplary embodiment.

In the figure, a system operating according to the method according to the invention is shown

A, B and C are individual GoID-GaIvanisieistraßen be galvanized in which workpieces 9, 9 'and 9 ". The gold plated workpiece at the end of the road is indicated by position 9a. In the plating line A z. B. a cyanide electrolyte in a Bath tank 10. In electroplating line B, a neutral electrolyte solution is used in a bath tank 10 ', and in electroplating line C an acidic electrolyte solution is used in a bath tank 10 ". As indicated by the dashed lines and arrows, the workpieces from each electroplating line pass through baths 10, 10 'and 10 "and then through the standing rinsing baths 11, 11' and 11", in which the gold carried out is washed off the workpieces for recovery purposes and is collected.

Each of the standing rinsing baths 11, 11 'and 11 "is via regulating valves 34,34' and 34" through pipes 35,35 'and 35 "washing solution supplied. The washing solution is supplied from the overflow / troughs 12, 12 'and 12" through connecting lines 13, 13 'and 13 ", which are connected to a main return line 14. The line 14 leads the washing solution from the standing rinsing bath of each electroplating line to a collecting tank 15 on the Treatment area ßzu. The collecting container 15 serves to remove the solution for electrolytic removal to prepare its gold content. A strongly alkaline agent, such as NaOH, will add to the solution Container? 15 from a container 16 through a Leituni; 17 and a regulating valve 18 and an inlet pipe 17λ fed. The actuation of the valve 18 is controlled by an electromagnet 19 a, which is via a pH control device 19 is electrically connected to an electrode assembly 20: In this way, the Solution in the right part of the container 15, the necessary amount of alkali automatically supplied to it with the to provide the necessary pH value.

The collecting container 15 is provided with a partition 15a which divides the container into two zones and provides an overflow edge for the treated liquid wedge so that it goes from the right zone to the left Zone can flow. An agitator with a motor 22, a propeller shaft 23 and a propeller 24 is used to vigorously stir the solution in the right zone.

An electrode assembly 21 is immersed in the solution of the left zone. She ^ sits a short electrode 21a and a long electrode 21b and is electrically connected to the motor of a pump 26 (see dashed line in the figure). When the liquid level reaches the end of the electrode 21a, the pump 26 is actuated to pump out treated solution. On the other hand, if for any reason the liquid level falls below the end of electrode 216, the motor of pump 26 will shut down. A conventional control device is used for this, or the electric motor of the pump 26 is operated manually. The electrode assembly 21 and the pump 26 can be omitted if, for. B. the collecting container 15 is higher with respect to the container 30 and the liquid can flow by gravity.

The solution containing gold, after it has been treated in the container 15 to produce an alkaline cyanide solution, is transferred by means of the pump 26 from the collecting container 15 via the line 27 to a recovery container 30 at the station E. After the gold in the container 30 has been electrolytically removed, the solution is pumped by a motor-operated pump 32 via an outlet line 31 and a supply line 33 which carries the solution through the supply tubes 35, 35 'and 35 "into the containers 11, 11 'and U "brings back.

The plant is operated continuously.

1 sheet of drawings

Claims (1)

Claim: Process for the recovery of gold from acidic and / or neutral discharge of electroplating baths, possibly in combination with the discharge of cyanide electroplating baths, characterized in that the discharges from rinsing baths in alkaline cyanide solutions are included, from which after adding alkali metal hydroxide and / or alkali metal cyanide for production and maintaining a pH value of 10 to 12 and a minimum content of 3.75 g / l cyanide the gold is deposited electrolytically in a known manner, whereupon the solution to the Rinsing baths is returned in the circuit.