Method for Extracting Gold and/or Silver and/or at Least One Platinum Metal

Abstract

A process for the winning of at least one of gold, silver, and at least one platinum metal includes introducing at least one starting material containing at least one of gold, silver, and at least one platinum metal into an aqueous solution containing at least one nitrile, and producing hydroxyl radicals in the aqueous solution.

Claims

1. A process for the winning of at least one of gold, silver, and at least one platinum metal, comprising: introducing at least one starting material containing at least one of gold, silver, and at least one platinum metal into an aqueous solution containing at least one nitrile; and producing hydroxyl radicals in the aqueous solution.

2. The process as claimed in claim 1, wherein producing the hydroxyl radicals comprises: introducing ozone into the solution to produce the hydroxyl radicals.

3. The process as claimed in claim 2, wherein the aqueous solution contains from 0.1 mol/l to 1.0 mol/l of at least one alkali metal hydroxide.

4. The process as claimed in claim 2, wherein the ozone is introduced into the solution through a porous diffuser below the at least one starting material.

5. The process as claimed in claim 2, further comprising: flowing the aqueous solution (20) flows and the ozone in the same direction over the starting material.

6. The process as claimed in claim 1, wherein producing the hydroxyl radicals comprises: producing the hydroxyl radicals by a Fenton reaction in the aqueous solution.

7. The process as claimed in claim 6, wherein the aqueous solution contains formic acid.

8. The process as claimed in claim 1, wherein the aqueous solution contains at least 0.1 mol/l of the at least one nitrile.

9. The process as claimed in claim 1, wherein the aqueous solution contains at least one substance selected from the group consisting of alcohols, surfactants and activated carbon.

10. The process as claimed in claim 1, wherein the aqueous solution is irradiated with UV light.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Working examples of the invention are depicted in the drawings and are explained in more detail in the following description.

[0014] FIG. 1 schematically shows a reactor in which a process as per a working example of the invention proceeds.

[0015] FIG. 2 schematically shows another reactor in which a process as per another working example of the invention proceeds.

WORKINGS EXAMPLES OF THE INVENTION

[0016] FIG. 1 shows how, in a working example of the invention, gold can be dissolved from a nickel substrate in a starting material 10, which in the present case is a printed circuit board. For this purpose, the starting material 10 is fastened in a frame 11. This is covered by an aqueous solution 20 which is stocked in a reactor 21. Fresh solution is continuously supplied through an inlet opening 22 which is arranged below the starting material 10 on the wall of the reactor 21, while solution enriched with cyano complexes of gold is discharged through an outlet opening 23 arranged above the starting material 10 in the wall of the reactor 21. The aqueous solution 20 contains 0.5 mol/l of acetonitrile and 0.5 mol/l of sodium hydroxide in the present working example. It additionally contains methanol, surfactants and activated carbons. Ozone 30 is introduced into the reactor 21 through a porous diffuser 31 which is arranged in the reactor 21 below the starting material 10 and below the inlet opening 22. It mixes with the fresh solution 20 which is introduced through the inlet opening 22 into the reactor 21 and flows around the starting material 10. The reactor 21 consists of a transparent material and is irradiated from the outside with light having a wavelength of less than 310 nm by means of a UV lamp 40. The ozone reacts photocatalytically with water molecules to form oxygen and hydroxyl radicals according to formula 1:

##STR00001##

[0017] A mixture 32 of unreacted ozone and the oxygen formed leaves the reactor 21 through a gas outlet 24 on its upper side.

[0018] The hydroxyl radicals undergo essentially two reactions in the solution 20:

[0019] According to formula 2, hydroxyl radicals react with the acetonitrile to form methanol and cyano radicals. These oxidize metallic gold to gold(I) cyanide:

##STR00002##

[0020] Furthermore, the hydroxyl radicals can oxidize gold at the metal surface itself to form gold(I) hydroxide according to formula 3. This is highly reactive and reacts with the acetonitrile to form methanol and gold(I) cyanide:

##STR00003##

[0021] The gold(I) cyanide goes into solution and leaves the reactor through the outlet opening 23. The gold can subsequently be precipitated from the cyanide leachate solution by known methods and the solution can subsequently be reintroduced into the reactor 21 through the inlet opening 22. In this way, from 0.5 to 2 milligrams of gold per square centimeter of surface of the starting material 10 and per hour can be obtained in the present working example. As soon as all the gold has been removed, no further metal goes into solution since nickel forms an inert protective layer composed of nickel hydroxide under alkaline conditions.

[0022] In a second working example of the process, a reactor 21 as depicted in FIG. 2 is used. This differs from the reactor of FIG. 1 in that the porous diffuser 31 for the introduction of ozone 30 and the gas outlet opening are omitted. Instead, an electric energy source 40 which is connected to two electrodes 51, 52 projecting into the reactor 21 below the starting material 10 is provided. In this working example, the aqueous solution additionally contains iron(II) sulfate and is continuously enriched with hydrogen peroxide by formation at a cathode before introduction through the inlet opening 22 through a conduit which is not shown. It contains 0.5 mol/l of formic acid instead of 0.5 mol/l of sodium hydroxide. As a result of application of an electric potential between the electrodes 51, 52, an electro-Fenton reaction according to formula 4 proceeds in the solution 20 within the reactor 21:

Fe.sup.2++H.sub.2O.sub.2.fwdarw.Fe.sup.3++OH.sup.−+OH.sup.+  (Formula 4)

[0023] The irradiation by means of the UV lamp 40 occurs at a wavelength of less than 580 nm. As a result, a photo-Fenton reaction according to formula 5 also proceeds in the solution 20:

##STR00004##

[0024] The photo-Fenton reaction brings about both regeneration of the iron(II) cations which have been oxidized in the electro-Fenton reaction by reduction and also neutralization of the hydroxyl anions produced there so that the pH of the solution 20 does not change. The hydroxyl radicals produced in the two Fenton reactions then react further as in the first working example of the process according to the formulae 2 and 3 and bring gold into solution in the form of gold(I) cyanide. The taking of the solution 20 enriched with gold(I) cyanide from the reactor 21 and the precipitation of metallic gold are effected in the same way as in the first working example.