DE3801340C1 - - Google Patents

Abstract

An agent for the elution of thiourea-noble metal complexes from active charcoal based on an acidic aqueous solution containing thiourea and an organic solvent, which has a content of 0.1 to 50 g./litre of thiourea and contains at least one organic solvent which is partly soluble in water. Noble metals e.g. gold and silver are by precipitation there of from the aqueous organic phase by the addition of base metals in the presence of a small amount of sulphite and optional reactivation of the active charcoal with an aqueous solution of a sulphite.

Description

The present invention relates to means and methods for the extraction of precious metals from activated carbon adsorbed thiourea complexes.

A special form of application for the extraction of This forms activated carbon adsorbed precious metal complexes So-called carbon-in-pulp process, the large-scale Has gained importance. This process uses grains Activated carbon of about 0.5 mm grain diameter or more, directly the finely ground suspension of ore or others Raw materials such as roasting residues and "lye" added after completion of the precious metal dissolution. The elaborate separation of the leached solid from the precious metal Liquid, because the activated carbon contains precious metals simple way through large-meshed sieves of the worthless Leaching residues can be separated.

In the further process, the precious metals from Activated carbon can be replaced. When using cyanides the precious metals are as leaching agents adsorbed cyanide complexes on the activated carbon. To The activated carbon must desorb the precious metal preferably under pressure at temperatures above 100 ° C alkaline cyanide solution are treated. This The process is technically complex since it is a particular one Working with the highly toxic cyanides is required.

The use of the compared to the cyanides much less harmful thiourea than leach reagent precious metals have also been known for a long time. Compared to cyanides, thiourea also has a higher dissolving speed for precious metals and its precious metal complexes are faster and in higher Dimensions of activated carbon adsorbed.  

There are therefore already processes that use thiourea To elute precious metal complexes from the activated carbon by the complex process known from cyanide leaching Applies printing technology. (see Gold recovery from the thiourea leach solution, W. T. Yen and D. M. Wyslouszil, Lakefield Research, Lakefield, Ontario. Presented at Gold and Silver Recovery Forum 85, October 14-15, 1985, Santa Fe, New Mexico). Another suggestion is with strongly acidic (50 g / l sulfuric acid), highly concentrated Thiourea solutions (100 g / l thiourea) up to 30 vol .-% acetone, worked (see Gold recovery from the thiourea leach solution, W. T. Yen and D. M. Wyslouszil, Lakefield Reasearch, Lakefield, Ontario. Presented at Gold and Silver Recovery Forum 85, October 14-15, 1985, Santa Fe, New Mexico). Since the Precious metals do not come from these strongly acidic solutions can be won is a previous one Neutralization with a considerable effort Neutralization chemicals and another filtration necessary.

Also the use of alcohol or glycol containing Solutions such as those used for the elution of cyanide adsorbed precious metals was suggested Thiourea-noble metal complexes not the goal (s. Engineering & Mining Journal, June 1987, pp. 48, 49).

According to DE-OS 34 01 961 meet concentrated Thiourea solutions above 50 ° C do the job, however the process is slow and relatively large Volumes of elution solution.

It was therefore the task of a technically simple and economically working process for the elution of Activated carbon adsorbed thiourea precious metal complexes to create and the precious metals from it in metallic To gain shape.  

This task was solved by the in the Defined means and methods.

Surprisingly, this means and the process under relatively mild conditions and in high selectivity, the precious metals silver and gold to extract the finely ground ore slurries. in the It also compares to older procedures Solutions of relatively low concentrations worked, so that loss of chemicals and organic solvents stay low.

According to the removal of the noble metal from the activated carbon with an agent that consists of a acidic, aqueous solution containing <50 g / l Thiourea and a partially water soluble organic solvent. As an organic solvent one uses in particular one or more Alcohols, substituted alcohols, esters, ethers (also cyclic ethers such as dioxane or tetrahydrofuran), ketones, Nitriles, acid amides (see Table 6). Preferably used one such means consisting of a to a pH from 1 to 3 adjusted, aqueous solution with contents from 1 to 50 g / l thiourea and 0.1 to 20 vol% an alcohol with 3 to 5 carbon atoms, one Glycol or glycol ether. Particularly preferably used an agent consisting of an aqueous solution, the has a pH of 2 adjusted by acid and levels from 1 to 50 g / l thiourea and 0.1 contains up to 10 vol .-% n-butanol (see Table 2).

The combination of thiourea and organic Solvent leads to a surprising synergistic Effect in the elution of the precious metal from the Activated carbon, since under the selected conditions neither acidified thiourea solution another acidified e.g. B. butanol-containing solution alone a satisfactory Allow precious metal to be brought out. First the combination in  Form of an acidified butanol-containing Thiourea solution leads to an unexpected result high output of precious metal (see Table 1). The inventive method of elution Activated carbon adsorbed thiourea precious metal complexes is introduced with the agent according to the invention Room temperature or elevated temperature up to 95 ° C by, 1 to 100 ml of an elution solution per 0.1 g of activated carbon is used, the concentration of which Thiourea is 0.1 to 50 g / l, the content of organic solvent is 0.1 to 20 vol .-% and their pH through acid to values between 1 and 5 was discontinued. Is the elution of the thiourea Precious metal complexes ended, so you drop the precious metals from the aqueous / organic phase after removal of the Activated carbon by adding base metals in the presence a small amount of sulfite and regenerates optionally the activated carbon with an aqueous Sulfite solution.

The elution of the noble metal Thiourea complexes at a temperature of 20 to 80 ° C through (see Table 3), selects a concentration of 1 up to 10 g / l thiourea in the elution solution the organic solvent content to 1 to 20% by volume and brings the pH of the solution by adding preferably sulfuric acid to 1.5 to 3. Especially is preferably used as the organic solvent Propanols, butanols, amyl alcohols or glycol ethers. These Solvents can be used alone or, if it turns out to be should prove appropriate, as a mixture, each in Combination with thiourea can be used. In Table 6 contains a number of solvents those in combination with an aqueous, acidic Thiourea solution (10 g / l thiourea; pH 2) clear synergistic effect when detaching the silver and / or gold complexes from the activated carbon occurs.  

A number of commercially available carbons can be used Products are used. These just have to with regard to their strength in aqueous solutions meet certain requirements to make them practical completely filtered off from the finely dispersed turbidity can be.

The method according to the present invention draws is further characterized by the fact that the elution method is very is selective for noble metals adsorbed on activated carbon. Simultaneously adsorbed other metals such as especially copper, lead or other elements, such as. B. Sulfur, arsenic, are not from the eluent or only insignificantly detached from coal. This allows the precious metals to be made in high purity the eluate, e.g. B. by cementing with base metals in finely powdered form such as iron, aluminum, Magnesium, zinc, can be obtained. It is preferred to use the cheap iron. You put something in the precipitation solution Sulfite in the form of sulfur dioxide or sodium sulfite; sodium pyrosulfite is preferably used in an amount from about 0.1 to 1 g / l. The addition of sulfite increases on the one hand, the spreading of the precious metal or lowers it on the other hand, the need for base metal for cementation (see Table 4). The cementation is preferably carried out by adding 1 to 10 mass units of base metal per unit of mass of complex bound precious metal a content of 0.1 to 1 g / l sulfite in the Reaction solution at a temperature of 40 to 70 ° C; they is largely within 0.15 to 4 hours Completely.  

Because in the course of repeated loading and unloading processes coal can become increasingly inactive, it is expedient to regenerate them continuously, d. that is, from to get rid of adsorbed contaminants to maintain the original loading capacity. As for this suitable procedure has been treatment with Sulfites such as B. sodium sulfite, sodium pyrosulfite, Sodium hydrogen sulfite at elevated temperature. The contaminated activated carbon is preferably treated a temperature of 50 to 95 ° C for 0.15 to 4 hours with a 1 to 100 g / l containing sodium sulfite aqueous solution. Then the activated carbon has again their original adsorption capacity for precious metal Thiourea complexes (see Table 5).

The following examples are intended to illustrate the invention explain.  

Example 1 Elution of silver from activated carbon with acidified thiourea solution, acidified butanol-containing solution and an acidified butanol-containing thiourea solution

For the proof of the synergistic effect when detaching The silver of activated carbon became an activated carbon of the Calgon GRC 22 type. This contained after a leaching process with thiourea 40% moisture and 3% silver in the dry matter.

50 ml each of solutions 1 to 3 (see table 1) with 0.1 g of activated carbon Calgon GRC 22 in a water bath at 70 ° C Shaken for 3 hours and then eluted Silver analyzed.

As can be seen from Table 1, an acidified butanol-containing thiourea solution practically the whole Silver detached from coal while using butanol or Solution containing thiourea only unsatisfactory Shares of silver can be obtained.  

Table I

Example 2 Influence of the concentration of thiourea and the Content of butanol in the elution solution to that Application on silver

The test conditions were analogous to those in Example 1 described. It became activated carbon of the type Calgon GRC 22 used, which was loaded with 0.52 wt .-% silver. Elution was carried out by shaking in a water bath for 3 hours at 70 ° C with increasing amounts of butanol and increasing Amounts of thiourea in the eluent.

The result is shown in a table.  

Table 2

Example 3 Influence of temperature on the application of silver

The test conditions corresponded to those of the Example 1. An activated carbon loaded with 2.8% silver Degussa Degusorb C 25 (as dry substance) was included a solution containing 50 ml / l butanol, 10 g / l thiourea contained and was acidified to pH 2 with sulfuric acid, For 3 hours at different temperatures Shake eluted. The result is shown in Table 3.

Table 3

Example 4 Cementation of silver from the elution solution

An elution solution from is used as the starting solution pH 2 and a content of 5 vol .-% butanol, 10 g / l Thiourea and 99 mg / l silver.

The cementation is carried out by adding 250 mg / l Iron powder and increasing additions of sodium pyrosulfite at 60 ° C for 2 hours.

Table 4

Example 5 Regeneration of the activated carbon by treatment with Sodium sulfite solutions

The activated carbon PICA G 210 A2 8-16 was used for the adsorption of silver from a leaching process with Thiourea from zinc roast had served.

After eluting the silver with acid Butanol / thiourea contained the sieved and washed coal 25% by weight moisture.

25 g of this coal were mixed in 1 l of water increasing amounts of sodium sulfite for 3 hours at 70 ° C treated and then again for the Silver adsorption used.

Table 5 shows the result with a regenerated activated carbon was obtained with increasing amounts of sodium sulfite treated and Extraction of the silver from a 350 mg / l silver containing elution solution was used.

Table 5

Example 6

Table 6 provides an overview of those used to elute Silver and / or gold complexes of thiourea from Activated carbon examined organic solvents.

Test conditions

Were eluted in each case

• a) 1 g of activated carbon with 40 wt .-% moisture and 0.52% by weight of silver in the dry matter;
• b) 0.5 g activated carbon with 40 wt .-% moisture and 2.55% by weight of gold in the dry matter

with 40 ml of an aqueous solution containing 10 g / l Thiourea, 0.66 g / l sulfuric acid (= pH 2) and 2 ml each of an organic named in the table Solvent contained (in experiments 7 to 10 were only 1 ml of the organic solvent added).

The elution time was 3 hours at 70 ° C in Water shaking bath.

The desorption of silver and gold complexes Thiourea behaves largely analogously, so that in In the case of gold elution, not all solvents were examined were.  

Table 6

Claims (7)

1. Acid, thiourea and an organic solvent containing solutions for the elution of thiourea-noble metal complexes adsorbed on activated carbon, characterized by a pH of 1 to 5, a content of thiourea of 0.1 to 50 g / l and 0.1 up to 20 vol .-% of an alcohol, an ether, an ester or a ketone. 2. Solution according to claim 1, characterized by 1 to 50 g / l thiourea, 0.1 to 10 vol .-% n-butanol and a pH of 2. 3. A process for the extraction of precious metals using a solution according to claims 1 and 2, characterized by the following reaction steps

• a) Elution of the thiourea-noble metal complexes from the activated carbon at room or elevated temperature with 1 to 100 ml of a solution per 0.1 gram of loaded activated carbon.
• b) Precipitation of the noble metals from the aqueous / organic phase by adding base metals in the presence of a small amount of sulfite and optionally reactivating the activated carbon with an aqueous solution of a sulfite.

4. The method according to claim 3, characterized in that the elution of the precious metal thiourea complexes at a temperature of 20 to 80 ° C, the Concentration of thiourea in the solution to 1 to 10 g / l, that of the organic solvent to 1 up to 20 vol .-% and the pH of the solution 1.5 to 3 brings. 5. The method according to claims 3 and 4, characterized characterized in that one for the precipitation of the precious metals 1 to 10 per unit of mass of complex metal Mass units of iron in powdered form as well 0.1 to 1 g / l of reaction solution sulfite is added. 6. The method according to claim 5, characterized in that the sulfite is added in the form of sodium sulfite. 7. The method according to claims 1 to 6, characterized characterized in that the activated carbon with a Solution containing 1 to 100 g / l sulfite in one Temperature from 50 to 95 ° C for 0.15 to 4 hours reactivated.