EP0097842B1 - Process for recovering noble metals from solutions - Google Patents

Description

The invention relates to a process for the extraction of precious metals from dilute aqueous or non-aqueous solutions which contain salts of base metals and / or other low-volatility inorganic or organic compounds. The precious metals that can be extracted include silver, gold and the platinum metals.

In the chemical technology of precious metals, aqueous and non-aqueous solutions occur in many areas, the precious metal content of which has to be obtained with the greatest possible separation of additional fiber present, such as base metal salts, neutral salts or low-volatile organic compounds.

In some cases, such as in some processes of hydrometallurgical precious metal extraction from ores, their secondary products or from recycling materials, the processing of such solutions is the focus of the precious metal extraction processes. Furthermore, the wet chemical separation of the noble metals (Pt, Pd, Rh, lr, Ru, Os, Au, Ag) and their separation from base metals as well as the noble metal cleaning lead to relatively strongly diluted waste solutions, such as mother liquors from precipitations and crystallizations or washing solutions. Your precious metal shares have to be recovered because of their high value. Finally, numerous chemical processes that can be carried out with the help of precious metals, e.g. be carried out in the form of catalysts, precious metal-containing waste solutions of various compositions. Such processes are almost always only profitable if they permit extensive recycling of the precious metal used.

Only in exceptional cases, especially if the solutions to be worked up consist only of noble metal compounds and a solvent that does not boil too high, simple or vacuum distillation leads to the isolation and sufficient concentration of the noble metals. If there are additional admixtures, such as base metal salts, neutral salts or organic, high-boiling compounds, the introduction of the waste solutions containing precious metals into the metallurgical process of a noble metal smelter can be a useful way of processing. All precious metals are completely absorbed by the molten lead, while all other components or their by-products pass into the exhaust gas, into the slag or into the sulfidic phase. The dissolved precious metals can be precipitated from aqueous or water-miscible solutions by reduction to the elemental state and can be sent to the further processing known per se. This reduction and thus the extraction of the noble metal concentrates can be carried out by means of electric current, by means of base metals such as zinc, iron or aluminum, or by means of reducing compounds such as hydrazine or sodium boranate. However, this reduction method has shortcomings, such as the often incomplete precipitation, the introduction of additional metals which pollute wastewater and the reduction of the copper, which is usually present in considerable quantities, the precipitation of base metal hydroxides, and the formation of inflammable hydrogen gas. In addition, the reduction reactions cannot usually be carried out in organic solutions. For organic solutions, especially for liquid waste from homogeneous catalytic processes in oxo synthesis, combustion and pyrolysis processes have been proposed for converting the partly highly diluted precious metals contained therein into concentrates.

These processes have the disadvantage that air pollution easily occurs, the phosphorus usually contained in these solutions remains in the ashes and can lead to difficulties when working up the concentrates.

Especially for the recovery of rhodium from residues of oxo synthesis, a process has become known from DE-AS 2911193 in which the residues are reacted with sulfur or a sulfur-releasing compound and the precipitate that forms is worked up. The disadvantage of this process is that it cannot be used in aqueous solutions, the sulfur usually forms additional reaction products which interfere with the work-up and is often absorbed by the organic solvents in such large quantities that it hinders their further processing.

It was therefore an object of the present invention to find a process for the extraction of noble metals from dilute aqueous and non-aqueous solutions which contain salts of base metals and / or other low-volatile inorganic or organic compounds, the process being easy to carry out, generally applicable and with a high noble metal yield should work without encountering difficulties when working up the concentrates and the other reaction products.

This object was achieved according to the invention in that the noble metals are precipitated by adding elemental tellurium or reducible tellurium compounds to the solution at temperatures of 100 to 250 ° C. and the precipitate is worked up in a known manner. The addition of the elemental tellurium or the reducible tellurium compounds is advantageously carried out at temperatures from 120 to 200 ° C., in the case of solutions with low boiling points of the organic solvents and in aqueous solutions preferably in closed pressure containers. However, it is also possible to use the low-boiling solvent e.g. to be replaced on the distillation route by a higher-boiling one.

Surprisingly, elemental tellurium or reducible tellurium compounds in Ge Contrary to the known methods and in contrast to the known sulfur and selenium are precipitants for precious metals from dilute solutions, which are highly effective in terms of precious metal yields, by the general applicability in both aqueous and organic solutions, and by the excellent selectivity between Precious metals and base elements, which include copper, stand out.

The resulting precipitates, which contain the noble metals elementally or in the form of tellurides, can be known in a known manner, e.g. can be worked up by roasting processes or by wet chemistry. The recovered tellurium or the tellurium-containing fraction can always be added to the precipitation process again, so that the tellurium consumption is very low, apart from the low drag-out losses. The tellurium thus represents a regenerable cementing agent. Tellurium has the further advantage that it is practically not absorbed by the organic waste solutions, for example oxo synthesis, so that the organic solvents freed from noble metal can possibly be burned without hesitation.

Selenium can also be used to recover precious metals from organic solutions, but it has practically the same disadvantages as the known sulfur.

The process according to the invention can be used both for aqueous noble metal solutions which may also contain further cations and anions, such as halides, cyanides, sulfates, thiosulfates or phosphates, and for organic solvents, for example alcohols, aldehydes, chlorinated hydrocarbons or organophosphorus compounds can contain.

The amount of tellurium added depends primarily on the precious metal content of the solutions. It can be determined by simple experiments.

• 1. In einem 250 ml Becherglas werden 100 ml Sumpf aus der Oxo-Synthese, der 644 ppm Rhodium enthält, mit 0,5 g Tellur versetzt und unter Rühren 1 Stunde bei 150°C behandelt. Der Niederschlag wird abfiltriert und konventionell auf Rhodium aufgearbeitet.

The following examples are intended to explain the process according to the invention in more detail:

• 1. In a 250 ml beaker, 100 ml of sump from the oxo synthesis containing 644 ppm of rhodium are mixed with 0.5 g of tellurium and treated with stirring at 150 ° C. for 1 hour. The precipitate is filtered off and worked up conventionally on rhodium.

The filtrate contains only 1 ppm rhodium. The yield of rhodium is more than 99% by weight.

The tellurium content in the filtrate is 35 ppm.

2. In a 10 beaker, 7.51 sump from the oxo synthesis, which contains 165 ppm rhodium, are mixed with 22.5 g of Te and treated with stirring at 150 ° C. for 3 hours. The precipitate is filtered off and worked up conventionally on rhodium.

The filtrate still contains 2 ppm rhodium. The yield of rhodium is more than 98% by weight.

3. In an 800 reaction vessel, 700 sump from the oxo synthesis containing 160 ppm of rhodium are mixed with 2.1 kg of tellurium and treated at 150 ° C. with stirring. The precipitate is filtered off and worked up conventionally on rhodium.

The filtrate still contains 2 ppm rhodium. The yield of rhodium is thus 98% by weight.

4. In a 250 ml beaker, 100 ml of sump from the oxo synthesis, which contains 495 ppm of rhodium, are mixed with 0.5 g of tellurium and treated with stirring at 200 ° C. for 1 hour. The precipitate is filtered off and worked up conventionally on rhodium.

The filtrate still contains 3 ppm rhodium. The yield of rhodium is more than 99% by weight.

5. 700 ml of a hydrochloric acid, ammonium chloride-containing waste solution from the platinum separation are treated in a pressure vessel after adding 25 g of tellurium for 3 hours with stirring at 150 ° C. The metal contents (mg / 1) before and after the treatment are shown in the following table:

6. 100 ml of a hydrochloric acid waste solution from the platinum separation containing ammonium chloride are mixed with 100 ml of glycol. The aqueous phase is evaporated while heating to 150 ° C. After adding 5 g of tellurium, the mixture is left to react at 150 ° C. for 1 hour.

The following table shows the metal contents (mg / I) before and after the treatment:

7. 700 ml of a hydrochloric acid, ammonium chloride-containing waste solution from the platinum separation are blunted with sodium hydroxide solution and then treated in a pressure vessel after adding 25 g of tellurium for 3 hours with stirring at 150 ° C.

The following table shows the metal contents (mg / I) before and after the treatment:

8. 700 ml of a hydrochloric acid ammonium chloride-containing waste solution from the platinum separation are saturated with sulfur oxide and treated in a pressure reactor after adding 10 g of tellurium for 3 hours at 150 ° C. with stirring.

The metal contents (mg / I) before and after the treatment were:

9. 700 ml of a hydrochloric acid, NH ₄ CL-containing waste solution from the platinum separation are treated in a pressure vessel after adding 40 g of tellurium for 3 hours at 200 ° C. The metal contents (mg / I) before and after the treatment were:

10. 700 ml of a fixer waste solution containing silver with 4000 mg Ag / I are mixed with 5 g tellurium in a pressure vessel and treated with stirring at 150 ° C. for 3 hours.

The silver content in the filtrate is 1 mg / I.

Claims (3)

1. A process for the recovery of noble metals from dilute aqueous or non-aqueous solutions, containing salts of non-noble metals and/or other difficultly volatile inorganic or organic compounds characterised in that the noble metals are precipitated by addition of elementary tellurium or reducible tellurium compounds to the solution at temperatures of from 100 to 250°C and the precipitate is worked up in known manner.

2. A process for the recovery of noble metals according to claim 1, characterised in that the tellurium or the tellurium compounds are added at temperatures of from 120 to 200°C.

3. A process for the recovery of noble metals according to claims 1 and 2, characterised in that precipitation is carried out in the presence of low- boiling solvents in a closed pressure vessel.