Method for extracting osmium and ruthenium from noble metal concentrates

A method for extracting osmium and ruthenium from noble metal concentrates, by:a) treatment of a noble metal concentrate containing osmium and ruthenium with nitric acid at a maximum temperature of about T=+30&deg; C.,b) heating of the resultant suspension/solution to a minimum temperature of about T=+85&deg; C.;c) capturing the resultant osmium tetroxide in an absorption solution;d) treatment of the suspension/solution having a temperature of about T=+20&deg; C. to 30&deg; C. with hydroxide at a maximum reaction temperature of about T=+65&deg; C.; ande) treatment of the alkaline suspension/solution from step d) with a substance for the oxidizing leaching of the ruthenium.

The invention relates to a method for extracting osmium and ruthenium from noble metal concentrates.

In Chem. Abstr. 92 (1980) Ref. No. 157222 W, a method is disclosed for the extraction of osmium and ruthenium from platinum alloys containing these elements, in which the alloy is treated with nitric acid and the resultant solution is heated such that osmium tetroxide gasses out.

The process for extracting ruthenium and osmium from ore concentrate, which is known in the state of the art and is in general use, is as follows:

First the ore concentrate is subjected to an alkalinely oxidizing fusion by means of hydroxide and then ruthenium and osmium are precipitated with ethanol. The solid phase is again decomposed with an alkalinely oxidizing fusion and dissolved. Ruthenium is distilled out and captured with an absorption solution containing hydrochloric acid. Then the absorption solution is concentrated in a circulating evaporator and osmium is then distilled out by means of H 2 O 2 , while ruthenium chloride remains in the liquid phase. The recovered osmium tetroxide is absorbed in an alkaline absorber, precipitated as a sulfide, the precipitate is separated from the liquid phase, melted with alkaline oxidation, and lastly distilled out as osmium tetroxide by adding hydrochloric acid, then absorbing in an alkaline absorber, filtering out after alcohol precipitation, and finally reduced with hydrogen to the pure osmium.

This process involves a number of sometimes time-consuming and therefore expensive steps and in many cases the osmium yield leaves much to be desired.

For this reason the problem arises of at least partially removing the above-stated disadvantages by means of a novel method for the extraction of osmium and ruthenium from noble metal concentrates, and especially to offer a cost-effective and less complicated process with a higher osmium yield.

In the process of the invention, first a noble metal concentrate containing osmium and ruthenium is treated with nitric acid at a maximum temperature of about T 30 C., and then the suspension/solution is heated to a minimum temperature of about T 85 C. The osmium tetroxide thus developing is collected in an absorption solution (this is a hydroxide solution), while thereafter the remaining suspension/solution freed of osmium and having a temperature of about T 20 C. to 30 C. is treated with hydroxide at a maximum reaction temperature of about T 65 C. The suspension/solution is alkalinized. Finally it is treated with an agent for the oxidative extraction of the ruthenium, for example by passing chlorine gas through it while a hypochlorite solution oxidizing the ruthenium forms simultaneously.

After the alkaline oxidative extraction an insoluble solid remains, which still contains a small amount of ruthenium. This residue is separated from the ruthenate solution by letting it settle and decanting it.

It is advantageous if, in capturing the osmium tetroxide a KOH absorption solution is used, since excellent results are found when the osmium is then precipitated.

Furthermore, it is advantageous if, when treating the suspension/solution with hydroxide the latter is added slowly and/or in portions to the suspension/solution in order to assure a controlled neutralization reaction at a not too high temperature (namely not higher than about T 65 C.).

Furthermore, it has proven advantageous for the absorption solution to be treated with ethanol after colleting the osmium tetroxide such that the resultant absorption-ethanol solution has a maximum ethanol content of about 5% by volume, since then the absorption and precipitation properties can be considered optimal.

Furthermore, it is advantageous if, after the absorption of the osmium tetroxide, ethanol is added in portions to the absorption solution, since this procedure results in optimal precipitation and a low residual osmium content.

For the further reduction of the residual osmium content it is advantageous if the absorption solution is stirred during and after the addition of ethanol.

It is furthermore advantageous if the suspension/solution is made alkaline with solid NaOH, since in this manner a definitely lower increase in volume results. The addition of solid NaOH takes place advantageously at a temperature of about T 30 C. to about T 65 C., since thus a very large percentage of ruthenium can be activated and dissolved out.

Lastly, it is especially advantageous for the oxidative recovery of the ruthenium if hypochlorite or peroxodisulfate is used, since in this way a greater oxidant yield can be achieved in comparison to the classical introduction of chlorine gas into a hydroxide solution, while avoiding the formation of oxygen.

The following example serves to explain the invention.

Example of the application of osmium distillation and ruthenium leaching

Input Material

291.2 kg of dried and ground residue from Os/Ru alcohol precipitation.

Apparatus

800 liter enameled steel vat

Absorption apparatus consisting of two fifty-liter absorbers filled with 45 liters KOH (25%) each and water jet pump for pumping the gas phase.

Description of the Process

The residue was processed in 3 portions of about 100 kg each.

The condensate (approx. 120 liters) and approximately 50 liters of VE water from the preceding distillation were placed in the reaction vat and then about 100 kg of residue was aspirated into the vat. The vat was sealed and the gas circulation turned on. At room temperature, 100 liters of 52% nitric acid was pumped in within 30 minutes. Then the vat was heated to about 85 C. and the osmium was distilled off in about 10 hours. The OsO 4 was absorbed in KOH (25%) in the absorption apparatus.

The suspension was cooled to about 30 C. and 75 kg of solid sodium hydroxide was added portion-wise, with cooling. The rate of addition was chosen so that the temperature did not exceed 65 C. Then the suspension was cooled again, and sodium hypochlorite solution (approx. 2 mol/l) was added at about 30 C. until the suspension definitely foamed up (about 150 to 180 liters of NaOCl solution). Stirring continued for 4 hours and then the ruthenate solution was pumped into a strainer box.

After each distillation the first absorber was emptied and filled with fresh 25% KOH. The second absorber was substituted only after every second Os distillation. The osmate solution was combined into greater portions. After the entire residue had been processed, the absorber solution (about 200 liters) was treated portion-wise with 10 liters of denatured ethanol. The mixture was stirred until a violet residue formed and the supernatant solution was clear. The residue was let settle overnight, the supernatant solution was decanted, the residue was filtered and washed with 3 liters of denatured ethanol and suctioned dry. The potassium osmate was weighed and passed on for osmium purification.

Evaluation Osmium balance 1.1 Analysis Results 1.1.1.1 Balancing Potassium Potassium Residue osmate Residue osmate Quantity 291.2 kg 7,800 g Input amount Amount with absolute respect to input Osmium 1.49% 4,463 g 4,200 g 97.3% Ruthenium balance 1.1.1.2 Analysis results 1.1.1.3 Balancing Ruthenate Ruthenate solution solution Residue Parts 1-3 Residue Parts 1-3 Amount 291.2 kg 1,830 l Input Amount with absolute respect to input Ruthenium 17.44% 24.3 g/l* 50.8 kg 87.5% *Solution separated from the solid by settling.