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How to recover the precious metal "ruthenium" from waste titanium anodes?
Classification:
Industry Information
Release time：
2019-12-09
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How to recover the precious metal "ruthenium" from waste titanium anodes?
Titanium-based coating electrodes using precious metal ruthenium as the active ingredient have been widely used in China's industrial water treatment, hydrometallurgy, chlor-alkali and other industries. Some earlier precious metal anode electrolytic cells and electrodialyzers can no longer be used due to the deactivation of the anode coating. Because the titanium substrate itself has a certain cost, the repair and reuse of waste ruthenium-titanium electrodes are increasingly being Value. The amount of ruthenium remaining on the waste electrode is 1.5 ~ 4.5g per square meter on average, which is considerable. In order to save costs and resources, recovering ruthenium while removing the coating to repair the electrode will not only help to repair the used electrode, but also have great economic benefits.
To recycle the "ruthenium" in the waste electrode, first try to peel off the waste coating containing ruthenium. There are many methods for peeling off the old coatings, which are mainly summarized as: molten salt method, hydrochloric acid boiling method, sulfuric acid boiling method, sulfuric acid electrolytic method. The test results show that the corrosion and amount of titanium substrates and the amount of media and economic benefits of various treatment methods are different. Among them, the sulfuric acid electrolytic method has lower cost, less corrosiveness to titanium substrate, and higher noble metal recovery rate.
First, the principle of the electrolytic recovery reaction
1. Electrolytic peeling of waste coating
The spent ruthenium-titanium-coated electrode that has lost activity is alternately used as a cathode and anode for electrolysis in sulfuric acid medium, without heating
Then, the anode is used as the cathode after the tank voltage rises sharply, and when the electrolysis is continued, the tank pressure drops significantly. When the ruthenium-titanium coating begins to peel off, the groove pressure gradually rises again. When the coating is completely peeled off, the groove pressure reaches stability again. At this time, the titanium substrate should be taken out in time, and after washing with water, it can be used as a substrate for recoating and repairing. Both solid precipitates peeled off from the electrolyte and dissolved ruthenium can be recovered.
2. Recovery of ruthenium
The ruthenium in the precipitate peeled off by the electrolytic method mainly exists in the state of RuO2, Ru. Now it is oxidized by alkali, and then K2RuO4 is leached with hot water, and then oxidized with sodium hypochlorite. The ruthenium in the solution exfoliated by the electrolytic method exists in the Ru3 + or RuO42- state, and is oxidized with sodium hypochlorite to RuO4. It was then reduced to a RuCl3 hydrochloric acid solution by absorption with hydrochloric acid. Finally, the RuCl3 solution was distilled under reduced pressure to crystal β-RuCl3 · xH2O. This product can still be used as an active material for preparing ruthenium-titanium electrodes. To make metal ruthenium, RuCl3 can be further oxidized to RuO2, and then reduced with H2 to obtain the metal "ruthenium".
Because the "ruthenium" content in the used electrode coating is different, the measured results cannot be compared. Therefore, the recovery of ruthenium is determined by using a newly coated electrode. The theoretically recovered amount of "ruthenium" is calculated by the gravimetric method and based on the ruthenium-titanium ratio in the coating solution, and then measured by thiourea spectrophotometry. The amount of ruthenium in the solids and solution of the exfoliated material under the method was used to calculate the recovery rate.
