Anode sulfur

The objective of the present work was to measure the CC, the CD formation, and the CE in a laboratory cell using the techniques outlined above, in order to study the effect of the anode sulfur content during experiments of 6 h duration. 

Experiment Anode material number Anode sulfur content (wt%) HS coke content (wt%) Butts content (wt%)... 

Figure 1.5.3 Influence of the anode sulfur content on the carbon consumption (CC)...

If we include the graphite data, we see that increasing anode sulfur content leads to increasing CC. The correlations between the CC and the sulfur content are then ... 

Increasing anode sulfur content caused enhanced surface roughening and more CD, according to the relationship (including the graphite data) ... 

The results of this study are indicative of an important link between the anode sulfur content and the CE during aluminum electrolysis. 

Nearly all fuels used to operate carbonate fuel cell power plants contain sulfur. Sulfur compounds deactivate nickel-based catalysts used in the carbonate fuel cell anode. Sulfur has a tendency to be chemisorbed on active nickel, forming nickel sulfide (as shown in Reactions 4-6). The catalyst deactivation causes loss of reforming activity and hence limits the catalyst life. For stable long-term carbonate fuel cell operation, the sulfur concentration in fuel needs to be reduced to a lower level prior to introduction to the anode by utilizing an efficient fuel desulfurization system. As a rule-of-thumb, sulfur should be removed to bring the concentration down to the sub-ppm level. 

At the anode, a chemical oxidation reaction is bound to take place. In normal fixers, sulfite (SOj ) is oxidized and acid (H ) is released as a consequence of this oxidation. Due to the decrease of the sulfite concentration and the decrease in the pH, the fixing solution becomes unstable and sulfur precipitation starts to occur when the pH of the fixer decreases below 4.0. In the case of hardening fixers, there is also an upper limit to the pH, since aluminum-hydroxides starts to precipitate when the pH exceeds 5.0. 

Selenium is found in a few rare minerals such as crooksite and clausthalite. In years past it has been obtained from flue dusts remaining from processing copper sulfide ores, but the anode metal from electrolytic copper refineries now provide the source of most of the world s selenium. Selenium is recovered by roasting the muds with soda or sulfuric acid, or by smelting them with soda and niter. 

Small amounts of propionitrile and bis(cyanoethyl) ether are formed as by-products. The hydrogen ions are formed from water at the anode and pass to the cathode through a membrane. The catholyte that is continuously recirculated in the cell consists of a mixture of acrylonitrile, water, and a tetraalkylammonium salt the anolyte is recirculated aqueous sulfuric acid. A quantity of catholyte is continuously removed for recovery of adiponitrile and unreacted acrylonitrile the latter is fed back to the catholyte with fresh acrylonitrile. Oxygen that is produced at the anodes is vented and water is added to the circulating anolyte to replace the water that is lost through electrolysis. The operating temperature of the cell is ca 50—60°C. Current densities are 0.25-1.5 A/cm (see Electrochemical processing). 

In both the sulfuric and nitric acid processes, the dorn metal must be in shot form prior to treatment to secure a reasonably rapid reaction. A number of steps also may be required in processing the dorne metal to remove miscellaneous impurities, particularly in treating material from copper-anode slime (31). 

Copper-containing lead alloys undergo less corrosion in sulfuric acid or sulfate solutions than pure lead or other lead alloys. The uniformly dispersed copper particles give rise to local cells in which lead forms the anode and copper forms the cathode. Through this anodic corrosion of the lead, an insoluble film of lead sulfate forms on the surface of the lead, passivating it and preventing further corrosion. The film, if damaged, rapidly reforms. 

The excellent corrosion-resistant lead dioxide, Pb02, film formed on anodes and lead—acid battery positive grids in sulfuric acid has enabled lead insoluble anodes and lead—acid batteries to maintain the dominant positions in their respective fields. 

The main cause of anode wear is electrochemical oxidation or sulfur attack of anodic surfaces. As copper is not sufficiently resistant to this type of attack, thin caps of oxidation and sulfur-resistant material, such as platinum, are bra2ed to the surface, as shown in Eigure 15a. The thick platinum reinforcement at the upstream corner protects against excessive erosion where Hall effect-induced current concentrations occur, and the interelectrode cap protects the upstream edge from anodic corrosion caused by interelectrode current leakage. The tungsten undedayment protects the copper substrate in case the platinum cladding fails. 

The zinc electrolyte contains ca 60 kg/m zinc as sulfate and ca 100 kg/m free sulfuric acid. It is electrolyzed between electrodes suspended vertically in lead or plastic-lined, eg, poly(vinyl chloride), concrete tanks. The insoluble anodes are made of lead with small amounts of silver. The anodic... 

Wrought and cast nickel anodes and sulfur-activated electrodeposited rounds are used widely for nickel electro deposition onto many base metals. 

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