Lead sulfate cathodic reduction

A correlation has been found between expander activity and the rate of reduction of lead sulfate to lead [5]. For example, the curves presented in Fig. 7.3 evidence that the current of PbS04 reduction and FI2 evolution decreases with increase of expander activity. The observed decrease in cathodic current is attributed to adsorption of the additives on the electrode surface and on the surface of PbS04 crystals. 

Thallium is prepared from filter dust obtained after roasting of sulfide ores. The dust is dissolved in sulfuric acid. Then thallium co-precipitates with lead sulfate. The lead manufactured by reduction with coke contains thallium metal. Lead is first removed in two electrolytic processes, and in a second step thallium is precipitated on a steel cathode. As an alternative, thallium can be won from a sulfuric acid solution with an ion-exchange technique. The annual production of thallium compounds corresponds to 30 tonnes of thallium, but the production of the metal is not large - in the whole world less than 10 tonnes. 

As observed, lignosulfonate (0.5 wt%) can adsorb on lead particles, preventing the continuous growth of PbS04, increasing the surface area of the lead material, and suppressing the formation of orthorhombic PbO phase [12]. The adsorption of an expander can affect the anodic oxidation of Pb, cathodic reduction of lead sulfate, morphology of lead sulfate, and both porosity and surface area of NAM. An... 

Cathodic protection with impressed current, aluminum or magnesium anodes does not lead to any promotion of germs in the water. There is also no multiplication of bacteria and fungi in the anode slime [32,33]. Unhygienic contamination of the water only arises if anaerobic conditions develop in the slurry deposits, giving rise to bacterial reduction of sulfate. If this is the case, HjS can be detected by smell in amounts which cannot be detected analytically or by taste. Remedial measures are dealt with in Section 20.4.2. 

In addition to reduction of its ores in furnaces, manganese can be produced by electrolysis. The electrolyte is manganese sulfate that is produced by treating ore with sulfuric acid, (TMnOj + 2HjSO —> 2MnSO + + 2H2O). The anode is lead alloy, and the cathode is... 

Phthalimide was hydrogenated catalytically at 60-80° over palladium on barium sulfate in acetic acid containing an equimolar quantity of sulfuric or perchloric acid to phthalimidine [7729]. The same compound was produced in 76-80% yield by hydrogenation over nickel at 200° and 200-250 atm [43 and in 75% yield over copper chromite at 250° and 190 atm [7730]. Reduction with lithium aluminum hydride, on the other hand, reduced both carbonyls and gave isoindoline (yield 5%) [7730], also obtained by electroreduction on a lead cathode in sulfuric acid (yield 72%) [7730]. 

Numerous methods for the synthesis of salicyl alcohol exist. These involve the reduction of salicylaldehyde or of salicylic acid and its derivatives. The alcohol can be prepared in almost theoretical yield by the reduction of salicylaldehyde with sodium amalgam, sodium borohydride, or lithium aluminum hydride by catalytic hydrogenation over platinum black or Raney nickel or by hydrogenation over platinum and ferrous chloride in alcohol. The electrolytic reduction of salicylaldehyde in sodium bicarbonate solution at a mercury cathode with carbon dioxide passed into the mixture also yields saligenin. It is formed by the electrolytic reduction at lead electrodes of salicylic acids in aqueous alcoholic solution or sodium salicylate in the presence of boric acid and sodium sulfate. Salicylamide in aqueous alcohol solution acidified with acetic acid is reduced to salicyl alcohol by sodium amalgam in 63% yield. Salicyl alcohol forms along with -hydroxybenzyl alcohol by the action of formaldehyde on phenol in the presence of sodium hydroxide or calcium oxide. High yields of salicyl alcohol from phenol and formaldehyde in the presence of a molar equivalent of ether additives have been reported (60). Phenyl metaborate prepared from phenol and boric acid yields salicyl alcohol after treatment with formaldehyde and hydrolysis (61). 

An acetylene may be reduced to an olefin by sodium in liquid ammonia, ° by electrolytic reduction at a spongy nickel cathode, or by partial hydrogenation over metal catalysts. Catalysts for the hydrogenation include nickel, ° iron, colloidal palladium, and palladium on barium sulfate or calcium carbonate. Pure trans olefins are obtained from dialkylacetylenes by reduction with sodium in liquid ammonia. The yields ate better than 90%. Catalytic hydrogenation leads to mixtures of cis and trans olefins in which the cis isomers predominate. ° Mono- and di-arylacetylenes have also been reduced. ... 

Electrolytic reduction of isatin using a lead electrode and a saturated sodium carbonate solution as electrolyte gave dihydroxy-indole, whereas a mercury cathode and lead anode in neutral sodium sulfate gave hydroxyindole. Electrolytic reduction of 1-methylisatin using lead cathodes and 20% sulfuric acid gave 1-methyldihydroxy-indole a mercury cathode and neutral sodium sulfate gave 1-methyl-hydroxy indole. 

Dithioesters can be reduced in anhydrous acetonitrileor in methanol,the best results being obtained with dimethyl sulfate as alkylating agent. The most convenient procedure involves a simple electrolysis cell with a lead cathode and methanol as solvent. Eight substrates (68 X = SMe) were tested, with R equal to phenyl, chloro- and methoxy-substituted phenyls, and f-butyl. Unlike the corresponding reductions of thioamides, the reactions were not entirely clean and gave substantial amounts of side products such as (70). The product dithioacetals (69 X = SMe, R = Me) were formed in yields of 40-60%. On two of the substrates, better yields (ca. 70%) could be obtained in anhydrous acetonitrile, but a more sophisticated apparatus was required. One enolizable substrate (71) was tested, but the yield was only 30%. ... 

A great advantage of electrochemical reactions compared with chemical conversions is the effective contribution to pollution control. The direct electron transfer from the electrode to the substrate avoids the problem of separation and waste treatment of the frequently toxic end products of the chemical oxidants or reductants. Furthermore, by electrodialysis, organic acids or bases can be regenerated from their salts without the use of sulfuric acid or sodium hydroxide, for example, which lead to the coproduction of sodium salts or sulfates as waste [79]. At the same time, inorganic acids and bases, necessary for chemical production, are provided by this process. An application of electrodialysis has been demonstrated in the preparation of methoxyacetic acid by oxidation of methoxyethanol at the nickel hydroxide electrode [80]. Finally, unwanted side products can be converted into the wanted product, which increases the economy of the process and reduces the problem of waste separation and treatment. This is accomplished in the manufacture of chloroacetic acid by chlorination of acetic acid. There the side product dichloroacetic acid, formed by overchlorination, is cathodically converted to chloroacetic acid [81]. 

Fig. 318. Preparation of chromium (II) sulfate by electrolytic reduction, pjar q porous clay cell s sampling tube t gas outlet tube u stirrer with Hgseal w lead cathode w lead anode.

The solution pH was adjusted to 5.8-6.0 and copper was deposited at -O.30 volts ys. a standard calomel electrode (S.C.E.)j blemuth was deposited at -0.40 volts and lead at -0.60 volts. The solution was acidified to pH 2 or less and tin was deposited at -O.60 to O.65 volts. The cathode was removed while rinsing with distilled water after each deposition was complete (indicated by. reduction of current to a constant minimum value) and a clean electrode Introduced. The separation talces about four hours for up to 100 mg amounts of each metal (LI6).. Moderate amounts of nitrate or sulfate were not found to be objectionable. 

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