Reduction from Aqueous Solutions

Metals above magnesium form soluble hydroxides and carbonates react with water to liberate hydrogen 

Metals below sodium will precipitate from carbon ate solution as carbonates or oxides 

Metals below magnesium can be precipitated from solution as either hydroxides or oxides 

Metals above manganese can be electrolyzed only from fused salts. Metals, manganese to silver, can be electrolyzed from aqueous solutions 

Metal oxides, iron throu coiner, are easily reduced by hydrogen 

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Of course, RDP is very suitable to deposit noble metals in view of their facile reduction from aqueous solutions. A number of studies have shown that attractive results can also be obtained with non-noble metals and with metal oxides and metal sulfides. De Jong [9, 42] has studied the deposition of molybdenum (hydr)oxide by reduction of ammonium molybdate with hydrazine according to the reaction... 

The deposition of RE metals from aqueous solutions does not work because of the highly electropositive nature of the REE. Therefore, industrial production of RE metals is carried out by fused salt electrolysis or metaHothermic reduction. 

Electrowinning from Aqueous Solutions. Electrowinriing is the recovery of a metal by electrochemical reduction of one of its compounds dissolved in a suitable electrolyte. Various types of solutions can be used, but sulfuric acid and sulfate solutions are preferred because these are less corrosive than others and the reagents are fairly cheap. From an electrochemical viewpoint, the high mobiUty of the hydrogen ion leads to high conductivity and low ohmic losses, and the sulfate ion is electrochemicaHy inert under normal conditions. 

Unloaded silica does not recover HPA from aqueous solution. The surface of silica gel modified with quarternary ammonium salts (QAS) gets anion-exchange properties. The aim of the work is the elaboration of solid-phase reagents on the base of ion associate of HPA with QAS immobilized onto silica surface for the determination of phosphoms and organic reductants. Heterocyclic (safranine and lucigenine) and aliphatic (trinonyloctadecyl ammonium iodide and tetradecyl ammonium nitrate) compounds have been examined as QAS. 

Nitric oxide is the simplest thermally stable odd-electron molecule known and, accordingly, its electronic structure and reaction chemistry have been very extensively studied. The compound is an intermediate in the production of nitric acid and is prepared industrially by the catalytic oxidation of ammonia (p. 466). On the laboratory scale it can be synthesized from aqueous solution by the mild reduction of acidified nitrites with iodide or ferrocyanide or by the disproportionation of nitrous acid in the presence of dilute sulfuric acid ... 

Anhydrous NaC102 crystallizes from aqueous solutions above 37.4° but below this temperature the trihydrate is obtained. The commercial product contains about 80% NaC102. The anhydrous salt forms colourless deliquescent crystals which decompose when heated to 175-200° the reaction is predominantly a disproportionation to C103 and Cl but about 5% of molecular O2 is also released (based on the C102 consumed). Neutral and alkaline aqueous solutions of NaC102 are stable at room temperature (despite their thermodynamic instability towards disproportionation as evidenced by the reduction potentials on p. 854). This is a kinetic activation-energy effect and, when the solutions are heated near to boiling, slow disproportionation occurs ... 

Iodide ions reduce Cu to Cu , and attempts to prepare copper(ll) iodide therefore result in the formation of Cul. (In a quite analogous way attempts to prepare copper(ll) cyanide yield CuCN instead.) In fact it is the electronegative fluorine which fails to form a salt with copper(l), the other 3 halides being white insoluble compounds precipitated from aqueous solutions by the reduction of the Cu halide. By contrast, silver(l) provides (for the only time in this triad) 4 well-characterized halides. All except Agl have the rock-salt structure (p. 242). Increasing covalency from chloride to iodide is reflected in the deepening colour white yellow, as the... 

Tellurium and cadmium Electrodeposition of Te has been reported [33] in basic chloroaluminates the element is formed from the [TeCl ] complex in one four-electron reduction step, furthermore, metallic Te can be reduced to Te species. Electrodeposition of the element on glassy carbon involves three-dimensional nucleation. A systematic study of the electrodeposition in different ionic liquids would be of interest because - as with InSb - a defined codeposition with cadmium could produce the direct semiconductor CdTe. Although this semiconductor can be deposited from aqueous solutions in a layer-by-layer process [34], variation of the temperature over a wide range would be interesting since the grain sizes and the kinetics of the reaction would be influenced. 

In this study, the chemical reduction in aqueous solution using conventional and ultTMonic hydrothermal reduction method were conducted for the preparation of fine nickel powders from the aqueous solution of nickel salt by reducing with hydrazine. The differences in the reaction parametera and final product properties resulting from two methods were identified to find the effects of ultrasound. 

Many other metal displacement reactions can be visualized, but not all of them occur. Some metals are oxidized readily, but others are highly resistant to oxidation. Likewise, some metal cations are highly susceptible to reduction, but others resist reduction. Zinc displaces copper ions from aqueous solutions, but copper will not replace zinc ions, because Cu is easier to reduce than Zn . Zinc will not displace ions, because... 

On account of the fact that the electrode potential of molybdenum is more negative than the discharge potential of hydrogen, principle difficulties arise to cathodically electrodeposit molybdenum chalcogenide films from aqueous solutions. Theoretically, the deposition of pure molybdenum by electrolytic reduction of molybdates in acidic aqueous solutions is possible according to the reaction... 

B. Meddings and V. N. Mackiw, Gaseous Reduction of Metals from Aqueous Solutions, in Unit Processes in Hydrometallurgy, p. 354, Gordon and Breach, New York, 1964. 

Liu, J.-F. Nistorica, C. Gory, I. Skidmore, G. Mantiziba, F. M. Gnade, B. E. 2005. Layer-by-layer deposition of zirconium oxide films from aqueous solutions for friction reduction in silicon-based microelectromechanical system devices. 

Removal of the dipeptide ester from the Co(N)4 center is best achieved (1) by electrolytic reduction of aqueous solutions at an Hg electrode ( — 1.0 V vs S.C.E., pH 5, NaCl/HCl electrolyte) and with recovery by ion-exchange (1, 2, 25) or reversed-phase HPLC separation (24). In the latter cases the Co(III)-dipeptide ester was first converted to the Co(III)-dipeptide acid by overnight hydrolysis in 6 M... 

In 1976 a paper published by Modes et al. described the codeposition of CdSe using a solution made by dissolving CdS04 and Se02 in sulfuric acid [129]. This appears to be the first of a large number of similar studies where II-VI compounds were formed from aqueous solutions by co-reduction of Cd+ and HSeOs" (or HTe02, as performed in the classic study by Panicker et al. [218]. 

Electrochemical deposition of metals and alloys involves the reduction of metal ions from aqueous, organic, and fused-salt electrolytes. In this book we treat deposition from aqueous solutions only. The reduction of metal ions in aqueous solution is... 

Baizer, working at the Monsanto Company, showed that good yields of adiponitrile are obtained from aqueous solutions by reduction at mercury or lead in the presence of a high concentration of quaternary ammonium salt [62]. Tetraethyl-ammonium toIuene-4-sulphonate was favoured as electrolyte. The first commercial plant operating the process was commissioned in 1965. It used a divided cell system with a lead cathode and aqueous tetraethylammonium ethylsulphate as electrolyte, with the addition of acid to regulate the pH. A lead anode with an anolyte of dilute sulphuric acid was employed. 

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