Aluminum dissolution

Sysoeva et a/.114 made a systematic potentiostatic investigation of anodization in KOH solutions in the concentration range between 0.1 and 12.5 M and in the potential range between -1.5 and 0.5 V vs. SCE. They found a maximum in the aluminum dissolution rate at a KOH concentration of 3-5 M This is interpreted in terms of a change in the mechanism of passivation At low KOH concentra-... 

Incorporation of promoters can occur via two distinct mechanisms. A local pH drop at the leach front caused by the aluminum dissolution can cause a solvated promoter to deposit via a shift in the solubility equilibrium. Zincate shows this behavior, depositing as zinc oxide as the pH drops at the leach... 

Sum and Skyllas-Kazacos [44] studied the deposition and dissolution of aluminum in an acidic cryolite melt. The graphite electrode was preconditioned (immersed in cryolite melt) to saturate the surface of the electrode in sodium before aluminum deposition could be observed. Current reversal chronoamperometry was used to measure the rate of aluminum dissolution in the acidic melt. Dissolution rate was mass transport controlled [45] and in the order of 0.8 10 7 and 1.8 10 7 molcm 2s 1 at 1030 °C and 980 °C respectively [44]. 

Successful commercialization of the technology requires further research to significantly improve aluminum dissolution efficiency. If the ACE Separator can be engineered to regularly... 

According to the vendor, recent work has been accomplished regarding the aluminum dissolution efficiency. The fluidized-bed system has a dissolution factor 10 times (lOx) that of the parallel electrode system. The parallel electrode system is no longer offered commercially by Recra Environmental, Inc., but remains available for testing purposes. 

Fig. 12. Potentiodynamic anodic current-potential curve of aluminum dissolution in an alkylalumlnum electrolyte (EL II/T) (a) after addition of 1 1 complex (b) without 1 1 complex [186].

FIGURE 34.29 Influence of diffusion dialysis on aluminum dissolution. 

FIGURE 34.30 pH change and aluminum dissolution in fresh WTR feed/residual WTR during diffusion dialysis. 

An explanation might be found if monomer chemisorption takes place instead. Indeed boehmite dissolution occurs by means of its lateral surfaces [19] monomer chemisorption on lateral boehmite surface would block surface functional sites and thus inhibit at least partially boehmite dissolution. Therefore, at intermediate molybdenum loading, as monomer concentration in solution is not negligible compared to AHM concentration, monomer adsorption on boehmite lateral surfaces should compete with aluminum extraction. Fig. 8 reports boehmite dissolution kinetics carried out at pH=4.8, for two [AHM] concentrations (intermediate and high molybdate loading). This result could support the fact that aluminum dissolution is slowed down at intermediate molybdenum loading and that no substantial moly-bdate adsorption could take place a plateau is reached in the adsorption isotherm (Fig. 1). 

Steps 1, 2, and 3 account for the initially high rate of dissolution of alkali and alkaline earth metals (Na", K, Ca ) from feldspars, and the relative lack of silica and aluminum dissolution. This is termed incongruent (nonstoichiometric) dissolution, meaning that a portion of the mineral structure is dissolving selectively, leaving a residue enriched in silica and alumina. Step 4 accounts for the later stage of congruent (stoichiometric) dissolution, in which the elements are released into solution in proportion to their mole fractions in the structure. 

Cathodic protection needs careful potential control to avoid cathodic corrosion. With increasing cathodic polarization, the rate of aluminum dissolution increases, as is shown in Fig. 28. This effect is called cathodic corrosion of aluminum and is attributed to the formation of OH ions at the metal surface during the reduction of oxygen or water. 

Acidification of the soil is not necessarily caused by acid rain. The rain is acidic all over the world. The pH of rain in Japan was 4.72 (average, 2008-2012). The acid rain can dissolve aluminum from wastes. We should be careful about the influence of aluminum dissolution on agriculture that directly relates to food. 

Fig. 9.3 (a) dependence of the reaction rate constant on pH (initial Cu " concentration 3.56 g/dm, initial amount of A1 powder 1.5 g). (b) Dependence of calculated current of aluminum dissolution on pH ((initial Cu " concentration 3.56 g/dm, initial amount of A1 powder 1.5 g) (Reproduced from Ref. [3] with permission from The Electrochemical Society)... 

Porous coatings of copper onto aluminum are shown by the SEM images in Fig. 9.17. These samples were obtained by an immersion of aluminum powders into alkaline Cu(II) solutions [3]. Due to porosity of the deposited copper, the electrolyte penetrates through pores and reacts with aluminum. In this way, simultaneous reactions of aluminum dissolution, hydrogen evolution, and copper deposition occur. A complete dissolution of aluminum and a production of hollow copper particles are shown in Fig. 9.17. 

R. Foley and T. Nguyen, The Chemical Nature of Aluminum Corrosion V. Energy Transfer in Aluminum Dissolution, Journal of The Electrochemical Society, vol. 129, no. 3, pp. 464-467, 1982. 

Chloride levels. A high level of chloride in a marine-industrial environment, such as 30-40 mg/m /day, leads to a high density of pitting of aluminum and its alloys. Incorporation of chlorides into the aqueous layer on an aluminum substrate from deposition of sea salts, aerosol particles or from an organic gas containing chlorine may lead to the formation of AICI3 or A1(0H)2C1, which are soluble in weak acidic solution and do not offer resistance to aluminum dissolution. Sulfides and sulfates. In aqueous layers, SO2 dissolves and ionizes to produce HSO ion. 

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