Dissolution of metal species

The primary oxidation reaction involves the anodic electrochemical dissolution of metal species M, according to the following reaction ... 

M Carrott, CM Wai. UV-Vis spectroscopic measurement of solubilities in supercritical CO2 using high pressure fiber optic cells. Anal Chem 70 2421-2425, 1998. Mike J. Carrott, Brenda E. Waller, Neil G. Smart, Chien M. Wai, High solubility of U02(N03)2 2TBP complex in supercritical CO2. Chem Commun 373-374, 1998. CM. Wai, B Waller. Dissolution of metal species in supercritical fluids—principles and applications. Ind Eng Chem Res 39 3837-3841, 2000. 

The only reports of directed synthesis of coordination complexes in ionic liquids are from oxo-exchange chemistry. Exposure of chloroaluminate ionic liquids to water results in the formation of a variety of aluminium oxo- and hydroxo-contain-ing species [4]. Dissolution of metals more oxophilic than aluminium will generate metal oxohalide species. FFussey et al. have used phosgene (COCI2) to deoxochlori-nate [NbOa5] - (Scheme 6.1-1) [5]. 

Adsorbed species may also accelerate the rate of anodic dissolution of metals, as indicated by a decrease in Tafel slope for the reaction. Thus the presence of hydrogen sulphide in acid solutions stimulates the corrosion of iron, and decreases the Tafel slope The reaction path through... 

In this equation, aua represents the product of the coefficient of electron transfer (a) by the number of electrons (na) involved in the rate-determining step, n the total number of electrons involved in the electrochemical reaction, k the heterogeneous electrochemical rate constant at the zero potential, D the coefficient of diffusion of the electroactive species, and c the concentration of the same in the bulk of the solution. The initial potential is E/ and G represents a numerical constant. This equation predicts a linear variation of the logarithm of the current. In/, on the applied potential, E, which can easily be compared with experimental current-potential curves in linear potential scan and cyclic voltammetries. This type of dependence between current and potential does not apply to electron transfer processes with coupled chemical reactions [186]. In several cases, however, linear In/ vs. E plots can be approached in the rising portion of voltammetric curves for the solid-state electron transfer processes involving species immobilized on the electrode surface [131, 187-191], reductive/oxidative dissolution of metallic deposits [79], and reductive/oxidative dissolution of insulating compounds [147,148]. Thus, linear potential scan voltammograms for surface-confined electroactive species verify [79]... 

The mode of dissolution of metal borates in aqueous solution is complex. Hydrolysis of the borate anion can result in completely different boron species that are stable only under particular conditions of pH, temperature, and concentration. 

An additional study on the same system has been reported, including a comparison of direct electrochemical and conventional chemical dissolution of metallic copper in TMTD solutions in various solvents under conditions of simultaneous ultrasonic treatment of the reaction system [133,620]. It has been shown that the system TMTD-copper-solvent could serve as a perfect model to study the influence of simultaneous application of ultrasonic treatment (see Sec. 3.5) on the syntheses of complexes of the transition metals in different nonaqueous solutions, by using and testing several techniques [620]. Several other studies on the interaction of copper and iron species with thiruam sulfides have also been reviewed [621]. 

Hence, the equilibrium situation of many active metal electrodes in solution involves the dynamic deposition-dissolution of surface species related to solution components in a steady state, which leaves the surface films at a constant average thickness. 

Figure 3 A schematic view of formation of multilayer surface films on active metals exposed fresh to solution phase. Stage I Fresh surface-nonselective reactions Stage II Initial layer is formed, more selective surface film formation continues Stage III Formation of multilayer surface films Stage IV Highly selective surface reactions at specific points partial dissolution of surface species Stage V Further reduction of the surface species close to the active metal, deposition-dissolution of surface species at steady state the surface film is comprised of a multilayer inner compact part and an outer porous part.

The vast majority of engineering materials dissolve via electrochemical reactions. Chemical processes are often important, but the dissolution of metallic materials requires an oxidation of the metallic element in order to render it soluble in a liquid phase. In fact, there are four requirements for corrosion an anode (where oxidation of the metal occurs), a cathode (where reduction of a different species occurs), an electrolytic path for ionic conduction between the two reaction sites, and an electrical path for electron conduction between the reaction sites. These requirements are illustrated schematically in Fig. 1. 

Radiochemical methods are applied for the study of a wide range of electrochemical surface processes. The most important areas are as follows - adsorption and -> electrosorption occurring on the surface of electrodes the role of electrosorption in -> electrocatalysis -> deposition and dissolution of metals - corrosion processes the formation of surface layers, films on electrodes (e.g., polymer films), and investigation of migration processes in these films study of the dynamics of - electrosorption and - electrode processes under steady-state and equilibrium conditions (exchange and mobility of surface species) electroanalytical methods (e.g., radiopolarog-raphy). 

Fig. 10.8. Simple biogeochemical model for metal mineral transformations in the mycorhizosphere (the roles of the plant and other microorganisms contributing to the overall process are not shown). (1) Proton-promoted (proton pump, cation-anion antiport, organic anion efflux, dissociation of organic acids) and ligand-promoted (e.g. organic adds) dissolution of metal minerals. (2) Release of anionic (e.g. phosphate) nutrients and metal cations. (3) Nutrient uptake. (4) Intra- and extracellular sequestration of toxic metals biosorption, transport, compartmentation, predpitation etc. (5) Immobilization of metals as oxalates. (6) Binding of soluble metal species to soil constituents, e.g. clay minerals, metal oxides, humic substances.

The electrodeposition of tin, Sn, has been reported in both basic and acidic EMICI-AICI3 ionic liquid [26]. A divalent tin species, Sn(II), can be introduced by the anodic dissolution of metallic tin. The introduction of a tetravalent tin species, Sn(lV), is also possible by dissolving tin tetrachloride, SnCL,. However, the evaporation of SnCl4 occurs in the case of an acidic ionic liquid. The irreversible reduction of Sn(IV) to Sn(II) occurs at around 0.91 and —0.9 V in the acidic and basic ionic liquids, respectively. The electrodeposition of metallic Sn is possible by the reduction of Sn(II) ... 

The electrodeposition of lead, Pb, has been investigated in an acidic EMICl-AICI3 ionic liquid [27]. A divalent lead species, Pb(II), can be introduced by dissolving lead dichloride, PbCl2, or the anodic dissolution of metallic Pb. Metallic Pb is obtained by the reduction of Pb(II) ... 

EMICl- [22, 37, 38, 51-54], and BMICI-AICI3 [55] ionic liquids. In the case of acidic ionic liquids, it is possible to introduce monovalent and divalent copper species, Cu(l) and Cu(II), by dissolving copper chloride and dichloride, respectively, and by the anodic dissolution of metallic copper. Metallic Cu can be obtained by the reduction of Cu(I). The formal potentials of Cu(I)/Cu in an acidic MPCl-BPC1-, EMICI-AICI3 are reported as 0.777 [49], 0.784 [50], and 0.837 [52] V, respectively. Cu(I) can be also obtained by the reduction of Cu(II), of which the formal potentials in the acidic MPCl- and BPCI-AICI3 are reported as 1.851... 

Typical examples of processes involving two or more adsorbed species are reactions of corrosion or anodic dissolution of metals, oxygen evolntion, etc. In the case of two adsorbed species B and C, the electrochemical... 

Lustig S, Zang S, Beck Wand Sghramel P (1998) Dissolution of metallic platinum as water soluble species by naturally occurring complexing agents. Mikrochim Acta 129 189-194. 

---