Magnetite dissolution

Magnetite Dissolution/reduction Alkaline solution with N2H4... 

Substituted magnetite Dissolution/reprecipitation Alkaline solution with M ... 

Snowball, 1. F, 1993. Geochemical control of magnetite dissolution in subarctic lake sediments and the implications for environmental magnetism. J. Quat. Sci. 8 339-346. 

Both magnetite dissolution and dissolution of the base metal contribute Fe to the solution. Separating the two contributions is at best a difficult procedure. Most of that effort focused on the dissolution rate of the base metal through a passive film. The rate of that process appears to depend on the ratio of film thickness, I, to the metal/solution potential difference, dissolution process implies transfer of metal ions to the oxide phase, followed by ion diffusion through the oxide, transfer through the oxide solution interface, and finally hydration of the Ions. Thus, the potential difference at the Helmholtz layer is given by... 

A variety of rate laws in addition to Equation (16)—and its integrated form. Equation (15)—were examined, but these were less successful at fitting the data for magnetite dissolution. Most notable of these is the Erofeev relation, which like the Tanaka expression was developed to treat solid-state decomposition reactions in which a solid product phase is formed. This has the form... 

Other work on the mechanism of magnetite dissolution in chelants was recently reported. Hausler looked at magnetite dissolution in ammonium EDTA at pH values from 4.2 to 7.0, and found that hydrazine accelerated the dissolution rate at a pH of 7 but not at 4.2. Instead of invoking the accepted reductive dissolution mechanism, he proposed an unusual N2H4-Fe(lil)EDTA complex to explain his results. 

Two overall equations can be written for magnetite dissolution from steel surfaces. Equation (26) summarizes the species that are involved when no chelant is present ... 

A number of high temperature, magnetite dissolution tests were run in 1-L titanium autoclaves. Transfer flasks were fabricated from AISI316 stainless steel so that a concentrated chelant solution could be injected into the autoclave when the test temperature had been reached. 

Canada Spekkens, P. Ontario Hydro Research Division Chemical Research Division Mechanisms of magnetite dissolution in organic acids... 

THE INFLUENCE OF POTENTIAL, TEMPERATURE, pH, AND HYDRODYNAMICS, ON THE KINETICS OF MAGNETITE DISSOLUTION... 

This report describes a fundamental investigation of the mechanism and kinetics of magnetite dissolution. The work discussed in this paper emphasised the electrochemical nature of the magnetite dissolution reaction (MDR). This report describes the effect of temperature, pH, decontamination reagent formulation and mass transport upon the MDR. 

The dissolution fluxes of ionic species are expressed in chemical (nmol.cm. s" ) rather than electrochemical (pA.cm" ) units. This dissolution flux is the rate of iron released to solution, and not rate of magnetite dissolution. Rates expressed in the former manner exceed those expressed in the latter manner by a factor of three. This factor arises from the stoichiometry of magnetite (Fe304). 

Many individual controlled-potential experiments were performed using different electrode rotation rates and in electrolytes of different composition, pH and temperature. In this way, this set of data allowed the determination of the effects of these parameters and potential upon the kinetics and mechanism of magnetite dissolution. 

Influence of potential and electrolyte composition upon the kinetics of magnetite dissolution... 

The use of RDE and RRDE electrodes allowed the investigation of the effects of mass transport of upon the kinetics of magnetite dissolution, by means of varying the rotation frequency of the electrode. The dependence of the current density upon potential and electrode rotation frequency (/) for a magnetite RDE in perchloric acid is shown in Figure 7. From this figure it is apparent that mass-transport effects are observed, the current density increases as / increases, but that these effects are limited to potentials close to E.,. The dependence of current density upon /, for potentials close to E, is further analysed by the methods described in Appendix A. Figure 8 shows the... 

The results presented in this paper serve to emphasize the electrochemical nature of the MDR. Electrochemical techniques were used to determine the influence of temperature, pH, potential and RDE rotation frequency upon the kinetics of the MDR. The findings of this study are both internally consistent, and consistent with other published results [1,2]. The mechanism of magnetite dissolution was identified, permitting the development a quantitative model of the kinetics of the MDR. The predictions of this model are shown to be In good accord with experimental observations. The development of this model is an important step towards the goal of achieving a quantitative model of decontamination processes. 

Consequently, for the case of the dissolution flux arising from magnetite dissolution (Vpg), the use of equations A.5 and A.6 leads to ... 

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