Hydrolysis, iron

It can be seen, therefore, that ferrous iron and chalcopyrite oxidation are acid-consuming reactions, while pyrite oxidation and iron hydrolysis are acid-producing reactions. Thus, whether the overall reaction in a dump is acid producing or acid-consuming depends on the relative proportions of chalcopyrite and pyrite and on the pH conditions. In practice, sulfuric acid additions to the leach solution applied to the dump are usually required to overcome the acid consuming reactions of the gangue minerals and to keep the pH in a suitable range, typically 2 to 2.4, to optimize bacterial activity and minimize iron hydrolysis. 

General reference W. Schneider, Iron Hydrolysis and the Biochemistry of Iron -The Interplay of Hydroxide and Biogenic Ligands, Chimia 42, 9-20 (1988). 

Iron hydrolysis and solubility revisited Observations and comments on iron hydrolyses characterizations. Marine Chem. 70 23—38 Byrne, R.H. Kester, D.R. (1976) Solubility of hydrous ferric oxide and iron speciation in seawater. Marine Chem. 4 255—274 Byrne, R.H. Luo,Y.-R. (2000) Direct observations of nonintegral hydreno ferric oxide solubility products K Sq = [Fe ][H ] Geo-chim. Cosmochim. Acta 64 1873-1877 Cabrera, F. de Arambarri, P. Madrid, L. ... 

Eventually this process forms the neutral species Fe(H2O)3(OH)30, which precipitates as amorphous iron hydroxide, which may settles out of the water column. Figure 3 shows the predicted effect of pH on the relative concentrations of the various iron hydrolysis species with and without considering the iron hydroxide solid, which dominates the speciation above pH 3.0 at 1 dM total iron. The log of the solubility product of this solid is -38.8, indicating that iron is very insoluble at natural pH values. Over time, this metastable amorphous material converts to more thermodynamically... 

Hydroxamic acids are in general colorless, somewhat low-melting solids. However, most of them can be crystallized and the potassium salt of benzhydroxamic acid forms beautiful plates. In terms of stability to acid, the hydroxamic acid bond is intermediate between that of amides and esters. By use of carefully controlled conditions it is possible to split the hydroxamic bond in the presence of the peptide linkage. In the absence of iron, hydrolysis is effected cleanly with hot mineral acid in base extensive degradation occurs even without a contaminating metal ion. Once it has been liberated from the hydroxamic acid linkage the hydroxylamino moiety should always be maintained at a pH below the pKa ( 5). 

The exposure of sulfide minerals contained in mine wastes to atmospheric oxygen results in the oxidation of these minerals. The oxidation reactions are accelerated by the catalytic effects of iron hydrolysis and sulfide-oxidizing bacteria. The oxidation of sulfide minerals results in the depletion of minerals in the mine waste, and the release of H, SO4, Fe(II), and other metals to the water flowing through the wastes. The most abundant solid-phase products of the reactions are typically ferric oxyhydroxide or hydroxysulfate minerals. Other secondary metal sulfate, hydroxide, hydroxy sulfate, carbonate, arsenate, and phosphate precipitates also form. These secondary phases limit the concentrations of dissolved metals released from mine wastes. 

Equilibrium and rate constants for the hydrolysis and chloride complexation of Fe(III) and Fe(II) ions are necessary in a detailed study of iron redox chemistry. Table I lists an internally consistent set of values for the relevant equilibrium constants. Their accuracy is discussed later in the context of a brief sensitivity analysis of the data. The rates of iron hydrolysis and chloride complexation reactions are also mentioned. 

Schneider, W. Iron hydrolysis and the biochemistry of iron The interplay of hydroxide and biogenic ligands. Chimia 42 (1988), 9-20. 

Iron hydrolysis is similar to that of aluminium. The p of the first step of Fe(HI) hydrolysis,... 

They therefore took advantage of the iron hydrolysis - precipitation and acid regeneration process that occurs con-currently with leaching at elevated temperatures in pressure acid leaching (PAL). It was noted that PAL residues contained significant quantities of sulfate, consistent with precipitation of hydronium alunite, H30.Al3(S04)2(0H)6. 

Hydrolysis reactions and the precipitation of iron oxyhydroxide phases also play a key role in the corrosion of metallic iron. Corrosion reactions can involve both ferrous and ferric iron hydrolysis species and the formation of surface coatings of either iron(ll) or iron(lll) (oxy)hydroxide phases. The understanding of corrosion and its effects has received a considerable amount of attention. 

Byrne, R.H., Luo, Y.-R., and Young, R.W. (2000) Iron hydrolysis and solubility revisited observations and comments on iron hydrolysis characterisations. Mar. Chem., 70, 23-35. 

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