Goethite Subject

The principal differences between the goethite and the jarosite processes take place following the hot acid leaching of the zinc ferrite residues. In the goethite process, the liquor from hot acid leaching, holding (in g l-1) 100 Zn, 25-30 Fe3+ and 50-60 H2S04, is initially subjected to a reduction step, where the ferric iron is reduced to the ferrous form by reaction with unroasted zinc sulfide concentrate at 90 °C ... 

AMD are often very heterogeneous and reactive systems. Therefore, to describe their properties is often an issue of analytical concern as it is difficult to obtain representative samples of the affected watercourses. The instability of AMD is related to the formation and transformations of ochre-products, such as jarosite, schwertmannite and goethite (Bigham et al. 1996). Mineralogical transformations involving these ochre-precipitates have been the subject of intensive research (Kawano Tomita 2001 Kim et al. 2002 Knorr Blodau... 

Many exposed BIF sequences have been subjected to deep weathering and metamorphism, where hematite and goethite are, for the most part, secondary alteration products (e.g., Beukes and Klein 1992). In a few cases, however, primary hematite is found as finely disseminated... 

Oxidized upper zones of Fe-rich rocks with high concentrations of Fe oxides are found in pyritic (gossan) and ultrabasic rocks. These rocks are often the subject of exploration owing to their content of such non-ferrous metals as Cu, Co, Ni and Zn. These metals are intimately associated with the iron oxides, mainly goethite and he-... 

Iron oxides, the common components of dispersed systems in industry and nature, are also the subject of the colloid chemistry studies. The most frequently examined are hematite, goethite and magnetite. Their edl parameters... 

Figure 8.2. Desorption of (a) As(lII) and ( ) As(V) from goethite on the onset of dynamic flow conditions. Goethite-coated quartz sand was loaded with arsenic at various fractions of the adsorption maxima, as determined by batch incubations and Langmuir isotherm tits, and then subjected to continuous injection of minimal groundwater medium.

Two-step adsorption kinetics of metd cations at iron oxides has been observed for several metals (26-28) and mainly attributed to interaction of the metal cations with different sites of the metal oxide surface (29). Diffusion of cations into micro- or macropores can be ruled out for synthetic goethites (30) due to an essential lack of porosity as determined by t-plot analysis (31). However, diffusion processes may be important for other oxides, especially amorphous iron oxides or oxides with certain coatings and oxide surfaces which have been subject to substantial dissolution processes. Thus, other processes than diffusion must have caused the two different kinetic domains of Fe(II) sorption to iron oxide surfaces. 

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