Goethite system

Palmquist, U. Ahlberg, E., Lovgren, L. Sjo-berg, S. (1999) competitive metal ion adsorption in goethite systems using in situ volta-metric methods and potentiometry. J. Coll. Int. Sci. 218 388-396... 

In the weathering environment, the protons may be buffered by solid-phase buffer systems. In our experiments, the solutions are buffered by NaHC03 (goethite system), by adding an initial excess of base (magnetite system) or by using a pH-stat device (lepidocrocite system). 

A double relaxation was obtained for the goethite system. Combining results from static and kinetic studies, a bimolecular adsorption/desorption reaction mechanism was postulated for the fast relaxation,... 

Figure 1. Activity diagram of jarosite-alunite-potassium feldspar-gibbsite-goethite system at 1 bar and 298 K. Modified from Bladh (18). Tailings pore water from Grants Mineral Belt, New Mexico and Maybell, Colorado are denoted by O and, respectively. Median ground water composition (19) is represented by. ...

One mechanism that is consistent with the observed properties of the particles in these suspensions involves the dissolution of amorphous Si02 and adsorption of soluble silicate on the Fe(OH)3 surface. This process could occur in parallel with the heterocoagulation mentioned earlier. Soluble silicate species might then compete with Se03 or PO4 for surface sites as suggested by Goldberg (8) for the P04/silicate/goethite system. Sorption of silicate species onto Fe(OH)3 need not affect cationic adsorbates. Benjamin and Bloom (10) demonstrated that adsorption of cations is often minimally affected by anion adsorption even under conditions where anion-anion competition is severe (11). 

For the nickel-citrate-goethite system (Figure 7), the oxide becomes more competitive with increasing pH because of the greater coulombic attraction predicted by the Nernst equation. Unlike silica. Nr is the... 

For the case of nickel-ligand-goethite systems, the results for sulfate, citrate, and NTA could be accounted for by the model used, although some small degree of specific adsorption appeared to take place for citrate and NTA complexes. The evidence for this is not conclusive. However, for both nickel glycine and nickel cyanide, specific energies of adsorption of —3 and —7 kcal/mol, respectively, were calculated. 

Figure 18. Three-dimensional depiction of the nickel-cyanide-goethite system (conditions as given in Figure 17)...

An example of such a discrepancy is obtained from comparison of spectroscopic (XAS) data for the arsenate goethite system. The Fourier-transformed spectra obtained for identical conditions (i.e.. Fig. 3 in Ref. 44 and Fig. 2 in Ref. 45) show some difference. The authors of Ref 45 did not realize how close their conditions were to the ones by Waychunas et al. [44] for one of the samples and they, therefore, did not discuss this issue. 

In a second example, we calculate how pH affects sorption onto hydrous ferric oxide, expanding on our discussion (Section 10.4) of Dzombak and Morel s (1990) surface complexation model. We start as before, setting the dataset of surface reactions, suppressing the ferric minerals hematite (Fe203) and goethite (FeOOH), and specifying the amount of ferric oxide [represented in the calculation by Fe(OH)3 precipitate] in the system... 

Micro-XRD and micro-XANES analyses showed that the earliest stage of sulfide alteration is marked by the progressive oxidation of sulfide-S to sulfate-S that is then rapidly leached out from the system. Sulfide oxidation starts from particle rims or from intra-grain microfractures and is accompanied by a progressive loss of sulfur sulfides are then pseudomorphically replaced by goethite and minor bemalite. In addition to sulfides, many gangue silicates are efficiently altered and only quartz is preserved within the altered layers. 

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... 

It may prove possible to apply titration calorimetry data in one further direction. If AG can be estimated for SAL-goethite complexation and reaction enthalpies can be obtained under equilibrium conditions, then an entropy change for this reaction can also be derived. This can only be done, however, if the adsorption reaction can be shown to be reversible. Since this has not been proven as yet in our systems, such thermodynamic extensions of titration calorimetry can only be speculative at this time. 

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