Hematite, isoelectric point

The charge of HPA, RNase and hematite vary with pH, with isoelectric points of 4.8, 9.3 and 6.5, respectively. 

A comparison of the adsorption effects of oxalic and citric acids on hematite leads to some rather useful conclusions. Electrophoretic mobilities as a function of the pH show a substantial shift in the isoelectric point of the iron oxide on addition of these acids to the dispersion, even at concentrations as low as 10 mol dm (Figure 11) [25]. The latter is a clear indication of the strong bond between the solutes and the... 

Based on these equilibria, one can schematically visualize the surface orientation of DFOB species at pH values below and above the isoelectric point of hematite (pH 8), by taking into consideration the charge on the adsorbate species, as illustrated in Fig. 21 [30]. At the low pH value the adsorption density of DFOB is low, due to its flat configuration on the solid surface, which also provides for... 

Ma et al. studied the adsorption behavior or PVP-SDS mixtures at two different mineral surfaces, Ti02 and FezOs [47,49]. They determined an isoelectric point of pH 5.1 for both surfaces. This result is in line with other i.e.p. determinations [54,55]. The abnormally low value recorded for natural hematite compared to synthetic FezOa means that the former is contaminated by SiOa. 

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