Iron oxide isoelectric point

The basic flow sheet for the flotation-concentration of nonsulfide minerals is essentially the same as that for treating sulfides but the family of reagents used is different. The reagents utilized for nonsulfide mineral concentrations by flotation are usually fatty acids or their salts (RCOOH, RCOOM), sulfonates (RSO M), sulfates (RSO M), where M is usually Na or K, and R represents a linear, branched, or cycHc hydrocarbon chain and amines [R2N(R)3]A where R and R are hydrocarbon chains and A is an anion such as Cl or Br . Collectors for most nonsulfides can be selected on the basis of their isoelectric points. Thus at pH > pH p cationic surfactants are suitable collectors whereas at lower pH values anion-type collectors are selected as illustrated in Figure 10 (28). Figure 13 shows an iron ore flotation flow sheet as a representative of high volume oxide flotation practice. 

The Electrical Double Layer and Electrochemical Properties 235 Tab. 10.6 Isoelectric points and points of zero charge of iron oxides. 

Silicon, titanium, chromium, and aluminum oxides should be relatively acidic, with isoelectric points near 4.0, 6.0, 7.0, and 7.0, respectively. Iron oxide should be intermediate, with an isoelectric point near 9.0. Parks predicted the isoelectric point of nickel oxide to be of the order of 10-12. Other investigators [20] have reported the isoelectric point of nickel oxide to be near 9.4. 

As further discussed in Chapters 2 and 7, the sorption of arsenic on iron (oxy)(hydr)oxides is very sensitive to pH and competing anions, such as phosphate and sulfate (Goh and Lim, 2004). In general, the sorption of inorganic As(V) decreases as pH values rise from 3 to 10 (Su and Puls, 2001, 1489). H2As04 is the dominant As(V) ion at pH 3-6. At pH <6, the surfaces of iron (oxy)(hydr)oxides usually have net positive charges (i.e. they are below their zero points of charge (ZPCs) and isoelectric points ... 

Kittaka, S., Sasaki, S., and Morimoto, T., Spherical particles and their surface properties. Part 4. Spherical particles of vanadium oxide, manganese oxide and iron oxide and their isoelectric points, J. Mater. Sci., 22, 557, 1987. 

In an investigation of epoxide joints on iron and titanium using y-APS as a primer, Boerio [39] concluded that although the film structures formed by y-APS adsorbed onto the two metals were very similar, the performance of the films as adhesion promoters was very different. He concluded that the performance was determined by the orientation of the APS molecules at the oxide surface rather than by the overall structure of the film. The orientation was determined by the isoelectric point of the oxide and the pH at which the films were adsorbed onto the oxide [39,40]. A comprehensive account of the structure of APS silane films is provided by Ishida and co-workers [41]. 

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... 

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