The Lasentec focused beam reflectance measurement (FBRM) probe provides in situ particle characterisation over a wide range of suspension concentrations. This is a significant advantage over conventional instruments that require sampling and dilution. However, FBRM gives a chord distribution, rather than a conventional diameter distribution. Both theoretical and empirical methods for converting from chord to diameter data are available, but the empirical method was found to be more successful.
The adsorption of water-soluble polymers (e.g., flocculants, coagulants) onto mineral particles is typically
characterized by “trains” of adsorbed polymer segments with “loops” and “tails” of unadsorbed polymer
segments that extend into the solution. Ex situ spectroscopic studies carried out in the past have been
complicated by the way in which the unadsorbed segments of the polymer interact with the surface of the
substrate upon drying. In this study, an in situ Fourier transform infrared attenuated total reflection
technique was used to examine the interaction of poly(acrylic acid) and hematite at pH 2. A hematite colloid
was deposited onto a ZnSe crystal, and the poly(acrylic acid) solution was subsequently pumped across
the coated crystal at a known rate. Polymer adsorption was irreversible and could be described by a
Langmuir isotherm, the rate of curvature of which suggested that the adsorption was weak. The mode
of adsorption was shown to be bidentate chelate complexation by the carboxylate functional group to a
surface ferric ion. Pimelic acid, a simple model compound effectively representing a polymer consisting
of only two monomer functionalities, adsorbed onto hematite in the same manner at pH 2 and gave no
infrared spectral peaks associated with unadsorbed carboxylate groups, thereby supporting the proposed
adsorption mechanism. The technique could also discriminate between the adsorbed and the unadsorbed
segments of the adsorbed polymer molecule, however; the fraction of adsorbed segments was difficult to
quantify. When a number of assumptions were made, it was found that at most 9% of the carboxylate
functional groups of the polymer were adsorbed onto the hematite.
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