Hematite Colloids

Amal, R. Coury J.R. Raper, J.A. Walsh,W.P. Waite, T.D. (1990a) Structure and kinetics of aggregating colloidal hematite. Colloids Surfaces 46 1-19... 

Degueldre, C., Ulrich, H. G. Silby, H. 1994. Sorption of 243Am onto montmorillonite, illite and hematite colloids. Radiochimica Acta, 65, 173-179. 

Tiller and O Melia (1993) compared their polymer adsorption statistics calculations with data from laboratory experiments on the interaction of polyacrylic and polyaspartic acid as well as of humic acids with hematite. Their conclusion is that, at low ionic strength, anionic polyelectrolytes affect the coagulation of positively charged particles by altering the net surface charge in a way similar to that of multivalent, monomeric anions. Steric repulsion, at low ionic strength (i.e., in fresh water), plays little or no role in the stabilization of hematite colloids by the organic macromolecules used in their work calcium... 

Penners, N.H.G.. Koopal. L.K., and Lyklema. J.. Interfaciai electrochemistry of haematite (a-FcjOj) Homodisperse and heterodisperse sols. Colloids Sutf.. 21.457,1986. Shchukaiev. A.. Boily, J.-E, and Fehny. A.R., XPS of fast-frozen hematite colloids in NaCl aqueous solutions I. Evidence for the formation of multiple layers of hydrated sodium and chloride ions induced by the 001) basal plane, J. Phys. Chem. C, 111, 18307. 2007. 

Cromieres, L. et al.. Sorption of thorium onto hematite colloids, Radiochim. Acta, 82, 249, 1999. 

Kovacevic, D. et al., The use of elecUokinetic potential in the interpretation of adsorption phenomena Adsorption of salicylic acid on hematite, Colloids Surf. A, 140, 261, 1998. 

Kumar, S. et al.. Effect of humic acid on the sorption of technetium on hematite colloids using Tc and Tc as tracers, J. Radioanal. Nucl. Chem., 274, 229, 2007. 

Some methods which required special attention, such as concentration of NOM, drawings and hydrodynamic analysis of the filtration equipment, synthesis of hematite colloids, instrument calibration (DOC and W), and solution speciation are shown in Appendix 1, 2, 3, 4, and 5, respectively. 

The synthesis of monodispersed, spherical hematite colloids of four primary particle sizes is described in detail in Appendix 3. The main properties of these colloids are also given in Appendix 3. 

Figure 4.19 depicts hematite colloids in possible aggregation and colloid-organic interaction stages. The pictures are obviously simplifications, but nevertheless help to understand the different filtration behaviour of these particulate assemblages. 

Figure 4.19 Postulated structures (A) stable hematite colloids in absence of organics, (B) reaction limited aggregation (RLAJ, (C) diffusion limited aggregation (DLAJ, (D) SPO aggregates with organics, (E) OPS colloids stabilised with organics, (F) OPS colloids stabilised with NOM, (G) OPS colloids stabilised with organics and destabilised with calcium.

Figure 4.20 2.eta potential of hematite colloids as a function of pH in absence of organics and salt solution. 

Figure 4.21 2.eta potential of hematite colloids at pH 3 without background solution with FA and at pH 8 in presence of background solution with HA. 

Background Salt, Hematite 1 Figure 4.22 Zeta potential of hematite colloids... 

The method was used to measure the size of primar) hematite colloids (see Appendix 3) and the solubility of organics in the presence of calcium. The latter results can be summarised in a number of points. Firstly, no particulates were measured for FA. FA was prepared ar pH 3, pH 6, in the presence of 75 mM NaCl, and in the presence of 25 mM CaClz at pH 8 and 10. A regation or precipitation were not observed under any of these conditions. This indicates that the interaction between FA and calcium is minimal and that FA is vety soluble, even at high salt conditions. 

Table 5.5 Deposition and rejection of hematite colloids, organic rjection, and flux decline as a function of organic type and concentration, calcium concentration andpH (GVWP membrane, SPO).

Figure 5.12 Complete blocking and Cace filtration law for stable hematite colloids at pH 3.0 as a function of colloid si e.

These membrane filtration results are presumably again correlated with the different aggregation behaviour of the hematite colloids for different concentrations of fulvic acid. Indeed, as shown in Figure 6.27, the cake resistance is at a minimum at the fulvic acid concentration (approximately 1 mg.L ) where the zeta potential of the hematite particles is close to zero and where rapid aggregation has previously been observed to occur (Amal et al (1992)). At fulvic acid concentrations either side of this critical concentration, aggregation has been seen to be retarded due to the presence of high residual surface charge. 

For the 10 kDa membrane (see Figure 6.42) the DOC rejection in the OPS case is similar to that found in the absence of colloids (refer to Figure 6.31). The UV rejection is higher due to the additional rejection of UV absorbing hematite colloids. 

Adsorption of FA on the hematite colloids may have a similar effect if charge is neutralised before being reversed. The aggregate structure effect could only be observed at certain primary particle to pore size ratios. While the effect is strong for the 100 kDa membrane when looking at the 75 nm primary colloid size, the same effect was not observed with the 10 kDa membrane. Therefore,... 

In the presence of OPS colloids, the flux decline is fully reversible and the particles themselves do not cause flux decline. This is because the hematite colloids are very large compared to the membrane pores. The colloids may adsorb some of the larger molecules which are responsible for fouling. 

Ferric chloride pretreatment of the solutions which also included hematite colloids confirmed the trends of low organic, but high cation rejection at the high dosage. 

In the presence of pre-prepared hematite colloids (OPS and SPO systems as described in Chapter 4), rejection is as shown in Table 8.8. The rejection is compared to organic rejection of membranes without pretreatment in Figure 8.6. In the presence of these colloids the scatter in the data is reduced, possibly due to the formation of a more stable deposit. The rejections with MF are now comparable to those obtained with NF. 

When colloidal hematite particles are present (Table 8.10) the effect of ferric chloride dosing is smaller and resistances are highest for the 100 kDa membrane. In the presence of the hematite colloids it appears as if permeation drag becomes important and pressure plays a minor role. 

The variation of membrane area due to ferric chloride dosage is listed in Table 8.15. The sample experiments chosen are those in the absence of additional hematite colloids. For MF and UF, organic... 

Table A3.3 Characteristics of hematite colloids and, ferric chloride floes for comparison (Crosby etal. (1983)).

Interferences are expected from colloids (not retained by the 0.45 im filter), and various UV absorbing inorganics such as ferrous iron. When hematite colloids or ferric chloride coagulant were added to samples, the UV measurement did not give any information about carbon content, as the absorbance of hematite or ferric chloride was identical or higher than that of the organics. 

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