Hematite suspensions

Effect of Metal Ion. To the hematite suspension already characterized one adds Pb(II). The surface complex formation is characterized by... 

Calculate the concentration of surface species and the surface charge as a function of pH for a hematite suspension which has the same characteristic as that used in the experiments of Liang and Morgan. 

Summary plot of experimentally derived stability ratios, Wexp, of hematite suspensions, as a function of added electrolyte or adsorbate concentration at pH around 6.5 (pH = 10.5 for Ca2+ and Na+). Hematite concentration is about 10-20 mg/ . The stability ratio, Wexp, was determined from measurements on the coagulation rate it is the reciprocal of the experimentally determined collision efficiency factor, a. 

Estimate the variation of surface charge of a hematite suspension (same charac-teristics as that used in Example 7.2) to which various concentrations of a ligand H2U (that forms bidentate surface complexes with the Fe(III) surface groups, FelT such a ligand could be oxalate, phtalate, salicylate or serve as a simplified model for a humic acid we assume acidity constants and surface complex formation constants representative for such ligands. The problem is essentially the same as that discussed in Example 5.1. We recalculate here for pH = 6.5. 

Fig. 7.11 gives results on coagulation of hematite suspension by fatty acids. As concentration is increased, an influence on hematite coagulation rate becomes notice-... 

Experimentally derived stability ratio, Wexp, of hematite suspensions, plotted as a function of fatty acid concentration at pH 5.2. The ionic strength is 50 milimolar NaCI and hematite concentration is 34.0 mg/ . Laurie acid is denoted by C, capric acid by C10, caprylic add by Cs and propionic acid by C3. (From Liang and Morgan, 1990)... 

Rate of the photochemical reductive dissolution of hematite, = d[Fe(II)]/dt, in the presence of oxalate as a function of the wavelength at constant incident light intensity (I0 = 1000 peinsteins "1 lr1). The hematite suspensions were deaerated initial oxalate concentration = 3.3 mM pH = 3. (In order to keep the rate of the thermal dissolution constant, a high enough concentration or iron(II), [Fe2+] = 0.15 mM, was added to the suspensions from the beginning. Thus, the rates correspond to dissolution rates due to the surface photoredox process). 

Light-induced dissolution of hematite in the presence of oxalate at pH 3. The deaerated hematite suspension was irradiated with light that had passed a monochromator (X = 375 nm I0 = 4 W nr2). Initial oxalate concentration = 3.3 mM. 

In parallel with the emission measurements, in situ Mossbauer absorption measurements on hematite suspensions treated in a similar manner as in the emission measurements were performed to check the effects of aqueous phase pH on the substrate. The absorption spectra obtained in the pH region 5-12 consisted of the same well-defined sextet as dry hematite powder, indicating that no appreciable change occurred in the state of dispersion and particle size of hematite in the studied pH range. 

Figure 3. Photochemical and thermal solubilization of hematite in deoxygenated hematite suspensions containing S(IV). (Reproduced from Ref. 42. Copyright 1985, American Chemical Society.)...

Smith, R.W. Schneider, I.A. Misra, M. (1994) Flocculation of fine hematite suspensions with conventional and bioflocculants. Abstracts 8 Int. Conf Colloid Surf. Chem. Adelaide... 

FIGURE 8.9 Photomicrograph of the highly ordered structure observed in a spindle-like hematite suspension. 

Figure 12.6 Experimentally derived stability ratio, of a hematite suspension plotted as a function of pH for different ionic strengths. The pH of the PZNPC is indicated. Dashed lines are drawn through the experimental points as a guide. The solid line has been model-calculated. From Ae/uaric Sciences 52(1) 32-55, L. Liang and J. J. Morgan, Chemical aspects of iron oxide coagulation in water Laboratory studies and implications for natural systems, Copyright 1990 by Birkhauser Verlag, Basel, Switzerland. Used by permission.

Figure 4. Effect of acidic and basic contamination, u, on the results of mass titration with a hematite suspension [47]. u/mol g- ( ) - 10- , ( ) 0, (a) lO" , ( ) lo-. ...

Figure 5a. Potentiometric acid-base titration of a concentrated hematite suspension [47].

Figure 6. The dependence of pHp c value of a hematite suspension on temperature. The ionic strength (10 mol dm ) was controlled by NaNOa [68].

Ramos-Tejada M.M. et al.. Interfacial and rheological properties of humic acid/ hematite suspensions, 7. Colloid Interf. Sci., 268, 85, 2003. 

Nsib. R, Ayed, N., and Chevalier, Y, Dispersion of hematite suspensions with sodium polymethacrylate dispersants in alkaline medium. Colloids Sutf. A, 286, 17, 2006. 

Preocanin, T., Krehula, S.. and Kallay, N., Enthalpy of surface reactions Temperature dependency of pH of acidic or basic concentrated hematite suspension, Appl. Surf. Sci., 196, 392, 2002. 

Sadowski, Z., The role of surfactant salts on the spherical agglomeration of hematite suspension. Colloids Surf. A, 173, 211, 2000. 

Figure 2 Adsorption density, F, of hematite suspensions as a function of total phtha-late concentration. Adsorption was under the following conditions hematite solid con-centration=17.6mg/l, pH=6.2 and (NaC104)= 5 millimolar. Solid line corresponds to a SCF/DLM model calculation.

Figure 5. (a) Experimentally derived stability ratio, of a hematite suspension, plotted as a function of polyelectrolyte concentration in the presence of 1 millimolar NaCl. Hematite concentration is 17.2 mg/1. (b) Electrophoretic mobility of a hematite suspension as a function of fulvic acid concentration at pH 6.58. Hematite concentration is 8.6 mg/1 and ionic strength as KCl is 5 millimolar. 

The potentiometric titrations were first applied by Bolt [18] to the study of double layers on oxides with silica sols and later by Parks and de Bruyn [5] with a-Fe203 (hematite) suspensions. Their investigations confirmed the potential-determining role of H and OH" and indicated that the oxide double layers are significantly different from the well-characterized classic double layers at the Agl/ and Hg/solution interfaces. 

Fane et al. (1982) discussed the possibility of UF flux enhancement by particulates. It was found that rigid particles larger than 1 pm could enhance flux. Cohesive and compressible particles, even if large, would cause flux reduction. Milonjic et al. (1996) filtered hematite suspensions and found that increased pressure and stirring lead to a increased flux. Chudacek and Fane (1984) measured deposit layers of several pm on UF membrane by macrosolutes and silica colloids. 

Hematite suspensions were equilibrated at various defined pH, salt, and fulvic acid concentrations for 17 hours with stirring at 220 rpm prior to membrane filtration. 

Figure 6.21 Cake resistance after filtration of 2.8 L of hematite suspension for different KCl concentrations ([a-Fe,OJ =10 mgL, pH = 3, AP = 300 kPa, stirrer speed = 520 rpm). The critical coagulation concentration at which aggngation is considered to change from reaction limitation to diffusion limitation is also shown.

Figure 6.22 Mass of cake formed on membrane filtration of hematite suspensions formed (and suspended) in 20 mM and 100 mM KCl. Cake masses deduced from both direct weight measurement and from amount of (X-Fe,0 retained (as determined bj iron analysis) are shown ([a-FefiJ = 10 mgL, pH = 3, AP = 300 kPa, UF cell stirrer speed = 520 rpm).

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