Hematite strengths

The adhesion between two solid particles has been treated. In addition to van der Waals forces, there can be an important electrostatic contribution due to charging of the particles on separation [76]. The adhesion of hematite particles to stainless steel in aqueous media increased with increasing ionic strength, contrary to intuition for like-charged surfaces, but explainable in terms of electrical double-layer theory [77,78]. Hematite particles appear to form physical bonds with glass surfaces and chemical bonds when adhering to gelatin [79]. 

Iron Oxides. In addition to the black iron oxide, there are several natural and synthetic yellow, brown, and red oxides. As a class, they provide inexpensive but dull, lightfast, chemically resistant, and nontoxic colors. The natural products ate known as ocher, sieima, umber, hematite, and limonite. These include varying amounts of several impurities in particular, the umbers contain manganese. Their use is limited because of low chroma, low tinting strength, and poor gloss retention. 

Hematite. This additive can be used to increase the specific weight of a cement slurry to as high as 19 Ib/gal. This is an iron oxide ore with a specific gravity of about 5.02. Hematite requires the addition of some water when it is used as an additive. Hematite has minimal effect on thickening time and compressive strength of the cement. 

Ilmenite. This additive has a specific gravity of about 4.67. It is a mineral composed of iron, titanium and oxygen. It requires no additional water to be added to the slurry thus, it can yield slurry specific weights as high as the hematite additive. Ilmenite also has mineral effect on thickening time and compressive strength of the cement. 

Figure 1.96. Log /oj-pH diagram constructed for temperature = 200°C, ionic strength = 1, ES = 10 m, and EC = 10 m. Solid line represents aqueous sulfur and carbon species boundaries which are loci of equal molalities. Dashed lines represent the stability boundaries for some minerals. Ad adularia. Bn bomite, Cp chalcopyrite, Ht hematite, Ka kaolinite, Mt magnetite, Po pyrrhotite, Py pyrite, Se sericite. Heavy dashed lines (1), (2), and (3) are iso-activity lines for ZnCOs component in carbonate in equilibrium with sphalerite (1) 4 co3=0-1- (2) 4 ,co3=0-01- (3) 4 co3 =0-001 (Shikazono, 1977b).

Figure 1.196. /oj-pH ranges for hot-spring-type deposits and low sulfidation-type deposits. Temperature = 250°C, ES = 0.01 mol/kg H2O, ionic strength = 1. Ka kaolinite, Al alunite, SI liquid sulfur, Kf K-feldspar, Hm hematite, Mt magnetite, Py pyrite, Po pyrrhotite. Bn bomite, Cp chalcopyrite. 

Ilmenite has a specific gravity of 4700 kg/m. It requires no addition of water when added to the slurry. Ilmenite has a minimal effect on the thickening time and compressive strength. Barite requires more water then hematite when added to the cement. This results in a decrease of the compressive strength of the set cement. 

Fig. 6. Plateau-values, I"P1 /mg m 2, of adsorption isotherms of lysozyme (LSZ), ribonuclease (RNase), a -lactalbumin (aLA), calcium-depleted (X -lactalbumin (aLA(-Ca )) and bovine serum albumin (BSA) on hydrophobic polystyrene (PS) and hydrophilic hematite (a — Fe203) and silica (Si02) surfaces. An indication of the charge density of the surface is given by the zeta-potential, C, and of the proteins by + and signs. Ionic strength 0.05 M T = 25°C. (Derived from Currie et al. 2003).

Fig. 3.4a gives plots of charge resulting from surface protonation vs pH for various oxides. Dots represent experimental data from different authors (Table 3.1a) from titration curves at ionic strength I = 0.1 M (hematite = 0.2 M). It is interesting to note that the data "of different oxides" can be "normalised" i.e., made congruent, if we chose the master variable... 

Surface protonation isotherms. Dots represent experimental data from titration curves at ionic strength I = 0.1 (Hematite, I = 0.2). References are indicated in Table 3.1. The concentration of protonated sites MOH is given in moles nr2. BET surface data were used to calculate the surface concentration. 

Specific surface area 40 m2 g 1, acidity constants of FeOHg pK., (int) = 7.25, K 2 = 9.75, site density = 4.8 nrrr2, hematite cone = 10 mgle. Ionic strength 0.005. For the calculation the diffuse double layer model shall be used. 

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)... 

The three most abundant minerals forms are Fe203 (hematite), Fe(OH)j (hydrous ferric oxide or ferrihydrite), and FeO(OH) (goethite). The chemical reactions describing their dissolution and K in slightly acidic water at 25°C, 1 atm, and the ionic strength of... 

Kso can be obtained from K o by replacing by K laon- (K = ion product of water) as shown in the following example involving hematite in a low ionic strength solution at 25 °C ... 

The solubility and the hydrolysis constants enable the concentration of iron that will be in equilibrium with an iron oxide to be calculated. This value may be underestimated if solubility is enhanced by other processes such as complexation and reduction. Solubility is also influenced by ionic strength, temperature, particle size and by crystal defects in the oxide. In alkaline media, the solubility of Fe oxides increases with rising temperature, whereas in acidic media, the reverse occurs. Blesa et al., (1994) calculated log Kso values for Fe oxides over the temperature range 25-300 °C from the free energies of formation for hematite, log iCso fell from 0.44 at 25 °C to -10.62 at300°C. 

Avena and Koopal (1999) used reflectometry to study the kinetics of adsorption of Aldrich humic acid on hematite. Uptake was fast (diffusion-controlled) at low pH, but slow at pH > 5. The rate of uptake rose with ionic strength above the iep, but decreased with ionic strength below the iep. The adsorption of humic acid onto hematite rendered its surface hydrophobic and made it a suitable sorbent for hydrophobic organic compounds (Murphy et al., 1992). 

Andrade, E.M. Molina, F.V. Gordillo, G.J. Posadas, D. (1994a) Adhesion of colloidal hematite onto metallic surfaces. II. Influence of electrode potential, pH, ionic strength, colloid concentration, and nature of the electrolyte on the adhesion on mercury. J. Colloid Interface Sci. 165 459-466... 

Dang, M.-Z. Rancourt, D.G. Dutrizac J.E. La-marche, G. Provencher, R. (1998) Interplay of surface conditions, particle size, stoichiometry, cell parameters, and magnetism in synthetic hematite-like materials. Hyperfme Interactions 117 271-319 Daniele, P.G. Rigano, C. Sammartano, S. Zeland,V. (1994) Ionic strength dependence of formation constants - XVIII. The hydrolysis of iron(III) in aqueous KNOj solutions.Ta-lanta41 1577-1582... 

A.V. (1997) Adsorption of a corticoid on colloidal hematite particles of different geometries. J. Colloid Interface Sd. 187 429-434 Verdonck, L. Hoste, S. Roelandt, F.F. Van der Kelen, G.P. (1982) Normal coordinate analysis of a-FeOOH - a molecular approach. J. Molecular Structure 79 273-279 Vermilyea, D.A. (1966) The dissolution of ionic compounds in aqueous media. J. Electro-chem. Soc. 113 1067-1070 Vermohlen, K. Lewandowski, H. Narres, H-D. Schwager, M.S. (2000) Adsorption of polyelectrolytes onto oxides - the influence of ionic strength, molar mass and Ca " ions. Coll. Surf. A 163 45-53... 

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