Kaolinite strengths

Binders. To create needed physical strength in catalysts, materials called binders are added (51) they bond the catalyst. A common binder material is a clay mineral such as kaolinite. The clay is added to the mixture of microparticles as they are formed into the desired particle shape, for example, by extmsion. Then the support is heated to remove water and possibly burnout material and then subjected to a high temperature, possibly 1500°C, to cause vitrification of the clay this is a conversion of the clay into a glasslike form that spreads over the microparticles of the support and binds them together. 

Typical adsorption isotherms are shown in Figs. 16 and 17. Despite the large experimental scatter, a steep increase in adsorption can be seen at low concentrations, followed by a plateau at concentrations exceeding the CMC. Similar behavior has been observed before with model surfactants [49-54] and has also been predicted by modem theories of adsorption [54]. According to Fig. 16, adsorption increases modestly with salinity provided that the calcium ion concentration remains low. The calcium influence, shown in Fig. 17, cannot be explained by ionic strength effects alone but may be due to calcium-kaolinite interactions. 

Gangue minerals and salinity give constraints on the pH range. The thermochemical stability field of adularia, sericite and kaolinite depends on temperature, ionic strength, pH and potassium ion concentration of the aqueous phase. The potassium ion concentration is estimated from the empirical relation of Na+/K+ obtained from analyses of geothermal waters (White, 1965 Ellis, 1969 Fournier and Truesdell, 1973), experimental data on rock-water interactions (e.g., Mottl and Holland, 1978) and assuming that salinity of inclusion fluids is equal to ffZNa+ -h m + in which m is molal concentration. From these data potassium ion concentration was assumed to be 0.1 and 0.2 mol/kg H2O for 200°C and 250°C. 

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. 

Mahoney JJ, Langmuir D (1991) Adsorption of Sr on kaolinite, illite, and montmorillonite at high ionic strengths. Radiochim Acta 54 139-144... 

Kaolinite, Al2Si205(0H)4 or Al203-2Si02-2H20 , is a sheet silicate with A1 atoms in octahedral and Si atoms in tetrahedral coordination the corresponding electrostatic bond strengths are ... 

Clays used in foundries include hydrous alumina silicates, known as bentonites. Their properties provide cohesion and plasticity in the green state and also high strength when dried. There are three clays that are commonly used in foundries western bentonite [sodium bentonite, burnout point 1290°C (2350°F)], southern bentonite [calcium bentonite, burnout point 1065°C (1950°F)], and fire clay [kaolinite, burnout point 1425°C (2600°F)]. 

Adsorption on Kaolinite. For kaolinite, the polymer adsorption density is strongly dependent on the solid/liquid ratio, S/L, of the clay suspension. As S/L increases, adsorption decreases. This S/L dependence cannot be due totally to autocoagulation of the clay particles since this dependence is observed even in the absence of Ca2+ at pH 7 and at low ionic strength where auto-coagulation as measured by the Bingham yield stress is relatively weak (21). Furthermore, complete dispersion of the particles in solvent by ultra-sonication before addition of... 

Adsorption of nonionic and anionic polyacrylamides on kaolinite clay is studied together with various flocculation properties (settling rate, sediment volume, supernatant clarity and suspension viscosity) under controlled conditions of pH, ionic strength and agitation. Adsorption and flocculation data obtained simultaneously for selected systems were correlated to obtain information on the dependence of flocculation on the surface coverage. Interestingly, optimum polymer concentration and type vary depending upon the flocculation response that is monitored. This is discussed in terms of the different properties of the floes and the floe network that control different flocculation responses. Flocculation itself is examined as the cumulative result of many subprocesses that can depend differently on system properties. 

Providing a flat surface can be achieved, tapping mode AFM topological and phase imaging can be used to investigate HPAM adsorption and mineral surfaces. Information on the film height, the strength of interaction between polymer-mineral surface and an indication of the adsorption process may be obtained. HPAM adsorption on kaolinite was observed to form a flat uniform layer... 

The ratio of the values for the NMR relaxation times in water and at the silica surface are in good agreement with that observed experimentally. Effects due to ionic strength are minor. For kaolinite there is no published experimental data for comparison due to problems with uneven coagulation. However, predicted values for kaolinite are of the same order as for silica. 

Assuming a correlation between surface complexation and aqueous hydrolysis exists, the trend in strengths of surfaces complexes for An in different oxidation states onto a given mineral would be in the order An4+ > AnC>2+ > An3+ > AnOj. Several authors have provided evidence for linear relations between the first hydrolysis constant of metals and the intrinsic constant associated to the formation of surface species of metals as S-OMamorphous silica (Schindler Stumm 1987), hydrous ferric oxides (Dzombak Morel 1990), aluminum (hydr-)oxides and kaolinite (Del Nero et al. 1997, 1999a). 

The effect of water content on the acidity of kaolinite was examined by Solomon and co-workers (235, 236). Kaolinite dried at 110°C (0% water) had strongly acidic sites, comparable to 90% sulfuric acid (pKa < —8.2), as indicated by the Hammett indicator method. The strongest sites were readily poisoned by water. At 1% wt water content the strongest acid sites were equivalent in strength to 48% sulfuric acid (pKa = 3.0). With... 

Figure 1. Butylamine titration vs. acid strength for clays dried at 120°C. Key -----, attapulgite — —, montmorillonite -----, kaolinite and vertical lines denote titer uncertainties. (Reproduced from Ref. 10. Copyright 1957, American...

Detailed experimental procedures have been previously reported (Ko, 1998 Ko et al., 1998a,b) therefore, they are only briefly described here. Phenanthrene (Aldrich, 99.5+%), naphthalene (Aldrich, 99+%), SDS (Sigma, 99.5+%), and Tween 80 (Aldrich, no purity reported) were used as received selected physicochemical properties for these compounds are shown in Table 1. Kaolinite, a nonswelling 1 1 layer phyllosilicate clay and common constituent of many subsurface environments, was used as received from Sigma. Solution pH and ionic strength were adjusted as necessary with 0.5 M HC1 and/or 0.5 M NaOH and NaCl, respectively. Aqueous phenanthrene and naphthalene concentrations were quantified by fluorescence (PTI, Inc.) at the excitation/emission wavelengths of 250/364 and 278/322 nm, respectively. A total organic carbon (TOC) analyzer (Shimadzu Model 5050) was used to determine aqueous SDS concentrations and Tween 80 concentrations were determined by UV absorbance at 234 nm. 

Figure 2. Surfactant sorption on kaolinite for two ionic strength conditions (as added NaCl) at pH 4,6. Error bars for some data points are smaller than the symbols. Kaolinite concentration was 100 g/L. Adapted from Ko et al, (l998a).

Figure 7. Effect of pH on phenanthrene distribution (A. 0) and organic carbon normalized partition (/ ) coefficients for sorbed SDS, The ionic strength was 0.1 M NaCl, and the kaolinite concentration was 100 g/L. Error bars for some data points are smaller than the symbols. The solid line is the average Kx value for pH values above the PZC of kaolinite, The predicted value is based on an equation from Schwarzenbach et al. (1993), Adapted from Ko et al. (1998a).

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