Reagent-based selective separations of minerals are of great industrial importance. The basis of these separations is the competitive differential adsorption of the reagent onto a number of minerals. An X-ray photoelectron spectroscopic (XPS) study of the adsorption of polyacrylamide onto kaolin, feldspar and quartz is described. Initial data confirmed the utility of XPS for the study of polyacrylamide adsorption onto silica glass slides. Further results indicated the utility of the technique for the direct measurement of adsorption of polyacrylamide onto individual aliquots of kaolin, feldspar and quartz. Adsorption was relatively greatest onto kaolin. Feldspar displayed less adsorption and quartz very little. An imaging method was used to characterize, at least relatively, the competitive adsorption of polyacrylamide onto kaolin in the presence of mixtures of kaolin and quartz. This is a potential new technique for study of competitive adsorption.

Five Fe–bearing dioctahedral smectites (three nontronites and two Fe-rich smectites) were purified using a variety of physical and chemical procedures. The structural formulae indicate one nontronite and one Fe-rich smectite to be montmorillonitic, whereas the other three smectites are beidellitic. Mössbauer spectra showed Fe to be exclusively trivalent and were fitted with three doublets, two of which had quadrupole splittings characteristic of Fe3+ in octahedral coordination, whereas the third had a distinctly lower quadrupole splitting. Although the position of the Si–O stretching band in the infrared spectra could reflect tetrahedral Fe3+, the lack of distinctive features prevented a definitive attribution of this component to tetrahedral Fe3+. The 18O/16O data suggest that fractionation of nontronite-water at ambient temperatures (1000 lnα = 23 ± 2‰) is lower than that of Fe-rich smectite (1000 lnα = 27 ± 2‰). The estimated formation temperatures of the samples are below 70°C.

Montmorillonite was modified by replacing the exchangeable cations with betaines

(CH3)3N+ - (CH2)n - COO-M+ (n = 3, 5, 7, 10)

The betaine derivatives delaminated in water and formed a colloidal dispersion. Air-drying of this material yielded hard pieces which were difficult to redisperse. The dried material became redispersible in water when the Na ions (counterions to the carboxyl groups) were replaced by Li ions. Colloidal dispersions of this material were more stable against salts than Li+- or Na+ - montmorillonite. Extremely high LiCl concentrations (>1 mol/l) were needed to coagulate the betaine derivatives (n>5) in the presence of diphosphate. The increased salt stability resulted from lyospheres around the silicate layers or thin packets of them which reduced the van der Waals attraction. Addition of organic solvents destabilized the dispersion by compressing the diffuse ionic layer (DLVO theory). The delaminated particles then aggregated to small flocs which settled very slowly. Neither band-type structures nor cardhouses were formed at conditions comparable to network formation and stiffening of Li- and Na-montmorillonite dispersions. Rheological measurements revealed the liquefying action of the betaines. Dispersions of butyrobetaine montmorillonite (15 g solid/l) revealed a relative viscosity (related to the dispersion medium water) ηrel ≈ 2. The longer chain derivatives showed a value slightly >1 whereas Li+-montmorillonite had ηrel = 8. Yield values were not formed at pH ≈ 7. Only at acidic conditions did the butyrobetaine montmorillonite dispersion showed a small yield value (<200 mPa).

Batch reactor experiments were performed at 35°C and 80°C to determine the effect of high molar KOH solutions on the mineralogy and solution chemistry of two different smectites. The Ceca smectite is a nearly pure montmorillonite, and the Ibeco clay has a significant component of 35% beidellitic charge. Each reactor was charged with 1 g of <2 mm fraction smectite and 80, 160, 240 ml of 0.1–4 M KOH solution. In these experiments, the changes in solution composition and mineralogy were monitored as a function of time.

In the experiments, at all temperatures and under all chemical conditions, the smectite appears to change in diffracting domain size, which decreases with time. This probably reflects a change in crystal shape. The structures then become more illite rich and the diffracting domain continues to decrease.

The hydrothermal reactivity of a smectite saturated with K was studied experimentally at 300°C and 100 bar in (Na,K) chloride solutions (Na/K = 0, 50 and 100, liquid/solid ratio = 10/1). X-ray diffraction, TEM and microprobe results show: (1) a partial to total dissolution of the initial smectite layers; and (2) the crystallization of newly-formed euhedral I-S. Random I-S is formed after 7 days, but an ordered mixed-layer I-S containing <30% expandable layers formed in the longest runs (112 days). The I-S is characterized by non-expandable layers of two distinct types: dehydrated smectite and illite. The Si content is lower in the I-S than in the initial smectite, thus creating a charge deficit, mostly compensated by the introduction of Na to the interlayer space, and yielding a silica release to the solution and subsequent crystallization of quartz and cristobalite.

Naturally occurring sepiolite has been used as a support in the preparation of Ni and Pd catalysts. A precipitation procedure has been applied for both metals to deposit the precursor on to the support surface. The interaction between the sepiolite and the metal precursor has been studied by use of IR and solid-state MAS-NMR. Results show that SiOH groups are consumed in forming the Ni precursor whereas no specific interactions occur in the case of the Pd. However, strong interactions between metal precursor and the tetrahedral sheet occur for both metals leading to precursors which show a high stability under reducing conditions.

The Scherrer equation links the measured width of an X-ray diffraction peak (Scherrer width, SW) to the number of stacked cells (N) in the direction normal to the diffracting planes. The formula is only valid for one d-value occurring in the coherently diffracting domain. This equation can be modified for weakly swelling mixed-layer minerals. This assumes that the peak broadening caused by the mixed-layering is proportional to the amount of swelling component (S) and that the effects of size and mixed-layering are additive.

If two SW can be measured on XRD patterns from samples treated in two different ways (such as air dried or glycolated), N and S can be determined. This equation is applicable to illite-smectite mixed-layer minerals with high illitic content. The results are most accurate for N>30. The use of Scherrer's equation is discussed.

The adsorption of the metachromic dye acridine orange (AO) by Na-beidellite was investigated by visible spectroscopy. Different types of clay-AO association were identified from the appearance and location of absorption bands α or β. The colloidal properties were determined from curves of the absorbance vs. the degree of saturation. Three regions were identified in the absorbance curve. In the first region beidellite is peptized with small amounts of AO and the dye penetrates into the interlayer space where it undergoes metachromasy due to π interactions between the aromatic entity and the oxygen plane of the clay. With larger amounts of AO (second region), the clay flocculates due to the aggregation of the dye cations in the interparticle space of the flocs. In excess AO (third region), beidellite is gradually peptized, forming small tactoids with monomeric AO in the interlayer space and at the same time adsorbing dimeric and polymeric AO cationic species at the solid-liquid interface. Compared with the other smectites, AO shows the greatest tendency to undergo metachromasy in the presence of beidellite.

Sandstones and mudstones of the Skagerrak Formation from the Danish Sub-basin have been studied to assess the origin of the clay minerals, their diagenesis and their transformation/ conversion temperatures (compared to modelled maximum burial temperatures). Detrital smectite and vermiculite occur only at shallow levels. Conversion of smectite into random S-I took place at >47°C and of random S-I into ordered I-S at >74°C. The omnipresent illite increases in amount with burial. The amount of authigenic kaolinite (kaolin) decreases with increasing temperature (>75°C), possibly due to the growth of chlorite. Random S-C is converted into ordered S-C between 70°C and 105°C and chlorite is most abundant at maximum burial temperatures (150°C). This investigation suggests that diagenesis of clay minerals begins at relatively low temperatures, and emphasizes the importance of the availability of necessary ions (K+, Mg2+, Fe2+) for the reactions, besides time and temperature, as controlling parameters.

A series of Mn-goethites was synthesized at highly alkaline conditions. The samples were aged for 15 days at a final [KOH] of 0.3 M. Products were washed free from non-goethite phases using 3 M H2SO4. The bulk mineralogy of the samples was determined by X-ray diffraction and verified on selected individual crystals by electron diffraction. The samples had a relatively low magnetic susceptibility (300≤MS≤400×10-9 m3/kg). As revealed by total acid dissolution, the Mn mole fraction XMn ranged from zero to 0.125. Five samples (XMn: 0.025, 0.050, 0.077, 0.099, 0.125) were selected to investigate the variability of the XMn value in single goethite needles (crystals) by analytical electron microscopy (AEM) using rastered and spot analyses. Linear regressions of both as a function of total Mn yielded unit slopes and zero intercepts, indicating that acid dissolution gave the same results as AEM. Spot AEM, however, revealed significant variation of Mn distribution within individual crystals which argues in favour of Mn zoning in goethite. Inhomogeneous transformation of ferrihydrite to goethite may partly explain the Mn zoning.

The Cu,Cr-, Zn,Cr- and Cu,Al-layered double hydroxides have been synthesized by the coprecipitation method and characterized by elemental analysis, PXRD, SEM/EDS and BET. The mixed oxide materials obtained upon calcination at 873 K show very high catalytic activity for the combustion of toluene and ethanol. The best sample is derived from the Cu,Cr-LDH precursor with a Cu:Cr ratio of 2, composed of copper oxide and copper chromite. This catalyst gave 50% conversion of toluene and ethanol at temperatures of 45 and 15 K lower, respectively, than the reference commercial catalyst. Catalytic tests with a mechanical mixture of CuO and CuCr2O4 demonstrate that the use of an LDH precursor is essential for optimum results. The importance of the simultaneous presence of both Cu and Cr, the influence of the Cu:Cr ratio on the catalytic activity and the role of the interface boundaries in the CuO-CuCr2O4 mixed oxide system are discussed.

The adsorption by different silicate minerals of some heavy metals, present in industrial waste water, has been studied. These adsorbents (mainly clay minerals) are readily available, inexpensive materials and offer a cost-effective alternative to conventional treatment of wastes from the metal finishing industry. The results show that some mineral species are suitable for the purification of such residual waters down to the limits prescribed by current legislation concerning industrial wastes. The Langmuir model was found to describe such adsorption processes best. Sepiolite (Orera, Spain) has an adsorption capacity of 8.26 mg g-1 for Cd2+, the capacities depending on the metal adsorbed in the order: Cd2+ > Cu2+ > Zn2+ > Ni2+. This mineral shows the highest sorption capacity relative to the other minerals studied. Factors in the reaction medium such as pH and ionic strength influenced the adsorption process.

Catalytic properties of Cu-doped alumina-pillared montmorillonite samples have been tested in the liquid phase oxidation of toluene, o-, m-, and p-xylene with hydrogen peroxide. The results show that the clay samples possess significant activity for both the oxidation of methyl groups and hydroxylation of the aromatic ring. Physicochemical characterization of the catalysts using XRD, BET, ESR and ICP-AES techniques show that they are porous materials with Cu species located in the interlayer, present either as isolated Cu2+ ions anchored at alumina pillars or as patches of amorphous CuO. The dependence of the overall yields on the amount of Cu dopant is discussed and explained in terms of the catalyst structural properties.

To gain a deeper understanding of the geochemical processes involved in the interactions between ionic solutions and clay minerals in natural systems, the dissolution rate of an Fe-rich saponite from Mt. Prinzera (Taro Valley, Italy) was measured as a function of pH and time at 25°C. Also, its ability to adsorb Cr was studied at varying metal concentrations (3.22, 5.50, 8.50 mEq l-1) and with different competing anions (CH3COO-, Cl-, NO3-). It was found that there is a correlation between the experimentally determined release rate constant (k), as defined by the relase of Si, and pH. In acidic solutions, the k values correlate negatively with pH, whereas the opposite occurs for basic solutions. The extent of Cr uptake was measured by analysis of the liquid portion separated by centrifugation after a controlled period of exposure. The Cr adsorbed for different concentrations and anionic environments shows the dependence of Cr uptake on the initial metal concentration and on accompanying anions in the order CH3COO-, Cl-, NO3-.

Ochre sediments from acid mine drainage in Cornwall have been investigated using X-ray diffraction, thermal methods, infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and chemical methods in order to determine their mineralogical and chemical composition. Fresh sediments consist of ferrihydrite and goethite. Large fractions of these minerals are dissolved by the ammonium oxalate treatment reflecting their poorly crystalline structure. Fresh sediments contain large amounts of surface-adsorbed SO4 (up to 9.3%) which is readily desorbed by the PO4 treatment. Goethite is the only mineral present in relatively older sediments and the mineral is well crystallized with rod-shaped morphology. Environmental conditions, such as pH and SO4 content, are not favourable for the presence of schwertmannite at the site. Iron minerals appear to be precipitating around filamentous algae and the shape of algae is preserved in the Fe oxide matrix. The ubiquitous presence of algae in close association with Fe minerals indicate their possible role in the crystallization of Fe oxides.

Raman spectra of a selection of kaolins with widely varying TiO2 contents revealed the presence of anatase in 17 of 18 samples. A significant positive correlation was observed between the intensity of the main anatase Raman band at ~145 cm-1 and the total TiO2 contents of the kaolins as determined by chemical analysis. No TiO2 modification other than anatase was detected in any of the samples.

The determination of the anatase contents in kaolins by XRD becomes increasingly difficult as the concentration of this mineral decreases below ~0.5%. In contrast, anatase and brookite concentrations an order of magnitude lower can still be readily identified by Raman spectroscopy. The specificity and sensitivity of Raman spectroscopy for these TiO2 polymorphs, coupled with the simplicity and rapidity of measurement, therefore make this a viable technique for the routine study of these accessory minerals in kaolins.

X-ray diffraction (XRD), infra red (IR) spectroscopy, gloss goniophotometry and stylus profilometry were used to investigate the alignment of kaolinite applied as a thin coating on a polyester film substrate. The principles and applicability of the analytical methods are reviewed and discussed in the context of a kaolinite coating. X-ray diffraction and transmission IR were used to measure kaolinite misalignment and orientation distribution in the coating. Transmission IR measures the coating bulk; XRD data are surface biased, but contain contributions from the bulk. Attenuated total reflectance-IR (ATR-IR) provides a direct measure of kaolinite alignment within ~1 µm of the coating surface and also allows an assessment of surface smoothness. Gloss goniophotometry and contact profilometry measure surface microroughness and macroroughness, respectively, rather than kaolinite particle orientation. However, the properties of roughness and orientation are related. Bulk and surface texture are not necessarily correlated and a combined approach using both bulk and surface sensitive techniques is required for a full understanding of coating structure.

Due to its channels of molecular dimensions and a high specific surface area, sepiolite has many industrial applications which require high resistance to thermal effects in addition to a large surface area. On heating, sorbed water molecules are removed causing changes in the pore size distribution. In this study, the effects of thermal treatment on the pore structure of sepiolite and the acid-treated sepiolite samples were investigated. The solid density of sepiolite, measured by a He displacement technique, was 2.08 g cm-3 and total porosity was ~0.58. Both of these values showed an increase at 100°C, then decreased with further temperature increase due to crystal deformation and channel plugging which occurred at elevated temperatures. The BET surface area of the original sepiolite was 148 m2 g-1, and increased to 263 m2 g-1 at 100°C and then started to decrease. Approximately 16% of the total volume was in the micropores at 100°C. The acid pre-activation caused restrictions in possible crystal deformation during thermal treatment. The micropore volume increased to 20% and BET surface area reached values >500 m2 g-1 for the acid-treated samples.

The fine silt (2–5 μm) and fine clay (<0.1 μm) fractions from four acid soils developed from moraines of increasing age (80, 400, 3,000 and 6,500 years old) in Switzerland, were studied by X-ray diffraction and chemical analyses. The soil parent material is homogeneous at the four sites and the soils can be considered as forming a chronosequence of soil development leading to the formation of Podzols. Mineralogical evolution of silt-sized phyllosilicates and fine clay fractions follows different pathways according to their composition and the soil horizon in which they are located. Dioctahedral and trioctahedral minerals in the soil parent material were both weathered in the Bw and Bs horizons but the trioctahedral phase more strongly and faster than the dioctahedral one. Weathering products are mica-vermiculite mixed-layers, vermiculite and finally gibbsite and Fe oxy-hydroxides. Weathering of the trioctahedral fraction was faster in the eluvial A or E horizons than in the B horizons, being almost complete after 3,000 years of soil development. Appreciable weathering of the dioctahedral fraction occurs only in the eluvial horizons leading to the formation of mica-smectite mixed-layers and smectite. Although smectite has been reported in the E horizon of Podzols in different environments, the significant finding in this work is the presence of this mineral in soils developed from the same parent material. This supports the fact that smectite is the end- product of mica alteration in strongly leached and acidified E horizons of Podzols.

The ability to produce humic-like polymeric compounds, with D-glucose and L-tyrosine as starting materials, was evaluated in different mineral systems: (1) Ca-, Al- and Cu(II)-saturated montmorillonite; (2) Ca-, Al- and Cu(II)-saturated kaolinite; (3) quartz in the presence of two different amounts of the same cations (according to the cation exchange capacity of the clays); and (4) untreated quartz (as control). All systems proved to be effective in the formation of humic-like compounds, particularly quartz, in the presence of cations. The effectiveness in promoting humification reactions was strictly related to the amounts of added cations. In the reaction conditions considered, the humification appears to be due more to the cations than to the type of clay minerals. The clayey systems synthesized more complex (aromatic) substances than the quartz ones.