Patricia Aparicio

Mineralogical interference on kaolinite crystallinity index measurements

This study examines the influence of minerals and amorphous phases associated with kaolin and kaolinitic rocks on kaolinite crystallinity indices (KCI) derived from X-ray diffraction (XRD) data in order to select the best index for systematic studies of commercial kaolins or geological sequences. For this purpose, 8 kaolins of differing structural order were chosen and used to prepare mixtures containing different weight fractions of quartz, feldspar, illite, smectite, chlorite, halloysite and iron hydroxide and silica gels. An additional 17 samples of kaolin were also studied to test the results and evaluate the restrictions. KCIs used included Hinckley (HI), Range and Weiss (QF), Liètard (R2), Stoch (IK), Hughes and Brown (H&B) and Amigó et al. (full width at half maximum, FWHM), and the “expert system” of Plançon and Zacharie.Based on more than 15,000 KCI determinations, the HI and QF are influenced by quartz, feldspar, iron hydroxide gels, illite, smectite and halloysite. IK can be used in the presence of quartz, feldspar and iron hydroxide and silica gels. Also, R2 is the only KCI that could be measured in the presence of halloysite; FWHM indices should not be used in the presence of chlorite and/or halloysite; and H&B should only be used with pure kaolinite samples. The “expert system” of Plançon and Zacharie is strongly affected by the presence of other mineral phases, particularly with more than 25% of well-ordered kaolinite. Their system is less sensitive to other mineral phases when only disordered kaolinite is present, and it should not be used with kaolinite of medium order-disorder because the well-ordered phase is present in an inappreciable proportion (<10%). KCI is only measurable in kaolinitic rocks if kaolinite is >20 wt% and the precision increases with an increase in the quantity of kaolinite. In all cases, the reliability will depend on the other minerals present. When a KCI can be measured accurately, the others can be obtained by using the empirical relationships reported in this paper.

Residence and fractionation of rare earth elements during kaolinization of alkaline peraluminous granites in NW Spain

Abstract A geochemical and mineralogical study has allowed us to address the factors controlling distribution pattern, residence and behaviour of rare earth elements (REE) during kaolinization of Variscan granitoids in NW Spain. Mineral composition of the deeply weathered samples is dominated by kaolinite, with minor amounts of quartz, muscovite-illite, alkaline feldspar and traces of resistant minerals (rutile, ilmenite, zircon and monazite). Variable amounts of Si, Na, Ca, K, Rb, Cs, Ba, U and P were lost from the weathering profile, as a result of feldspars, mica and apatite breakdown, whereas Al, Fe, Ti, Zr, Th, Hf and REE were concentrated in the residual kaolin. Chondrite-normalized REE patterns of the kaolins show an overall enrichment of light REE (LaN/SmN = 1.22 - 2.53), heavy REE depletion (GdN/YbN = 2.42 - 15.10) and a strong negative Eu anomaly (Eu/Eu* = 0.11 - 0.25), probably inherited from the parent granite. Nevertheless, the normalization to the parent granite reveals some REE fractionation and increasing positive Eu anomalies with advancing weathering, in response to the breakdown of feldspars. Different grain-size fractions show similar REE distribution patterns, but differ in concentration levels. Although the fine fractions are the most important REE reservoir, there is no positive correlation with clay mineralogy. The correlative behaviour among P2O5, Th and REE in the <2 μm fraction suggests that monazite plays a dominant role controlling the REE budget in the weathering profile.

Current Industrial Applications of Palygorskite and Sepiolite

Abstract Sepiolite and palygorskite are very versatile materials due their properties. This chapter gives an overview of the applications and markets of the products that are currently manufactured with sepiolite and, to a lesser extent, palygorskite. An special emphasis is given to new applications and those that are being developed and are expected to become a reality in the near future. The shape of the particles and the large and active surface area are a source of physico-chemical and rheological characteristics useful in a wide variety of systems. The particular surface of this silicate influenced by six generations of processing methods opens new windows for applications that provide new solutions for industrial problems. New materials based on palygorskite and sepiolite, such as nanoclays, hybrids, bio-hybrids, biomimetic and functional materials, are being developed and studied for different uses that require new and better performance advanced materials.

A new kaolinite order index based on XRD profile fitting

Abstract The determination of kaolinite order-disorder by X-ray diffraction is problematic due to overlapping peaks from associated kaolin minerals and X-ray amorphous phases. This paper presents a new index (Aparicio-Galán-Ferrell index - AGFI), measured on 02l and 11l reflections after decomposing individual peaks in the complex diffraction band in an effort to reduce interferences. The new index was tested with three kaolins, of varying structural order, and their admixtures containing different percentages of quartz, feldspar, illite, smectite, chlorite, halloysite and Fe hydroxides and silica gels. The AGFI is highly correlated with the percentage of low-defect kaolinite and the Hinckley Index. It is not as prone to interference by associated minerals and X-ray amorphous phases as other indices. The AGFI can be used to determine kaolinite order-disorder in a wide variety of kaolins and kaolinitic rocks; the only prerequisite is that the kaolinite content should be >10 wt.% in order for the results to be reproducible.

Technical properties of compounded kaolin sample from Griva (Macedonia, Greece)

Abstract The purpose of this paper is to establish the possible industrial applications of Griva kaolin. This kaolin comes from the alteration of gabbroic rocks from the Griva area, Macedonia, Greece. Mineralogically, the kaolin is composed mainly of kaolinite associated with vermiculite and plagioclases, and traces of quartz, amphiboles, halloysite and smectites. The kaolin grain-size analysis shows that the kaolin is mostly finer than

A proposal for reducing F and Cl emission in the brick industry using new formulations

Abstract Emissions of F and Cl by the brick and tile industry of Bailen (Jaen, Spain) can be reduced by preparing mixtures of the three clays traditionally used in that area (white, and blonde Tertiary loams and Triassic red loam), which F content ranges between 850 and 1200 ppm, with an Al-rich clay of low F content ( 30% because its higher F initial content and its lower proportion of carbonate produce higher emissions. For Cl, the initial content is very low (

An application of profile fitting and CLAY++ for the quantitative representation (QR) of mixed-layer clay minerals

Abstract Clay mineral quantification by XRD is difficult when mixed-layer clay minerals and discrete clay types are both present. New procedures for peak decomposition and pattern simulation offer increased opportunities to obtain mineral abundance estimates. This proposed methodological sequence, for quantitative representation (QR) of complex clay samples, involves: (1) determination of layer type, mixed-layer proportion and order (R); (2) simulation of XRD patterns using MULCALC, an adaptation of NEWMOD; and (3) interpretation of the clay assemblage by fitting the whole pattern with CLAY++, a statistical program. The product is a QR of individual phases or a summation of layer types. The absence of quantitative reference standards means results cannot be checked for accuracy, but the statistical fit is highly reproducible and less prone to operator error. The QRs may be obtained with simulated or actual reference mineral patterns in the database. Results for freshwater marsh samples illustrate the approach.

Kaolin fractal dimension. Comparison with other properties

Abstract The fractal dimension values of several kaolins with different structural order and properties have been calculated from N2-adsorption isotherm data according to the Neimark method. All kaolins show a fractal regime in the same nitrogen relative pressure range, with fractal dimension values ranging between 2.38 and 2.57. The correlation between fractal dimension and other kaolin characteristics (structural order of kaolinite, BET surface area, brightness and particle-size distribution) was determined. The correlation matrix shows that the fractal dimension (Ds) is highly correlated with the degree of structural order-disorder and is also moderately correlated with the particle-size distribution and brightness. No correlation was observed between BET and Ds, probably because the first is a measurement of the accessible surface while Ds represents the scaling properties of the area. As Ds is a parameter easily calculated and related to the degree of surface heterogeneity, and well correlated with other kaolinite parameters, it can be used to estimate a set of kaolin technical properties for suitability of the kaolin in the paper industry.

Chapter 16 – Sepiolite and Palygorskite as Sealing Materials for the Geological Storage of Carbon Dioxide

Abstract This research provides experimental data on the reactive behaviour of sepiolite and palygorskite with CO2 in presence of water and under dry conditions, at temperatures of interest for geological CO2 sequestration. Results suggest that sepiolite and palygorskite are capable of sequestering CO2 through both a physical and a mineral mechanism. The physical trapping is higher for palygorskite than for sepiolite. But at the same time, these minerals are subject to attack by CO2 in either a dry or a wet environment, leading to partial decomposition of their structure, together with a reduction in volume and mechanical resistance. In the case of palygorskite, however, carbonates formed during reaction with CO2 can precipitate. Thus, a portion of the CO2 is chemically bound (‘trapped’). More importantly, the structural integrity of palygorskite is largely preserved. A geochemical modelling needs to be developed in order to predict the long-term reactive effect of geological CO2 storage when sepiolite- and palygorskite-rich rocks were used as sealing materials.

Fuchsite and other Cr-rich phyllosilicates in ultramafic enclaves from the Almadén mercury mining district, Spain

Abstract Fuchsite and other Cr-rich phyllosilicates, paragenetic with dolomite, are present in some ultramafic enclaves from the ‘frailesca’ rock (a lapilli- to block-size pyroclastic lithic-tuff), in the Almadén mercury mining district, Spain. Analyses (EMPA and TEM) of fuchsite and Cr-chlorite showed a relatively large range in levels of Cr2O3. Petrographic relationships between these phyllosilicates and primary relics of Cr-spinel crystals, as well as their high Cr content, indicate that these Cr-rich minerals originated from primary chromian spinels through an early hydrothermal alteration stage. The hydrothermal fluids accounting for this early alteration would be of relatively high temperature, high aCO2 and aK, and variable aNa/K. In a later alteration stage, fuchsite was partially or totally replaced by illite and Cr-illite, giving rise to an argillitic alteration.