Search results for "Kaolin"
showing 10 items of 90 documents
XRD microstructural analysis of mullites obtained from kaolinite–alumina mixtures
2000
Abstract A microstructural study of mullite obtained by the reaction sintering of kaolinite–α–alumina mixtures in the range 1150–1700°C has been performed by using X-ray line profile analyses together with scanning and transmission electron microscopy equipped with microanalysis by energy dispersion (SEM-EDS, TEM-AEM). Two kinds of morphology corresponding to primary (elongated grains) and secondary (equiaxed grains) mullite have been observed. A bimodal crystallite size distribution has been detected through XRD microstructural analysis from 1300°C. The results obtained by this method are compared with SEM/TEM data.
Optimization of the coagulation–flocculation treatment: influence of rapid mix parameters
1999
[EN] Turbid waters, containing suspended and colloidal particles, are normally treated by coagulation–flocculation followed by clarification; the process usually consists of the rapid dispersal of a coagulant into the raw water followed by an intense agitation commonly defined as rapid mixing. Rapid mixing is influenced by chemical and physical parameters and the final result of the whole treatment depends on this step. The study focused on the most important parameters of rapid mix design: velocity gradient and rapid mix time. Wastewaters from a tannery processing stored ovine hides were treated with aluminium(III) or iron(III) salts. Experimental results indicate that rapid mix time has a…
Determination of the depth profile distribution of guest species in microporous materials using the voltammetry of immobilized particles methodology:…
2014
A model for determining the in-depth profile distribution of electroactive species hosted in inorganic microporous matrixes using the voltammetry of immobilized particles methodology is described. The method, based on the analysis of cyclic voltammetric data at different potential scan rates, allows us to determine the in-depth profile variation of the concentration of electroactive guest species as well as the evaluation of the (oxidized form)/(reduced form) concentration ratio in cases where two oxidation states of the electroactive species coexist. The application to Maya blue-type materials prepared from lapachol, a naphtoquinonic dye, and palygorskite and kaolinite clays is reported. T…
�ber den ?Hygrophyllit? im Rotliegenden des Saar-Nahe-Gebietes, ein Beitrag zur Diagenese pyroklastischer Gesteine
1971
In certain areas rhyolitic tuffs of the Upper Rotliegend include a greenish, talc-like substance, called “Hygrophyllit”. It has been found too at the base of the Rotliegend in the Saarland. It is shown, that Hygrophyllit corresponds to decomposed pumice, related to the acid permian volcanism. X-ray, DTA and chemical investigations yielded, that Hygrophyllit consists essentially of a mixed layer mica-Ca-montmorillonite with random interstratification and previously about 33 % expandable layers. In consequence there are in the Rotliegend of the Saar-Nahe-Basin three different diagenetic developments of acid pyroclastic rocks: The formation of Kaolinite in the Lower Rotliegend, of devitrificat…
Imaging connected porosity of crystalline rock by contrast agent-aided X-ray microtomography and scanning electron microscopy
2017
We set out to study connected porosity of crystalline rock using X-ray microtomography and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) with caesium chloride as a contrast agent. Caesium is an important radionuclide regarding the final deposition of nuclear waste and also forms dense phases that can be readily distinguished by X-ray microtomography and SEM-EDS. Six samples from two sites, Olkiluoto (Finland) and Grimsel (Switzerland), where transport properties of crystalline rock are being studied in situ, were investigated using X-ray microtomography and SEM-EDS. The samples were imaged with X-ray microtomography, immersed in a saturated caesium chlorid…
Crystallite size of kaolinites as indicator of different geochemical types of bauxite
2009
A simple microstructural X-ray diffraction analysis using the Voigt function method reveals differences between bauxite deposits in the Iberian Range Catalanides area (NE, Spain). The highest values of apparent crystallite sizes, measured by volume weighted Dv values from 001 kaolinite reflection, have been found in bauxites of type 1.
Modeling plutonium sorption to kaolinite: Accounting for redox equilibria and the stability of surface species
2015
Abstract Plutonium with its particularly complex redox chemistry may be thermodynamically stable in the states + III to + VI depending on the redox conditions in the environment. Mineral surfaces can also affect Pu redox speciation. Therefore, the interpretation of Pu sorption data becomes particularly challenging, even for simplified laboratory experiments. The present study focuses on Pu sorption to kaolinite. Am(III), Th(IV), Np(V) and U(VI) literature sorption data are used as analogues for the corresponding Pu redox states to calibrate a simple surface complexation model, and the Nernst formalism is applied. Two independent pH–pe diagrams, one for the kaolinite surface and another for …
Redox tuning and species distribution in Maya Blue-type materials: a reassessment.
2013
Maya Blue-type specimens prepared from indigo (1 wt %) plus kaolinite, montmorillonite, palygorskite, sepiolite, and silicalite are studied. Liquid chromatography with diode array detection, ultra-performance liquid chromatography coupled with mass spectrometry, and pyrolysis-silylation gas chromatography-mass spectrometry analyses of the extracts from these specimens combined with spectral and solid-state voltammetry, electrochemical impedance spectroscopy, and scanning electrochemical microscopy techniques provide evidence for the presence of a significant amount of dehydroindigo and isatin accompanying indigo and other minority organic compounds in all samples. Solid-state electrochemist…
Synthesis of zeolite/geopolymer composite for enhanced sequestration of phosphate (PO43−) and ammonium (NH4+) ions; equilibrium properties and realis…
2021
Abstract Zeolite impeded geopolymer (Z/G) was synthesized from natural kaolinite and diatomite. The structure (Z/G) was characterized as an enhanced adsorbent for PO43− and NH4+ ions from aqueous solutions, groundwater, and sewage water. The synthetic Z/G structure exhibits sequestration capacities of 206 mg/g and 140 mg/g for PO43− and NH4+, respectively which are higher values than the recognized results for the geopolymer and other adsorbents in literature. The sequestration reactions of PO43− and NH4+ by Z/G are of Pseudo-Second order kinetic behavior considering both the Chi-squared (χ2) and correlation coefficient (R2) values. The sequestration reactions occur in homogenous and monola…
Alkali activated materials using pumice from the Aeolian Islands (Sicily, Italy) and their potentiality for cultural heritage applications: Prelimina…
2020
Abstract In this paper, the potentialities of pumice-based geopolymers have been explored with the aim to evaluate their use as restoration materials. In particular, the behaviour of Aeolian pumice during alkali activation process, either alone or in binary mixtures with metakaolin, has been assessed using sodium hydroxide and sodium silicate activators. Hardened products were characterized by: X-ray diffraction; infrared spectroscopy; thermo gravimetry and electron microscopy. Furthermore, Hg-intrusion porosimetry, water absorption, compressive strength and colorimetric measurements were carried out in order to define the technical features of the produced geopolymers. The results reveal t…