Kaolinite

Summary

Kaolinite (ˈkeɪ.ələˌnaɪt,_-lɪ- ) is a clay mineral, with the chemical composition Al2Si2O5(OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral sheet of alumina () octahedra. Kaolinite is a soft, earthy, usually white, mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicate minerals like feldspar. It has a low shrink–swell capacity and a low cation-exchange capacity (1–15 meq/100 g). Rocks that are rich in kaolinite, and halloysite, are known as kaolin (ˈkeɪ.əlᵻn) or china clay. In many parts of the world kaolin is colored pink-orange-red by iron oxide, giving it a distinct rust hue. Lower concentrations yield white, yellow, or light orange colors. Alternating layers are sometimes found, as at Providence Canyon State Park in Georgia, United States. Kaolin is an important raw material in many industries and applications. Commercial grades of kaolin are supplied

Official source

https://en.wikipedia.org/wiki/Kaolinite

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La synthèse d’analogues à la L-Lysine : Fmoc-q-Lysine-(Boc)-OH et Fmoc-q-Lysine-(Alloc)-OH et ses applications.

UNIL1996

The sediment-contact test using the ostracod Heterocypris incongruens: Effect of fine sediments and determination of toxicity thresholds

Rebecca Bebon

The toxicity test using freshwater ostracods of the species Heterocypris incongruens is a sub-chronic static test that exposes individuals to whole sediments over a period of 6 d, the endpoints being mortality and growth. We tested the hypothesis that endpoints of the sediment bioassay using Heterocypris incongruens are affected by the presence of fine sediment particles by testing control sediment supplied with the commercial test kit with increasing proportions of kaolin clay as a proxy for fines. While mortality was not affected, the results showed that increasing the presence of clay reduced ostracod growth. Based on the variability in growth, a sublethal toxicity threshold of 35% is proposed to distinguish effects due to sediment properties from those due to toxicity. The relevance of this threshold was verified using data from toxicity tests of ambient sediment samples with low levels of contamination. (C) 2016 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2016

The combination of calcined kaolinitic clays and limestone in Limestone Calcined Clay Cement (LC3) is a promising approach to reduce the cost and the CO2 emissions of cement production by reducing the clinker content of cement. This thesis investigates the feasibility of using various grades of calcined clays in LC3. LC3-50 blends with a clinker content reduced to 50% are studied. The factors controlling the reactivity of LC3-50 blends containing various grades of calcined kaolinitic clays were first studied. A benchmark test of mortar strength was developed. Similar strength to plain Portland cement (PC) can be obtained even for clays with 40% of calcined kaolinite only. Moreover, strengths are strongly dependent on the calcined kaolinite content of the calcined clay. The development of the new Rapid, Relevant and Reliable (R3) pozzolanic test allows the evaluation of the reactivity of calcined clays after only 24 h by isothermal calorimetry and 3 days simply using an oven, and it allows the prediction of the strength development of LC3-50 mortars. To explain strength results, a phase assemblage study was carried out. In order to determine the amount of reacted metakaolin, three methods were tested and mass balance was found to be the most reliable one. The phase assemblage study showed that a critical refinement of pore connectivity is reached already at 3 days for LC3-50 blends with high calcined kaolinite content. From this point on, clinker hydration is slowed down, and the formation of crystalline hydration products is limited. The on-going reaction of metakaolin leads to the higher incorporation of aluminium in the calcium alumino silicate hydrate (C-A-S-H). The C-A-S-H was fully characterized in terms of composition, morphology and density. No change in morphology was observed by Transmission Electron Microscopy. The C-A-S-H density determined by 1H-Nuclear Magnetic Resonance was also found to be similar between PC and LC3-50 with different calcined kaolinite content. Combining all this information, a good relationship is obtained between strength and gel space ratio for PC and for the LC3-50 blends. Finally, the chloride resistance was tested through ponding and chloride binding isotherm tests. The results also support previous findings for the use of calcined clays with a calcined kaolinite content of at least 40% to get a better chloride resistance than PC. These results are mainly explained by the pore connectivity refinement of LC3-50 blends compared with PC. The chloride binding is the highest for clays with 40-50% of calcined kaolinite.

EPFL2017