Kaolinite amorphous material

The problem with limited selectivity includes some of the minerals which are problems for XRD illite, muscovite, smectites and mixed-layer clays. Poor crystallinity creates problems with both XRD and FTIR. The IR spectrum of an amorphous material lacks sharp distinguishing features but retains spectral intensity in the regions typical of its composition. The X-ray diffraction pattern shows low intensity relative to well-defined crystalline structures. The major problem for IR is selectivity for XRD it is sensitivity. In an interlaboratory FTIR comparison (7), two laboratories gave similar results for kaolinite, calcite, and illite, but substantially different results for montmorillonite and quartz. 

Chemical dissolution techniques indicate kaolinite from Cornwall contains 3.1-4.9% of easily soluble Si02 and 1.5-5.9% of easily soluble A1203 (Follett et al., 1965). Most of this material is presumably present as amorphous material. Experiments (by the senior author) with Georgia kaolinite indicate the amount of amorphous material varies as a function of particle size and preparation (Table LX). Amorphous silica and alumina is a common constituent of kaolinite and considerable care must be taken in determining and interpreting the significance of the Si/Al ratio of kaolinites. 

Eberl, D., 1970. Low-temperature synthesis of kaolinite from amorphous material at neutral pH. Conf. Clay Minerals Soc., 19th, Abstr., p. 17. 

Electroacoustic studies of silica at high ionic strengths produced controversial results similar to those discussed in Section 4.3.2. Amorphous materials [1813,1870] showed a shift in the IEP to high pH at 1-1 electrolyte concentrations of 0.1 M or higher. The shift was more substantial in the presence of Cs than in the presence of other monovalent cations. This result is in line with the cation specificity series reported in Section 4.1.5. However, the IEP of quartz [1813] was not shifted in the presence of 1-1 electrolytes. Montmorillonite and kaolinite [2271] showed shifts in the IEP and similar cation affinity series as amorphous silica. Contradictory results are reported for goethite [76,1318]. 

Kaolin is the common name used for kaolinite (. v.), a white clay mineral of composition Al4[Si40io](OH)g derived from the weathering of feldspars. Correctly, kaolin consists of both crystalline and amorphous material, whereas kaolinite is completely crystalline. Particle size is normally extremely fine, though typically it appears as a highly laminated agglomerate of platelets (one author graphically describes it as a booklet ). Calcium, magnesium and potassium are also commonly associated with kaohn as trace elements. 

The resulting XRD pattern (Figure 3a), displayed a broad peak characteristic of an amorphous material. The calcination at 700°C of kaolin involved the transformation in dehydrated kaolinite, but some crystallized peaks were also detected and were due to traces of illite clay present as a contaminant. The shift in 20 peak position observed in the geo-material XRD pattern by comparison with the dehydrated kaolinite XRD pattern provided evidence for dissolution of Si04 and AIO4 species which came from dehydrated kaolinite, into the alkaline environment, during the geopolymerization reaction as detected by ATR measurements. 

Alluvial soils of the Mississippi River plain have been studied by de Mumbrum and Bruce [I960]. The main minerals in these soils are montmorillonite, mica, kaolinite, quartz, and some amorphous material with occasional chlorite, and interstratified montmorillonite-vermiculite was found at 54 in. (1.37 m) depths in fine silt. 

The adsorbents have been prepared fi-om the halloysite (H) - mineral fi-om kaolinite group with an admixture of carbonaceous materials refinery waste deposits (RSI), sediment communal sewage (CSew) and cellulose (Ce), and the fiaction of these mixtures were within 30 - 70 wt.%. The mbcture of raw material was thermally (carbonaceous materials carbonization, 973 K) and hydrothermally (crystallization of the amorphous metahalloysite in alkaline solution to zeolitic structure of NaA type, 373 K) pretreated in order to cilitate their specific structure [1,2]. 

Zeolites, particularly zeolite A, can be manufactured from kaolinitic clays, which as particularly found in Central Europe, Great Britain, Japan, China and USA. To transform kaolin into zeolite, it has to be thermally converted, e.g. by shock heating to > 550°C, to metakaolin. The metakaolin is then su.spended in sodium hydroxide solution and converted at 70 to 100°C into zeolite A. Some of the impurities contained in the natural raw material are retained in the final product. If amorphous silica is added, Si02-rich zeolites are produced. This process enables the transformation of preformed bodies into zeolite materials. 

Thus, the secant relationship (4.20) with the angular definition modified for aluminosilicates (MacKenzie et al. 1985) has been used to shed light on the possible existence of a Si-Al spinel suggested to form when the clay mineral kaolinite is heated to 980°C. On the basis of the known structure of the closely-related 7-alumina spinel, the T-O-T angle of the postulated tetrahedral Si site in such a structure predicts a chemical shift of - 79 ppm for this site. Such a resonance would normally be masked by the broad resonance of the amorphous Si02 also present, but when this material was selectively removed by leaching with KOH solution, the predicted Si peak was detected (MacKenzie et al. 1996) (Figure 4.13). Measurements of the relative intensity of this... 

Secondary silicates form as clay minerals in soils after weathering of the primary silicates in igneous minerals. The secondary silicates include amorphous silica (opal) at high soluble silica concentrations and the very important aluminosilicate clay minerals kaolinite, smectite (montmorillonite), vermiculite, hydrous mica (il-lite), and others. Kaolinite tends to form at the low silicate concentrations of humid soils, whereas smectite forms at the higher silicate and Ca concentrations of arid and semiarid soils. The clay fraction of soils usually contains a mixture of these day minerals, plus considerable amorphous silicate material, such as allophane and imogolite, which may not be identifiable by x-ray diffraction. 

Soils and clays, in general, when calcined give off adsorbed, interlayer, and hydrated types of water. These effects produce endothermal peaks or loss of weight in DTA and TG, respectively. The endothermal peaks are followed by exothermal peaks that are caused by re-crystalliza-tion. Although many types of clay minerals such as montmorillonite, illite, and some shales show these effects, they are not suitable as pozzolans in concrete. Metakaolin, formed by heating kaolinite, seems to be the most suitable additive material for cement. Heating of kaolinite involves removal of adsorbed water at about 100°C and dehydroxylation at above 600°C, followed by the formation of metakaolinite, an almost amorphous product. The sequence of reactions is as follows ... 

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