Crystallization processes in zeolitic rock mixed with NaOh
Rashchenko S.V. 1,2, Kazantseva L.K. 2
1Novosibirsk State University; 2 V.S. Sobolev Institute of Geology and Mineralogy sb ras, Novosibirsk, Russia
rashchenko@igm.nsc.ru
A lot of attention is paid today to the glass-foam building materials, manufactured by sintering of powdered glass with gasifiers. The resulting product is very efficient in construction due to perfect heat-insulating properties, lightness and ecological compatibility. However, the powdered glass is rather expensive and rare material. Another promising source for foam building materials is natural zeolitic rocks. Their main advantages are widespread occurrence and ability to self-foaming without synthetic gasifier.
In order to increase the foaming ability of zeolitic rocks, the addition of NaOH before sintering is commonly used. However, the process of interaction between NaOH and zeolites is poorly understood yet. To reveal details of this process, the following experiment has been carried out.
A thoroughly grinded sample of zeolitic tuff was mixed with NaOH aqueous solution. A part of obtained soft mass was used to form granules, which were dried at 100 °C to air-dry state and then kept in air for 7 days. Another part of prepared mass was heated in wet state at 90 °C for 10 hours; after this treatment granules were prepared and dried at 100 °C as well. The granules of both types have been investigated with scanning electron microscopy and X-ray diffraction.
As a result, two new phases have been observed in alkalized zeolitic rock. The fibrous crystals (typical for growth through micropores), formed when dried granules were kept in air, are the carbonate compound Na3H(CO3)2·2H2O, named trona. It appears due to zeolitic absorption of carbon dioxide and water vapour from air, and considerably increases the composition foaming ability. Thus, a foam material with density of ~150 kg/m3 has been prepared from carbonatized granules, whereas as-dried granules have given a foam material of ~250 kg/m3.
The spherical nanocrystals of NaP zeolite (NaxAlxSi16–xO32·yH2O) have grown in alkalized zeolitic rock during hydrothermal process at 90 °C. They form from amorphous sodium hydrosilicate and, on the contrary, greatly decrease the composition foaming ability, resulting in foam material with density of ~350 kg/m3.
The results obtained indicate that mixing of zeolitic rock with NaOH gives a very reactive phase (‘amorphous sodium hydrosilicate’), which can not only crystallize into Na-zeolites, but also actively absorb CO2 and H2O from air, forming fibrous crystals of hydrocarbonate. Understanding of both these processes is of great importance in manufacturing of foam building materials from natural zeolitic rocks.
Micro-ftir study of quartz crystals from Zhelannoye deposit, Subpolar Urals
Shtenberg M.V.1,2, Repina S.A.1
1 Institute of mineralogy UrB ras; 2 South-Ural State University, Miass, Russia
shtenberg@mineralogy.ru
Quartz is the most popular mineral to get the information about conditions of formation. In its composition and structure are showed main stages of geological environment evolution. Quartz crystals are the most informative to trace changes in composition on various zones and sectors of growth. Infrared spectroscopy is an effective method to investigate various hydrogen-bearing groups.
The quartz crystals (citrines, smoke, clear) were collected from Zhelannoye deposit, Subpolar Urals. The double polished sections parallel to (0001) were prepared. We measured unpolarized infrared spectra in the 5500-2000 cm-1 region, using a MultiScope Perkin Elmer FTIR microscope equipped with a MCT detector under the condition of 4 cm-1 resolution at room temperature. All spectra were co-added 128 scans. The measured area was restricted by the 50x50 μm2 square aperture for each spot. Spots were measured along profile line in 1 millimeter.
The absorbance spectra were normalized by thickness of sample. Curve-fitting analysis was carried out by using PeakFit for Windows software. Overlapping absorption bands in each spectrum were resolved into 9 bands, which include Al-OH bands at 3315 cm-1, 3378 cm-1 and 3432 cm-1, Al-O(Li) bands at 3403 cm-1, 3440 cm-1, 3482 cm-1 and 3512 cm-1, and an Si-O bands at 3200 cm-1 and 3300 cm-1 [1]. A Lorentzian function was used as a model of OH bands and Gaussian function for Si-O bands. The basic relationship between IR intensity and concentration was given using Beer-Lambert law. The equation was used [2]:
CH = A·∆, (1)
CH – the H amount in 106 Si; A – the calibration factor; ∆ – the integrated absorbance under the OH band, normalized by the sample thickness. The hydrogen amount was converted in weight-part concentration OH groups.
The zonal structure in weakly colored citrine crystals using binocular microscope was established (fig.). The shadows of the Brazilian growth twins at crystal rim and sericite powder at the upper faces were described. It is supposed, the growth twins and sericite powder were formed as a result of the imposed mechanical strains. The zoning profile was revealed, that the content of Al-O (Li) groups in the crystal rim is less, than in the core part. It is possible to assume, that during the rim crystallization the conditions accompanied with the Li depletion in hydrothermal fluids were changed. Also smoky quartz crystals from this deposit were studied. Similar shadow zone wasn’t observed there and OH-groups location is uniformly from core to rim.
Thus, IR microspectrometry method allows to reveal OH-groups location in different quartz crystal zones and determinate a change the mineral-forming condition changing.
All spectra measurements were executed at “Geoanalyst” Centre in the Institute of Geology and Geochemistry, Urals Branch of Russian Academy of Science. This work is supported by FTP “Scientific and scientific-pedagogical personnel of innovative Russia” (GC № 14.740.11.1212 of 14.06.2011).
Fig. The zoning profile of concentration Al-OH and Al-O(Li) groups in citrine.
References:
1. Kats A. (1962) Hydrogen in Alpha-quartz. Philips Research Reports, 17 201-279.