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Abstract
Natural raw materials used in this study are bentonite and volcanic rocks of alkaline affinity. Bentonites were collected from the area between latitude 29° 14` -29° 15` and longitude 30° 24` 20``- 30° 25` 22`` in Alamein area, found as horizontal bed about 3 m thick that increases to the East and covered by about 1m limestone. The thickness of the succession increases south ward where bentonite and limestone beds attain 7-10 m and 3 m thick respectively. Using XRD, IR, and SEM, the bentonite composed mainly of montmorillonite, kaolinite and illite as clay minerals with quartz, albite and calcite as non clay minerals. The
physical and mechanical tests were conducted on bentonitic clay materials showing that; bentonite was predominantly silt (51 %) and clay (49 %). The plastic limit is 23, 58 %, liquid limit is 151, 36 % and plasticity index is 127, 78 % as well as the value of consistency (IC)
attains 1,132. The liquidity index value (IL) is negative (- 0,132) as ranged between 0 and -1 suggesting that, the bentonite is mainly of viscous condition with activity value is 2,61 with swelling value of 213% to form thixotropic gel. Interstitial water held in the clay mineral lattice is an additional major factor controlling the consistency index and cation exchange capacity.
The nature of the zeolites obtained from bentonite confirmed that the end product of transformation is strongly dependent upon the nature of the raw material, in particular on the
SiO2/A12O3 ratio and a function of time of treatment as well as the concentration of the alkali
solution used. Hydrothermal treatment of a bentonite in NaOH media at 80 ºC and 120 ºC, resulted in the formation of low-silica zeolites (sodalite and cancrinite) and high silica zeolite
(Na-P1 and natrolite). The increase in Al:Si ratio might favors the formation of other zeolite phases on thermal treatment at higher temperatures or for longer durations.
Two months crystallization period, produced sodalite and Na-P1 and at higher temperature (120 °C), sodalite phase was the only product however the alkali concentration was 3 or 5 molar, or the crystallization period was short or long.
Volcanic rocks used in this study were collected from the area between longitude 25° 58` 19`` -25° 58` 21``N and latitude 34° 05` 10``-34° 05` 11`` E in Qusier area, Eastern Desert of Egypt. They are enriched in alkalies and classified as rhyolite and near the borders of trackyandesite and trackyte due to their alkaline affinity with SiO2 / Al2O3 ratio 4.58. These rocks are fine grained in size and exhibit pinkish grey colour and dominantly constitute from feldspar (almost white in colour), quartz with mafic minerals including biotite, chlorite and opaque minerals.
Na-P1, cancrinite, natrolite and sodalite have been prepared from the naturally occurring alkaline volcanic with NaOH of varying concentrations (3 and 5 molar) at different temperatures (80 and 120 ºC) for many crystallization periods (8 hours, one week and one
month). Low concentration of NaOH is suitable for the formation of Na-P1 zeolite and with increasing the concentration to 5 molar leading to the formation of sodalite as major
constituents with Na-P1 zeolite in minor amount. Temperature is also an effective factor in the formation of zeolite Na-P1. At 80 ºC, Na-P1, cancrinte and sodalite have been prepared.
Increasing the temperature to 120 ºC, natrolite was formed. The zeolitization of the reactants was enhanced by the increasing of the crystallization period. Grain size influences only the
habit of cancrinite. Rossett like shaped cancrinite formed from the reactants of small grain size (< 0.045mm diameter) while hexagonal cancrinite formed from reactants of large grain
size (between 0.063-0.125 mm diameter).
construction as base-layer.