Synthesis and Characterization of Zeolite A from Kaolin of Ethiopia: Studies of its application as detergent builder and in tannery wastewater treatment
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Date
2016-11
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Addis Ababa Universty
Abstract
Zeolite A is a synthetic sodium aluminium silicate often also referred to as Zeolite NaA
or Zeolite 4A with LTA framework type. It is the universal type of synthetic zeolite used
for detergent manufacturing and water softening to substitute the environmentally
unfriendly material sodium tripolyphosphate (STPP). Despite its remarkable potential,
the high cost of zeolite A has restricted its effective use in detergents. Based on this, in
this work detergent-grade zeolite A has been synthesized using kaolins of Ethiopia;
Ansho and Bombowha kaolins. The synthesis was done by two different methods: the
conventional hydrothermal and alkali fusion methods. The process parameters for the
synthesis of detergent-grade zeolite A, like the metakaolination temperature, alkaline
concentration, crystallization time crystallization temperature and gel formation
conditions have been systematically studied. The characterization of the synthesized
zeolite was carried out by X-ray diffraction (XRD), Scanning electron microscopy
(SEM), Thermogravimetric analysis (TGA) and Inductively coupled plasma optical
emission spectroscopy (ICP-OES) study confirms its formation. By the conventional
hydrothermal synthesis, cation exchange capacity (CEC) exceeding 290 mg of CaCO3/g
and average particle size of 3.0 μm, whereas by the alkali fusion method, cation exchange capacity (CEC) greater than 300 mg of CaCO3 and average particle size of 4.0 μm are
achieved, which make the zeolite A obtained as promising detergent builder. The study
also included evaluating the detergency action of the powder detergent formulated with
the synthetic zeolite A by analyzing some physicochemical properties like foam height,
pH value, moisture content and alcohol and water insolubility test. The results show that
this detergent has comparable detergency with a known commercial powder detergent.
Wastewater treatment from tanneries is another environmental issue that needs great
attention in Ethiopia. In this work we have investigated the removal of Cr(III) from
tannery wastewater with Cr(III) > 2000 ppm collected from various tannneries in
Ethiopia. This was done using the synthetic zeolite A prepared using kaolin from
Ethiopia and other natural adsorbents for comparison. The results indicate that 99.8%
removal and about 200 mg/g adsorption capacity of Cr(III) with 100 g/L and 5 g/L
adsorbent dosage, respectively. The adsorbent dosage was varied systematically from 2
g/L to 100 g/L. Kinetic and adsorption isotherm studies have been conducted using
zeolite A as adsorbent. The removal efficiency of the synthetic material for Cr(VI) was
also evaluated incomparison with other natural adsorbents from Ethiopia. In this aspect
the natural adsorbents bentonites and synthetic clay materials hydrotalcite ans nanohydrotalcatite
have been found to be efficient. The natural bentonite exihibited the
maximum removal of 90% and the hydrotalcite exhibited 100% removal of Cr(VI).
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Keywords
Zeolite