TITLE:
Zeolite Synthesis under Insertion of Silica Rich Filtration Residues from Industrial Wastewater Reconditioning
AUTHORS:
Andrea Hartmann, V. Petrov, J.-C. Buhl, K. Rübner, M. Lindemann, C. Prinz, A. Zimathies
KEYWORDS:
Zeolites, Superalkaline Conditions, Filtration Residues, Re-Use of Industrial Waste, Reaction Kinetics, Silica Residue
JOURNAL NAME:
Advances in Chemical Engineering and Science,
Vol.4 No.2,
April
14,
2014
ABSTRACT: Zeolite
synthesis was studied using two silica rich filtration residues (FR 1 and FR 2)
as Si-source and sodium aluminate in a direct synthesis at 60°C at strong
alkaline conditions (8 M - 16 M NaOH). In addition to these one-pot syntheses,
a two-step process was investigated. Here, an alkaline digestion of FR at 60°C
was followed by gel precipitation with sodium aluminate and gel crystallization
under usual conditions of 80°C - 90°C. The results show that the substitution
of chemical reagent sodium silicate by a waste material like FR as Si-source is
possible but requires fine tuning of the reaction conditions as zeolite
crystallization is a process under kinetic control. The solubility behaviour
and impurities of the inserted filtration residues strongly influenced the
course of reaction. Thus zeolites like hydrosodalite or intermediate zeolite
between cancrinite and sodalite, or zeolite NaA or Z-21 in cocrystallization
with hydrosodalite could be observed in the one pot syntheses already in a short time interval between 1
- 4 h depending on the alkalinity. The two step process yield to zeolites NaA
and NaX in very good quality. The reaction process of FR in both reaction
methods was characterized by chemical analyses, X-ray powder diffraction,
Fourier transform infrared spectroscopy as well as scanning electron microscopy. Surface area and water content of selected products were further characterized
by the BET-method and by thermogravimetry. Summing up the results, we can show
that zeolite formation from filtration residues is possible by several reaction
procedures as model cases for a re-use of industrial waste materials. Beside
the importance for environmental protection, the reactions are of interest for
zeolite chemistry as the re-use of FR is possible under economically conditions
of low energy consumption at 60°C and short reaction periods.