Optimisation of zeolite LTA synthesis from alum sludge and the influence of the sludge source

Generation of alum sludge(AS)at drinking water treatment plants represents an environmental liability and adds to the cost of water purification.Consequently,this study explored the feasibility of using low and high carbon containing alum sludge from two water treatment plants to synthesize zeolite LTA.The hypothesis was that zeolite LTA synthesis was dependant upon alum sludge source and that a range of strategies may be required to optimize zeolite crystallinity.Zeolite characteristics such as morphology,phase composition,crystallinity,and particle size distribution were recorded."One pot"hydrothermal synthesis of precursor gel with molar composition 4.2 Na2O:Al2O3:1.2 SiO_(2):168 H2O at 80℃ for 3 hr resulted in 25 and 46 wt.%zeolite LTA from high and low carbonaceous sludge,respectively.Prior to hydrothermal reaction stage it was discovered that ageing of the gel,addition of zeolite LTA seeds,ultrasonic treatment and calcination all promoted zeolite LTA formation.Calcination of the alum sludge at 700℃ for 2 hr before hydrothermal synthesis resulted in particle size reduction and the highest amount of crystalline zeolite LTA:79 wt.%from low carbon sludge and 65 wt.%from high carbon sludge.Notably,the zeolite crystallinity reported in this study was the higher than previous studies on this topic.The outlined approach may allow value adding of alum waste and produce a commodity which could be used locally by the water treatment plant as a water softener.

High-efficient Synthesis of Zeolite LTA via a Wet-gel Crystallization Route

Zeolite LTA has been largely used as good adsorbent and detergent builder with a huge amount of demand Numerous efforts have been devoted to the exploration of new synthetic methods for preparing zeolites more conve- niently and efficiently. Herein, we reported a wet-gel crystallization route to synthesize zeolite LTA from simple filtration of the initial reaction mixture followed by heating for crystallization. The products were characterized in detail by means of X-ray diffraction, Raman spectra, scanning electron microscopy and elemental analysis. The yields of the solid products were also investigated, which suggested that the wet-gel method afforded an obvious improve- ment of products yield compared with the conventional synthesis route. For application as detergent builder, the cal- cium ion exchange rates of the wet-gel synthesized zeolites were similar with that of conventional LTA zeolites. Therefore the wet-gel route would be potentially important in industry due to its advantages of easy-performing, high-yielding and energy-saving.

Facile preparation of compact LTA molecular sieve membranes on polyethyleneimine modified substrates

A facile preparation strategy was proposed for preparation of compact zeolite LTA membranes on polyethyleneimine(PEI)modified substrates without seeding.Through the functionalization of substrates by using PEI,compact LTA membranes can be formed on various kinds of substrates.A well-intergrown and phase-pure LTA membrane with a thickness of about 3.0μm is successfully prepared on the a-Al_(2)O_(3)disk after crystallization for 24 h at 60℃.Besides LTA membrane,wellintergrown zeolite FAU membranes can also be formed on PEI-modified a-Al_(2)O_(3)substrates,suggesting the universality of this strategy.The zeolite LTA membranes synthesized on PEI-modified a-Al_(2)O_(3)tubes were evaluated for the separation of alcohols/water mixture through pervaporation.The as-synthesized zeolite LTA membranes display high pervaporation performances.For the separation of 10 wt%isopropanol/water solution at 90℃,a high separation factor of44991 and a water flux of 1.73 kg m^(-2)h^(-1)are achieved.