Synthesis and characterization of zeolite from waste coal flyash for tailored application in bio-refining and process water cleaning: An innovative approach towards a cleaner circular economy

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Kemian tekniikan korkeakoulu | Master's thesis
Renewable Materials Engineering
Degree programme
Master's Programme in Bioproduct Technology
The purpose of the investigation was to assess if Finnish coal flyash (CFA) waste could be used to synthesize zeolites. The world produces 750 million tonnes of CFA annually which is also the largest quantity waste produced. This figure will only increase as India, China, South America and Africa charges ahead with industrialization. The global recycle rate is 15% annually. Finland produces about 750,000 tonnes of CFA per year. It is also estimated that millions of tonnes of CFA is backfilled globally. Hence there is great potential to use it for high value applications as the raw material security exists. There are also disposal and environmental issues related to CFA which makes it our obligation to find a great solution. The recent trend towards circular economy, waste to value, sustainability, EU and National environmental legislations also provides a great platform to find a solution. Other reasons have been analysed from engineering, policy making, markets, scientific & innovation, national and regional impact, international trade, geographic location and future study perspectives. The literature section provides insights into CFA, structure, transformation, mechanism, combustion process, applications, environmental issues etc. The Zeolite section gives a deep understanding of origin, history, classification, trends in development, structure, morphology, applications, properties, circular economy context of zeolites, synthesis methods, raw material variations etc. There are 174 zeolite framework types in zeolite families and we put special emphasis on NaX (Faujasite framework) with tailored descriptions. The literature highlights CFA Zeolites, its differences with pure chemical ones, synthesis methods, previous works and global pilot projects. Conversion of Finnish CFA to Zeolite was a grand success. The overall process involved sieving, batch preparation, ageing, hydrothermal treatment, washing/filtration, drying and grinding. We sieved CFA to collect unburnt carbon (0.2% weight basis) and obtain consistent particle range. Creation of appropriate chemical composition, ageing for 24 hours (650 rpm at 21℃), hydrothermal treatment for 24 hours at 60℃-85℃. Washing is followed by drying the product for 16h and grinding it with mortar and pestle. CFA Zeolites have been made for the first time in Finland and Northern Europe. Both the CFA and CFA Zeolites were analysed using XRD, EDX, SEM and BET. CFA consisted of amorphous SiO2 and Al2O3 along with crystalline quartz (SiO2) and mullite (SiO2.Al2O3). The LOI was 4.57% (weight basis). The BET value for CFA was 366. 73 m2/g. The CFA Zeolite was pure phase NaX and crystalline without competing GIS, SOD, LTA phases. The BET surface area of CFA Zeolite was approx. 1800-2000 m2/g. This is the first time such high values have been reported in the world. The process was scaled up from lab to bench scales. Various repetitive tests were conducted in lab and bench scales to have consistent results. Statistical analysis was conducted to obtain quality control guidelines.
Kontturi, Eero
Thesis advisor
Talling, Bob
coal fly ash (CFA), zeolite, circular economy, alkaline activation, geopolymers, NaX
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