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Coal fly ash has been proposed as an alternative raw material for zeolite synthesis, however, the mobilization of toxic elements of this material into zeolite products, washing water and effluent is rarely addressed. In this study, Brazilian coal fly ash was used in the integrated synthesis (two steps) of zeolites Na-P1 and 4A and the distribution of approximately 40 major, minor and trace elements was investigated in all the input and output flows involved in the process. The mobilization of several elements was observed in the zeolite products, a number of which are highly toxic, such as As, Cd, Cr, Ni and Pb. With regard to the amount present in the ash, both zeolites were enriched in several elements, such as Ni in zeolite Na-P1 and As in zeolite 4A. The latter exhibited high purity, with most of the elements investigated having concentrations close to those measured in commercial zeolite 4A. Important information was gathered regarding zeolite synthesis using fly ash, which will ensure safer application of these materials and, if necessary, propose a contaminant-free synthesis route.

Various zeolites (4A, Y, 13X) and related fillers (molecular sieves and coal fly ash) were used to prepare PLA composites and to assess their degrading effect on the polyester matrix under different processing conditions, at various zeolite/filler loadings. In this objective, untreated fillers, as well as washed and thermally activated zeolites, were used. PLA-zeolite composites were produced by melt-blending step followed by the evaluation of rheological information and molecular and thermal characteristics. The degradation of PLA during the preparation and processing of PLA-zeolite composites, or due to the presence of fillers, was evidenced by specific analyses (SEC, DSC, TGA, TG-FTIR). PLA degradation was mainly dependent on the nature of zeolite, filler loading, and thermal and processing history. The results of the study suggest that a stronger degradation effect is obtained by the addition of zeolite 4A into PLA (at loading of 5-10%) with respect to other zeolites (e.g., 13X and Y). It was also revealed the key roles of the temperature and residence time (as parameters in melt-mixing process), free alkalinity level, and water uptake in determining the ultimate characteristics of composites. The washing and thermal activation pretreatments of fillers have diminished in some cases the degradation of PLA matrix. Finally, the study also highlights the zeolite grades capable of being used to produce new PLA composites with competitive properties and those that could be of interest to improve PLA recycling by pyrolysis.

The high Si and Al contents in the amorphous phase of coal fly ash have been used for its conversion into zeolites. This process converts a toxic low-value by-product into a product used in a number of environmental applications, but has the disadvantage of introducing contaminants. Despite the large number of studies on the conversion of fly ash into zeolites, few report this drawback or discuss the efficiency of the proposed processes from a technical or ecological perspective. In this respect, the present study conducts a detailed assessment of two routes for integrated hydrothermal synthesis of zeolites 4A and Na-P1 obtained from coal fly ash. The processes are evaluated and compared in relation to the presence of undesirable metals and elements in the different steps of synthesis, as well as the feedstock and final product. Different performance parameters are presented and applied in the assessment of both processes and the most sustainable is recommended.