Hydrothermal synthesis of zeolites using sanitary ware waste as a raw material

Zeolites are extensively produced by hydrothermal treatment of different raw materials, such as kaolin. Sanitary ware (SW) is a kaolin-based ceramic ware usually found in sinks, urinals and bathtubs whose production is led by Spanish domestic clay product industry. SW production generates approximately 8% of solid waste in Spain, which increases landfills sizes and pose economic, social and technical problems. This study aims to evaluate the feasibility of solid waste of SW industry to produce zeolites once subjected to a conventional hydrothermal treatment during different times and temperatures. Ground SW was subjected to dissolution in a highly basic medium (NaOH 5 M) inside a Teflon-lined stainless steel reactors, at temperatures of 100, 150 and 200 °C for 1 to 30 days. X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize both the raw material and resultant mineral phases. Quartz and mullite present in SW transform into zeolites, as temperature and time increase. Mineral assemblage at 100 °C includes zeolite P, Na-faujasite and sodalite as major component and analcime, natrolite, and zeolite A as minor, which behave as metastable phases and their relative abundance depends on aging time. Analcime and cancrinite crystallization is favored by high temperature (150 °C to 200 °C) and increasing aging time produces analcime disappearance. Cancrinite is the dominant mineral after 30 days. Conventional SW waste is an optimal raw material for zeolites synthesis under high alkaline hydrothermal conditions. Combining time and temperature it is possible to drive crystallization towards a target phase.