Harnessing salt slag and diatomite sludge by co-recycling for zeolite production.

Developing alternative uses for waste is one of the main concerns of modern industry, as proper waste management is necessary to pave the way towards a circular economy and sustainability. In this study, the sustainable synthesis of zeolites using salt slag, a hazardous waste product from the secondary aluminium industry, and diatomite sludge, an agri-food waste product, was explored. The aluminium salt slag and diatomite sludge served as the aluminium and silicon sources, respectively, for the LTA and NaP zeolite formulations through a one-pot hydrothermal process. The key synthesis parameters, temperature (70–90 °C), reaction time (2–24 h), and NaOH concentration (0.38–1 M), were systematically varied to adjust the type, crystallinity and textural properties of the zeolites. The synthesised materials exhibited specific surface areas of 12.7–22.5 m2 g−1 and cation exchange capacities ranging from 1.57 to 2.54 meq g−1. FTIR analysis confirmed the formation of zeolitic phases, whereas microstructural characterisation revealed a progressive topotactic transformation from cubic LTA to NaP crystalline aggregates. These findings demonstrate the potential of this approach to produce functional zeolites and promote circular economy practices by co-recycling industrial waste through industrial symbiosis.