Scaling up, mass balance and techno-economic study of a hydrothermal process used to synthesize zeolite from aluminosilicate residues obtained from lithium production

The processing of spodumene ore for lithium extraction produces large quantities of aluminosilicate residues that need to be properly managed. This paper focuses on the scale-up feasibility and performance evaluation (i.e. zeolite properties, mass balance, operating costs) of a hydrothermal process developed to synthesize zeolite from these aluminosilicate residues. The chemical composition, ion exchange capacity and mineralogical analysis (scanning electron microscopy, X-ray diffraction) of the synthesized product were carried out. Laboratory-scale experimental results showed that the addition of stirring during the aging phase increases the ion-exchange capacity of the final product by around 36 %, and leads to a modification of the zeolite structure, while facilitating its recovery. In addition, a zeolite with a structure like NaP zeolite was produced with a very good ion exchange capacity (80 mg Ca/g). Based on the most performant conditions obtained at laboratory scale, a large-scale production process was performed. It was found that the characteristics of the zeolite produced at laboratory and scale up were quite similar, which highlighted the robustness of the proposed process. Besides, the mass balance analysis results showed that the zeolite production yield was around 94.8 % of the initial mass of aluminosilicate residues. In addition, the percentage of Al originating from the aluminosilicate residues recovered in the final zeolite is 84 %, however only 56 % of Si is recovered in zeolite. Finally, a techno-economic analysis of the zeolite synthesis process was performed using SuperPro Designer v.12 software for a plant capacity of 5 tons of aluminosilicate residues per hour and a sale value of the zeolite produced of US$ 1.00/kg. The production cost for zeolite was determined at US$ 0.62/kg. It was found that the production of zeolite from these residues proves to be economically profitable with a payback period of 4.5 years and net present value (NPV) (at 7 % interest) of US k$ 48,108.