Nowadays, it is widely used for plasterboard and stucco manufacturing, construction, fire-proofing, biomedical applications, and even some forms of 3D printing. It is estimated that 100-200 million tonnes are used each year , making it one of the most widely consumed mineral resources. However, as there are no significant natural deposits of bassanite existing on the Earth's surface, it has to be synthesized. The main route to obtain hemihydrate is a thermal treatment of gypsum at temperatures typically between 150 °C and 200 °C to remove some of the structural water . Depending on the method used, αor β-hemihydrates are obtained either in humid/wet conditions or in dry air. Both types of hemihydrate will revert to gypsum when in contact with water, undergoing an exothermic hydration process that leads to the setting and hardening of the final gypsum-based material . α-and β-hemihydrates differ in reactivity due to different crystal morphologies and structural defects, but whether they have the same crystal structure is still debated . From an economic point of view, it is important to achieve hemihydrate synthesis in the shortest possible time with the lowest possible energy input is important since the mining of the raw material, gypsum, is relatively inexpensive and the energy expenditure is a significant portion of the synthesis or processing . If dehydration is carried out in kilns and the energy is produced from fossil fuels, the environmental costs are particularly high. Using solar energy to dehydrate gypsum to produce β-hemihydrate is one way to improve the carbon footprint . Alternatively, α-hemihydrate is produced from gypsum using an autoclave process . The widespread use and growing demand for calcium sulfates has led to the recognition that in some geographical regions, including the EU, calcium sulfate will be classified as a critical raw material within the next decade . Therefore, the search for alternative, more sustainable synthesis routes, which are not based on raw natural gypsum, and instead include calcium sulfate from waste, is of particular importance . Furthermore, considering the environmental impacts and monetary costs of gypsum disposal, targeted processing of calcium sulfate waste is crucial .