Waste Phosphogypsum – Toward Sustainable Reuse in Calcium Sulfoaluminate Cement Based BuildingMaterials

The Croatian fertilizer plant Petrokemija d.d. – Kutina produces phosphoric acid by the wet process natural phosphate rock sulfuric acid digestion. Unfortunately, large quantities of phosphogypsum are produced by this process as an unwanted byproduct. In this work, calcium sulfoaluminate cement production has been investigated as a possible way of phosphogypsum reuse. Due to the use of large quantities of industrial byproducts of various origins for calcium sulfoaluminate cement production, radionuclide activity has been determined and found to be lower than permissible levels. Mechanical properties of standard 3:1 mortar specimens have been determined from 5 kg pilot scale batches, and 28-day compressive strengths are somewhat less than 20 MPa. Mineralogical composition of calcium sulfoaluminate cement prepared has been determined by qualitative X-ray diffraction powder analysis showing the presence of Klein compound but alsosulfospurrite that could contribute to the further increase in long-term strength