Thermochemical energy storage using phosphatic pebbles

Calcium magnesium carbonate, also known as dolomite, is dispersed throughout Florida as a constituent of phosphate-mined resources. The mineral is problematic in the phosphoric acid production of phosphate for agriculture and must be separated so that it does not negatively affect the process. This means that this natural resource has no beneficial end use. In the present study, we characterize high-concentration dolomite phosphatic pebbles from the Florida Industrial and Phosphate Research Institute and examined their feasibility for thermochemical energy storage at high temperatures. The dolomite mineral composition was studied prior to and after calcination (decarbonation) using scanning electron microscopy with energy-dispersive X-ray spectroscopy, powder X-ray diffraction, Fourier Transform Infrared Spectroscopy, and thermogravimetric analysis. The local samples were compared to a commercial dolomite sample and results confirm a high percentage of dolomite in the central Florida samples. Thermogravimetric analysis and powder X-ray diffraction indicated that the dolomite calcination is not fully complete at lower temperature, and at least 700 °C heat is required for the release of CO2 from the dolomite pebbles. Overall, the results show that the waste dolomite phosphatic pebbles are suitable for potential use in high-temperature thermochemical energy storage with long-term reversibility and cyclability.