A comparative study of seed crystals for the phosphorus crystallization process.

This study was performed to select a preferred seed crystal material for the phosphorus crystallization process through a comparative study of four materials: electron arc furnace, blast furnace and converter slag, and phosphate rock. Leaching and phosphorus removal tests were conducted to evaluate the efficacy of the four materials as seeding agents. Converter slag demonstrated a much larger leaching capacity with respect to calcium and hydroxide ions than did either electron arc furnace or blast furnace slag. The average phosphorus removal efficiencies of phosphorus rock, and the electron arc furnace, blast furnace and converter slag were 35.9%, 74.2%, 99.1%, and 94.5% following 20, 17, 32, and 175 days of leach time, respectively. Consideration of both technical and cost factors suggests that converter slag may have competitive advantages over the other three seed materials. X-ray diffraction (XRD) analysis showed that peak patterns for hydroxyapatite increased slightly as the hydrous flow time was extended. Scanning electron micrograph (SEM) images revealed that finely distributed cubic crystals were deposited on the surfaces of converter slag. When analyzed by energy dispersive x-ray spectrometer (EDS) mapping, the crystals gave a composition mole ratio (Ca/P) of 1.97 and they were determined to be hydroxyapatite.