Fluoride removal from phosphogypsum: A study on pre-industrial scale and its mathematical analysis

This study discusses fluoride removal efficiency from phosphogypsum (PG) on lab-scale experiment matrix designed by Box-Behnken method. Temperature, solid/liquid ratio, and time were introduced as factors into various salt solution media to predict the fluoride removal efficiency from PG. Experiment matrices were designed according to salt solution types, namely sea water, 5% NaCl and 10% NaCl solutions. According to the factor- response analysis, results indicate that fluoride removal efficiency and temperature are directly proportional. The optimum fluoride removal conditions based on the experimental data obtained by the multi-variable design matrix were determined by the Design Expert v 12 software, in which temperature, time, and solid/liquid ratio were reported to be 80?C, 3 h and 0,174 in the case of sea water, respectively. 73,31% fluoride removal was predicted via the optimum conditions determined by the software, however experimental validation studies showed an actual 74,99% fluoride removal efficiency. Since the actual vs. predicted data show high consistency, results might also be useful when industrial-scale fluoride removal to a pre-determined level is required prior to a particular use of PG. This study provides a novel pre-industrial scale fluoride removal inventory especially for fertilizer and cement industry, in which PG has a high potential as an alternative raw material and fluoride removal might be of importance in recycling applications.