RADIONUCLIDE FLOW DURING THE CONVERSION OF PHOSPHOGYPSUM TO AMMONIUM-SULFATE

Approximately 30 million tons of the by-product phosphogypsum are curr ently produced annually by the phosphate fertilizer industry in Florid a. Nearly all of this material is stockpiled because radioactive impur ities prevent utilization of what could otherwise be a useful agricult ural amendment or construction material. Long-term storage and mainten ance of this material presents economic as well as potential environme ntal concerns. One partial solution to this problem may be conversion of phosphogypsum to ammonium sulfate by the so-called Merseberg ammono carbonation process. Ammonium sulfate is an excellent fertilizer which supplies sulfur as well as nitrogen to soils. We have assessed the fl ow of the natural decay-series radionuclides U-238, Ra-226, Pb-210 and Po-210, through the Merseberg process by the analysis of starting mat erials and products from overseas industrial-scale plants. Results ind icate that the radionuclides associated with phosphogypsum do not repo rt to the ammonium sulfate product but are found instead almost exclus ively in the by-product calcium carbonate. Thus, the radiochemical res ults are encouraging in terms of using this process as an option for p artial removal of waste phosphogypsum Although there is a clear and re cognized need for increased sulfur addition to many crops, the price o f sulfur has been so low and alternative supplies of ammonium sulfate so common that investment in this process has been discouraged. Recent price increases and demand for ammonium sulfate may make the Merseber g process more attractive. Copyright (C) 1996 Elsevier Science Ltd.