As in Chapter 1 (Stewart et al., 2005, this publication), this chapter has been written to serve both the scientific community (SI units) and fertilizer industry (non-SI units). In particular, fertilizer grades are expressed in an X-Y-Z format where X = available nitrogen (N), Y = available phosphorus (P) expressed as a weight percentage of P 2 O 5 equivalent, and Z = available potassium (K) expressed as a weight percentage of K 2 O equivalent. There is no equivalent system of fertilizer grades in the SI system other than expressing the composition as g kg Ϫ1 of N, P, and K. To convert %N to g N kg Ϫ1 multiply by 10, to convert P 2 O 5 to g P kg Ϫ1 multiply by 4.37, and to convert %K 2 O to g K kg Ϫ1 multiply by 8.33. For example, a 16-16-16 fertilizer in the N-P 2 O 5-K 2 O system would be 160-70-133 in a N-P-K system. In this chapter, the industry units of fertilizer and ore grades will be used and the reader can convert to SI units with the guidelines given above if needed. A related issue is the use of the term phosphate to describe P by the fertilizer industry. In a strict sense, the use of phosphate should be restricted to describe P in the form of orthophosphate (PO 4 Ϫ3) or condensed phosphates (e.g., P 2 O 7 Ϫ4). One cannot ensure that all P in ores or fertilizer products is present as phosphate. However, it is generally accepted that nearly all is in the form of phosphate in these materials and the term phosphate will be used in this chapter.

The use of marginal-quality phosphate rock and the increased use of the sludge fraction from wet-process phosphoric acid have created grade problems in the production of 18-46-0 fertilizers. Detailed solid-phase characterizations determined from chemical composition, optical microscopy, X-ray diffraction, and infrared spectroscopy made on 15 commercial 18-46-0 fertilizers are described and discussed. These characterizations are correlated with the process parameters to show the relationship of physical and chemical parameters on 18-46-0 grade. These samples represented a wide range of impurities from Florida, North Carolina, and western phosphate rock sources. Several reasons for grade problems and suggested methods for alleviating them were identified in this research study.

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The overall goal of this project is to assess the technical and economic feasibility for producing fertilizer-grade ammonium sulfate from gypsum produced as part of limestone flue gas desulfurization (FGD) processes. This is the first year of a twoyear program with cooperative effort among the ISGS, the UIUC, AlliedSignal, SE-ME, Henry Fertilizer, Illinois Power Co. (IP), and Central Illinois Public Services (CIPS). In the previous quarter, chemistry of the process and process conditions have been reviewed and the information was used to set up a reactor system. The system was used to conduct several laboratory tests. FGD-gypsum produced at the Abbott power plant in Champaign, IL was used as a raw material. The scrubber, a Chiyoda Thoroughbred 121 FGD, produced a filter cake product contains 98.36% gypsum (CaSO4.2H20), and less than 0.01% calcium sulfite (CaSO,). Conversion of FGD-gypsum to ammonium sulfate were tested at temperatures between 60 to 70°C for a duration of five to six hours. A yield of up to 82% and a punty of up to 95% for the ammonium sulfate production was achieved.In this quarter, more bench-scale experiments including a mass balance analysis were conducted. Based on the weight of the ammonium sulfate produced and its theoretical yield from a total conversion of calcium sulfate feed, a yield of up to 83% and a purity of up to 99% for the ammonium sulfate production was achieved. Also, a more complete literature survey was conducted and a preliminary process flow sheet was developed. Using the flow sheet and engineering data, the economics of the process are being estimated. The cost estimates results will be reported in the next quarter. Also, any beneficial process variation to be considered and process limitations that need further research will be identified. EXECUTIVE SUMMARYProgress made under the United States Department of Energy's Clean Coal Technology program and the 1990 amendments to the Clean Air Act that mandate a 2-stage 10-million ton reduction in sulfur dioxide emissions in the United States have definitely promoted the use of FGD technologies. In addition to capital costs for equipment and operating expenses, plants burning high sulfur coal and using FGD technologies must also bear increasingly expensive landfill disposal costs for the solid waste produced. The FGD technologies would be less of a financial burden if successful commercial uses were developed for the gypsum-rich by-products of wet limestone scrubbing. Conversion of FGD-gypsum to a marketable product could be a deciding factor in the continued use of high-sulfur Illinois coals by electric utilities.The conversion of FGD-gypsum to calcium carbonate and ammonium sulfate by reacting it with COz and ammonia or by reacting it with ammonium carbonate is being studied in this program. A variation of this process could provide electric utilities a means to convert the C 0 2 and SO2 in their flue gas to useful commercial products. The fertilizer industry would also be provided with a large source of ammonium sulfa...

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