Current established technology for making sulfuric acid (H2SO4) and cement clinker by-product from phosphogypsum (such as the OSW process developed by Chemie Linz, Austria) is not economic when compared with sulfur burning. It has only been applied in a few locations (Austria, China, and South Africa) where special circumstances prevail. Both M. W. Kellogg (United States) and Lurgi (West Germany) have sought to improve the technology for phosphogypsum processing, but the data published so far indicate that the work of neither is likely to lead to a viable process.
A more promising approach is that developed by Davy McKee Corporation (DMC) and Florida Institute of Phosphate Research (FIPR) in a joint research program. Their work entails the use of a circular grate reactor, which significantly reduces capital investment costs. However, the disposal of the CaO rich solid by-product is still a problem: DMC-FIPR indicate that the addition of iron pyrites to the phosphogypsum produces a solid by-product of adequate quality for bulk use in road construction. Pilot-scale development of the DMC-FIPR process is scheduled to begin in early 1988.
In this review we evaluate the basic version of the DMC-FIPR process in which iron pyrites are added to phosphogypsum and petroleum coke is used as the reducing medium. DMC-FIPR have also described several cogeneration versions that use coal or natural gas as the fuel and that may be applied more economically for retrofitting existing facilities. We do not evaluate those alternatives here because of their site-specific nature. We show that for a grassroots case with 2,800 short tons/day (St/d) of H2S04 capacity, the product value for H2SO4 is higher than for sulfur burning. Higher by-product credit and rising sulfur prices could narrow the gap, but the main opportunities for the new process are likely to be in cogeneration schemes for retrofitting (where future action may be accelerated by environmental policy) or in special circumstances such as in countries where the delivered cost of imported sulfur is high.