Recovery of sulfur from phosphogypsum: conversion of calcium sulfate to calcium sulfide.
Tuscaloosa, AL: U.S. Department of the Interior, Bureau of Mines, RI 9323, 1990 Jan; :1-10
In a cooperative effort between the U.S. Bureau of Mines and the Florida Institute of Phosphate Research, with input from the phosphate industry, the conversion of phosphogypsum to sulfur has been investigated. The first step in the conversion scheme involves reduction of phosphogypsum to calcium sulfide. Effects of temperature, catalyst, reaction time, and type of reductant (carbon monoxide and coal) are discussed. It was determined that phosphogypsum could be reduced to calcium sulfide at 850 deg. to 1,000 deg. C, using either coal or carbon monoxide as the reductant. The required temperature was lowered to 750 deg. C using ferric oxide or magnetite as a catalyst for the reduction reaction. Results indicate that as the volatiles content of the coal is increased, reaction temperature may be decreased to obtain a given conversion, or if the reaction temperature is maintained constant, the conversion can be increased. Best results were 95- to 100-pct conversion using a high-volatile coal at 800 deg. to 850 deg. C. Addition of a catalyst increased calcium sulfide yield when low- or medium-volatile coals were used as reductants, but had little effect when high-volatile coals were used.
Gypsum; Oxidation-reduction-reactions; Coal; Catalysts; Recovery; Carbon-monoxide; Calcium-sulfates; Reduction-Chemistry; Phosphate-deposits
IH; Report of Investigations
NTIS Accession No.
Recovery of sulfur from phosphogypsum: conversion of calcium sulfate to calcium sulfide