ENVIRONMENTAL IMPACTS OF PHOSPHOGYPSUM

Phosphogypsum is an acidic by-product from the phosphate fertilizer industry. Large quantities are produced world-wide and it is estimated that by the year 2000 up to 280 million tonnes will be produced annually. Although phosphogypsum is mainly calcium sulfate dihydrate, it contains elevated levels of impurities which originate primarily from the source phosphate rock used in P fertilizer production. The main environmental concerns associated with phosphogypsum are: (i) movement of fluoride, sulfate, total dissolved solids, certain trace elements, and radionuclides from the U-238 decay series below phosphogypsum stacks into groundwater supplies; (ii) radon-222 exhalation which may pose a health risk to workers on the site or people living close to stacks; (iii) acidity; and (iv) radon-222 exhalation from soil into residential homes when agricultural land previously treated with phosphogypsum is converted to residential usage. In order to fully understand the environmental impact of phosphogypsum, it is necessary to understand the geochemical and hydrological processes that control the composition of phosphogypsum leachates and the attenuation of environmentally sensitive chemical species when these leachates enter soil environments. This article will review the chemistry of phosphogypsum and the environmental concerns associated with phosphogypsum that is stockpiled in waste repositories or is used as an agricultural soil amendment.