HETEROGENEOUS DISTRIBUTION OF TRACE-ELEMENTS AND FLUORINE IN PHOSPHOGYPSUM BY-PRODUCT

Phosphogypsum (PG), a by-product from phosphate fertilizer production, is composed mainly of gypsum (CaSO4 . 2H(2)O) but also contains minor quantities of trace elements (TE), rare earth elements (REE) and F. S ome elements may be elevated in quantities to be of environmental conc ern. This study determined the distribution of TE, REE and F among thr ee size fractions (< 20 mu m, 20-53 mu m, > 53 mu m) in PGs derived fr om three different phosphate rock sources. Fine fraction PG (< 20 mu m ) composed of < 10% of total PG mass but was highly enriched in TE, RE E and F compared to unfractionated PG. For PG derived from Idaho rock, Se in the fine fraction was enriched 830 times over soil and 415 time s over shale while Cd was enriched in the fine fraction 70-fold over s hale and soil. Fluorine was elevated 37 times in the fine fraction com pared to shale. The same trends were observed for PG derived from Togo and Florida rocks. Elevated elemental concentrations in fine particle s and particle sorting during PG deposition may contribute to chemical heterogeneity of PG repositories, and make elements more susceptible to mobilization processes, such as leaching and erosion. Removal of fi nes will improve the utilization of PG in other industries, such as fo r use as an amendment to agricultural soils.