Changes in trace metal concentrations throughout the phosphogypsum lifecycle

Phosphogypsum (PG) samples from four distinct sources in the Southeastern US were analyzed to explore the variation in total metal content between newly generated (fresh) PG and PG disposed of in phosphogypsum stacks for different lengths of time (stack). Fresh PG exhibited greater total metal concentrations relative to stack PG, including those identified in the literature as important from a risk assessment perspective (As, Cd, Co, Cr, Cu, Pb, and Zn). The pH varied between fresh and stack PG, with some stack samples exhibiting lower pH than fresh samples, however the relationship between pH and age of sample was not linear. Stack samples with pH values similar to fresh samples possessed lower concentrations of total inorganic metals than fresh samples suggesting that process water drainage and stack location play an important role in the reusability of PG as they can affect the pH of stack PG and total inorganic metal concentrations. Overall observations show that stacking PG for three or more years prior to beneficial reuse provides a construction material with lower total metal concentrations than fresh PG.