Lead release from smelter and mine waste impacted materials under simulated gastric conditions and relation to speciation

Under acidic conditions in the stomach of humans, the nature of phases in contaminated solids significantly influence lead (Pb) release and bioaccessibility. ii This study focused on Pb solid-phase speciation and release kinetics and the relationship between the two. Contaminated soil and waste materials from a Ph mining and processing site contained 279-7770 and 495-83400 mg/kg total lead (Pb-t), of which 47-76% and 38-55%, respectively, were extractable (Mg Cl-2 + NaOH + EDTA). Release rates were measured with a stirred-flow reactor under simulated gastric conditions at a pH of 1-3 and at temperatures of 278-328 K. During the first 10 min, Pb release rates at 297 K and pH 1 were high (53 and 31 mg (g of Pb-t)(-1) min(-1), soil and waste, respectively), and most samples released > 50% of Pb-t within the first 10 min. Between 10 and 60 min, Pb was generally released at lower rates (11 and 3 mg (g of Pb-t)(-1) min(-1) soil and waste, respectively). Lead release kinetics and solid-phase speciation indicate that Ph is present in at least two different solid phases. A kinetic model representing two simultaneous first-order reactions suggested the presence of a fast and a slow reacting pool; corresponding half-lives were in the range of 1 and 10 min, respectively.