Heavy metals released from leaf litter exposed to different fire temperatures. A laboratory experiment.
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The leaf litter of three Mediterranean species, Quercus suber (Q.S.), Quercus robur (Q.R.) and Pinus pinea (P.P.), was exposed to different fire temperatures, 150°, 200°, 250°, 300°, 350°, 400°, 450°, 500°, and 550°C in a muffle furnace for 2 hours. We measured the Calcite (CaCO₃) content of the ash and the pH and release of heavy metals Aluminium (Al), Manganese (Mn), Iron (Fe) and Zinc (Zn) in a slurry of ash and deionised water. CaCO3, in the ash appears at 400°C and increases with temperature. The pH values are low at low fire temperatures, rise at medium temperatures, followed by a stabilization at higher temperatures. Heavy metals concentration in solution are higher in the low pH slurries where CaCO3 is absent in the ash. In general, at low and medium fire temperatures, Al and Mn in ash slurries are more soluble than in an unheated control sample and this concentration in test solution decreases at higher temperatures. Fe and Zn in solution decrease with exposure to higher temperatures, even at low pH. At higher temperatures, the effect of pH and CaCO3 inhibits the presence of heavy metals in solution.
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