Extração sequencial e especiação de metais pesados no decorrer do processo de compostagem de resíduos sólidos domiciliares.

It carried out sequential extraction for heavy metals speciation in organic trash during composting, objecting the understanding of chemical Cu, Mn and Zn transformations and it’s environmental risks. The extractors utilized in sequence and the respective fractions (beginning and ending of composting) were MgCl2 (soluble fraction – 5, 2% to Cu; 6, 7% to Mn; <1 to Zn; 2, 3% to Ni; 0.7, 0.1% to Pb; 24, 33% to Cd); CH3COONa (carbonate – 4, 3% to Cu; 24, 28% to Mn; 25, 20% to Zn; 6, 7% to Ni; 18, 13% to Pb; 37, 33% to Cd); Hidroxilamina+HOA (reduced/ oxidated) – 4% to Cu, 6, 21% to Mn and 22, 17% to Zn; 10, 14% to Ni, 38, 21% to Pb and 0% to Cd); H2O2+NH4OAc (organic – 22, 41% to Cu, 3, 4% to Mn; 7, 4% to Zn; 6, 14% to Ni, 39, 49% to Pb and 0% to Cd) and HNO3+HClO4 (remaining portion – 65, 50% to Cu, 61, 40% to Mn; 45, 58% to Zn; 76, 62% to Ni, 4, 17% to Pb; 38, 34% to Cd). The results show that composting process provides that the biggest fractions of Cu is organic or residual, Mn in carbonate or reduced forms and the Zn remains in the residual or reduced forms, Ni and Pb are organic or residual and the Cd remains in the residual or carbonate forms, offering bigger ambient risks. Key works: organic wastes, composting, ambient risk.