Química e mineralogia da fração sólida do material acumulado nos antigos lixões de Novo Israel e Horto Municipal na área urbana de Manaus

Abstract

The way the item is associated with the soil is decisive for its bioavailability . Several attributes are relevant in your the partition geochemistry, among them, the mineralogical composition, organic matter content and pH. Aiming to evaluate the potential of retaining elements in the solid portion of the material accumulated in urban areas in Manaus were selected two areas, the Garden City and the district of the Novo Israel where are located old landfills in the city. We collected 52 samples corresponding to three profiles, one in each place and a third for a natural soil. Were determined by X-ray diffraction (XRD) mineralogical composition, pH in water and KCl, the percentage of organic matter, characterization of the humic acids by infrared spectrometry and chemical speciation of the elements by sequential extraction of Zn, Cu, Pb, Ni, Cr, Mn, Fe, Cd, Ca, Mg, Na and K. The elements associated with water-soluble fraction, exchangeable, amorphous, organic matter, oxy-hydroxides of residual Fe and were quantified by atomic absorption spectroscopy. The results show pH acid in Natural soil (4.2-4.7) and more alkaline in the material accumulated on the old landfills (6.2-7.6). These values indicate reversal in the net charge of the material from negative to positive in 100% of the samples of the Novo Israel and 50% of Garden City. The percentage of organic matter that is higher in the material accumulated (8%) than in the natural soil (2%), is compatible with of functionals groups of alcohols phenols or carboxylic acids, as well as, compounds aliphatic, aromatic and amides, , that indicate the presence of humic substances. The mineralogical analysis show up the predominance of kaolinite and traces of oxy-hydroxides of Fe. The sequential extraction showed that the majority of the items have preference for the residual fraction, however, the amorphous fractions, organic matter, oxy-hydroxides of Fe, also contribute to the setting of the elements. Only Ni, Cr and Cd in Garden City, and Cr and Cd in Novo Israel are restricted to the residual fraction, which means they are more stable and with less contamination in the material studied. The Zn, Mn, Ca, Mg and K are more content in soluble fractions and exchangeable and are more bioavailability to the contamination of groundwater, plants and animals. For the material naturally, there was enrichment for most elements, in both the Garden City (Zn, Cu, Pb, Mg and K) as the Novo Isral (Zn, Cu, Pb, Cr, Mn, Cd, Ca, Mg and K).