Extrações sequenciais de chumbo e zinco em solos de área de mineração e metalurgia de metais pesados

Abstract

A extração sequencial permite obter informações mais detalhadas sobre origem, modo de ocorrência, disponibilidade biológica e físico-química, mobilização e transporte dos metais pesados em ambientes naturais. Com o objetivo de estudar as formas de Pb e Zn foram selecionados oito perfis de solos de diferentes locais dentro de área de mineração e metalurgia de Pb, no município de Adrianópolis (PR), Vale do Rio Ribeira. As amostras foram coletadas nas profundidades de 0 a 10, 10 a 20 e 20 a 40 cm. Foram determinados os teores totais de Pb e Zn e sua especiação nas formas: solúvel; trocável; ligada a carbonatos; ligada à matéria orgânica; ligada aos óxidos de Fe de Al de baixa cristalinidade; ligada aos óxidos de Al cristalinos e filossilicatos 1:1 e 2:1; e residual. Com base nos valores percentuais de participação de cada fração nos teores totais, procedeu-se ao agrupamento das amostras similares por meio da análise de componentes principais (PCA). Houve basicamente duas formas de contaminação dos perfis de solo, sendo uma em decorrência das partículas das chaminés e a outra em função do acúmulo de rejeitos sólidos sobre os solos. A primeira foi mais prejudicial ao ambiente em razão dos maiores teores totais e de formas mais disponíveis no solo (solução mais trocável). De modo geral, houve maior associação de Pb aos carbonatos, seguida das frações residual e óxidos de Fe e Al de baixa cristalinidade. O Zn apresentou-se em formas mais insolúveis, aumentando a participação da fração residual nos teores totais. A PCA foi sensível às diferentes formas de Pb nos solos, pois promoveu o agrupamento das amostras, principalmente, em função da participação das formas trocáveis, ligadas aos óxidos de Fe e Al e ligadas aos carbonatos, em relação aos teores totais.

Lead and zinc in the structure of organic and mineral soil components

“…The average content of Pb in this mineral phase (extraction with 5 mol L -1 NaOH at 220 o C for 1.5 h) was 2,712.2 mg kg -1 , much higher than the average content extracted by Kummer et al (2011) (945.7 mg kg -1 ) with a weaker extraction method (1.5 mol L -1 NaOH at 75 o C for 1 h). On the other hand, there was an inversion in Pb concentration and in the average participation in total levels of this metal in the residual phase compared to the data of Kummer et al (2011) (592.7 vs. 2,062.5 mg kg -1 and 1.8 vs. 26.3 %, respectively), which is consistent with the greater extraction power (total contents at each step) of the method proposed here for sequential analysis.…”

“…Due to high concentrations of Pb carbonate (Table 3), the participation of these forms in total metal content was also significant (Figure 2). Kummer et al (2011) used the sequential analysis in the same soil samples for speciation of the total Pb and Zn concentrations in their more reactive forms (partial extraction of mineral and organic phases - Mann & Ritchie, 1993) and obtained an average concentration (24 samples) of Pb associated to carbonates (single extraction with 0.1 mol L -1 pH 5 Na acetate) of 1,921.6 mg kg -1 . Raising the concentration of Na acetate and the number of extractions increased the average of Pb concentration for the same fraction to 4,362.9 mg kg -1 .…”

“…The data of Kummer et al (2011), who subjected the same soil samples to seven steps of sequential extraction of reactive forms of heavy metals, were used to compare the performance of the extraction methods proposed here.…”

“…The XRD, equipped with Ni filter and using CuKa radiation, was carried out at 20 kV and 40 mA. Andrade et al (2009a,b), Barros et al (2010a,b), Buschele et al (2010), Kummer et al (2010Kummer et al ( , 2011 and Melo et al (2012) discussed in detail the relationship between total Pb and Zn soil contents (Tables 3 and 4) with the sampling locations (Table 1) and the level of diffusion of these contaminants in soils, water, sediments, organisms, and plants in the study area.…”

“…Liang et al (2010) also considered the possibility of isomorphic substitution of Mg 2+ for Pb 2+ in the trioctahedral brucite sheet. Kummer et al (2011) subjected the same samples as used in this study (from different locations in a heavy metal mining and metallurgy area, Adrianópolis -PR, Brazil) to seven steps of conventional sequential extraction (Mann & Ritchie, 1993) for the speciation of the total Pb and Zn levels in the more reactive forms of greater environmental interest. Therefore, the potential for contamination of soil, plant, water, sediments and organisms was extensively discussed by Kummer et al (2011) and in other studies developed in the same area, focused on environmental aspects (Andrade et al, 2009a,b;Barros et al 2010a,b;Buschele et al, 2010;Kummer et al, 2010;Melo et al, 2012).…”