Interação de metais com substâncias húmicas de terra preta de índio da Amazônia e do tipo húmicas de carvão hidrotérmico
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Data
2019-06-12
Autores
Silva, Leila Soares da
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Universidade Estadual Paulista (Unesp)
Resumo
As substâncias húmicas (SH) são compostos resultantes da degradação química e biológica de resíduos vegetais e animais, que estão organizadas como estruturas supramoleculares. Elas são amplamente distribuídas em solos, águas naturais e sedimentos. As Terras Pretas de Índio (TPI) da Amazônia são solos tipicamente conhecidos por possuírem alta fertilidade, o que tem sido atribuído ao elevado teor de matéria orgânica humificada, recalcitrante e à riqueza de nutrientes. Estudos têm demonstrado que a carbonização hidrotérmica (CHT) de biomassa produz um material rico em carbono recalcitrante, denominado carvão hidrotérmico (CH). O processo emprega temperaturas brandas de no máximo 300°C, biomassa úmida e pressões autogeradas. Sendo assim, este trabalho teve como objetivo avaliar a interação das substâncias do tipo húmica (STH) extraídas do CH em comparação com as SH dos solos TPI (SH TPI), visando avaliar o potencial agronômico do material que está sendo produzido. Neste trabalho a CHT foi conduzida utilizando os subprodutos do setor sucroenergético: bagaço de cana-de-açúcar e vinhaça. A CHT foi realizada à 232°C empregando uma mistura de bagaço de cana-de-açúcar e vinhaça com adição de porcentagens de ácido sulfúrico de 1 e 4% (v/v) ao meio reacional. As SH foram extraídas da TPI seguindo o modelo aplicado pela Sociedade Internacional de Substâncias Húmicas (IHSS), empregando-se o mesmo modelo para extração da STH do CH. A SH TPI e as STH foram caracterizadas por técnicas espectroscópicas na região do infravermelho e do ultravioleta-visível, ressonância magnética nuclear e por fluorescência molecular. Os espectros de infravermelho mostraram que há bandas de grupos funcionais similares presentes nas SH TPI, e nas STH 1 e 4%, sendo que bandas de grupamentos alifáticos são mais visíveis na STH 4%. A fluorescência molecular mostrou a presença de grupos fluoróforos complexos do tipo húmico derivados de lignina para as SH TPI e STH porém, houve um leve deslocamento das STH1 e 4% em relação à SH TPI para uma região com grupamentos menos conjugados, corroborando com os resultados de infravermelho. Os espectros de 13C RMN mostraram apenas três picos para STH 4% devido à maiores alterações estruturais relacionadas com a porcentagem de H2SO4 utilizado na preparação do CH 4%. A capacidade complexante entre as SH, bem como das STH com os íons metálicos Cu(II), Al(III), Fe(III) e Co(II) foi realizada utilizando as técnicas de supressão de fluorescência molecular e infravermelho, nas quais os dados obtidos foram tratados pela Análise de Fatores Paralelos e Análise de Correlçao Bidimensional, respectivamente. Constantes de estabilidade condicional (Kc) variaram de 4,5 a 6,0 e a concentração de sítios ligantes (Lig) das SH e STH foi maior nos ensaios com o metal Co(II). Os principais grupos funcionais identificados como sendo responsáveis pela interação das SH e STH com os metais foram O-H de grupos hidroxilados, C=C de aromáticos, COO- de ácidos carboxílicos e C-O de polissacarídeos.
Humic Substances (HS) are composed of the chemical and biological degradation of plants and animals, which are organized as supramolecular structures. They are widely distributed in soils, natural waters and sediments. The Amazonian Dark Earth (TPI) are soils known by the by high fertility, which have been conditioned to the high , recalcitrant and humified organic matter content, as well as the richness of nutrients. Studies have shown that hydrothermal carbonization (HTC) of biomass produces a rich recalcitrant carbon material, named hydrochar (HC). This process is carried out mild temperatures of up to 300 °C, humid biomass and selfgenerated pressures. Therefore, this study aimed to evaluate the interactions of Humic-like Substances (HLS) extracted from HC and to compare them with the HS extracted from TPI soils (HS TPI), in order to assess the agronomic potential of the HC. For this, the CHT was conducted using the by-products of the sugar-energy sector: sugarcane bagasse and vinasse. The CHT was carried out at 232 ° C using a mixture of sugarcane bagasse and vinasse with additions of 1 and 4% (v / v) sulfuric acid to the reaction medium.HS were extracted from TPI following the model applied by the International Society of Humic Substances (IHSS), as well as for extracting of HLS from HC.HS TPI and HLS were characterized by spectroscopic techniques in the infrared and ultraviolet-visible region, 13C nuclear magnetic resonance (NMR) and molecular fluorescence. Infrared spectra showed that there are bands of similar functional groups present in HS TPI, and in HLS 1 and 4%, in which bands of aliphatic groups are more visible in HLS 4%. Molecular fluorescence showed the presence of lignin-derived complex humic fluorophore groups for HS and HLS. However, there was a slight shift for the region relative to the less conjugated groups of HLS 1 and 4% compared to HS TPI, corroborating with infrared results.13C NMR spectra showed only three peaks at 4% HLS, which is due to the major structural changes occurring due to the higher percentage of H2SO4 used in the preparation of 4% HC. The determination of the complexing capacity of HS and HLS with metal ions Cu(II), Al(III), Fe(III) and Co(II) was performed using fluorescence quenching and infrared techniques, in which the data obtained were treated by the Analysis of Parallel Factors and Analysis of Two-Dimensional Correlation, respectively.. Conditional stability constants (Kc) varied from 4.5 to 6.0 and the concentration of binding sites (Lig) of HS and HLS was higher in the Co (II) assays. The main functional groups identified as being responsible for the interaction of HS and HLS with the metals were O-H of hydroxyl groups, C=C of aromatics, COO of carboxylic acids and C-O of polysaccharides.
Humic Substances (HS) are composed of the chemical and biological degradation of plants and animals, which are organized as supramolecular structures. They are widely distributed in soils, natural waters and sediments. The Amazonian Dark Earth (TPI) are soils known by the by high fertility, which have been conditioned to the high , recalcitrant and humified organic matter content, as well as the richness of nutrients. Studies have shown that hydrothermal carbonization (HTC) of biomass produces a rich recalcitrant carbon material, named hydrochar (HC). This process is carried out mild temperatures of up to 300 °C, humid biomass and selfgenerated pressures. Therefore, this study aimed to evaluate the interactions of Humic-like Substances (HLS) extracted from HC and to compare them with the HS extracted from TPI soils (HS TPI), in order to assess the agronomic potential of the HC. For this, the CHT was conducted using the by-products of the sugar-energy sector: sugarcane bagasse and vinasse. The CHT was carried out at 232 ° C using a mixture of sugarcane bagasse and vinasse with additions of 1 and 4% (v / v) sulfuric acid to the reaction medium.HS were extracted from TPI following the model applied by the International Society of Humic Substances (IHSS), as well as for extracting of HLS from HC.HS TPI and HLS were characterized by spectroscopic techniques in the infrared and ultraviolet-visible region, 13C nuclear magnetic resonance (NMR) and molecular fluorescence. Infrared spectra showed that there are bands of similar functional groups present in HS TPI, and in HLS 1 and 4%, in which bands of aliphatic groups are more visible in HLS 4%. Molecular fluorescence showed the presence of lignin-derived complex humic fluorophore groups for HS and HLS. However, there was a slight shift for the region relative to the less conjugated groups of HLS 1 and 4% compared to HS TPI, corroborating with infrared results.13C NMR spectra showed only three peaks at 4% HLS, which is due to the major structural changes occurring due to the higher percentage of H2SO4 used in the preparation of 4% HC. The determination of the complexing capacity of HS and HLS with metal ions Cu(II), Al(III), Fe(III) and Co(II) was performed using fluorescence quenching and infrared techniques, in which the data obtained were treated by the Analysis of Parallel Factors and Analysis of Two-Dimensional Correlation, respectively.. Conditional stability constants (Kc) varied from 4.5 to 6.0 and the concentration of binding sites (Lig) of HS and HLS was higher in the Co (II) assays. The main functional groups identified as being responsible for the interaction of HS and HLS with the metals were O-H of hydroxyl groups, C=C of aromatics, COO of carboxylic acids and C-O of polysaccharides.
Descrição
Palavras-chave
Capacidade complexante, Terra preta de índio da Amazônia, Substâncias húmicas, Carvão hidrotérmico, Complexation capacity, Amazonian dark earth, Humic substances, Hydrochar