Espectroscopia de RMN no estado sólido aplicada em estudos de biocarvões e hidrocarvões contendo fósforo
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Data
2023-12-11
Autores
Santoro, Mariana Coelho
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Universidade Federal do Espírito Santo
Resumo
This work deals with the preparation and characterization of different biochars and hydrochars obtained through slow pyrolysis and hydrothermal carbonization (HTC) of organic precursors, aiming applications in soils as sources of phosphorus (P). In the first part of the work, a set of hydrochar samples obtained from the HTC of poultry litter, synthesized at different temperatures, residence times and initial pH, were studied. In a second part, hydrochar samples were synthesized through the HTC of microalgae cultivated in a wastewater treatment plant, and the effects of different temperatures, residence times and MgO addition to the raw material were studied, focusing on the speciation of P. The main tools used to understand the chemical nature and the modifications that occurred during the hydrothermal process of these two sets of samples were the standard protocol of measurements for fractionation of P species and solid-state 13C and 31P nuclear magnetic resonance (NMR) spectroscopy. The 13C NMR spectra of the hydrochars showed that the structural changes of the precursors during the HTC depend mainly on the heat treatment temperature and that, in the range of investigated temperatures, the hydrochars obtained are composed mostly of aromatic and alkyl groups, regardless of the residence time. In addition, the results showed that HTC altered the physical state and solubility of different P species, with the increase in temperature and residence times causing an increase in the amount of total phosphorus in the hydrochars. The addition of MgO in the hydrothermal treatment of microalgae has proven to be a viable way to significantly reduce losses and increase the total and water-soluble amounts of phosphorus in the hydrochars. In another branch of the work, biochar samples obtained from two types of lignocellulosic residues - coffee husk and coconut shells - were studied. The samples were physically activated with steam and modified with Ca or Mg to be used in phosphate adsorption experiments from aqueous solutions of ammonium phosphate or human urine as sources of P. Solid-state 31P NMR was used in conjunction with thermogravimetry and X-ray diffraction to characterize these biochars. The Mg-modified samples showed adsorption of 96% of the phosphates present in human urine, with precipitation of struvite and other disordered Mg phosphates. Thus, the chemical modification of biochars with Mg compounds proved to be a viable route to produce phosphate adsorbents that can be used as slow-release phosphate fertilizers.
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Fertilizantes fosfatados , RMN no estado sólido , Biocarvões