Síntese e caracterização de substâncias semelhantes aos ácidos húmicos de carvão de eucalipto, e sua interação com diclorofenol, cálcio, manganês e alumínio / Synthesis and characterization of humic acid-like substances from eucalypt charcoal, and its interaction with diclorofenol, calcium, manganese and aluminium

Patrick Marques Trompowsky

A wide range of commercial products containing humic substances have been applied successfully in agricultural and environmental remediation systems. Regarding their beneficial remediation characteristics, there is a high potential to adsorb heavy metals and organic pollutants, thus reducing their bioavailability. Industrially, they are extracted from non-renewable carbonaceous materials, like peat and coal, in which the use of renewable carbon sources does not occur. Brazil is the worlds largest charcoal producer, a prime material for pig iron and steel industries. Charcoal is formed by controlled pyrolysis of woody material, acquiring in the process a structure with a high aromatic C content. Charcoals from Eucalyptus saligna and E. grandis were produced in seven final carbonization temperatures, varying from 250 to 550 C. Humic acid-like substances (HA) and low weight fulvic acid-like substances (FA) were synthesized from these charcoals through acid oxidation with concentrated HNO3 under reflux conditions, and extracted by the International Humic Substances Society (IHSS) standard procedure. The HA production yield was measured, and they were characterized by thermogravimetric, elemental analysis, FTIR and C13 NMR techniques. An adsorption study was carried out with Al3+, Ca2+, and Mn2+ ions, and with an organochloride compound (diclorofenol) in pH 4,5. As adsorbents, two concentrations of HA (200 and 400 mg.L-1), one concentration of charcoal (10000 mg.L-1) and four concentrations of a modified charcoal (50, 250, 500 and 1000 mg.L-1), prepared through a mild nitric acid oxidation, were utilized. Different degrees of aromatic condensation generated by different charring temperatures influenced the yields of HA and FA, where the highest HA yield was obtained at the 450 C charring temperature, and the highest AF at 300 C. The HA substance had an elementary composition similar to HA from soils rich in pyrogenic carbon. FTIR and C13 NMR analyses showed a material rich in condensed aromatic structures, that increased as the char temperature rose, and a significant presence of carboxylic groups, besides other functional groups containing N incorporated by the nitric acid treatment. These analyses were confirmed by thermogravimetric and elemental analysis. Toxicity studies are necessary, because of the presence of nitrobenzene groups on the molecule. Adsorption studies showed a similar behavior with humic acids described in other research, reinforcing the potential of charcoal as a possible prime-material in the commercial production of HAs. The interaction with Al and Ca resulted in the insolubilization of the HA permitting its removal by vacuum filtration with a 0,45 μm pore size membrane. This insolubilization was not observed in the interaction with Mn and diclorofenol. In comparison, studies with pulverized charcoal and modified charcoal generated interesting results, showing the incorporation of hydrophilic groups by the nitric acid treatment and also the importance of polycyclic aromatic structures in the adsorption of small aromatic molecules. The methodology utilized did not determine if an absorption process was relevant in the sorption of solutes to the treated and non-treated charcoal, therefore its participation can not be neglected. The material is promising for the treatment of pulp and paper factory wastewater.

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