Isolamento, purificação e estudos de complexação de substâncias húmicas / Isolation, purification and complexation studies of humic substances

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

The aim of the present work was to study the humic substances, with emphasis to the humic acid (HA) fraction isolated from sediments of the Tietê River, collected at the Barra Bonita reservoir. The extraction of the humic acid was performed according to the procedure proposed by the International Humic Substances Society (I.H.S.S.). A commercial humic acid from Aldrich was studied in parallel. Both HA samples were characterized by elemental analysis, molecular absorption in the visible (E4/E6 ratio) and infrared regions, and ash contents. The acid-base properties of both humic acids were studied by potentiometric titrations, adopting the discrete site distribuition model and the modified Gran functions for data fitting. Six classes of titratable groups were characterized in 0,1 mol.L-1 (NaCI) ionic medium, with pKa values between 3 and 10. The sum of carboxylic groups (titratable groups with pKa <7) was greater than the sum of aminic and phenolic groups for both humic acids. These results were compared with those provided by classical methods such as baryta adsorption and calcium acetate, as well as condutometric titration. The complexing properties were studied with regard to Cu2+,Pb2+, Cd2+ and Zn2+, by potentiometric titration with solid membrane copper ion-selective electrode and amalgam electrodes for the other ions. The following stability was observed for both HAs complexes: log KHA-Cu >log KHA-Pb >log KHA-Cd approximately equal to log KHA-Zn. With regard the complexing capacity (Cc),the following order was observed: CcPb >CcCu >CcCd approximately equal to CcZn.

ASSUNTO(S)

metais Ácidos complexação Ácido húmico humic acid potenciometria complexation acids metais pesados potentiometry Ácido base metals acid base heavy metals

ACESSO AO ARTIGO

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