Comparison of Affinity of Soil and Lignitic Humic Acids to Cu(II) and Cd(II) Ions

abstract

English

Lignites are known to have relatively high amount of humic substances (HS). Lignite in natural form or various lignite-derived products may be therefore used as, e.g., sorbents, soil remediators or conditioners, organic fertilizers. Except perhaps the former application example, lignitic HS could substitute or support naturally occurring materials. It is necessary to know whether there are any differences between lignite and, e.g., soil HS, pertinent for the intended application. In our search for non-energetical applications of South-Moravian lignite, its functioning in soil treatment technologies is also evaluated. This contribution presents results of comparative study of adsorption of Cu(II) and Cd(II) ions to solid humic acids extracted from South-Moravian lignite and several types of soils from Slovakia. Sorption experiments were made in batch system at laboratory temperature. Soils, natural lignite, and HS extracted from both lignite and soils served as solid sorbents. When adsorption equilibrium was established, solid phase was centrifuged and metal ion concentration in the liquid phase was determined by spectrometry (Cu) or polarography (Cd). Adsorption isotherms were then constructed. Solid phase was then subjected to sequential desorption experiments with ammonium nitrate and then with EDTA. Various adsorption isotherm equations were tested for their data-fitting capability. Equation parameters, sorption capacity, and adsorption strength are compared across all samples and separately for soil HS-lignite HS. Lignite HS adsorbed the highest percentage of copper from all solutions regardless their concentration. Maximum adsorbed amount computed from Langmuir isotherm was higher only for gleyic fluvisol. Sorption capacity of any HS in experiments with Cd was not achieved and all samples adsorbed approximately the same amount (about 90%) which slightly decreased with increasing initial concentration of Cd. The highest amount was sorbed on calcaric chernozem HS; lignite HS sorbed similar amount as HS from calcaric fluvisol and haplic luvisol. Total desorption of Cd was lowest for lignite HS and high initial concentrations of Cd (above 5 mg/l). Otherwise, desorbed amount from lignite HS was comparable to those from dystric cambisol and haplic luvisol. Generally, copper is bonded most strongly to lignite HS, particularly at its high initial concentrations (e.g., with initial concentration 0.1 mol/l only 20% is desorbed comparing to 50-100% from soil HS). Reported preliminary results give reasonable prospect of successful application of lignite-derived HS and products prepared from them in in-situ soil remediation technologies

humic acids, afinity, adsorption, metal ions

KLUČÁKOVÁ, M.; BARANČÍKOVÁ, G.; MAKOVNÍKOVÁ, J.; MADARAS, M.; PEKAŘ, M.

2004

17. 3. 2004

Northeastern University

Boston

50

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