Cr-III binding by surface polymers in natural biomass: the role of carboxylic groups

Lodeiro, Pablo, Fuentes, Adrian, Herrero, Roberto and Sastre de Vicente, Manuel E. (2008) Cr-III binding by surface polymers in natural biomass: the role of carboxylic groups. Environmental Chemistry, 5 (5), 355-365. (doi:10.1071/EN08035).

Abstract

The chromium(III)-binding capacity of several biomaterials has been described under fixed conditions of pH (4.5) and initial metal concentration (100 mg L-1). Three of these materials (Sargassum muticum, orange peel and bracken fern) have been selected and subjected to different studies. Fourier transform infrared and scanning electron microscopy techniques were used to describe the structure of the biomaterials, supporting the hypothesis of a mechanism of metal complexation via carboxylic groups. Potentiometric titrations revealed the quantity of carboxyl groups present in S. muticum, orange peel and bracken fern: 1.78, 0.49 and 0.67 mmol g(-1), respectively. Moreover, a model considering different types of binding sites was used to simulate the process and determine the apparent pK values of the main functionalities. The number of carboxylic groups was clearly correlated with the maximum amount of Cr-III binding by the materials. A Langmuir competitive model was used to determine the complexation constants for chromium, log K-Cr, which are very close (similar to 3), supporting the idea of the implication of essentially one acid functionality. Desorption studies were conducted for different times employing H2SO4 and sodium citrate.

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