Adsorption of arsenic anions in water using modified lignocellulosic adsorbents

Abstract

Arsenic is the main natural pollutant in groundwater, the sole source of human consumption in several countries. Prolonged exposure to this element is a major global public health problem due to its high toxicity. Faced with this problem, several conventional techniques for arsenic removal have been described. Among all of them, adsorption by means of natural or modified lignocellulosic material is a technique that has a great advantage due to its low cost. This paper studies the adsorption of arsenic ions dissolved in water by means of eucalyptus bark fibers (hybrid of Eucalyptus urophylla and E. grandis) and aquatic macrophyte leaves. The adsorption capacity in each fiber altered by hydrolytic treatments was evaluated. The concentration of arsenic ions was determined by energy dispersive X-ray fluorescence spectrometry. The adsorbent material was characterized by physicochemical parameters and the surface chemical characteristics were determined by FTIR and Boehm methods. Adsorption conditions under different pH, kinetics, and adsorption isotherms were studied. The best adsorption capacity for arsenic ions occurred at pH 6 with acid modified eucalyptus bark fibers. The carboxylic and phenolic surface functional groups of the acid-modified adsorbent increased compared to the distilled water-treated fibers. The arsenic adsorption kinetics was found to be described by the pseudo-first-order model. The Langmuir and Redlich-Peterson isotherms at a temperature of 20 °C were the models with the best fit to the experimental data, with a slight advantage for the Langmuir model. The maximum adsorption capacity of total arsenic ions was 0.944 mg g−1. The proposed technique represents a sustainable and low-cost alternative to the current more expensive and complex treatments.

Keywords

• Adsorption
• Lignocellulosic waste
• Toxic metals
• Arsenic
• Eucalyptus bark