Effective Desorption of Humic Substances from Amberlite XAD-2 Resin with Sodium Dodecyl Sulfate

Abstract

Naturally occurring humic substances, the major organic constituents of river, lake and pond water, are structurally complex and polyelectrolytic compounds with varying functionalities. They are not well-defined substances, but can generally be divided into three fractions: humic acid, fulvic acid and humin. Humic and fulvic acids are known to interact with metal ions, hydrated metal oxides, clay minerals and organic compounds.1-3 They are also considered to be precursors of toxic halogenated compounds formed during the chlorination of water.4 Therefore, the study of aquatic humic substances is highly required in geochemistry, environmental sciences and water treatment. In most cases, however, the concentrations of humic and fulvic acids are too low to study them directly. Large volumes of water should therefore be treated for the collection of appreciable amounts of humic substances.In our laboratory, an effective enrichment technique was proposed by using coprecipitation-flotation in a flow system 5 , where humic and fulvic acids were coprecipitated with indium hydroxide and continuously floated to the solution surface with numerous nitrogen bubbles. The gathering precipitate was dissolved in hydrochloric acid, which was passed through an Amberlite XAD-2 resin column to separate humic substances from the indium carrier. The humic substances were then desorbed with an alkaline solution of sodium dodecyl sulfate (SDS). 6 The anionic surfactant was essential for complete desorption, but appreciable amounts of SDS were found in the final humic solution.7 Unfortunately, an effective removal of the SDS has not yet been developed.The present paper describes a simple technique for the separation of humic substances from SDS molecules. An alkaline mixture of humic substances and SDS was passed through the XAD-2 resin column, on which the SDS was selectively and strongly retained, leaving the humic substances in the column effluent. Experimental ApparatusA Shimadzu UV-180 spectrophotometer was used for the measurement of absorbances at 400 nm to determine humic substances. Because the absorptivity varied with the solution pH, each sample was always adjusted to pH 13 before the determination. A Retsch Model MM vibrating pulverizer was used for grinding XAD-2 resin with an agate vial (18 mm inner diam.×50 mm height) containing two agate balls (12 mm in diam.). All separation procedures were carried out on a Hitachi ECV-843 BY clean bench. ReagentsA humic acid solution (0.25 mg cm -3 ) was prepared by dissolving humic acid (extracted from peat soil, Nakarai Chemicals) in a 0.1 mol dm -3 sodium hydroxide solution and passing through 1.0 µm Nuclepore membrane filters. A fulvic acid solution (0.5 mg cm Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa, Japan The adsorption and desorption of humic and fulvic acids on a non-ionic macroreticular resin, Amberlite XAD-2, were studied from the view point of the concentration of aquatic humic substances. Microgram or milligram quantities of humi...

Adsorption and desorption of humic acid on aminated polyacrylonitrile fibers

“…Various adsorbents, including activated carbon, resin, chitosan, metal oxides, and polypyrrole-coated granules, have been reported to adsorb humic acid from water in literature [5][6][7][8][9][10][11][12][13]. The surface electrostatic interactions between the positively charged adsorbents and the negatively charged humic acid has been found to play an important role in the adsorption process.…”

Efficient removal of humic acid in aqueous solution using polyaniline adsorbent

“…Various adsorbents such as activated carbon [5][6][7][8], metal oxides [9][10], resins [11][12] and amino adsorbents have been developed to remove the aqueous HA [13][14][15]. Among them, amino-adsorbents have been found to have a strong affi nity for aqueous HA owing to the strong interaction between the carboxyl and phenolic groups of HA molecules and the protonated amino groups of adsorbent [13][14][15].…”