Environ. Sci. Technol. 2003, 37, 5792-5798
Sorption of Basic Dyes onto Iron Humate P A V E L J A N O Sˇ * Faculty of Environmental Studies, University of Jan Evangelista Purkyneˇ, Kra´lova Vy´ˇsina 7, 400 96 U Ä stı´ nad Labem, Czech Republic
Iron humate (IH) was examined as a new low-cost sorbent for removing basic dyes (Methylene Blue, Methyl Violet, Crystal Violet, Malachite Green, and Rhodamine B) from waters. The sorption of the dyes from aqueous solutions was described by a multisite Langmuir isotherm; the sorption capacities ranging from ca. 0.01 to 0.09 mmol/g were calculated from the parameters of the isotherm for individual dyes. A more detailed study was carried out with Methylene Blue to examine an influence of the composition of aqueous phase on the sorption. pH and the presence of inorganic salts have only minor effects on the sorption. The presence of anionic surfactant (sodium dodecyl sulfate, SDS) increases dramatically the sorption of Methylene Blue. A model describing the sorption of basic (cationic) dyes in the presence of anionic surfactants was proposed; two main mechanisms are considered in this model: the sorption of cationic dyes onto the polar (or cation-exchange) active sites and the sorption of relatively small dye-surfactant aggregates onto the nonpolar part of the sorbent. Experimental dependencies comply well with those predicted from the model. Both in the presence as well as in the absence of SDS, the dye sorption proceeds relatively quicklysmost of the dye is sorbed within the first several hours. Leachability of the dye from the loaded sorbent was found to be very low, especially with water as leachant.
the manufacture of steel (9), fly ash (10, 11), activated slag from the fertilizer plants (12), and others. The sorption of dyes on conventional sorbents, such as activated carbon (12, 13) or silica (14), has been extensively studied, too. Commercial sorbents (zeolites, polymeric resins, ionexchangers, and granulated ferric oxide) were compared for a decolorization of wastewater from the textile industry (15). Humic substances are ubiquitous materials occurring in huge amounts in soils, sediments, and waters. They form an active constituent of some of the above-mentioned sorbentss peat and coal. Humic acids (HAs) representing a major part of the humic substances are manufactured on an industrial basis, usually by an alkaline extraction from low-rank brown coals (16). HAs are insoluble in neutral and acidic media and can be used for the sorption of metal cations from waters (17, 18). More advantageous, however, seems to be an application of the salts of HAs with polyvalent metal cations (metal humates) that are markedly less soluble in aqueous solutions (19). Metal humates can be prepared in a relatively simple way by a precipitation of HAs with suitable metal compounds (20). A stable form of iron humate (IH) can be prepared by the precipitation with an aqueous solution of iron(II) sulfate (21). This IH was designed as a supplement providing iron and organic matter for vegetation and animal feedstocks (21, 22). A similar kind of IH is produced in the plant manufacturing HAs and their derivatives from brown coal. IH originates as a waste product during a treatment of wastewaters with iron salts. The precipitated and dried IH is commercially available, and it is recommended for removing heavy metals from waters (23, 24). No attempts have been done to examine an applicability of IH as a sorbent for the removal of organic pollutants. The goal of this study was to show that basic dyes can be effectively adsorbed onto IH. The sorption capacities of IH were determined for Methylene Blue, Methyl Violet, Crystal Violet, Malachite Green, and Rhodamine B. For Methylene Blue, a more detailed study was carried out, and factors influencing the sorption (pH, presence of inorganic salts or surfactants) were examined. Basic data about the kinetics of sorption were also obtained.
Experimental Section Introduction Adsorption techniques employing solid sorbents are widely used to remove certain classes of chemical pollutants from waters, particularly those that are hardly destroyed in conventional water-treatment plants. One of the problematic groups represents dyes and pigments, which are emitted into wastewaters from various industrial branches, mainly from the dyes manufacturing and textile finishing. The adsorption process provides an attractive alternative for the treatment of contaminated waters, especially if the sorbent is inexpensive and does not require an additional pretreatment before its application. A number of nonconventional sorbents have been tried for the removal of chemical pollutants. A brief review of the potentially low-cost sorbents was published by Bailey et al. (1); it is, however, focused on removing of heavy metals. Natural materials and waste products from industry and agriculture were tested to remove dyes from waters: peat (2, 3), chitin (4), apple pomace and wheat straw (5), sulfonated coal (6), organomontmorillonite (7), coir pith (8), slag from * Corresponding author phone: +420-47-530 9748; fax: +42047-530 9758; e-mail:
[email protected]. 5792
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 24, 2003
Sorbent. The sorbent was obtained from Severoceske Doly (North-Bohemian Mines), Bilina, Czech Republic, where it is produced by a precipitation of wastewaters containing humic substances with iron salts. IH is supplied dried and granulated with grain sizes of ca. 0.5-3 mm. According to the manufacturer’s specification, IH should comply with the following criteria: content of humic substances > 53%, ash content < 27%, maximum admissible concentrations of heavy metals 10 mg/kg (Pb), 1 mg/kg (Cd), 30 mg/kg (Cr), 20 mg/kg (As), and 2 mg/kg (Hg). The composition and some properties of IH are listed in Table 1. IH was used as received, without any additional pretreatment, with an exception of a size classification by sieving. If not stated otherwise, the fraction with grain sizes less than 1 mm was used. This fraction does not contain very fine powdered particles. The surface area measured by the standard BET technique (N2 adsorption) was less than 20 m2/g. It is, however, expected that the surface area for the hydrated sorbent (in aqueous solutions) is much greater, analogously to hydrous metal oxides (25). Basic Dyes. Methylene Blue (Basic Blue 9), Malachite Green (Basic Green 4), Methyl Violet (Basic Violet 1), and Crystal Violet (Basic Violet 3) were obtained from Lachema, Brno, Czech Republic. Rhodamine B (Basic Violet 10) was obtained from Merck, Darmstadt, Germany. 10.1021/es020142o CCC: $25.00
2003 American Chemical Society Published on Web 11/12/2003
TABLE 1. Composition and Properties of IH dry mass (105 °C), % loss of ignition (650 °C), % elemental composition,a % Na Mg Al Si S (sulfate) K Ca Fe Cr, Mn, Co, Ni, Cu, Zn, As, Ag, Cd, Sn, Ba, Hg, Pb leachability with waterb pH of extract conductivity, mS/m COD,c mg/L Fe, mg/L Cu, Zn, Cd, Pb, Hg, mg/L
89.6 73.7 3.1 0.1 1.9 2.1 4.2 1.6 0.4 11.1
