Sorption of basic dyes onto iron humate.

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 quickly--most 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.