Adsorption of humic substances

Humic substances were concentrated more than 50-fold on the XAD-4 quaternary resin, but a saturated HCl/methanol solution was required for the desorption. This eluant was not concentrated further because the concentration of humic substances could be measured directly with a spectrophotometer. Total recovery of humic substances was higher in the bench-scale experiments than in the pilot plant studies. On the basis of the pilot plant results (see summary of experiment 3), it appears that the adsorption of humic substances was affected by the higher velocity or the loading capacity because 458 was recovered in the effluent water. The higher velocity in the pilot plant studies did not have a similar effect on other compounds such as quinaldic acid, for example, which was recovered at almost 100. It is believed that caffeine, which was concentrated during bench-scale studies, was also affected by the higher velocity in the pilot plant studies. 

Teermann 1 P, Jekel M R (1999) Adsorption of humic substances onto p-FeOOH and its chemical regeneration. Conference Proceedings of the International IAWQ-1WSA Joint Specialist Conference on Removal of humic substances from water , 0degaard, H. (Ed.), Trondheim, Norway, 24.-26. June 1999 (Water, Science Technology, in press). 

Tipping, E., 1981. The adsorption of humic substances by ion oxides. Geoch. Cosmoch. Acta, 191-199. 

Yoon, T. H., Johnson, S. B., and Brown, G. E., Jr. (2005). Adsorption of organic matter at mineral/water interfaces 4. Adsorption of humic substances at boehmite-water interfaces and impact on boehmite dissolution. Langmuir 21,5002-5012. 

Weng, L., Van Riemsdijk, W. H., Koopal, L. K., and Hiemstra,T. (2006). Adsorption of humic substances on goethite Comparison between humic acids and fulvic acids. Environ. Sci. Technol. 40,7494-7500. 

Jekel, M.R., The stabilization of dispersed mineral particles by adsorption of humic substances, Water Resour. Res., 20, 1543, 1986. 

TABLE 30 Effect of pH on the Surface Charge of an Activated Carbon Before and After Adsorption of Humic Substances... 

ADSORPTION OF HUMIC SUBSTANCES ON ACTIVATED CARBON PREPARED FROM LOCALLY AVAILABLE WASTE MATERIALS... 

The adsorption of humic substances on activated carbon has been studied experimentally for a selected commercial quality and 2 qualities of home-made carbon derived from hardwood sawmill wastes. 

As a first step, adsorption isotherms were determined for a commercially available humic substance and for its humic and fulvic acid fraction. Secondly the adsorption of humic substance from a river water and a marshland water was investigated. 

Much has been published [ 1—3, 6—8 ] on the identification and quantification of parameters that the adsorption of humic substances by activated carbon, and on the practice application of these finding to water treatment. 

Their adsorptive capacity for phenol, pentachlorophenol, dodecylbenzenesulphonate, and p-toluenesulphonate were measured [9 ] From these results the carbons J23 and J32 and the reference carbon F 400 (Calgon corporation) were selected to study the adsorption of humic substances. 

P. H. Boening, D. D. Beckmann, V. L. Snoeyink, Activated carbon varsus resin adsorption of Humic Substances, JAWWA, 72, 1, 54-59(1980). 

Organic adsorbates that are more hydrophobic exhibit different adsorption behavior, particularly at higher concentrations. Long-chain fatty acids adsorb to oxide surfaces in part through surface complexation, as shown by electron spin resonance spectroscopy (32). At higher concentrations at the surface, however, favorable interactions between sorbed molecules (hemimicelle formation) appear to dominate and result in greater than monolayer adsorption (40, 41). Because humic substances (like the fatty acids) are amphiphilic, both surface complexation and hydrophobic interactions may be involved in the adsorption of humic substances on oxide surfaces. 

The preceding discussion relies on an analogy between complexation in solution and complexation at the mineral surface, a fundamental tenet of the surface complexation model (27). Strong complexation of metals in solution by humic substances is well-documented (16, 42-44). Thus surface complex formation is a likely mechanism for the adsorption of humic substances on oxide surfaces. 

The effects of calcium and magnesium on the adsorption of humic substances have not been entirely explained. Humate adsorption on goethite is increased in the presence of calcium and magnesium, and clear saturation is not observed. These effects have been attributed to coadsorption of the divalent cations (47, 48) and may be related to the ability of calcium and magnesium to coagulate some fraction of humic substances (57, 58). 

Adsorption of humic substances on oxides markedly affects particle surface charge and colloidal stability. In these effects, a contrast may be noted... 

Humic substances, although a major fraction of soil DOM, do not facili- ate oxide dissolution in laboratory studies. The mobilization of metals in soils mav, however, be indirectly affected by humic substances. Solubilization of -metals may be inhibited by competitive adsorption of humic substances and LMW organic ligands. The opposite effect—an enhancement of metal morn ility—might result from the stabilization of dissolved metals as humate -omplexes. 

Adsorption of a complex mixture such as NOM, in which polyelectrolytes predominate, involves both electrostatic and nonelectrostatic interactions as weU as molecular sieving effects. Several researchers [53—55] reported that the adsorption of humic substances altered the surface properties of carbons because their... 

The influence of the pore size distribution of carbon on NOM uptake has been recognized by several researchers [57, 63]. Likewise, Karanfil and coworken [64] and Kilduffand coworkers [65] concluded that the adsorption of humic substances was largely governed by molecular size distribution in relation to pore size. Moreover, a good linear relationship (Fig. 25.6) was foundbetween the amount adsorbed by different carbons and their pore volume between 0.8 and 50 nm [61, 66] when the adsorption was carried out at pH 3. This is because electrostatic effects are minimized under these experimental conditions and nonelectrostatic interactions predominate. The adsorption mechanism would be due to hydrophobic and/or TT-TT-electron interactions, and in this case as with other electrolytes (see above). 

Morris, G. and Newcombe, G. (1993). Granular activated carbon the variation of surface properties with the adsorption of humic substances, f. Colloid Interface Sci., 159, 413-20. 

La France, P. and Mazet, M. (1989). Adsorption of humic substances in the presence of sodium-salts. J. Am. Water Works Assoc., 81, 155-62. 

Summers, R.S. and Roberts, P.V. (1988). Activated carbon adsorption of humic substances. I. Heterodisperse mixtures and desorption./. Colloid Interface Sci., 122, 367-81. 

Ebie, K., Li, F., and Hagishita, T. (1995). Effect of pore size distribution of activated carbon on the adsorption of humic substances and trace organic compounds. Water... 

Lee, M.C. and Snoeyink, V.L. (1980). Effect of GAC pore size distribution and alum pretreatment on the adsorption of humic substances. Proceedings AWWA Annual Conference. Water for the World - Challenge of the 80 s, pp. 319-28. 

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