IntroductionThe removal of toxic heavy metals such as cadmium, zinc, and lead has become an important concern to manufacturing industries with respect to water purification and wastewater treatment. Several physicochemical technologies have been used for this purpose, including adsorption, ion exchange, and Ž . membrane separation processes Clifford et al., 1986 . Adsorption and ion-exchange processes have been found less expensive than membrane processes for most industrial applications. Most resins have higher affinity for alkaline earth Ž . Ž calcium and magnesium and alkali metals sodium and . potassium , and have poor selectivity for heavy metals. Improving resin selectivity by introducing new types of polymers into the matrix is a complex and expensive process. In comparison, an established technology that proves less expensive for the removal of trace metals, particularly radionuclides and Ž . heavy metals, is granular activated carbon GAC adsorption Ž . Motojima et al., 1978Motojima et al., , 1979aClifford et al., 1986 . Although GAC fixed-bed adsorbers are technologically feasible for the removal of heavy metals, they are not widely Correspondence concerning this article should be addressed to M. Pirbazari. used due to their low adsorbent capacity and questionable Ž . regenerability Clifford et al., 1986 . On the other hand, impregnation or immobilization of a selective chelating agent Ž . such as 8-hydroxyquinoline oxine on activated carbon would Ž provide a superior sorbent material for heavy metals Stevens, . 1987 . The nonpolar oxine is well adsorbed on activated car-Ž . bon, and such surface modified activated carbon SMAC would manifest higher adsorption capacity and easy regener-Ž . ability for heavy metals Vogt, 1948;Motojima et al., 1978 . Among various chelating agents, oxine is highly selective for Cd, Zn, Pb and other heavy metals as compared to alkaline earth and alkali metals present in most waters and wastewa-Ž . ters Stevens, 1987;Abollino et al., 1990 . Additionally, oxine is relatively nontoxic as it has been widely used for medicinal Ž . and agricultural applications Phillips, 1956 . Thus, good selectivity for heavy metal ions, easy adsorbent regenerability, and low toxicity of oxine makes oxine-impregnated SMAC a suitable candidate for the removal of heavy metals. A few studies have been conducted on the application of oxine-impregnated activated carbon for the removal of radionuclides such as Co-58, Co-60, Mn-54, and Fe-57 from nuclear wastes Ž . by coworkers 1978, 1979a,b . These re- May 1999 Vol. 45, No. 5 AIChE Journal 1135searchers observed that oxine-impregnated carbon was significantly more effective in the removal of these radioactive metal ions than pure activated carbon. An important aspect in the use of oxine-impregnated SMAC is the consideration of mechanisms pertaining to the sorption of oxine on activated carbon, and subsequent chelation of metal ions on the adsorbent-impregnated oxine. It is important to note that the sorption of oxine on activated carbon can be attrib...

Handbook of Chemistry and Physics," The Chemical Rubber Publishing Co., Cleveland, Ohio, 1961, p 334, sioned. Thus, the value of the skewed Gaussian is always in ordinate units while the value of W (Equation 3) is in abscissa units. The area in Equation 11 has units of ordinate times abscissa. All the moments {i>n, fik) have values in abscissa units to the ftth power. CONCLUSIONDetermination of the four parameters (Y, , x0, b) of the skewed Gaussian distribution function (6) provides a complete description of an asymmetric peak. Not only can the shape of the peak be reproduced but the moments of the distribution can be calculated. Use of the non-linear least squares method ( 7) to obtain the four parameters permits the calculation of the errors of the "final values." Errors of the calculated moments of distribution may then also be estimated. This is in marked contrast to the numerical calculation of moments of the distribution from discrete experimental values where no such estimates of the errors are possible although they can be quite large.

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