The influence of simple organic acids on sorption of inorganic ions at the goethite/water interface

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" The influence of simple organic acids on sorption of inorganic ions at the goethite/water interface "
M. A. Ali

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112875
Doc. No	:	TLpq304101598
Main Entry	:	M. A. Ali
Title & Author	:	The influence of simple organic acids on sorption of inorganic ions at the goethite/water interface\ M. A. Ali
College	:	Carnegie Mellon University
Date	:	1994
student score	:	1994
Degree	:	Ph.D.
Page No	:	237
Abstract	:	Sorption of humic substances, a mixture of complex organic acids, onto minerals and their interactions with inorganic ions can have a strong influence on fate and transport of solutes in natural aquatic systems. These interactions are not well understood. There has been limited success in applying surface complexation models to describe mineral-organic acid-ion interactions, primarily because of the complex nature of humic substances. In this research, the influence of two simple organic acids, phthalic acid and chelidamic acid, on sorption of the inorganic ions SO4\sp{2-}, Ca and Cu was investigated in goethite/water suspensions in single- and multisorbate systems. These two organic acids have some structural similarity to humic acids in that they possess carboxylic and phenolic functional groups, the predominant functional groups associated with humic substances.Surface complexation modeling of sorption data was performed with the Generalized Two Layer Model (GTLM) of Dzombak and Morel (1990). The primary objectives were to gain insights into mineral-organic acid-ion interactions and to investigate the ability of the GTLM to describe and predict sorption in multisorbate systems. Sorption characteristics of sulfate and the organic acids on goethite in single-sorbate systems were similar and resembled those reported for sorption of humic substances on oxide panicles. Sorption affinities of sulfate and the organic acids were comparable and sulfate effectively competed with the organic acids for sorption sites on goethite, particularly at low pH. Predictions of sorption in sulfate-organic acid binary-sorbate systems based on single-sorbate data fits represented competitive sorption data fairly well over a wide range of conditions. However, there were underpredictions of minor component sorption in the presence of a major component, which may be explained by sorbate-specific surface site heterogeneity and/or by inaccurate representation of coulombic effects in the GTLM. The effects of the simple organic acids on sorption of Cu were similar to those reported for the effects of humic substances on sorption of Cu In the presence of the organic acids, sorption of Cu was significantly enhanced at low pH values. Sorption of Cu in the presence of the organic acids was reproduced over a wide range of conditions with the GTLM by invoking Cu-organic acid ternary surface complexes. Reduced sorption of Ca due to formation of Ca-organic acid nonsorbing solution complexes was also predicted by the GTLM reasonably well. Sulfate was found to have a significant influence on sorption of Cu in the presence of the organic acids. Addition of sulfate to Cu-organic acid binary-sorbate systems resulted in significant reduction of Cu sorption at low pH values, primarily due to competition for surface sites between sulfate and Cu-organic acid ternary surface complexes. The successful prediction of sorption in ternary-sorbate systems based on surface reactions and equilibrium constants derived from single- and binary-sorbate systems provides a validation of the extrapolation of sorption from simple systems to multicomponent systems through surface complexation modeling.
Subject	:	Applied sciences
	:	Civil engineering
	:	Civil engineering
	:	Environmental science
	:	Health and environmental sciences