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Title: Chemical modeling of boron adsorption by humic materials using the constant capacitance model

Author
item Goldberg, Sabine

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2014
Publication Date: 4/23/2015
Citation: Goldberg, S.R. 2015. Chemical modeling of boron adsorption by humic materials using the constant capacitance model. Soil Science. 179(12):561-567.

Interpretive Summary: Boron is a nutrient ion that is toxic to plants at elevated concentrations. Toxic concentrations can occur in agricultural soils and irrigation waters especially in arid regions. A better understanding of the adsorption behavior of boron on humic materials in soils is necessary. Boron adsorption on humic acids from various environments was described using a chemical model as a function of solution pH and solution boron concentration. Results can be used to describe born adsorption behavior on diverse humic materials of interest in environmental and agricultural situations.

Technical Abstract: The constant capacitance surface complexation model was used to describe B adsorption behavior on reference Aldrich humic acid, humic acids from various soil environments, and dissolved organic matter extracted from sewage effluents. The reactive surface functional groups on the humic materials were assumed to be a carboxyl site, XOH and a phenol site, YOH. Initially, total concentrations of the sites, XOHT and YOHT and the proton dissociation constants for the carboxyl site, LogKX- and the phenol site, LogKY- were optimized by fitting the constant capacitance model to potentiometric titration data on reference Aldrich humic acid. Subsequently, the model was fit to experimental B adsorption by optimizing two tetrahedral B surface complexation constants: LogKXB- for a carboxyl site and LogKYB- for a phenol site. The model was well able to describe the experimental B adsorption data both as a function of solution B concentration (isotherm data) and solution pH (envelope data) for all humic materials. The ability to represent changes in B adsorption as a function of solution pH is the main advantage of the constant capacitance model over adsorption isotherm equations. Results from the current study can be used to describe B adsorption on diverse humic materials of interest in environmental and agricultural situations.