Surface Complexation Model to Describe Competitive Arsenic Adsorption onto Iron Oxides

EPA Grant Number: F07A20355
Title: Surface Complexation Model to Describe Competitive Arsenic Adsorption onto Iron Oxides
Investigators: Epps, Amanda Van
Institution: The University of Texas at Austin
EPA Project Officer: Lee, Sonja
Project Period: January 1, 2007 through January 1, 2010
RFA: STAR Graduate Fellowships (2007) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Environmental Engineering , Drinking Water


Advances in technology for removing arsenic from drinking water are of critical importance both in the U.S. and worldwide. Research into means of low-cost treatment for removal of arsenic has led to the development of a “solar oxidation and removal of arsenic” (SORAS) process in which sunlight, lemon juice, and air are used to remove arsenic from drinking water. Because the system relies only on these three things, it holds promise for low-cost arsenic removal in places such as Bangladesh where there is widespread arsenic contamination in groundwater but little large-scale treatment of drinking water.

It is difficult, however, to predict how much arsenic can be removed because of the interference of background water chemistry on the arsenic adsorption processes. Recent work at the University of Texas at Austin has attempted to develop a surface complexation and mass transport model for the removal of arsenic in a packed bed of granular ferric hydroxide. The model should allow prediction of arsenic removal based on known groundwater characteristics in the same way that existing models predict removal of organic contaminants by granular activated carbon. Developing a similar model to predict the effectiveness of SORAS would need to account for the effects of silica, carbonate, calcium, and citrate.

The objective of this research is to use both equilibrium adsorption data and spectroscopic studies to develop such a model for SORAS. The model would describe arsenic adsorption onto amorphous ferric hydroxide in a multi-solute system.


The research approach will be to collect experimental data to isolate and understand the effect that each of the four solutes (silica, carbonate, calcium, and citrate) alone has on arsenic removal. Next, both experimental and spectroscopic data for combinations of these ions will be studied to determine the effect of multi-solute systems on arsenic removal. These data will be used to develop solute parameters for a surface complexation model. Finally, experimental results will be compared to those predicted by this model, and the model’s ability to predict experimental results will be evaluated.

Expected Results:

The output of this work would be a set of self-consistent model parameters that would describe the adsorption of arsenic onto iron oxides in the presence of other solutes. The model could be used to predict the potential for removal of arsenic from drinking water by adsorption onto iron oxides and the expected effectiveness of the system based on background water chemistry.

Supplemental Keywords:

arsenic, SORAS, adsorption, iron oxides, surface complexation, mathematical model, carbonate, silica, calcium, citrate,, RFA, Scientific Discipline, Water, Drinking Water, Environmental Engineering, drinking water monitoring, arsenic removal, modeling, remediation, treatment, drinking water contaminants

Progress and Final Reports:

  • 2007
  • 2008
  • Final