Teaching Adsorption Chemistry by Constructing Surface Complexation Models (SCM) in PHREEQC

Adsorption modeling is important to understand and predict
both
how water contamination occurs, and how it might be prevented or remediated.
Surface complexation models (SCM) help us understand adsorption under
changing environmental conditions. This computational class introduces
undergraduate students to adsorption and surface complexation
and provides a foundation in geochemical modeling using freely available
PHREEQC software from USGS. Practical capabilities are developed by
(1) performing aqueous speciation reactions, (2) determining the surface
charge of suspended metal oxide/mineral powders using potentiometric
titration data, (3) calculating pH adsorption edges and adsorption
isotherms, (4) applying PHREEQC to answer possible water treatment
scenarios, and (5) using Visual Basic coding with loops to generate
large data sets. This class is contextualized around arsenic contaminated
groundwater and its treatment using iron oxide minerals, with hundreds
of millions at risk worldwide (e.g., India, Bangladesh, Mexico). Participants
report increases in their understanding of adsorption chemistry and
confidence in the application of geochemical models to perform predictive
SCM calculations.