  Chromates are widely used for their anticorrosive properties. Unfortunately,
they are highly hazardous with environmental agencies regulating their levels
to below 10 ppb in drinking water. As anion exchange resins are typically used
for removal, predictive dynamic models are necessary to make quick decisions
rather than relying on experimental data that could take several days to
implement. With various dynamic models currently applied to simulate the ion
exchange process, the Thomas model was picked for its simplicity and better
accuracy when compared to other models. The Thomas model contains two
parameters, the constant (KT) and the maximum resin capacity (qm), which are
empirically calculated. Unfortunately, the model demonstrated large parameter
fluctuations with no correlation to varying contact times or inlet chromate
concentrations. Therefore, fixing both parameters will lead to failed model
predictive behavior. By fixing the value of qm and proposing a linear
relationship of KT with resin contact time and inlet chromate concentration,
the accuracy of the model was improved five-fold, demonstrating its potential
for better process controls.
