The availability of fast personal computers has allowed ion association models to be developed for the relatively inexpensive and widely available “PC” platforms.
Ion association models predict the equilibrium distribution of species for a cooling water, oil field brine, waste water, or other aqueous solution of commercial interest. Scale potential indices based upon the free ion concentrations estimated by ion association models have been used extensively in the past decade to predict scale problems in industrial cooling water systems.
Indices calculated by the models have been found to be transportable between waters of diverse composition and ionic strength. They have overcome many of the problems encountered with simple indices which do not account for ion pairing. This paper discusses the application of ion association model saturation level indices to predicting and resolving scale formation problems in cooling water systems, oil field brines, and for optimizing storage conditions for low level nuclear wastes.
Examples are presented in case history format which demonstrate the use of the models in field applications.
INTRODUCTION
Simple indices are widely used by water treatment personnel to predict the formation of scale. In many cases, simple indices are used as the basis for adjusting controllable operating conditions such as pH to prevent scale formation.
Simple indices include the Langelier Saturation Index,1 Ryznar Stability Index,2 Stiff-Davis Saturation Index,3 and Oddo-Tomson index4 for calcium carbonate. Indices have also been developed for other common scales such as calcium sulfate and calcium phosphate.
The simple indices provide an indicator of scale potential, but lack accuracy due to their use of total analytical values for reactants. They ignore the reduced availability of ions such as calcium which occurs due to association with sulfate and other ions.5 The simple indices assume that all ions in a water analysis are free and available as a reactant for scale forming equilibria.
For example, the simple indices assume that all calcium is free. Even in low ionic strength waters, a portion of the analytical value for calcium will be associated with ions such as sulfate, bicarbonate, and carbonate (if present). This leads to over-prediction of the scaling tendency of a water in high ionic strength waters. The impact of these “common ion” effects can be negligible in low ionic strength waters. They can lead to errors an order of magnitude high in high ionic strength brines. Table 1 outlines some of the ion associations which might be encountered in natural waters.
- The Practical Application of Ion Association Model Saturation Level Indices to Commercial Water Treatment Problem Solving | SpringerLink
- [PDF] The Practical Application of Ion Association Model Saturation Level Indices to Commercial Water Treatment Problem Solving | Semantic Scholar
- Mineral Scale Formation and Inhibition – Google Books
- The Practical Application of Ion Association Model Saturation Level Indices to Commercial Water Treatment Problem Solving | Request PDF (researchgate.net)
- The Practical Application of Ion Association Model Saturation Level Indices to Commercial Water Treatment Problem Solving | French Creek Software