Integrated chemical-physical processes modelling - I. Development of a kinetic-based model for mixed weak acid/base systems

A kinetic model for mixed weak acid/base systems is described. In the model , the weak acid/ base equilibria have been formulated in terms of the kinet ics of the forward and reverse reactions for the dissociation of the weak a cid/bases. The compound H (+) is explicitly included and pH is calculated f rom the H (+) concentration via pH = -log(H (+))= -log f(m)[H (+)]. For the conditions considered, the weak acid/ bases included are the water, carbon ate, ammonium, phosphate and short-chain fatty acids systems. However, the modelling approach is completely general and can be applied to include any other weak acid/base of importance. Ion pairing, precipitation of calcium c arbonate and carbon dioxide gas exchange also are included. The model was v alidated by comparing model predictions with those obtained from convention al equilibrium chemistry based algorithms. A very good correlation was obta ined. Compared to the equilibrium approach, the kinetic approach offers sev eral advantages in that it facilitates seamless integration of (i) precipit ation, gas stripping and dissolution kinetics of minerals and gases within the mixed weak acid/base chemistry structure and (ii) the biological kineti c models for wastewater treatment systems to extend application of these mo dels to situations where the pH is not constant. (C) 2000 Elsevier Science Ltd. All rights reserved.