Practical thermodynamic model for acidic sulfate solutions

Practicable thermodynamic description of sulfuric acid — water system is essential when modeling of acidic sulfate solutions required in process optimization and waste management. Traditional Pitzer model is limited up to 6 mol/kg (35w%) sulfuric acid solutions. Local composition models such as electrolyte NRTL can deal H2SO4-H2O systems up to high concentrations but their use is practically limited to vapor-liquid equilibrium. Mole fraction based version of Pitzer equation is capable to describe H2SO4-H2O system up to 40 mol/kg (80w%) acid concentration at temperatures range from 328 K (55°C) down to 200 K but the number parameters is quite extensive for practical purposes. Recently developed NPL Pitzer model has proved to be capable to describe sulfuric acid -water system in temperature range 0–55 °C using only five parameters with simple temperature dependency of a+b/T. The capabilities of NPL Pitzer model is demonstrated here in wide temperature range up to 40 mol/kg (80w%) solutions with H2SO4-H2O and H2SO4-FeSO4-H2O systems.