Hannu Sippola

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.

Activity of Supercooled Water on the Ice Curve and Other Thermodynamic Properties of Liquid Water up to the Boiling Point at Standard Pressure

A simple model for thermodynamic properties of water from subzero temperatures up to 373 K was derived at ambient pressure. The heat capacity of supercooled water was assessed as lambda transition. The obtained properties for supercooled water such as heat capacity, vapor pressure, density and thermal expansion are in excellent agreement with literature data. Activity of water on ice curve, independent of used electrolyte and Debye−Hückel constant applied in modeling, is also calculated. Thus, the ice curve activity of supercooled water can be used as a universal basis for thermodynamic modeling of aqueous solutions, precipitating hydrated and anhydrous solids. A simple model for heat capacity, density and thermal expansion of ice are also derived from 170 K up to melting point.

Thermodynamic Model for Acidic Metal Sulfate from Solubility Data

Acidic metal sulfate solutions are generated in a large scale in the hydro- and pyrometallurgical industries. Acid mine drainage has long been a significant environmental problem in coal and metal mining. Acidic metal sulfate solutions are also produced in steel industry. The demand of recycling and reuse of materials has increased significantly especially in EU. Dumping a neutralized deposit is not an option any more. Thus, several techniques of recycling and reuse of sulfuric acid and/or metal sulfates from the side streams are needed.