Majzlan J., 2017: Solution calorimetry on minerals related to acid mine drainage – methodology, checks, and balances. Acta Geologica Slovaca, 9, 2, in press.

Solution calorimetry on minerals related to acid mine drainage – methodology, checks, and balances

Juraj Majzlan

Institute of Geosciences, Carl-Zeiss-Promenade 10, Friedrich-Schiller University, D-07745 Jena, Germany

Abstract

Solution calorimetry is an established technique to measure thermodynamic properties of solids. Two common options for the solvents and measurement regimes include acid-solution calorimetry with aqueous solvents at temperatures between 0–100°C and high temperature oxide-melt calorimetry, with oxide solvents at 700–1000°C. The usual outcome of a set of solution calorimetry experiments is the enthalpy of formation of a phase studied, calculated from a thermochemical cycle with a set of reference phases. Thermochemical cycles apply the Hess’ law in a form of linear equations. In this paper, the choice and pitfalls of various reference phases is discussed, with a focus on oxysalts (oxides, sulfates, arsenates) related to acid mine drainage. The accuracy and precision in the systems H₂O and Fe₂O₃-H₂O is documented by a number of control thermochemical cycles, summarized in this work. Calorimetry on systems including Ca, Cu, Al, As, Sb, Na, and K is also deliberated. For As, X-ray absorption spectroscopy showed that the final oxidation state of arsenic is identical irrespective of the initial oxidation state. In general, the statistical uncertainty of the calorimetric experiments is smaller than the precision of the data, as judged from enthalpies of various reactions. The accuracy of the data, however, does not suffer with due care. Hence, solution calorimetry, with its advantages and disadvantages, is an important method that delivers high-quality thermodynamic data.

Key words: calorimetry, thermodynamics, enthalpies of formation, mine drainage

Manuscript received: 2017-05-29

Revised version accepted: 2017-07-17