Thermodynamics of the conversion of calcium and magnesium fluorides to the parent metal oxides and hydrogen fluoride

摘要

The authors have used thermodynamic modeling to examine the reaction of calcium fluoride (CaF(sub 2)) and magnesium fluoride (MgF(sub 2)) with water (H(sub 2)O) at elevated temperatures. The calculated, equilibrium composition corresponds to the global free-energy minimum for the system. Optimum, predicted reaction temperatures and reactant mole ratios are reported for the recovery of hydrogen fluoride (HF), a valuable industrial feedstock. Complete conversion of MgF(sub 2) is found at 1,000 C and a ratio of 40 moles of H(sub 2)O per 1 mole of MgF(sub 2). For CaF(sub 2), temperatures as high as 1,400 C are required for complete conversion at a corresponding mole ratio of 40 moles of H(sub 2)O per 1 mole of CaF(sub 2). The authors discuss the presence of minor chemical constituents as well as the stability of various potential container materials for the pyrohydrolysis reactions at elevated temperatures. CaF(sub 2) and MgF(sub 2) slags are available as wastes at former uranium production facilities within the Department of Energy Complex and other facilities regulated by the Nuclear Regulatory Commission. Recovery of HF from these wastes is an example of environmental remediation at such facilities.