Electrochemical determination of the thermodynamic parameters of sphalerite, ZnS

• The ZnS/ZnO equilibrium were studied by the EMF method in two different cells.
• Solid state buffers Ag/Ag2S and Cu/Cu2S were used to fix the sulfur partial pressure.
• Free energy of formation of sphalerite (ZnS) was calculated at temperatures from 782 to 1288 K.
• The standard enthalpy of formation of sphalerite was calculated via 3rd-law method.
• EMF data from different cells are consistent.

Thermodynamic properties of sphalerite (β-ZnS, F4-3m) were studied by the method of high-temperature galvanic cell with separate gas space and Y2O3-stabilized ZrO2 as solid-state electrolyte. The temperature dependences of the cell electromotive force (EMF) were obtained for the reaction ZnS+2Ag+NiO=ZnO+Ag2S+NiZnS+2Ag+NiO=ZnO+Ag2S+Ni in the temperature range 782–1050 K, and for the reaction ZnS+2Cu+NiO=ZnO+Cu2S+NiZnS+2Cu+NiO=ZnO+Cu2S+Ni in the temperature range 848–1288 K.The standard parameters of sphalerite were analyzed by the second law of thermodynamics. The standard enthalpy of formation of ZnS, ΔfHoZnS(298 K) = −201.07 ± 1.3 kJ mol−1, was calculated for the reaction Zn(s) + S(s) = ZnS(β) using the third law of thermodynamics (Gef method) and data on standard enthalpy of formation for ZnO, NiO, Ag2S, and Cu2S. From the EMF results for the ZnS/ZnO equilibrium and using the known data on free energy of formation of ZnO, NiO, Ag2S and Cu2S, the free energy of sphalerite formation was found according to the reaction Zn(l) + 0.5S2(g) = ZnS(β): ΔfGZnSo(T)±1000Jmol-1=-273,870+107.30·T,(782-9)ΔfGZnSO(T)±1300Jmol-1=-268,892+102.67·T,(848