Wanjing Cui,Xuebing Fan,Ying Liao,Xiaoping Yu,Yafei Guo,LingZong Meng,Tianlong Deng
The study of the solid-liquid phase equilibrium for (NaCl + NaClO 3 + H 2 O) system is of significance to understand the thermodynamic property of the aqueous solution of ionic membrane electrolysis process to promote the production of sodium hydroxide (caustic soda). The solubilities and the physicochemical properties including density, refractive index and pH for this ternary system at 293.15 and 333.15 K and 0.1 MPa were measured using the isothermal dissolution method. Based on Pitzer ion-interaction model and its extended HW model, the solubility equilibrium constants K sp of NaClO 3 and the mixing ion-interaction parameters ( θ Cl,ClO3 , Ψ Na, Cl,ClO3 ) at 293.15 and 333.15 K were parameterized in this work. The Debye-Hückel limiting slope A ø , the Pitzer single-salt parameters of NaCl and NaClO 3 and the solubility equilibrium constants K sp of NaCl at 293.15 and 333.15 K were taken from the relative temperature-dependence formula in the literature. A comparison shows that the calculated solubilities of the ternary system at 293.15 and 333.15 K agree well with the experimental data. The calculated results of densities and refractive indices using the empirical equations agree well with the experimental data at 293.15 and 333.15 K.
The slow leaching rate of molybdenite (MoS 2 ), due to its inert nature, and low recovery hinders the application of traditional hydrometallurgical processing. This study investigated the effects of grinding speed and time, molar ratio of sodium chlorate (NaClO 3 , oxidant) to MoS 2 , leaching time and temperature on the leaching efficiency of molybdenum (Mo). Grinding at low speeds via mechanical activation decreased particle size. However, at speeds over 450 rpm for 1.0 h, or at lower speeds but with longer time, it triggers a solid-state reaction (mechanochemistry) producing soluble Na 2 Mo 2 O 7 . This may be due to the existence of an energy threshold for the solid-state reaction. The most suitable activating conditions were 600 rpm for 0.5 h, with a molar ratio of NaClO 3 : MoS 2 = 5, leached in 0.1 M NaOH solution for 2.0 h at 348 K, giving rise to a Mo recovery of 74.8%. The initial acid leaching stage of the ground mixture is dominated by the dissolution of Na 2 Mo 2 O 7 , giving rise to elevated Mo recovery. The later stage is controlled by the dissolution of MoS 2 , slowing down the increase in Mo extraction. As compared to alkaline conditions, acidic leaching of MoS 2 ground at low speeds (non solid-state reaction) gives greater Mo recovery, due to the greater activity of NaClO 3 to MoS 2 under acidic conditions. However, the greatest Mo recovery is achieved in alkaline solution for MoS 2 ground at high speed (solid-state reaction) due to the occurrence of mechanochemical reaction.
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