Enthalpy changes for the reaction of HCl(aq) with Na2WO4(aq) were measured at T=298.15K in a HT-1000 calorimeter. The standard enthalpy of reaction for the formation of W7O6-24(aq) was calculated on the basis of the experimental results, △Hom(298.15K)=-320.7-1.0)kJ•mol-1. Combining this with the values from the literature led to the standard enthalpy of formation of W7O6-24 (aq), △fHom(298.15K)=-6689.8kJ•mol-1.

By using a specially designed and constructed isopiestic apparatus, we measured the osmotic coefficients at 313.2K for the NaOH-NaAl(OH)4-H2O system with the total alkali molality, mNaOHT (mNaOH+mNaAl[OH]4), from 0.05mol/kg H2O to 12mol/kg H2O and αK (mNaOHT/mNaAl(OH)4) from 1.64 to 5.53. The mean standard deviation of the measurements is 0.0038. Several sets of the Pitzer model parameters for NaOH-NaAl(OH)4-H2O system were then obtained by regressing the measured osmotic coefficients with the Pitzer model and the Pitzer model parameters for NaOH(aq). One set of the results is as follows: β(0) NaOH: 0.08669, β(1)NaOH: 0.31446, β(2) NaOH: β0.00007367, C(1)NaOH: 0.003180, β(0) NaAl(OH)4: 0.03507, β(1) NaAl(OH)4: 0.02401, C(1) NaAl(OH)4: β0.001066, θOH-Al(OH)4-: 0.08177, ψNa+OH-Al(OH)4-: -0.01162. The mean standard difference between the calculated and the measured osmotic coefficients is 0.0088. With the obtained Pitzer model parameters, we calculated the values of K1=(γNaAl(OH)4, cal2-mAl(OH)4-, exp)/(γNaOH, cal2-mOH-, exp) for the gibbsite solubility. The results show that the obtained Pitzer model parameters are reliable, and the relative error of the calculated activity coefficients should be <2.1%. We also compared the calculated gibbsite solubility data among several activity coefficients models over a range of mNaOHT at various temperatures. The comparison indicates that our activity coefficients model may be approximately applied in the ranges of temperature from 298.2 to 323.2 K and mNaOHT from 0 to 8 mol/kg H2O. We also calculated the stoichiometric activity coefficients of NaOH and NaAl(OH)4 and the activity of H2O for the NaOH-NaAl(OH)4-H2O system, and these calculations establish their variations with mNaOHT and αK. These variations imply that the strengths of the repulsive interactions among various anions are in the following sequence: Al(OH)4-Al(OH)4-<Al(OH)4-OH-<OH-OH-, and the attractive interaction between Al(OH)4 and H2O is weaker than that between OH and H2O. Copyright.

The thermal behaviors of the leaching of mechanically activated sphalerite were investigated for the first time by calorimetry. The specific granulometric surface area and the structural disorder sphalerite were also analyzed by X-ray diffraction laser particle size analyzer and X-ray powder diffraction (XRD) analysis, respectively. A new method to measure the mechanically activated storage energy of minerals was proposed by designing a thermochemical cycle that made mechanically activated and non-activated mineral reaching the same final state while leaching in FeCl3 solution. The results indicate that the mechanically activated storage energy of sphalerite rises with the increased grinding time and is closely related to the lattice distortions and crystallite sizes. The calorimetric results of the products from sieved in water or ethanol medium and the products from 2h treatment of mechanically activated sphalerite under pure argon (99.99vol.%) at different temperatures indicate that the mechanically activated storage energy of sphalerite is caused mainly by changes of the crystal structure, and the reactivity of mechanically activated sphalerite is difficult to lose.

The enthalpy increments △T 273∶15KH0m of Na2W2O7(s) and Na2W4O13(s) were measured in the temperature range 273-979 K by the drop method using a high temperature Calvet HT-1000 calorimeter. The results can be represented by the polynomial equations: △T 273.15KH0m(Na2W2O7)=-71, 006+211.12T+10.720×10-2T2+2.566×106T-1 △T273.15KH0m(Na2W4O13)-136, 568+388.97T+6.643×10-2T2+6.950×106T-1 The expressions of the heat capacity against temperature for these two compounds were obtained from the differentiation of the above equations. By combining these results with data from the literature, smoothed thermodynamic functions have been calculated for Na2W2O7.

The standard enthalpy of decomposition of Na10H2W12O42-27H2O(s) at 298.15K was measured using the method of threestep calorimetry in a Calvet twin-vessel microcalorimeter. The standard enthalpy of formation of Na10H2W12O42-27H2O(s) at 298.15K was