Dewen Zeng

Trace Amounts of Aqueous Copper(II) Chloride Complexes in Hypersaline Solutions: Spectrophotometric and Thermodynamic Studies

Knowledge of the thermodynamic properties of aqueous copper(II) chloride complexes is important for understanding and quantitatively modeling trace copper behavior in hydrometallurgical extraction processing. In this paper, UV–Vis spectra data of Cu(II) chloride solutions with various salinities (NaCl, 0–5.57xa0mol·kg−1) are collected at 25xa0°C. The concentration distribution of Cu–Cl species is in good agreement with those calculated by a reaction model (RM). The simple hydrated ion, Cu2+, is dominant at low concentration, whereas [CuCl]+, [CuCl2]0 and [CuCl3]− become increasingly important as the chloride concentration rises. Moreover, the RM calculation suggests the present of a small amount of [CuCl4]2−. The de-convoluted molar spectrum of each species is in excellent agreement with our previous theoretical results predicted by time-dependent density functional theory treatment of aqueous Cu-containing systems. The formation constants for these copper chloride complexes have been reported and are to be preferred, except log10K2 ([CuCl2]0).

Thermodynamic Modeling of Poorly Complexing Metals in Concentrated Electrolyte Solutions: An X-Ray Absorption and UV-Vis Spectroscopic Study of Ni(II) in the NiCl2-MgCl2-H2O System

Knowledge of the structure and speciation of aqueous Ni(II)-chloride complexes is important for understanding Ni behavior in hydrometallurgical extraction. The effect of concentration on the first-shell structure of Ni(II) in aqueous NiCl2 and NiCl2-MgCl2 solutions was investigated by Ni K edge X-ray absorption (XAS) and UV-Vis spectroscopy at ambient conditions. Both techniques show that no large structural change (e.g., transition from octahedral to tetrahedral-like configuration) occurs. Both methods confirm that the Ni(II) aqua ion (with six coordinated water molecules at R Ni-O = 2.07(2) Å) is the dominant species over the whole NiCl2 concentration range. However, XANES, EXAFS and UV-Vis data show subtle changes at high salinity (> 2 mol∙kg-1 NiCl2), which are consistent with the formation of small amounts of the NiCl+ complex (up to 0.44(23) Cl at a Ni-Cl distance of 2.35(2) Å in 5.05 mol∙kg-1 NiCl2) in the pure NiCl2 solutions. At high Cl:Ni ratio in the NiCl2-MgCl2-H2O solutions, small amounts of [NiCl2]0 are also present. We developed a speciation-based mixed-solvent electrolyte (MSE) model to describe activity-composition relationships in NiCl2-MgCl2-H2O solutions, and at the same time predict Ni(II) speciation that is consistent with our XAS and UV-Vis data and with existing literature data up to the solubility limit, resolving a long-standing uncertainty about the role of chloride complexing in this system.

Isopiestic Measurements of Water Activity for the H2SO4–H3PO4–H2O System at 298.15 K

AbstractWater activity for the binary H2SO4–H2O and H3PO4–H2O systems, as well as the ternary H2SO4–H3PO4–H2O system has been measured using an isopiestic method at 298.15xa0K. The results for binary systems obtained in this work agree well with literature data. The results show that the isopiestic composition lines of the H2SO4–H3PO4–H2O system obey Zdanovskii’s rule at low concentrations, whereas at higher concentrations the isopiestic lines are observed to have positive deviations. The relative uncertainties of isopiestic molalities of parallel samples in each experimental run are better than 0.2xa0%. The measured water activities reported in this work can be used to parameterize thermodynamic models for chemical engineering of phosphorus and heavy metal hydrometallurgical processes.n

Effect of Solvent Activity on Solute Association: The Formation of Aqueous Nickel(II) Chloride Complexes Studied by UV–Vis and EXAFS Spectroscopy

Water activity is generally considered to affect ionic association in aqueous electrolyte solutions; however, it is usually ignored when the association reactions or constants are discussed. In this work, the effect of water activity on the association reaction

Experimental determination and modeling of gypsum and insoluble anhydrite solubility in the system CaSO4–H2SO4–H2O

{text{Ni}}_{{ ( {text{aq}})}}^{2 + } + n{text{Cl}}_{{ ( {text{aq)}}}}^{ - } rightleftharpoons {text{NiCl}}_{{n{text{ (aq)}}}}^{2 - n}

Experimental Determination and Modeling of the Solubility of CaSO4·2H2O and CaSO4 in the Quaternary System CaSO4 + MgSO4 + H2SO4 + H2O

Ni(aq)2++nCl(aq)-⇌NiCln(aq)2-n was investigated by EXAFS and UV–Vis spectroscopy measurements on NiCl2 aqueous solutions at room temperature with constant Cl−/Ni2+ ratio (~66) and various water activities; the latter were adjusted by adding MgCl2 and Mg(ClO4)2. Both the EXAFS and the UV–Vis spectra measurements indicated that the extent of Ni–Cl association increases in decreasing water activity environments, independent on the Cl−/Ni2+ ratio. Thus, the effect of water activity on the ionic association should not be ignored and more emphasis should be paid on it, especially, when the water activity is very low.

Species fine structure of transition metal Cu(II) in aqueous chloride-bearing solutions: Insights from X-ray absorption spectroscopy and ab initio XANES calculations

Solubility isotherms of the sparingly soluble salts CaF2(s) and CaSO4·2H2O(s) in their mixed aqueous solutions have been measured at 298.1xa0K. It was found that the CaF2(s) solubility decreases with increasing CaSO4 concentration in the solution and reaches about 1/3 of the CaF2(s) solubility in pure water in the CaSO4·2H2O(S) saturated solution. A thermodynamic model was developed to predict the CaF2(s) solubility isotherm in this system, in which the short range interactions of the species in the aqueous solution are represented by ion-association constants reported in literature, and the long range interaction, i.e., the electrostatic term, is represented by the well known Davies equation. The predicted solubility isotherm reasonably agrees with the experimental results. The contributions of the long-range term and the short-range term to the calculated solubility isotherm were investigated. It was concluded that the ionic association combining with the Davies equation is sufficient to represent the excess interaction of the CaF2xa0+xa0CaSO4 aqueous solution at 298.15xa0K. This model approach could be applicable for other dilute mixed electrolyte systems in which component activity coefficients are lacking and model parameters are difficult to determine.