Lan-Chi Koenigsberger

Solubility constants reported in the literature for ammonium hydrogenurate (NH4HU), an occasional constituent of urinary calculi in humans, show a large scatter, probably due to the tendency of hydrogenurates to form supersaturated solutions that persist over long periods of time. In this study, the solubility of NH4HU(s) was measured as a function of p[H] = − lg{[H+]/mol dm−3} (4.5–8) and temperature (25 and 37 °C) at constant ionic strength, Ic = 0.300 mol dm−3 NH4Cl, which is similar to the ionic strength of urine. Highly reproducible values for the solubility product (Ks0) of NH4HU(s) were obtained. The first dissociation constant (K1) of uric acid determined in this work agrees well with values obtained in our previous studies of uric acid solubilities in electrolyte solutions relevant to urolithiasis. This study confirms our earlier findings that in the ionic strength range of urine, the solubilities of uric acid and hydrogen urates as a function of p[H] can be described consistently by unique values of their solubility constants (Ks, Ks0) and the first dissociation constant of uric acid (K1). In addition, no appreciable complexation between uric acid or hydrogenurates and other urine constituents has been found.

An internally consistent thermodynamic network for arsenic minerals and aqueous species is being developed based on a high quality starting point: arsenolite and arsenolite solubility. Current research is refining the properties of scorodite solubility as a function of temperature along with improved aqueous species stability constants and activity coefficients for ions and ion pairs based on potentiometric measurements of redox, pH, and conductivity for 5-90 °C. The second and third hydrolysis constants for arsenic acid have been calculated as a function of temperature and thermodynamic properties have been derived.

The extraction of rare earth oxides from fluorapatite rich phosphate concentrates often involves a weak acid leach of fluorapatite and a sulphuric acid bake of the leach residue followed by water leach and precipitation to obtain an intermediate product. The main aim of this study was to determine and rationalize the solubility of rare earth metal ions in synthetic solutions representing various process liquors at the temperatures 40, 60 and 80 °C. The liquors contained different acid and metal ion concentrations with respect to sulphuric acid, phosphoric acid and sulphate salts of sodium, magnesium, aluminium, potassium, calcium and iron(III). A solid of mixed rare earth carbonates was used as the source of rare earth metal ions. The solubility tests and characterisation of solids using XRD were conducted at Murdoch University laboratories as part of the process development for the Arafura Resources Nolans rare earth project. The composition of initial carbonate solids and the solids and solutions formed after saturation were analysed for rare earth and other elements at TSW Analytical Laboratories in Perth using ICP-MS and ICP-OES. The precipitated solid in sodium-rich acidic sulphate solutions is the double salt NaRE(SO4)2 based on the solid assays. However, in acidic solutions free of sodium or of low concentrations of sodium the precipitated solid appears to be RE2(SO4)3.

Protonation constants for the biologically-important thioamino acids cysteine (CSH), penicillamine (PSH) and glutathione (GSH), and the formation constants of their complexes with Cu(i), have been measured at 25 °C and an ionic strength of 1.00 mol dm-3 (Na)Cl using glass electrode potentiometry. The first successful characterisation of binary Cu(i)-CSH and Cu(i)-GSH species over the whole pH range was achieved in this study by the addition of a second thioamino acid, which prevented the precipitation that normally occurs. Appropriate combinations of binary and ternary (mixed ligand) titration data were used to optimise the speciation models and formation constants for the binary species. The results obtained differ significantly from literature data with respect to the detection and quantification of protonated and polynuclear complexes. The present results are thought to be more reliable because of the exceptionally wide pH and concentration ranges employed, the excellent reproducibility of the data, the close agreement between the calculated and observed formation functions, and the low standard deviations and absence of numerical correlation in the constants. The present formation constants were incorporated into a large Cu speciation model which was used to predict, for the first time, metal-ligand equilibria in the biofluids of the human eye. This simulation provided an explanation for the precipitation of metallic copper in lens and cornea, which is known to occur as a consequence of Wilson's disease.

The solid-liquid solubility data for well defined nonaqueous binary and ternary systems are reviewed. One component includes hydroxybenzoic acid, hydroxybenzoate, and hydroxybenzoic acid salt, and another component includes a variety of organic compounds (hydrocarbons, alcohols, halogenated hydrocarbons, carboxylic acids, esters, et al.) and carbon dioxide. The ternary systems include mixtures of organic substances of various classes and carbon dioxide. The total number of compilation sheets is 270 for six types of system. Almost all data are expressed as mass percent and mole fraction as well as the originally reported units, while some data are expressed as molar concentration. Critical evaluation was carried out for the binary nonaqueous systems of 2-, 3-, and 4-hydroxybenzoic acids and hydroxybenzoates (methylparaben, ethylparaben, propylparaben, and butylparaben) in alcohols, 1-heptane, and benzene.

The solubility data for well-defined binary, ternary, and multicomponent systems of solid-liquid type are reviewed. One component, which is 2-, 3-, and 4-hydroxybenzoic acids, 4-hydroxybenzoate alkyl esters (parabens), or hydroxybenzoic acid salts, is in the solid state at room temperature and another component is liquid water, meaning that all of the systems are aqueous solutions. The ternary or multicomponent systems include organic substances of various classes (hydrocarbons of several structural types, halogenated hydrocarbons, alcohols, acids, ethers, esters, amides, and surfactants) or inorganic substances. Systems reported in the primary literature from 1898 through 2000 are compiled. For seven systems, sufficient binary data for hydroxybenzoic acids or parabens in water are available to allow critical evaluation. Almost all data are expressed as mass and mole fractions as well as the originally reported units, while some data are expressed as molar concentration.

Boehmite, rather than gibbsite, precipitation has been proposed in the literature as a potential energy-saving modification of the Bayer process for the production of alumina. Previous experimental studies have reported that true equilibrium solubilities were not attained during boehmite precipitation. Instead, a pseudo-equilibrium or an apparent 'steady-state' aluminate concentration of about twice the boehmite solubility was reached. In this work, the dissolution and precipitation reactions in synthetic and plant liquors using seeds of (i) pure boehmite and (ii) various boehmite/gibbsite ratios were investigated at 95 °C. Only boehmite precipitation was observed on pure boehmite seed at relatively low supersaturation (alumina (A)/total caustic (TC) 0.56). The aluminate concentrations measured as a function of time decreased continuously and did not exhibit an apparent 'steady state'. Stable equilibrium, as established by boehmite solubility measurements, was approached very slowly but not attained even after ten weeks. At higher supersaturation (A/TC 0.67), after an initial desupersaturation, 'steady-state' aluminate concentrations of about twice the boehmite solubility were observed. There is convincing evidence that these 'steady states' correspond to metastable solubility equilibria with gibbsite, which is precipitated initially and gradually transforms into the stable phase, boehmite. Gibbsite also nucleated in the case of pure boehmite seeds. 'Steady states' were attained in one up to several days and remained constant for one to ten days. The length of these periods correlated with the gibbsite content of the seeds. After sufficient recrystallisation of gibbsite to boehmite, the aluminate concentrations decreased significantly and eventually approached boehmite solubility, thereby following a much slower precipitation kinetics typical for boehmite. Due to short observation times, previous workers did not detect the end of the 'steady-state' periods and therefore failed to identify the observed 'steady-state' aluminate concentrations as arising from metastable solubility equilibria with gibbsite.

Densities of highly alkaline sodium aluminate Solutions have been measured by vibrating-tube densimetry over the temperature range 323 <= T/K <= 573 at a pressure of 10 MPa. Ionic strengths, 1, of these mixed solutions were 1 <= l/mol.kg(-1) <= 6, and the degree of Substitution of hydroxide by aluminate, alpha, ranged from 0.1 <= alpha <= 0.4, where alpha = m(A)/m and m(A) and m (= l) ire the aluminate and total molalities, respectively. Apparent molar volumes, V-phi, derived from the density data for the (NaOH + NaAl(OH)(4))(aq) Solutions, were found to follow Young's rule; that is, they depended linearly on the level Of Substitution of aluminate for hydroxide at all temperatures. The slopes of the Young's rule plots were independent of ionic strength at a given temperature but depended linearly on temperature. It is therefore possible to model V-phi (and hence the densities) of ternary (NaOH + NaAl(OH)(4))(aq) mixtures using only two parameters in addition to those needed for the correlation of the binary NaOH(aq) Solutions. This also means that the standard state (infinite dilution) partial molar volumes, V-2 degrees, of pure, hypothetical NaAl(OH)(4)(aq) call readily be obtained from V-2 degrees for NaOH(aq) by linear extrapolation using the two Young's rule parameters.

No reliable model for the prediction of densities has been reported for the title system. Since this is partly due to conflicting experimental data available in the literature, densities in the title system have been measured by high-precision vibrating-tube densimetry over wide concentration ranges. Measurements comprise binary (single electrolyte) and mixed (ternary) acidic solutions of titanyl sulfate at (25 and 50) °C as well as binary, ternary, and quaternary mixtures containing iron(II) sulfate at 25 °C. We have found that a pro-rata additivity rule for densities applies to a series of aqueous metal sulfate + sulfuric acid mixtures at constant total sulfate concentration, based on hypothetical densities in the supersaturated concentration ranges of the binary metal sulfate subsystems. These hypothetical densities can be readily obtained by extrapolation of the properties of mixed solutions. When included in Masson-type density correlations for the binary metal sulfate systems, the resulting model resolves the reported inconsistencies in density predictions for the FeSO4 + H2SO4 + H2O system. This is the first density model that includes TiOSO4 as a component.