Lan-Chi Koenigsberger

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 IUPAC Subcommittee on Solubility and Equilibrium Data has been selecting, editing and reviewing projects and manuscripts for publication as part of the IUPAC-NIST Solubility Data Series (SDS). This series provides comprehensive reviews of data from the primary literature for solubilities of gases, liquids and solids in liquids or solids. Data are compiled in a uniform format, critically evaluated and, where high-quality data from independent sources agree sufficiently, recommended values are proposed [1]. SDS Volume 102 was published recently [2]. A current IUPAC project is dealing with solubilities of subs tances related to urolithiasis [3]. Kidney stones consist of a range of inorganic and organic substances that are sparingly soluble in urine, thereby producing ionic and uncharged aqueous species which can undergo a wide variety of protonation and complexation reactions. Using these data as an example, this work explores the features of the JESS solubility database [4] that assist with the presentation, manipulation and critical evaluation of solubility data. In particular, the unique combination of databases available in JESS for speciation equilibria [5], physicochemical properties of solutions [6] and solubilities provides improved evaluation facilities, including the assessment of thermodynamic consistency among solubility, calorimetric and speciation data as described in a recent SDS volume [7]. Systems of different chemical complexity will highlight the benefits of applying the JESS software package to the production of future SDS volumes.

The extraction of rare earth metals from fluoroapatite rich phosphate concentrates often involves a weak acid leach of fluoroapatite and a sulphuric acid bake of 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 three temperatures 40, 60 and 80oC containing 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). Solid mixture of rare earth metal carbonates was used as the source of rare earth metal ions. The solubility tests and characterization of solids using XRD were conducted at Murdoch University laboratories. 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.

Reliable solubility data for oxides and hydroxides of heavy metals in alkaline solutions are relevant to a number of industrial and geochemical processes, including the production of high-purity alumina in the Bayer process, the formation of ores from geothermal solutions at high pH, hydrometallurgical leaching processes for the extraction of metal values from ores and plant residues, and the storage and processing of certain types of radioactive waste. Recent results obtained for various systems will be reported, including experimental and modelling aspects. A new facility for the storage, handling and processing of solubility data will be outlined.