M. Sadegh Safarzadeh

Solvent extraction of lanthanum(III) using the organic extractant 2-ethylhexyl phosphonic acid mono-2-ethylhexylester (PC88A) diluted in kerosene from three different aqueous media (sulfuric, nitric and chloride) was investigated. E_h-pH and speciation diagrams suggested that free lanthanum ion (La(III)) species predominate under the experimental conditions studied in this paper. The effects of several parameters on the extraction of lanthanum including initial pH (1.5–7), initial La(III) concentration (0.08–1.35 mmol/L), PC88A concentration (10–90 mmol/L) and temperature (25–55°C) were evaluated. In general, both hydrochloric and nitric acids were found to be more effective than sulfuric acid in terms of higher extraction of lanthanum. The stoichiometry of the extraction reaction and also the equilibrium constant were calculated. The extraction of La(III) was significantly enhanced by increasing pH and PC88A concentration and was only slightly increased by increasing temperature. Stripping studies showed that 1 mol/L acid concentration is adequate for effective stripping of lanthanum from the loaded organic. The stoichiometry of the extraction reaction was also investigated using density functional calculations and found to be in reasonable agreement with the experimental results.

A sulphuric acid bake-leach process was investigated for the extraction of rare earth elements (REEs), uranium, and thorium from a monazite concentrate. X-ray diffraction analysis showed the formation of water-soluble sulphates that readily dissolved during the water leach step. Nearly complete extraction of REEs, uranium, and thorium was achieved when the concentrate was baked at 250°C for 4 h with a sulphuric acid to concentrate (S/C) weight ratio of 4:1. At the 1:1 sulphuric acid to concentrate ratio ∼65% of REEs were leached while only ∼2–5% of uranium and thorium were extracted. Temperature (180–250°C) had little effect on the extraction of REEs, but greatly affected the extraction of thorium and uranium. In general, the extraction of thorium and uranium decreased with an increase in temperature. The effect of particle size (48–137 µm) was also tested and found to have little effect on the extraction of REEs. Acid consumption was calculated and found to increase with longer baking times (0.3–0.8 g acid/g concentrate). The major mineralogical phases formed because of the sulphation reaction included potassium cerium sulphate hydrate (2K₂SO₄·Ce(SO₄)₂·2H₂O), lanthanum sulphate hydrate (La₂(SO₄)₃·2H₂O), sodium praseodymium sulphite hydrate (NaPr(SO₃)₂·2H₂O), and neodymium sulphate hydrate (Nd₂(SO₄)₃·5H₂O), all of which were water-soluble.

Solvent extraction of yttrium (Y) from different aqueous solutions using the organic extractant 2- ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC88A) diluted in kerosene was investigated. Solution chemistry considerations were proposed to identify the predominant species in different aqueous media (H₂SO₄, HCl and HNO₃). In general, nitric and hydrochloric acids were found to be more efficient than sulfuric acid for yttrium extraction. Separation studies showed that nitric acid provide higher separation of Y(III) from light REES while sulfuric acid works better when separation of Y(III) from heavy REEs is desired.

While predominance area diagrams (PADs) are useful for the determination of the stable phases in the metal–sulfur–oxygen system, they are constructed at constant temperature. Varying the temperature results in shifting of the equilibrium lines and the stability areas thereof. Since the available tools in hands of an extractive metallurgist are temperature and oxygen potential, a more useful diagram would be one that shows the stability areas of different phases as a function of temperature and percent of oxygen in the roast gas. Such diagrams, called ‘roaster’ diagrams, derive directly from PADs. Although such diagrams are used by extractive practitioners, this type of diagram is unavailable in the open literature. In this paper, the relationship between the PADs and roaster diagrams is discussed and PADs and roaster diagrams for the Zn–S–O and Pb–S–O ternary systems are constructed. This information will serve as the foundation for more complex four-component systems to follow in subsequent publications.

Porphyry copper and mixed copper-gold sulfide deposits contain varying amounts of precious (gold and silver) and platinum group metals (PGMs). Currently, milling and froth flotation is the most common processing route for the treatment of high-grade base metal sulfide ores. During this process, the precious metals and PGMs are also concentrated and represent a possible opportunity for the beneficiation of these metals to increase the overall economic value of the ore. Although not yet commercialized, the high temperature pressure oxidation (POX) of copper concentrates provides an alternative processing route to traditional smelting technology. With increasingly aggressive air quality standards and rising upstream processing costs for smelting, hydrometallurgical processing options become progressively attractive. The treatment of POX residues for the recovery of precious metals has seen significant attention and multiple processing routes have been developed on various scales. Extraction and beneficiation of PGMs from copper concentrate POX residue has garnered significantly less attention and mechanistic questions remain to be answered. Based on a review of the processing options for PGM ores and concentrates, hydrometallurgical processing routes for the extraction of PGMs from copper concentrate POX residues are envisioned.