J. Brent Hiskey

Solvent extraction characteristics of thiosubstituted organophosphinic acid extractants

Abstract Organophosphorus reagents are well known in solvent extraction. Commercial operations for the separation of cobalt from nickel have been successfully carried out using organophosphoric, -phosphonic, and -phosphinic acid extractants. Two new reagents in this class are the mono and dithio analogs of the commercial dialkylphosphinic acid, Cyanex 272. The replacement of oxygen by sulfur in these reagents enables extraction to be carried out at much lower pH. Characterization of Cyanex 272, Cyanex 302 (bis-(2,4,4-trimethylpentyl)-thiophosphinic acid), and Cyanex 301 (bis-(2,4,4-trimethylpentyl)-dithiophosphinic acid) has been undertaken. A comparison of the solvent extraction behavior of metallurgically important first-row transition metal ions from acidic sulfate solution by these reagents is reported. Distribution coefficients shift to lower pH with increasing sulfur substitution and decreasing p K a of the extractant, the greatest effect being observed for nickel. Stoichiometry of the extraction reactions, and the nature of the metal complexes formed have been determined using slope analysis techniques and spectroscopic measurements.

Solvent extraction of copper by Cyanex 272, Cyanex 302 and Cyanex 301

The mechanisms of copper(II) solvent extraction by Cyanex 272, Cyanex 302 and Cyanex 301 are discussed. Extraction from sulfate media is strongly dependant upon sulfur substitution in the phosphinic acid and complete extraction of copper by Cyanex 302 and Cyanex 301 occurs below pH 0. Since conventional slope analysis is not possible under these conditions, the complex stoichiometries and geometries are inferred from analysis of the electronic, 31P-NMR and FAB-MS spectra of the complexed species. Cu(II) is reduced to Cu(I) on extraction by the sulfur-containing ligands, accompanied by the corresponding oxidation of the extractant. It is shown that copper combines in a 1:1 stoichiometric ratio with these ligands to form multinuclear oligomeric complexes, in which the ligands bridge between metal centers. The enhanced stabilities of the complexes formed with the sulfur-containing ligands are explained in terms of the Hard-Soft Acid-Base concept and pi bonding between the d orbitals of the metal center and the donor atoms.

Dissolution chemistry of gold and silver in different lixiviants

Cyanide has been recognized for a long time as a powerful lixiviant for gold and silver, forming very stable cyano complexes with both metals. While cyanide is very effective in leaching free milling ores, there are certain classes of gold and silver ores (i.e., carbonaceous, pyritic. arsenical, manganiferous, cuperferous) that are considered refractory to conventional cyanidation dissolution. Recently there has been considerable effort directed towards new and improved reagents for leaching these difficult-to-treat ores and concentrates. A large portion of this effort has been devoted to finding alternative lixiviants that might compete with conventional cyanidation. Furthermore, there is a general interest in developing non-toxic environmentally safe substitutes for cyanide. There are a number of reagents that form stable complexes with gold and silver e.g., thiourea, thiosulfate, halides, malononitrile, acetonitrile and polysulfides. The chemistry of gold and silver dissolution using alternative lixivi...

SOLVENT EXTRACTION OF SILVER BY CYANEX 272, CYANEX 302 AND CYANEX 30

ABSTRACT The solvent extraction of silver from nitrate media by the extractants Cyanex 272 (bis)2,4,4-trimethylpentyl)phosphinic acid), Cyanex 302 ( bis(2,4,4-trimethylpentyl)thiophosphinic acid) and Cyanex 301 ( bis( 2,4,4-trimethyl-pentyl)dithiophosphinic acid) is characterized. Extraction shifts to lower pH with increasing sulfur substitution in the phosphinic acid, in accordance with the increased extractant acidity imparted by the soft nature of the sulfur donor atoms. The effects of extractant concentration, aqueous-phase ionic strength and organic-phase diluent on the extraction behavior are examined. The stoichiometry of the extraction reactions and the geometry of the extracted complexes are postulated based on slope analysis and spectroscopic measurements. All three extractants behave as bidentate ligands and combine in a 1:1 stoichiometric ratio with silver. The sulfur-containing ligands form multi-nuclear oligomeric complexes in which the ligands bridge between metal centers.

AN ASSESSMENT OF THE LONG-TERM STABILITIES OF CYANEX302 AND CYANEX301 IN SULFURIC AND NITRIC ACIDS

ABSTRACT Cyanex 302 and Cyanex 301 are recently available solvent-extraction reagents, the major components of which are the mono- and dithiosubstituted analogs of bis(2,4,4-trimethylpentyl)phosphinic acid, respectively. Sulfur substitution in the phosphinic acid increases the acidity of the extractants, and makes them particularly suited to the extraction of soft Lewis acids. Sulfur-containing dialkylphosphoric-acid extractants previously developed, however, are known to be very susceptible to oxidation and decomposition. To evaluate the extents of reagent decomposition which could reasonably be expected under normal plant operating conditions, this study examines the hydrolytic, chemical and thermal stabilities of Cyanex 302 and Cyanex 301 when subjected to extreme experimental conditions and prolonged periods of exposure to sulfuric and nitric acids. It is observed that concentrated sulfuric acid has no long-term detrimental effect on either of these reagents, but that the strongly oxidizing nature of ...

Galvanic conversion of chalcopyrite

Galvanic interaction between particulate chalcopyrite (CuFeS2) and copper results in the rapid conversion of chalcopyrite to chalcocite. The effects of temperature, surface area, concentration of sulfuric acid and agitation were systematically evaluated. The kinetics were found to be controlled by a steady-state current flow controlled by the effective anodic and cathodic surface areas involved in the galvanic couple. The experimental activation energy was 11.5 and stoichiometric data and reaction products have been characterized. The overall kinetic system has been evaluated based upon an electrochemical model.

The effect of copper, acid, and temperature on the diffusion coefficient of cupric ions in simulated electrorefining electrolytes

Abstract Deposition and dissolution processes involved in copper electrorefining are significantly affected by the diffusion coefficient of copper within an electrolyte. It is believed that the diffusion coefficient of cupric ions under conditions similar to those encountered in commercial electrolytes is not precisely known. The effects of copper, acid, and temperature on copper diffusivity were measured for simulated industrial electrolytes. Copper and acid concentrations tested were 35–70 and 160–250 g L−1, respectively. Temperature was varied from 40°C to 65°C. Increasing the copper and acid concentrations slightly decreased the diffusivity of copper. The diffusion coefficient of cupric ions increased with increasing temperature according to the Arrhenius relationship. An activation energy of 19.2 kJ mol−1 was calculated from the data. The diffusivity data was utilized in a simple one-dimensional finite difference model. The model indicates that saturation of copper sulfate occurs very rapidly at the high current densities (3820 A m−2) used in accelerated passivation experiments.

Kinetics of gold cementation on copper in ammoniacal thiosulfate solutions

Abstract The rate of cementation of gold on rotating copper discs was investigated in ammoniacal thiosulfate solutions as a function of rotational speed of the copper disc, initial gold concentration, initial copper concentration, and temperature. The cementation reaction exhibited two distinct kinetic regions, an initially slow rate followed by an enhanced rate. With a disc rotating at 1500 rpm in a solution containing 0.25 M [S 2 O 3 2− ], 30 ppm [Au] 0 , and 30 ppm [Cu] 0 , the apparent rate constant was 4.7×10 −3 and 1.1×10 −2 cm s −1 for the initial and enhanced regions, respectively. At low initial copper concentrations, the temperature dependence was well behaved, yielding an activation energy of 5.9 kJ mol −1 . In a solution containing 30 ppm [Cu] 0 , there was a noticeable decrease in the reaction rate between 25 and 50 °C. This may be attributed to the decomposition of Cu(S 2 O 3 ) 3 5− and the formation of Cu 2 S, which creates a passivating film. The deposit morphology is relatively nodular under the conditions of this investigation. Importantly, EDS and XRD analysis confirmed that the deposits are Au–Cu alloys instead of pure gold. The composition ranged from Au 3 Cu to AuCu 3 intermetallic alloys depending on the initial Cu/Au ratio in solution.

An electrochemical study of the surface oxidation of arsenopyrite in alkaline media

AbstractThe electrochemical behavior of arsenopyrite (FeAsS) electrodes in alkaline cyanide solutions has been investigated in an attempt to gain a better understanding of its dissolution chemistry. Surface oxidation reactions of arsenopyrite have been studied using cyclic voltammetry for pH values between 8.1 and 12.0 and for cyanide concentration from 10-4 to 10-2 M. Anodic oxidation of FeAsS appears to be sensitive to both pH and cyanide, as indicated by a characteristic peak at 0.30 Vvs SHE for pH 11.3 and 10-2 M CN-. The anodic process corresponding to the main peak is described by the reaction: FeAsS + 9H2O = FeOOH + H2AsO3- + SO42- + 15H+ + 12e- The oxidation of the H2AsO3-to HAsO42- is detected by a second wave at higher potentials under quiescent conditions. At high pH, the main peak is insensitive to the presence of cyanide, whereas at low-alkalinity this peak is sensitive to cyanide.

Deposition of copper from a buffered oxide etchant onto silicon wafers

The deposition of copper from a buffered oxide etchant (BOE) onto bare silicon, silicon dioxide, and patterned silicon wafers has been investigated. Deposition does not occur on surfaces of silicon dioxide, while deposition on regions of patterned silicon dioxide are observed at levels which fall between the deposition on bare silicon and silicon dioxide. The duration of a wafer rinse, which follows each immersion into a BOE solution, the silicon material as well as substrate doping do not affect the amount of deposition. The process of copper deposition from a BOE solution occurs uniformly across the surface of the wafer. The deposition on bare silicon surfaces shows an Arrhenius behavior, with two distinct activation energies: 0.40 eV (38.6 kJ mol -1 ) when the surface concentration is less than 6×10 14 Cu atom cm -2 and 0.20 eV (19.3 kJ mol -1 ) when the surface concentration is greater than 6×10 14 Cu atom cm -1 . Surface roughness is observed to increase with the extent of deposition. An electrochemical reduction is used to describe the deposition of copper onto a silicon surface from a BOE solution