Terje Østvold

Raman spectroscopy of cemented cobalt on zinc substrates

Abstract Micro-Raman spectroscopy is used to characterize the cemented product formed during cobalt cementation with zinc dust in zinc sulfate electrolytes. The effect of copper and antimony on the cementation process is also examined. A Raman spectrum characteristic of a basic cobalt salt or mixtures of such salts is observed. The spectrum is similar to those found for Co(OH)2 in a ZnO matrix. The main Raman band of this salt has a frequency at 550 cm−1. Raman mapping over a larger area, 1000×1000 μm, of cemented products shows that the occurrence of this peak decreases dramatically during re-dissolution of cemented cobalt. The data indicate that a large fraction of the cemented Co2+ exists as a mixture of cobalt containing oxide and hydroxide.

Products formed during cobalt cementation on zinc in zinc sulfate electrolytes

Abstract The observed removal of Co 2+ during cementation on zinc is due to two reactions. One reaction is formation of a Co alloy or Co in solid solutions. The second reaction is formation of basic cobalt salts, and is a function of local high pH at the zinc surface and the concentration of Zn 2+ . The high local pH close to the zinc surface is created by evolution of hydrogen. This hydrogen evolution stops when the core of metallic zinc in the cemented particle is consumed, and basic cobalt salts in the particle may redissolve. Basic cobalt salts redissolve more easily than Co alloys and is the major reason for cobalt redissolution during the technical purification of the zinc sulfate electrolyte before zinc electrolysis.

Scale Formation in Reservoir and Production Equipment During Oil Recovery: An Equilibrium Model

This paper presents a reliable model for the solubility products of scale-forming minerals. Our model solubilities are in relatively good agreement ({plus minus}5% to 10%) with the most reliable solubilities in aqueous solutions of up to twice the seawater concentration at temperatures of 20 to 150{degrees} C and pressures up to 40 MPa. An equilibrium mode for the reactions responsible for scale formation is developed. The CO{sub 2} equilibria between the gas, oil, and water phases and in the water phase itself are considered. By combining a hydrodynamic model for the transport of water through an oil reservoir during waterflooding with the proposed equilibrium model, we can estimate the amount of precipitate formed in the reservoir.

The solubility of magnesium metal and the recombination reaction in the industrial magnesium electrolysis

Abstract The solubility and dispersion of Mg in the systems MgCl 2 , MgCl 2 -NaCl and MgCl 2 -KCl has been studied. An extensive study of Mg solubility in MgCl 2 did not show any influence on the content of MgO or added NaOH or Na 2 B 4 O 7 . At 750°C the solubility was found to be 0.16 mol%. The solubility increased with increasing temperature and decreased on the addition of NaCl or KCl. In 25 mol% NaCl-75 mol% MgCl 2 the solubility was as low as 0.02 mol% at 815°C. The amount of Mg dispersed was found to be negligible with the present experimental set-up. The results are discussed with reference to the back reaction between Mg and Cl 2 in the industrial electrolysis. It seems likely that the rate determining step in this reaction is the rate of formation of small metal particles in the melt.

Oxide solubility and Raman spectra of NdF3–LiF–KF–MgF2–Nd2O3 melts

The solubility of Nd2O3 in NdF3–LiF–MgF2 melts is about 0.08–0.38 mol% when the NdF3 concentration varies from 15 to 30 mol% at 900 °C. The solubility increases from 0.13 mol% at 750 °C to 0.22 mol% at 900 °C in the NdF3–LiF eutectic. When MgF2 is added to NdF3–LiF binary melts saturated with Nd2O3, the Nd2O3 solubility seems to decrease slightly at 30 mol% NdF3, while a slight increase was observed with 15 mol% NdF3 in the binary. When dissolving Nd2O3 in the NdF3–LiF eutectic Raman spectroscopy showed that the complex ions NdOF(x − 1)−x and Nd2OF(x − 1)−x + 3 may form in the melt. The most reasonable candidates seem to be: NdOF43− and NdOF54− among the mononuclear compounds and Nd2OF106−, Nd2OF84− among the binuclear complexes.

The influence of tartrate on cobalt cementation on a rotating zinc disc in zinc sulphate

Abstract Basic cobalt salts redissolve more easily than Co alloys; this is the major reason for cobalt redissolution during the technical purification of the zinc sulphate electrolyte before zinc electrolysis. The electrolysis is performed using a very pure zinc sulphate solution. Co 2+ is a harmful impurity in the electrolyte, and is therefore usually removed by cementation. This cementation process is very slow. Cu 2+ and Sb 3+ , which are used as cementation aids, are added as CuSO 4 and potassium–antimony–tartrate, KSbC 4 O 6 H 2 ·1.5H 2 O, respectively. Laboratory scale experiments show that large amounts of tartrate in the solution reduce the cementation rate of Co 2+ significantly. Accumulation of tartrate may cause operational problems in a zinc plant.

Solubility and Raman spectra of Nb(V) in LiF–NaF–KF–Na2O melts

Abstract The solubility of Nb(V) as a function of O 2− composition in the ternary eutectic LiF–NaF–KF (FLiNaK) melt at 700°C has been determined. Raman spectra at different oxide concentrations and temperatures were recorded. Based on chemical analysis of melt samples and bands in the spectra suggestions related to the Nb–O–F complex formation are given. The addition of Na 2 O to FLiNaK containing 0.22 mole kg −1 K 2 NbF 7 , show that at: n O / n Nb 7 2− at low oxide concentrations, which reacted with oxide to form monomeric NbOF 5 2− when r was increasing. Further additions of Na 2 O formed the NbO 2 F 4 3− species having a maximum concentration at n O / n Nb =2; when 2 n O / n Nb 3 was formed. At n O / n Nb =3, a minimum in the Nb(V) and O 2− solubilities were observed, but the structure of the species in the melt were uncertain. At higher oxide content, 3 n O / n Nb 3 (s) previously formed was dissolved, possibly with the formation of both corner and edge sharing distorted NbO 6 octahedra. The solubility of Nb 2 O 5 in FLiNaK was measured as a function of temperature (550–800°C), and the dissolution mechanism seems to be given by the reaction: Alk + +Nb 2 O 5 (s)+4F − =NbO 2 F 4 3− +AlkNbO 3 (s). Δ H 0 sol for the reaction (based on concentrations in mole kg −1 ) was found to be ≈90 kJ mol −1 K −1 .

Electrochemical Studies of the Molten System K 2NbF7 ‐ Na2 O ‐ Nb ‐ ( LiF ‐ NaF ‐ KF ) eut at 700°C

Various voltammetric methods have been used to study FLINAK (LiF-NaF-KF eutectic melt 46.5-11.5-42 mol %) melts containing about I mol % niobium-fluoro and -oxofluoro complexes with Nb in oxidation states (V) and (IV) at 700°C and varying amounts of Na 2 O in the range 0 4, all Nb and O added are dissolved. Strong indications of the coexistence of the oxygen rich Nb(V)OF complexes and O 2- ions in FLINAK at n O 0 /n Nb 0 > 4 have been found. An equilibrium/sampling/analysis technique was also used to study this system without Nb metal added. The results mainly agree with the results of the voltammetric studies. However, no indications of spontaneous reduction of Nb(V) to Nb(lV) were observed, even after 24 h.

The inhibition of calcium carbonate formation in aqueous supersaturated solutions. Spontaneous precipitation and seeded crystal growth.

The influence of the presence of humic, fulvic, and polyacrylic acid on the nucleation and crystal growth of calcium carbonate in aqueous supersaturated solutions was investigated in batch reactors at 25°C and pH = 8.50. The nucleation of calcium carbonate was investigated by free drift methods, and the crystal growth was investigated with seeded crystal growth experiments at constant supersaturation. In all cases calcite was found to form exclusively, and the presence of all tested compounds at concentrations between 0.1 – 1.0 ppm prolonged the induction time preceding the spontaneous formation of calcite. Humic acid at concentration up to 0.5 ppm inhibited the growth of calcite seeds up to 95% and polyacrylic acid at concentrations up to 0.1 ppm gave the same degree of inhibition. Polyacrylic acid was found to be stronger inhibitor. A concentration of 0.25 ppm of polyacrylic acid completely stopped crystal growth of calcite. Humic acid at concentration 1.0 ppm completely stopped crystal growth of calcite seed crystals. The retardation was explained by the adsorption of the polyelectrolytes onto the active growth sites of the crystals. Application of a Langmuir-type adsorption model on the kinetics data obtained in the presence of the inhibitors tested yielded a higher affinity constant of polyacrylic acid for the calcite seed crystals.

Norzink removal of cobalt from zinc sulphate electrolytes

Removal of cobalt from the zinc sulphate solution prior to electrowinning is essential in the hydrometallurgical zinc production process. In order to improve the cobalt removal process, Norzink has initiated a research program.