Kinetics Study of Adsorption Behaviors of Trivalent Metal Ions onto Chelating Resin: Comparison between Scandium(III) and Other Metal Ions

Scandium (Sc) lacks commercially viable independent deposits and is mainly recovered as a by-product of the smelting of other ores. In the process of recovering nickel from laterite ores, Sc is recovered from leaching solutions. The recovery of Sc requires its efficient separation and purification from other impurities. This study proposes a process for the selective separation and recovery of Sc from other trivalent cations in sulfuric acid solutions using an iminodiacetic acid chelating resin, Diaion™ CR11. The adsorption behaviors of trivalent ions Sc(III), Cr(III), Al(III), and Fe(III) onto CR11 in single- and multiple-metal systems were investigated to determine the appropriate Sc separation conditions. In systems containing single metal ions, pseudo-first-order and pseudo-second-order kinetic models were used to fit the data. Linear and nonlinear methods were used for fitting. The activation energies were calculated from the rate constants at a pH of 2.0 and at three different temperatures of 23℃, 60℃, and 80℃ and followed the order: Cr(III) > Fe(III) > Sc(III) > Al(III). In binary systems including Sc(III), the simultaneous adsorption of Sc(III) and other trivalent ions onto CR11 was investigated. Previously adsorbed Sc(III) on CR11 was displaced by the subsequent adsorption of Fe(III) or Cr(III) from the solution. The affinity of the metal ions to iminodiacetic acid and the adsorption reaction rate were critical factors for suitable selective Sc separation, indicating that prior removal of Fe(III) was necessary. Column experiments at 23℃ using a synthetic solution without Fe(III) showed that Cr(III) adsorption was suppressed, and that Sc(III) was efficiently adsorbed. Scandium can be efficiently recovered from a solution containing Sc(III) after prior removal of Fe(III) by adsorption at low temperature using CR11

Thermodynamic Design of Electrolyte for CuO/Cu₂O Bilayer by Anodic Electrodeposition

Electrodeposition of multilayered semiconductors requires a bath design to electrodeposit the upper layer(s) without dissolving the base layer(s) below. We present herein a reliable approach to bath design based on thermodynamics from the viewpoint of complexation with ligands. A CuO/Cu₂O bilayer film was targeted as an example. We searched a thermodynamic database of complexation constants for ligands that could form a complex with Cu(II) but not with Cu(I), and identified monoethanolamine as one of the best candidates. Using a Cu(II)-monoethanolamine alkaline aqueous bath, we experimentally confirmed that a CuO upper layer could be deposited without dissolving the Cu₂O base layer. We believe that this design is applicable to other bilayer films produced by electrochemical techniques

Initial Electrodeposition Behavior of Chromium from Hydrate-Melt Based Trivalent Chromium Baths

Trivalent chromium electrodeposition is expected to substitute the conventional hard chromium electroplating that requires harmful hexavalent chromium. Recently, we revealed that crystalline chromium, which is effective for hard chromium properties, can be electrodeposited from trivalent chromium baths using chloride-based hydrate-melts. Herein, we investigated the initial behavior of the trivalent chromium electrodeposition by in situ analyses using electrochemical quartz crystal microbalance (EQCM) and ex situ characterization of resulting electrodeposits. In the very initial stage of electrolysis, proton reduction proceeds preferentially, resulting in chromium hydroxide precipitation on the electrode due to the local pH increase. Chromium reduction was found to require a few seconds of induction time to start. The transient was interpreted by the Sand equation which also indicated proton depletion near the cathode. In the hydrate-melts, due to the depletion of free water, the high proton mobility due to Grotthuss mechanism is lost, resulting in the suppression of hydrogen evolution after the induction time. This explains why chromium electrodeposits are obtained at extremely high current efficiencies of 60%–80%. Additionally, the proton reduction of the initial electrolysis stage may lead to negative effects, for example, impairing adhesion of chromium electrodeposits

Basal-Plane Orientation of Zn Electrodeposits Induced by Loss of Free Water in Concentrated Aqueous Solutions

Concentrated aqueous solutions attract considerable attention because water electrolysis can be suppressed due to a decrease in the amount of free water. The present study focuses on electrodeposition behaviors of metallic zinc (Zn) using concentrated aqueous solutions containing bis(trifluoromethylsulfonyl)amide (Tf₂N⁻) anions. An increase in Tf₂N⁻ concentration significantly enhances water-anion interactions, giving characteristic infrared spectra for the breakdown of the hydrogen-bonding networks of water clusters, i.e. loss of free water. For the Tf₂N⁻ system Zn electrodeposits with the preferred orientation of hcp basal plane was observed, while, for the SO₄²⁻ system with the presence of the hydrogen-bonding networks, preferred orientation of basal plane was not observed. The preferred orientation of basal plane is not attributed to the adsorption of Tf₂N⁻ anions on the electrode, proved by the use of mixed Zn(Tf₂N)₂-ZnSO₄ concentrated solutions. The loss of free water in the concentrated Zn(Tf₂N)₂ solutions will suppress hydrogen adsorption at the cathode to promote surface diffusion of intermediate Zn⁺ adions and growth of Zn crystals. Consequently, the promotions and the easier growth of Zn basal planes with the lowest interfacial free energy will enhance the horizontal growth of Zn basal planes

High-density and low-roughness anodic oxide formed on SiC in highly concentrated LiCl aqueous solution

The wide bandgap and high carrier mobility of silicon carbide (SiC), as well as its physical and chemical stability, make it a promising material for a number of applications. One of the key requirements for these applications involves oxide formation on SiC. The usefulness of the oxide produced by anodizing is, however, limited since the anodic oxide formed on SiC in the usual dilute aqueous solution has a low density and high surface roughness. Here, we consider a new parameter in anodic oxide formation by focusing on the concentration of free water in the electrolyte, using a highly concentrated aqueous solution. In a concentrated solution, oxygen evolution, which results in a reduction in the density of the oxide, is suppressed, and the rate of formation of anodic oxide at defect sites effectively decreases to reduce the surface roughness. Furthermore, an interfacial layer with a higher density than SiO₂ is formed between SiC and SiO₂, buffering the difference in density between them. As a result, we successfully obtained an anodic oxide with a relatively high density and low surface roughness. This study provides a new approach to improving the properties of the anodic oxide formed on SiC

Ammonium·18-crown-6 bis(trifluoromethylsulfonyl)amide

We report synthesis and characterization of an ammonium-based molten salt, ammonium bis(trifluoromethylsulfonyl)amide-18-crown-6 (1/1), i.e. [NH₄⁺･18C6][Tf₂N⁻] (Tf = SO₂CF₃). Raman spectra shows [NH₄⁺･18C6][Tf₂N⁻] consists of NH₄⁺ ion encapsulated by 18C6 and Tf₂N⁻ anion. The melting point of [NH₄⁺･18C6][Tf₂N⁻] was around 100°C. At 140°C, the viscosity of [NH₄⁺･18C6][Tf₂N⁻] was 14.7 mPa s, the conductivity was 8.0 mS cm⁻¹, and the density was 1.23 g cm⁻³. These properties were comparable to those of common ionic liquids

Electrochemically active species in aluminum electrodeposition baths of AlCl3/glyme solutions

Electrochemically active species in aluminum (Al) electrodeposition baths using AlCl3 and less volatile solvents i.e. glymes were investigated. Raman spectroscopy revealed that all the glyme baths contained AlCl₄⁻ anions and Al-Cl-glyme cations as ionic species. Room temperature conductivities were as high as the order of 10⁻³ S cm⁻¹ for the diglyme (G2), triglyme (G3) and tetraglyme (G4) baths, whereas that for the butyl diglyme (butylG2) bath was only 10⁻⁴ S cm⁻¹ due to a lower concentration of ionic species. Surprisingly, electrochemical measurements showed that, among the glyme baths, only the G2 bath enabled electrodeposition of Al. Consequently, despite the similar structures of Al-Cl-glyme complex cations, only the G2 complex cations are electrochemically active. This suggests that the desolvation of glymes from Al-Cl-glyme cations and their subsequent reduction is exceptionally easy for the G2 complexes

An ionic liquid consisting of crown ether-coordinated hydronium cation and amide anion

We first report an ionic liquid (IL) that consists of hydronium (H₃O⁺) ion encapsulated by 18–crown–6–ether (18C6) and an amide anion. The composition of the crown ether–coordinated hydronium amide IL was estimated to be as [H₃O⁺•18C6][Tf₂N⁻]. The presence of H₃O⁺ was revealed from the characteristic bands of the hydronium ion present in the infrared spectra. The melting point of [H₃O⁺•18C6][Tf₂N⁻] was 68–70 °C. At 70 °C, the viscosity of [H₃O⁺•18C6][Tf₂N⁻] was 39.5 mPa s, the conductivity was 1.9 mS cm⁻¹, and the density was about 1.32 g cm⁻³. These bath properties of [H₃O⁺•18C6][Tf₂N⁻] were similar to those of common ILs at room temperature

Relationship between Copper(II)-Lactate Complexes and Cu₂O Electrodeposited Using Highly Concentrated Alkaline Solutions

The direct or indirect effects of two different copper(II)-lactate complex species, Cu(H‐₁L)L⁻ and Cu(H‐₁L)₂²⁻, on the orientation and electrical properties of Cu₂O electrodeposits were examined, where L⁻ = CH₃CH(OH)COO⁻ and H‐₁L²⁻ = CH₃CH(O⁻)COO⁻. To investigate the relationships between the copper(II)-lactate complex species and several properties of Cu₂O, a set of Cu₂O layers was electrodeposited from thermodynamically well-stabilized electrolytes of different pHs with unified overpotentials. The Cu₂O layers obtained at pH 9.5. In addition, marked differences were observed in the resistivity and carrier density of Cu₂O layers bordering pH 9.5, indicating the presence of a strong relationship between copper(II)-lactate complexes and these crystallographic or electrical properties. In terms of the cathodic reactivity of copper(II)-lactate complexes and changes in local pH in the vicinity of the cathode upon electrodeposition, we suggest that the two copper(II)-lactate complexes directly affected the electrical properties of Cu₂O and indirectly affected its crystallographic orientation