Presence Of Impurity Ions Research Articles

Potential influence mechanism of Mn and Co ions in the process of electrowinning of copper

The presence of impurity ions in the electrolyte during copper electrolysis influences anode performance and cathode quality. Lead anode corrosion causes resource loss and environmental pollution, emphasizing the need to study these impurities. The effects of Co2+ and Mn2+ on Pb-0.06 %Ca-1.2 %Sn anodes and cathode copper are investigated, establishing optimal ion concentrations. Mn2+ facilitates the growth of MnO2 on the PbO2 surface, enhancing corrosion resistance and catalytic activity, especially at a concentration of 2 mg/L. Additionally, the presence of Co2+ leads to the formation of Co3O4 and MnO2, further improving corrosion resistance and promoting oxygen evolution. A pilot experiment with Mn2+ at 2 mg/L and Co2+ at 120 mg/L achieves a current efficiency of 98.4 % and reduces the cell voltage to 1.817 V, successfully meeting energy-saving and efficiency-enhancing objectives.

Selective anion exchange adsorption of molybdenum(VI) at low concentrations from an acid leached vanadium shale solution containing aluminium and phosphorus

With a decline in high-grade molybdenum reserves, the development of other types of molybdenum resources have received increasing attention. Vanadium shale is a multi-metal shale and fine-grained sedimentary rock comprising small grains and various minerals. After leaching and extracting vanadium, the solution often contains a low concentration of molybdenum. However, because of the low molybdenum concentration, many processing plants treat it as an acidic wastewater, which wastes molybdenum resources and carries the risk of environmental pollution. The leaching process of vanadium shale mostly involves high-temperature and high-pressure operations, which greatly increase the content of impurity ions such as aluminium and phosphorus in the pregnant leach solution. These impurity ions increase the difficulty in separating and recovering molybdenum. In this study, the adsorption and separation of molybdenum at leach liquor of low molybdenum concentration were investigated. The effects of different factors such as: (i) pH of feed solution, (ii) adsorption time, and (iii) presence of impurity ions, aluminium and phosphorus, on the adsorption and separation of molybdenum using five different anion-exchange resins, D201, D296, D301, D314, and D301R, were investigated. The static adsorption and desorption test results showed a molybdenum adsorption capacity of 222 mg/g at pH = 1.5 by the D301 resin. The desorption efficiency using 20% NH₄OH was 96.1%. The adsorption efficiencies of aluminium and phosphorus were 1.31% and 3.10%, respectively. This is a better choice for separating molybdenum from complex solutions. The experimental results from spectra and theoretical calculations showed that the -NH group of D301 resin was combined with the O atoms of MoO3·3H2O, Al(SO4)2−, and H2PO4− by electrostatic attraction. The binding energies of these three species were − 311 kJ/mol, −231 kJ/mol, and − 62.0 kJ/mol respectively, indicating that D301 resin preferentially adsorbed MoO3·3H2O. Based on the above results, the D301 resin can adsorb molybdenum(VI) in complex solutions under low pH conditions, and this study is expected to promote the comprehensive recovery of valuable metals from vanadium shale.

Modified tailings of weathered crust elution-deposited rare earth ores as adsorbents for recovery of rare earth ions from solutions: Kinetics and thermodynamics studies

Weathered crust elution-deposited rare earth ores tailings are mainly composed of clay minerals, which can be used as efficient adsorption materials. In order to explore the possibility of recovering rare earth ions using tailings from mine waste liquid, the weathered crust elution-deposited rare earth ores tailings were modified to adsorb La3+ and Y3+ with respect to initial concentrations of La3+ and Y3+, temperatures and impurity ions, and the adsorption kinetics and thermodynamics were further discussed to analyze the adsorption behavior. The results show a higher adsorption capacity of heavy rare earth Y3+ than that of light rare earth La3+. The presence of impurity ions does not adversely affect adsorption of rare earth ions by the modified tailings. The adsorption performance is well fitted with the Langmuir adsorption isotherm model rather than the Freundlich adsorption isotherm model, and the maximum adsorption capacity is 0.0226 mmol/g and 0.0197 mmol/g for Y3+ and La3+, respectively. Pseudo-first-order, pseudo-second-order, intraparticle diffusion and Elovich model were applied to fit the adsorption results. The results show that the adsorption process of modified tailings for La3+ and Y3+ is more in line with the pseudo-second-order kinetic model, suggesting the dominated chemical adsorption. The adsorption activation energies of La3+ and Y3+ on modified tailings are 11.60 KJ/mol and 7.60 KJ/mol, respectively. Thermodynamic studies show that the adsorption process of modified tailings for La3+ and Y3+ is a spontaneous endothermic reaction in the experimental temperature range. The recovery of rare earth ions form the modified tailings can be carried out by the leaching solution of weathered crust elution-deposited rare earth ores, 0.2 mol/L (NH4)2SO4 solution. In addition, the modified tailings are reversible and keep functionality to reuse in several cycles after elution process.

Impact of impurities on drift wave instabilities in reversed-field pinch plasmas.

The drift wave in the presence of impurity ions was investigated numerically in reversed-field pinch plasmas, using the gyrokinetic integral eigenmode equation. By comparing the results of regular and hollow plasma density profiles, it was found that the ion temperature gradient mode for the hollow density profile case is much harder to excite. For the impurity effects, when the impurity density gradient is opposite to the electrons, namely when L_{ez} (L_{ez}=L_{ne}/L_{nz} with 1/L_{n} being the density gradient scale length, and the subscript "e" and "z" indicates electrons and impurity ions, respectively) is negative, the impurities can enhance the instability. On the contrary, when L_{ez} is positive, the instability is stabilized. Regarding the trapped electron mode (TEM), the growth rate for plasmas with a hollow density profile remains smaller than that of the standard density gradient. There exists a threshold in L_{ez}. When L_{ez} is less than this value, the impurities destabilize the TEMs, while when L_{ez} is greater than this value, the impurities stabilize the TEMs. In addition, the influence of the collisionality on the TEMs was also studied.

Scaling law for interchange transport in magnetically confined electron-positron plasmas with ion impurity

Interchange instabilities are a critical issue for confinement and transport in (otherwise exceptionally stable) planned magnetically confined quasi-neutral electron-positron plasma experiments. An additional ion impurity concentration can signifcantly affect the instability. The dispersion relation for interchange modes in perturbed inhomogeneously magnetized electron-positron plasmas in the presence of impurity ions is derived from full-f isothermal gyrofluid equations. The model includes arbitrary ion concentration and Debye screening effects. The resulting interchange growth rate of localized density perturbations is related to the cross-field propagation velocity and associated transport, which is reduced by an additional ion concentration compared to pure electron-positron plasmas. A simplified scaling relation is obtained from the exact analysis and compared with previous pure electron-positron plasma limits and empirical scalings based on simulation data.

Effect of impurity ions on the coupling between zonal flow and local turbulent transport in HL-2A plasmas

The effect of impurity ions on the coupling between geodesic acoustic mode (GAM) zonal flow and local turbulent transport has been studied using a Langmuir probe array in HL-2A ohmically heated deuterium plasmas. The experimental results illustrate that both the frequency and amplitude level of the GAM zonal flow significantly reduce with increase in the carbon ion concentration, which is qualitatively consistent with theoretical predictions (Xie et al 2018 Plasma Phys. Control. Fusion 60 025015). Meanwhile less energy is transferred from turbulence to GAM zonal flow due to the reduction in tilting and stretching of the turbulent vortex. Consequently, the impurity ions enhance the turbulence and turbulent transport owing to the reduced GAM zonal flow, as demonstrated by experiment. The experimental results presented here therefore reveal the dual roles played by impurity ions in the dynamics of GAM zonal flow, which could contribute to the understanding of inherent mechanisms governing turbulent transport in the presence of impurity ions.

Impurity effects on trapped electron modes in tokamak plasmas with inverted electron density profile

Impurity effects on trapped electron modes (TEMs) in tokamak plasmas with inverted electron density profile (IEDP) are numerically investigated with a gyrokinetic integral eigenmode equation. It is found that different from the negative gradient of normal electron density profile, the positive gradient of the IEDP has a stabilizing effect on TEM in the presence of impurity ions. The electron temperature gradient threshold for TEM excitation increases not only with the increasing absolute value of IEDP but also with increasing impurity content. Furthermore, the effects of different impurity species and different impurity peaking profiles on TEMs with the IEDP are analyzed in detail. It is shown that there is a transition point of impurity density profile, on both sides of which the impurity has opposite effects on TEM. The dependence of such a transition point on electron temperature and density gradients is obtained numerically. Besides, the synergistic effects of ion temperature gradient and impurity density gradient are studied, in which a similar transition point of the ion temperature gradient is also identified in the case of outwardly peaked impurity density profile. In addition, impurity effects on the characteristics of mode structure and on the radial transport coefficients in positive and negative magnetic shear regions are discussed as well based on quasi-linear mixing length estimation.

Study on the Effect and Mechanism of Impurity Aluminum on the Solvent Extraction of Rare Earth Elements (Nd, Pr, La) by P204-P350 in Chloride Solution

Solvent extraction is the most widely used method for separation and purification of rare earth elements, and organic extractants such as di(2-ethylhexyl) phosphoric acid (P204) and di(1-methyl-heptyl) methyl phosphonate (P350) are most commonly used for industrial applications. However, the presence of impurity ions in the feed liquid during extraction can easily emulsify the extractant and affect the quality of rare earth products. Aluminum ion is the most common impurity ion in the feed liquid, and it is an important cause of emulsification of the extractant. In this study, the influence of aluminum ion was investigated on the extraction of light rare earth elements by the P204-P350 system in hydrochloric acid medium. The results show that Al3+ competes with light rare earths in the extraction process, reducing the overall extraction rate. In addition, the Al3+ stripping rate is low and there is continuous accumulation of Al3+ in the organic phase during the stripping process, affecting the extraction efficiency and even causing emulsification. The slope method and infrared detection were utilized to explore the formation of an extraction compound of Al3+ and the extractant P204-P350 that entered the organic phase as AlCl[(HA)2]2P350(o).

Quasi-linear heat transport induced by ITG turbulence in the presence of impurities

The impurity effects on turbulent transport induced by ion temperature gradient (ITG) turbulence are numerically studied in tokamak plasmas, using a gyrokinetic quasi-linear model. The characteristics of the instability and heat fluxes in the presence of impurity ions are investigated for a broad parameter regime, including temperature and density gradients of main and impurity ions, concentration, charge and mass numbers of impurity ions, magnetic shear as well as wave vector spectrum. The heat fluxes are demonstrated to depend not only on the saturation amplitude of the instability but also on the phase shift between and . The peaking factor of temperature/density profile, defined as the ratio of major radius to gradient scale length when the total turbulent heat flux equals zero, is fitted with linear/quadratic functions. In addition, the contributions from diagonal and off-diagonal terms to heat fluxes are identified in detail, i.e. the main ion heat diffusion are proved to be dominated by off-diagonal (diagonal) terms for regions of weak (strong) ITG. In general, steep temperature gradients of main ions as well as hollow density profiles of impurity ions significantly enhance instability and heat fluxes. However, it is interesting to find that the effect of impurity ions with positive density gradient may transit from the enhancement to reduction of the quasi-linear heat flux of main ions in regions of steep ITG, corresponding to transport barriers (e.g. pedestal of H-mode and I-mode plasmas). Both strong and weak positive magnetic shear decrease heat transport.

Effects of trapped electrons on the ion temperature gradient mode in tokamak plasmas with hollow density profiles

The ion temperature gradient (ITG) mode in the presence of impurity ions and trapped electrons (TEs) is numerically investigated in tokamak plasmas with hollow density profiles, using the gyrokinetic integral eigenmode equation. It is found that in the inverted density plasma, the increase of the ITG enhances the growth rate and frequency of the ITG, and the density gradient plays an important role in the ITG modes. For weak density gradient situations, the trapped electron effects increase the instability of the ITG, while the impurity has an obviously stabilizing effect. For the strong density gradient cases, both the impurities and trapped electrons enhance the ITG instabilities. In addition, it is shown that the growth rate of the ITG decreases with positive magnetic shear s while the real frequency increases with positive magnetic shear. The growth rate of the ITG increases with negative magnetic shear s while the real frequency decreases with negative magnetic shear. The length of the calculated mode structure in the positive and negative magnetic shear intervals is also presented.

Kinetic micro-instabilities in the presence of impurities in toroidal magnetized plasmas

The theoretical and numerical studies on kinetic micro-instabilities, including ion temperature gradient (ITG) driven modes, trapped electron modes (TEMs) in the presence of impurity ions as well as impurity modes (IMs), induced by impurity density gradient alone, in toroidal magnetized plasmas, such as tokamak and reversed-field pinch (RFP) are reviewed briefly. The basic theory for IMs, the electrostatic instabilities in tokamak and RFP plasmas are discussed. The observations of hybrid and coexistence of the instabilities are categorized systematically. The effects of impurity ions on electromagnetic instabilities such as ITG modes, the kinetic ballooning modes (KBMs) and kinetic shear Alfvén modes induced by impurity ions in tokamak plasmas of finite β (=plasma pressure/magnetic pressure) are analyzed. The interesting topics for future investigation are suggested.

Pb2+–Calcite Interactions under Far-from-Equilibrium Conditions: Formation of Micropyramids and Pseudomorphic Growth of Cerussite

The presence of impurity ions is known to significantly influence mineral surface morphology during crystal growth from aqueous solution, but knowledge on impurity ion–mineral interactions during dissolution under far-from-equilibrium conditions remains limited. Here we show that calcite (CaCO3) exhibits a rich array of dissolution features in acidic Pb-bearing solutions. During the initial stage, calcite exhibits nonclassical surface features characterized as micropyramids that developed spontaneously. Subsequent pseudomorphic growth of cerussite (PbCO3) was observed, where nucleation occurred entirely within a pore space created by dissolution at the calcite/substrate interface. Uneven growth rates yielded a cerussite shell made of lath- or dendritic-shaped crystals. The cerussite phase was separated from the calcite by pores of less than 200 nm under transmission X-ray microscopy, consistent with the interface-coupled dissolution–precipitation mechanism. These results show that impurity metal ions exer...

Coupling of SWITG and SWTEM in the presence of impurities in tokamak plasmas

The coupling of the short wavelength ion temperature gradient mode (SWITG) and trapped electron mode (SWTEM) in the presence of impurity ions is numerically studied in tokamak plasmas. It is found that the coupling of SWITG and SWTEM modes is divided into hybrid and coexistent cases. The impurity ions always have stabilizing effects on the hybrid mode (namely, SWTE-ITG) with small ηi (ηi < 0.5), which is different from the conventional TE-ITG mode. In the lager ηi (ηi > 0.5) regime, the impurity ions with the density profiles peaked inwardly (outwardly) stabilize (destabilize) the SWTE-ITG mode. Another new finding in this paper is that the impurity ions stabilize the SWTEM mode independent of whether their density profile is peaked inwardly or outwardly. The result for the SWITG mode is similar to the SWTE-ITG mode in the lager ηi regime, except that the excitation of the SWTEM mode requires ηi higher than a certain threshold. In addition, the kθρs spectra, eigenmode structures, and the effects of different impurity ion species on the modes are discussed.

Study on lithium extraction from brines based on LiMn2O4/Li1-xMn2O4 by electrochemical method

Lithium rechargeable batteries have been used for lithium extraction in recent years. Here, we report on a highly selective lithium recovery system that consists of a LiMn2O4 positive electrode, a Li1-xMn2O4 negative electrode and a monovalent selective anion-exchange membrane. The effect of potential, temperature and coexisting ions on lithium extraction were investigated in this paper, and the lithium recovery system was applied to extract lithium from brine and concentrated seawater. The extraction capacity of Li+ reached 34.31 mg· (1g LiMn2O4) −1 at 1.2V. With higher reaction rate and lower energy consumption, 25°C (room temperature) was considered as the appropriate temperature. The system still remained high selective for Li+ even in the presence of impurity ions (K+, Na+, Mg2+, Ca2+). With simulated brine and concentrated seawater as source solutions, the concentrations of Na+, Mg2+ and Ca2+ were reduced more than 300, 70 and 100 times, consuming 18–19W h per mole of lithium recovered. And the electrodes still had high separation coefficients of Li+ and Men+ (Na+, Mg2+, Ca2+) after five cycles although a slight drop was existing.

Effects of Impurity Ions on the Metastable Zone Width of Phosphoric Acid in Tributyl Phosphate

The solubility (from 0.95 °C to 19.11 °C) and metastable zone width of phosphoric acid in tributyl phosphate (TBP) have been measured using a laser method. The results show that the solubility curve is remarkably dependent on temperature in the experimental temperature range. A polynomial fitting of the solubility data was obtained. The metastable zone width increases directly with the increasing rate of cooling but decreases with the increasing concentration of phosphoric acid in TBP. An apparent secondary nucleation order m for phosphoric acid in the TBP system was calculated using Nývlt’s approach and revised using a modified linear regression method. The effects of typical impurity ions (Al3+, Mg2+, and Fe3+) on the metastable zone width for phosphoric acid in TBP were also investigated. The presence of impurity ions can enhance the metastable zone width for phosphoric acid in TBP.

Coupling of ion temperature gradient and trapped electron modes in the presence of impurities in tokamak plasmas

The coupling of ion temperature gradient (ITG or ηi) mode and trapped electron mode (TEM) in the presence of impurity ions is numerically investigated in toroidal collisionless plasmas, using the gyrokinetic integral eigenmode equation. A framework for excitations of the ITG modes and TEMs with respect to their driving sources is formulated first, and then the roles of impurity ions played in are analyzed comprehensively. In particular, the characteristics of the ITG and TEM instabilities in the presence of impurity ions are emphasized for both strong and weak coupling (hybrid and coexistent) cases. It is found that the impurity ions with inwardly (outwardly) peaked density profiles have stabilizing (destabilizing) effects on the hybrid (namely the TE-ITG) modes in consistence with previous works. A new finding of this work is that the impurity ions have stabilizing effects on TEMs in small ηi (ηi≤1) regime regardless of peaking directions of their density profiles whereas the impurity ions with density gradient Lez=Lne/Lnz&amp;gt;1 (Lez&amp;lt;1) destabilize (stabilize) the TEMs in large ηi (ηi≥1) regime. In addition, the dependences of the growth rate, real frequency, eigenmode structure, and wave spectrum on charge concentration, charge number, and mass of impurity ions are analyzed in detail. The necessity for taking impurity ion effects on the features of turbulence into account in future transport experimental data analyses is also discussed.

Kinetic shear Alfvén instability in the presence of impurity ions in tokamak plasmas

The effects of impurity ions on the kinetic shear Alfvén (KSA) instability in tokamak plasmas are investigated by numerically solving the integral equations for the KSA eigenmode in the toroidal geometry. The kinetic effects of hydrogen and impurity ions, including transit motion, finite ion Larmor radius, and finite-orbit-width, are taken into account. Toroidicity induced linear mode coupling is included through the ballooning-mode representation. Here, the effects of carbon, oxygen, and tungsten ions on the KSA instability in toroidal plasmas are investigated. It is found that, depending on the concentration and density profile of the impurity ions, the latter can be either stabilizing or destabilizing for the KSA modes. The results here confirm the importance of impurity ions in tokamak experiments and should be useful for analyzing experimental data as well as for understanding anomalous transport and control of tokamak plasmas.

Statistical theory of flexoelectric effect in ferroelectric liquid crystals

The presence of impurity ions in a ferroelectric liquid crystal produces significant modulation in its polarization profile. We investigate this modulation both by a molecular statistical approach and by a suitable Landau–Ginzburg type free energy model. The molecular statistical approach predicts a value of the induced dipole moment into a host chiral mesogen by the electric field of the ions. The Landau–Ginzburg (LG) approach is based mainly on the flexoelectric effect that is generated by the ions through their electric field. The LG model captures the flexoelectric part of the polarization created by the distortion of the nematic director through the electric field of the ions. Then, the conditions of the helical stability of the chiral state are also investigated in the presence of ionic distortion of the nematic field in a ferroelectric medium.

General model for calcite growth kinetics in the presence of impurity ions

The concentrations of Sr, Mg and other elements in calcite are widely used to infer the conditions of mineral growth. However, such inferences are dependent on the mechanisms that govern the incorporation of minor constituents into the calcite lattice during growth. A particularly confusing observation is that both Sr and Mg are readily incorporated into growing calcite crystals at low concentrations but inhibit calcite growth at higher concentrations. Here we show that the growth rate dependence of Sr and Mg incorporation into calcite, as well the inhibitory effects on calcite growth of both incorporating and non-incorporating ions, can be predicted with an ion-by-ion crystal growth model where ion attachment is confined to kink sites on the crystal surface.The exchange of ions between active growth (kink) sites on the mineral surface and aqueous solution governs both the efficiency of incorporation of minor constituents and the kinetics of mineral precipitation. Ions such as Sr and Mg in calcite, that are not stoichiometric constituents, may attach to kink sites and impede crystal growth by either blocking propagation of the kink (kink blocking), or if incorporated into the growing mineral, straining the local crystal lattice, and hence increasing the mineral solubility (incorporation inhibition). Here we investigate the effects of including these growth inhibition mechanisms into a microscopic model for crystal growth based on kink creation, propagation and collision (CPC) theory. This model predicts that kink blocking by either incorporated or non-incorporated ions causes an exponential decrease in mineral growth rate with increasing impurity concentration, while incorporation inhibition results in more complicated functional forms of the growth rate effect depending on the thermodynamics of the solid solution. Applying this model to existing data on the partitioning of strontium and magnesium into calcite and the simultaneous effects on growth kinetics and mineral composition, we find that strontium uptake inhibits growth by enhancing mineral solubility while magnesium inhibits growth primarily by kink blocking. Our model should be widely applicable to understanding the impurity content of a large range of sparingly soluble minerals that form by precipitation from aqueous solutions.

Impurity effects on the ion temperature gradient mode in reversed-field pinch plasmas

Ion temperature gradient (ITG) driven modes in the presence of impurity ions are studied in reversed-field pinch plasmas by solving the gyrokinetic integral eigenmode equation. Detailed numerical studies for single and multiple impurity ion species indicate that the ITG modes are enhanced by impurity effects and the stability threshold values become higher than that in pure hydrogen plasmas when density gradients of the impurity ions are opposite to that of electrons and main ions. In addition, a mode is driven unstable by impurity ions no matter how low the main ion temperature gradient is when the destabilizing effect of the impurity ions is strong enough. These results resemble the effects of impurities in tokamak plasmas. Analysis of the typical RFX-mod experiments is performed and the results show that the ITG and impurity driven modes may be linearly unstable in the edge region of the plasmas when the observed radial profiles of the impurity ions are considered.