Induced redistribution of solvated cations cerium and nickel in water of their chloride solution
- The results of the experiments (without circulation of the solution)
- The results of the experiments (with circulation of the solution)
- Separation of solvated calcium and magnesium cations by the action of an external periodic electric field and a moving solution
- Magnetically induced mass transfer in salt solutions
The experimental setup used is presented on Figs. 1.14 and 1.15. The parameters of the experiments:
- • concentration of CeCT3, g/1 1,
- • concentration of NiCl , g/1 5,
- • frequency of the electric field, Hz 100 and 200,
- • ambient temperature of medium,°C 22,
- • the amplitude of the field strength in
solid half-cycle, V/cm 56,
- • the ratio of the amplitude of the negative halfperiod to positive period amplitude 750/150; 600/300,
- • time of action of electric field, h 0.5; 1; 2.
Fig. 1.35. The concentration of cerium cations c (g /1) in the experimental cell after exposure to a field of 100 Hz, 600/300 V for 4 hours 30 minutes.
The choice of elements and concentration values are due to the features of quantitative analysis on spectrophotometric equipment.
Duration of exposure to an electric field with a frequency of 100 Hz in the experiments was 30 min, 1 and 2 hours. Each experiment was performed three times.
Reading and processing of the obtained spectra was performed using the VISIONpro program. From the curves for solutions with a known concentration, a calibration graph was constructed based on which the concentrations of metal cations were determined.
The results of the experiments (without circulation of the solution)
Summary charts of experimental results after an hour-long exposure to an electric field with a frequency of 100 Hz and a strength of 750/150 V per solution of cerium and nickel chlorides are presented in Figs. 1.36 and 1.37. Concentration values are presented as a percentage of the value of the concentration of the stock solution.
An analysis of the results shows that the drift of cations of cerium and nickel have a similar character and are directed mainly down to the bottom of the section, drift intensity in the direction there are fewer electrodes. In general, there is a decrease in concentrations of cations (both cerium and nickel) in the central part of the section and their increase near electrodes, more significant potential
While maintaining the parameters of the electric field and reducing the exposure time up to thirty minutes there is a decrease in the concentration of both cerium and nickel in the central part of the section and, accordingly, an increase in concentration near the electrodes, more significant up potential. A distinct, as in the previous experiment, increase in the concentration of solvated cations in the bottom of the section is not observed. The reproducibility of he cation concentration distribution parameters with decreasing duration of the field exposure falls.
With an increase in exposure time to two hours, accumulation of the solvated cations in the upper part of the potential electrode section and in the bottom part of the ground electrode takes place The drift is mainly directed towards the bottom of the section. Distributions of the solvated cations under a two-hour exposure (as well as during a half-hour) are reproduced worse - stability of the process of separation of solvated cations is low.
Based on the results of the experiments, the points of optimal selection, dump and supply of the solution for the organization of the process of separation of cerium and nickel cations were determined.
Fig. 1.36. The distribution of nickel cations (as a percentage of the initial value of 100%).
Fig. 1.37. Distribution of cerium cations (as a percentage of the initial value of 100%) electrode. The error in determining the concentration of metal cations does not exceed 9%.
The concentrations of the components in the selection are equal: Ce3+-C‘; Ni2+- C'., and in the dump - C.” and C", respectively. In this case, the selection is enriched in Ce3+ cations and depleted in Ni2+ cations, but the dumping is vice versa: it is depleted in Ce3+ cations and enriched in Ni2+ cations.
The maximum separation coefficient can be obtained if the dumping is represented by point 9 (see Figs. 1.14, 1.15 - the bottom of the section at the potential electrode), behind the dumping - point 2 (central upper part of the section). Thus, after an hourly exposure of the field of 750/150 V with a frequency of 100 Hz to the aqueous solution of the mixture of the salts of CeCl, and NiCl, the concentration values in the absence of solution circulation through the section are: C = 1.1454; C = 1.1065; C"= 0.8122; ,C"= 0.9085.
i j i j
In this case, relative concentrations of cations or cerium and yttrium are: R. = 1.00000 (initial solution); R = C'JC = 1.0755 (selection) and Rj' = C'IC. = 0.8940 (dumping). ’
The separation coefficients without circulation of the solution are:
- • in the selection a. = R'/R, = 1.0755;
- • in the dumping = RJ.JR'' = 1.1186;
- • full q = a -p = .2021. 'J
The results of the experiments (with circulation of the solution)
Based on data from experiments with a motionless solution, a series of experiments was conducted with circulation of the solution through one section of the experimental setup. Saline pumping was provided using a peristaltic pump, the solution was supplied to the centre of the section (point 5 in Fig. 1.15), selection was carried out from points 1, 3, 7, 9 in Fig. 1.15. Experiments were carried out with an asymmetric electric field voltage of 750/150 V, frequency 100 Hz.
The results of the experiments (Fig. 1.38) are in good agreement with the results obtained in experiments with a stationary solution. An increase in the concentration of the solvated cations (ascerium and nickel) is observed in the bottom of the section in the region of the grounded electrode (point 7 in Fig. 1.15). A decrease in the concentration of cations occurs on the potential electrode in the upper parts of the section (point 3 in Fig. 1.15). Thus, when circulatingthe solution at a speed of 7 1/h the main direction of drift of the solvated cations (both cerium and nickel). Relative change in the concentration of solvated Ce3+ cations in the selection significantly exceeds the change in the concentration of Ni:+ cations.
With a decrease in the circulation rate of the solution to 1.7 1 / h, the total drift direction of cationic aquacomplexes remained, but its intensity decreased (Fig. 1.39).
Fig. 1.38. Distribution of cerium and nickel cations at a circulation rate of the solution ~ 7 liters/hour.
Fig. 1.39. Distribution of cerium and nickel cations at a solution circulation rate of к 1.7 liters/hour.
With an increase in the speed of pumping the solution to 14 liters per hour the overall distribution pattern of the solvated cations has changed somewhat. The maximum concentration value is observed at sampling point 7 in Fig. 1.15, and the minimum value has shifted from point 3 to point 9 in Fig. 1.15. At a given pumping rate, the variation in the concentration values in the experiments increased.
From the values obtained in the experiments, the values of the separation coefficients were calculated. For ‘selection’ point 7 in Fig. 1.15, in which the maximum difference in the concentrations of cations of cerium and nickel was observed was taken. The values of the separation coefficients during the selection of the ‘dumping’ solution at various points are given in Table 1.4.
The values given in Table 1.4 values suggest that stable separation of Ce3+ and Ni2+ cations can be achieved at a circulation rate of 7
Table 1.4. Values of separation coefficients of solvated cations Ce3and Ni- under the effect of asymmetric field (100 Hz, 750/150 Y)
Position of sampling point
Dumping at point 1
Dumping at point 3
Dumping at point 9
1/h, providing selection from point 7 (the bottom of the section of the ground electrode), and the dump from points 1 or 3 in Fig. 1.15 The maximum value of the separation coefficient is ensured when selecting the waste solution at point 3.
The maximum separation coefficient of the solvated cerium and nickel cations in the case of an aqueous solution of their chlorides was achieved in experiments under the action of an electric field of voltage 750/150 V with a frequency of 100 Hz per aqueous solution for an hour.
Separation of solvated calcium and magnesium cations by the action of an external periodic electric field and a moving solution
Figure 1.40 shows the nature of the change in the concentration of calcium ions in the internal (curve 1) and external (curve 2) zones in the frequency range from 20 to 180 Hz . The experiments were performed on the setup shown in Fig. 1.17. In the following sections, it will be shown that the initiation of the phenomenon of electroinduced drift should be expected at frequencies of tens of Hz, when a self-consistent field is formed in the solution, and the size of the solvated ion (cluster) formed by the ion and solvent molecules forming the solvate shell is inversely proportional to the square root of of the salt concentration in the solvent. Frequency values, in turn, are inversely proportional to the value of the moment of inertia of the cluster.]
As can be seen, in the range of 80-120 Hz there is a noticeable increase in the content of calcium ions in the inner zone of the working solution with a distinct maximum. It is important to note the corresponding decrease in their concentration in the outer zone, that is, it has a redistribution of the concentration of one of the ionic components between the interstices of the working solution takes place, which essentially means the process of their separation. It is likely that in this frequency range there is a deformation of the solvate shells of calcium ions, and possibly even static destruction of the outer layers of solvation, where the binding energy of the solvate water molecules with the central ion is minimal in comparison with the water molecules that make up the primary solvation shells. This circumstance creates the conditions for the directed transfer of desolvated ions in a potential field, which, in accordance with the terminology adopted earlier, determines the effect of their selective
Fig. 1.40. The influence of the frequency on the content of calcium ions in the separation zones at a voltage of 285 V (field strength in the cell 86.4 V/crn) and the initial concentration of 2.065 g/1. The circles indicate the concentration in the inner zone, the triangles indicate the concentration in the outer zone.
electro-induced drift. Since every electrolyte solution has the property of electroneutrality, then any change in the local volume of its electric charge - positive or negative - should lead to instantaneous compensation of this charge by moving ions of the corresponding type into this volume. So, if in our case there is a transfer of calcium ions from the outer separation zone to the inner one, creating in the latter an excess content of ions of a positive charge, then an equivalent amount of magnesium ions should be transferred from the inner zone to the outer one. This phenomenon can be interpreted both as a process of electromigration migration and as an exchange process between different classes of ions. Thus, in the inner zone there should be a decrease in the content of magnesium ions, and in the outer zone, on the contrary, an increase in the concentration of these ions. Indeed, if we turn to Fig. 1.41 then it becomes obvious that the change in the concentration of magnesium ions with respect to the content of calcium ions in the inner and outer separation zones in the indicated frequency range is clearly expressed inverse.
Fig. 1.41. The change in the concentration of magnesium ions in the separation zones at a voltage of 285 V (field strength in the cell 86.4 V/crn) and the initial content of 1.986 g/l. The circles indicate the concentration in the inner zone, triangles - concentration in the outer zone.
Ill its own way, the frequency dependence of the content of calcium ions is resonant in nature, that is, the concentration extremes for these ions are determined in a rather narrow frequency range.
The same can be said about the frequency dependence of the content of magnesium ions (Fig. 1.42). However, extreme concentrations of magnesium ions in the separation zones are observed in the region of more high frequencies, that is, when the energy of the external field exceeds the threshold values of the resonance phenomena for the same calcium ions. This is apparently due to the difference in the bond length of the solvation shell with the central ion. The radius of the outer electron shell of a magnesium ion is smaller than that of calcium ion; therefore, the coulomb interaction of the magnesium ion with water molecules that make up the solvate shells forms a shorter bond, which corresponds to a higher natural frequency of the bond. Cations have only the coordinating effect on the solvent molecules in the first and second solvate spheres, and the number of solvent molecules in the solvate shell is determined by the screening radius of the cation charge by the total charge of polarized solvent molecules.
Fig. 1.42. The frequency dependence of the content of magnesium ions in the separation zones at a voltage of 285 V (field strength in the cell 86.4 V/cm) and the initial concentration of 1.931 g/I. The circles indicate the concentration in the inner zone, the triangles indicate the concentration in the outer zone.
The following sections will show that the directional drift of the solvated ions is also excited at frequencies corresponding to various components of the rotational-translational motion of the ion-solvation shell system, and at frequencies corresponding to transitions of oscillatory movements into rotational ones wherein the frequency values are units of kHz. The resonance can be expected:
- • at the frequency of cooperative rotational motion of H,0 molecules combined into a solvation shell relative to an axis passing at a distance equal to the outer radius of the solvation shell from the energy centre;
- • at the frequency of cooperative rotational motion of H,0 molecules combined into a solvate shell relative to the centre of inertia of the solvated ion (cluster);
- • at the frequency of rotational motion of the cluster as a whole;
- • at the frequency of transition of the oscillatory motion to the rotational one.
Consequently, for the resonant deformation of the solvate shells of magnesium ions, a higher value of the external electric field energy will be required, which will increase with increasing frequency fluctuations. Theoretical ideas about the electroinduced drift of solvated ions indicate that one of the factors causing this phenomenon is the amplitude of the electric potential, which determines the electric fields. The experiments carried out at voltage values of 40 V (field strength in the cell 12.1 V/cm) showed that, within the limits of the measurement error, the concentrations of magnesium and calcium ions did not change and remained at the level of their initial values. Since potential is the main energy characteristic of an electric field, then, apparently, there is a certain threshold value of the electric field strength, which determines the energy minimum, which in a certain frequency range causes the deformation of the solvation shells of ions and, accordingly, their selective electro-induced drift. In the case under consideration the threshold value of the electric field lies in the range from 12 to 100 V/cm. In relation to the studied special character of separation, the total coefficients of the separation of cations of calcium and magnesium are determined by the measurement results. To talk about a single separation coefficient, complete information is needed on all possible mechanisms of selective mass transfer. The process of electroinduced drift at the interface between the outer and inner zones, which leads to the exchange of different-grade ions between these zones, is presumably prevailing. An additional driving force that provides, along with electromigration transfer, the movement of ions from the outer zone to the inner, can be represented by an excess hydrodynamic pressure, which occurs due to the difference in the speeds of the solutions in the inner and outer zones. In this regard, the question of how the velocity ratio affects the movement of solutions in zones on the effect of separation requires a separate consideration. The simultaneous mass transfer of a certain fraction of competing ions over a certain period of time across the border of the outer and inner zones over the entire area of their contact can, apparently, be interpreted as a single separation coefficient.
Magnetically induced mass transfer in salt solutions
The scheme for exciting intense mass transfer in a salt solution placed in an alternating magnetic field is quite simple and similar to a transformer circuit, the secondary winding of which is formed by a ‘coil’ of the solution (see Fig. 1.43). This ‘coil’ is located in a dielectric vessel (polymethyl methacrylate), placed in a variable magnetic field.
The field in the magnetic core of the transformer is excited by alternating current in a conventional primary winding. A feature of the circuit is that the ‘turn’ of the solution is ‘open’ by the diode or (which is the same) by the load of the ‘turn’ is a semiconductor junction. Only in this case, intense mass transfer is excited in the solution. The intensity of mass transfer suggests that the primary factor is the excitation of the motion of particles having a significant ‘hydrodynamic radius’. Only in this case, their motion due to friction can cause the movement of surrounding particles and the entire solution as a whole. These particles are aquacomplexes - clusters having submicron sizes. Clusters are formed by both cations and anions and are charge neutral at time intervals exceeding the time between Brownian collisions of solvent molecules.
The experiments were carried out on the basis of a magnetic circuit (transformer core) assembled from sheet electrical steel. Its dimensions were 400 x 200 * 50 mm. The primary winding contained 200 turns of copper wire with a diameter of 3 mm, the voltage on the primary winding was 150 V (50 Hz). The secondary winding was a polyethylene hose with a diameter of 20 mm, filled with a solution. In the case of an aqueous solution of CuS04 + H2S04 electrolyte, the voltage at the ends of the ‘open’ secondary winding changed from 1 to 3.2 V with an increase in the number of coils of the solution from 1 to 6. The current strength in the secondary circuit (in solution), ‘loaded’ on the diode, reached 2.8 A with the
Fig. 1.43. Excitation of mass transfer by the magnetic field.
number of turns equal to 6. Figure 1.44 shows the current-voltage characteristic of the ‘secondary’ winding ‘loaded’ on the diode. A very important (experimentally established) fact is that the current strength clearly depends on the diameter of the hose forming the secondary winding. With large hose diameters (with other conditions being identical), the current strength is greater. At small diameters, the current could not be excited at all. This clearly indicates that the current is formed by the directional movement of solvated ions having orders of magnitude greater mass as compared to the mass of a ‘bare’ ion. The Larmor radius of such solvated ions - clusters is large and comparable to the diameter of the hose inside which the mass transfer is excited. For small hose diameters, the induced motion of the solvated ions (clusters) is hindered by the appearance of collisions with the walls of the hose.
Excitation of a salt solution in a dielectric with an alternating magnetic field of oppositely directed currents of anionic and cationic clusters makes it possible to organize two technological processes.
The first is the enrichment (purification) of the solution by anions or cations, that is, the separation of chemical elements. The second is electrolysis. In this case, at the ends of the ‘open loop of the solution’ it is necessary to place the electrodes, which should still be ‘loaded’ on the diode.
Electrolysis will occur at the interface between the electrodes and the solution. For example, in the case of an aqueous solution of CuS04 + H,S04 electrolyte, intense copper evolution occurs on one of the graphite electrodes.
Fig. 1.44. Current-voltage characteristic of the ‘secondary winding’ from a solution of CuSO,.
The results of experiments on the effect of an asymmetric electric field on aqueous salt solutions show that when an asymmetric electric field is applied to a salt solution, selective drift of oppositely charged aquacomplexes is induced: cationic and anionic. In this case, a separation of the drift directions is observed: to the side of the ground and to the side of the potential electrodes. The solution accumulates electrical energy. When drifting in one direction for cationic (anionic) aquacomplexes, selection is observed due to the difference between the normal (with respect to the plane of the electrodes) components of the velocity vector of the centres of inertia. In an aqueous solution of a mixture of salts of CaCl, and MgCl, the effect of oriented, selective drift of cationic aquacomplexes occurs under the influence of an asymmetric electric field, the frequency of which does not exceed 5 kHz.
The ratio of the displacements due to the field-induced rotational- translational motion and the displacements caused by the chaotic motion of the solvated cations is determined by many parameters. Of these, field tension E and solution temperature T can be distinguished. The trajectory of the aquacomplex is determined by a set of at least 7 parameters: field strength; frequency asymmetry coefficient; bond lengths in a dipole (polarized aquacomplex); mass ratios of positive and negative parts of the dipole; masses of the aquacomplex as a whole; the polarization coefficient of the aquacomplex.
The performed experiments prove the possibility of using the discovered phenomenon of electroinduced selective drift of solvated ions in salt solutions under the action of the asymmetric electric field for organizing the technological process of enrichment of solutions by cations of the target metal.
It was found that the excitation of the effect of selective electroinduced drift of solvated ions can be observed in at least two frequency ranges. Within each of the intervals there are frequencies corresponding to eigenfrequencies of oscillations of the ‘ion-solvate shell’ system as a spherical rotator (rotation of the solvate shell relative to the central ion) or as a system of rigidly connected central ion and hollow shell.
The frequency dependence of the cation content in the solution of a mixture of their salts indicates that for each of the competing cations there is a certain frequency range in which the rate of directional drift of one of them increases significantly.