GB2107353A

GB2107353A - Selective electrolytic recovery of metal values

Info

Publication number: GB2107353A
Application number: GB08129834A
Authority: GB
Inventors: Vsevolod Borisovich Evdokimov; Alexandr Petrovich Kravchinsky; Alexandra Alexandrov Belyakova; Vladimir Leonidovich Myakishev
Original assignee: Moskovsky Gosudarstvenny Universitet Imeni M V Lomonosova
Current assignee: Moskovsky Gosudarstvenny Universitet Imeni M V Lomonosova
Priority date: 1981-10-02
Filing date: 1981-10-02
Publication date: 1983-04-27
Also published as: GB2107353B

Abstract

Metal values are selectively recovered from a liquor by passing the liquor through a cathodic zone, passing an anloyte through an anodic zone, increasing the pH of the liquor in the cathodic zone within the range of 1 to 14 by application of an electric field and selection of appropriate rates of supply of the anolyte and catholyte, the resultant rate of pH increase being such that in the cathodic zone conditions are created for selective recovery of an oxide or hydroxide of the metal at a corresponding pH of deposition. Apparatus for carrying out the process comprises a reactor having separate outlets and inlets for the catholyte liquor and an anolyte; a cathode 2 and an anode 3 coaxially positioned inside the reactor; a cylindrical manifold 8 located in the upper section of the reactor and having electrically insulated from each other (e.g. by spacer 9) an upper chamber 10 and a lower chamber 11 for collection of anodic and cathodic gases respectively; a membrane 4 coaxially secured in the lower section between the cathode and the anode; an electromagnetic coagulator 34, for acceleration of the formation of a solid phase, connected in series with a catholyte recycling pump and the reactor; and a unit for measuring pH of the catholyte. <IMAGE>

Description

SPECIFICATION Selective recovery of metals from leaching liquors The present invention relates to processes and apparatus for selective recovery of metals from leaching liquors.

The present invention is most useful in hydrometallurgy of non-ferrous metals for recovery of nonferrous, rare and noble metals, as well as rare-earth elements from liquors resulting from natural and artificial leaching.

The present invention can be also employed in the production of metal hydroxides, co-deposition of several hydroxides under strictly controlled pH of the medium without using alkalis as reagents for recovery of metals from waste waters from etching shops, in comprehensive purification of waste waters effluent from the production processes in non-ferrous and ferrous metallurgy, as well as for purification of water from any source.

There exists a category of ore bodies containing considerable amounts of useful components which might be utilized only by means of leaching. The leaching liquors contain gold, iron, copper, zinc, cadmium, and other metals. Concentration of metals in leaching liquors can vary from fraction of a gram per litre to 20-30 g/l. As a rule, in leaching liquors particles of silica are contained in a suspended state and the concentration of humic acid is relatively high.

Liquors resulting from natural or artificial leaching can be exemplified by waste waters from electroplating and etching shops, and waste from non-ferrous metallurgy plants, in particular from enrichment factories. Furthermore, liquors of natural and artificial leaching cover mine waters, as well as liquors produced in pile, tank, autoclave, and bacterial leaching processes.

The general volume of leaching liquors is ever growing during recent years owing to the necessity of processing of ore bodies which are economically inefficient to process by traditional hydrometallurgical methods, as well as the necessity of reprocessing different kinds of secondary raw materials.

The present invention provides a process for selective recovery of metals from leaching liquors in which cathodic and anodic zones are formed and a constant electric field is applied to these zones simultaneously passing the processed liquors; in the cathodic zone pH of the liquor is maintained within the range of from 1 to 14 by way of application of external electric and magnetic fields and selection of appropriate rates of the liquor supply and rates of variation of pH of the liquor to provide, in said cathodic zone, the conditions for selective recovery of oxides and hydroxides of different metals at a corresponding pH of deposition within the pH range mentioned above.

In the process according to the present invention, involving application of an electric field to the interelectrode space, there is no necessity to fill this space with activated carbon without, however, failing to accomplish the objects of the present invention. In the process chosen as a prototype, activated carbon acts a dispersed electrode making possible to attain a current yield of above 100%. At the same time, the presence of carbon in the interelectrode space makes the process inefficient and unsuitable for the treatment of concentrated liquors.

The process according to the present invention drastically differs from the prototype process in that the object of the invention is accomplished not through the use of activated coal as a specialpurpose agent in the cathode zone, but through the use of a disperse medium formed during separation of metals as hydroxides. The pH value of 14 is selected as the upper limit of the above-mentioned range because before pH 14 all metals from leaching liquors pass into the state of hydroxides. Leaching liquors having pH below 1 are not known. To accomplish the object of the invention, it is not sufficient to maintain pH within a certain range.It is necessary to select such rate of supply of the catholyte and anolyte separately into the cathodic and anodic zones and such external fields that, at a given porosity of the membrane, the catholyte with a higher pressure in the cathodic zone would move into the anodic zone through the membrane pores.

At the same time, into the anodic zone the anolyte should be fed at such a rate that no transfer of the anolyte into the cathodic zone would occur at this rate, but reduction of the electrical conductivity in the anodic zone would be compensated owing to oozing of the catholyte into it under the effect of the excess pressure in the cathodic zone. The selection of the actual rates of supply into the cathodic and anodic zones matched with the intensity of external electric and magnetic fields makes it possible to selectively recover metals from liquors both at small and high concentrations with the highest productivity at minimum power consumption. Criteria of the desired effect are the rate of pH variation and the rate of temperature variation in the cathodic zone.

For carrying out the process according to the present invention a special apparatus is required which makes it possible to effectuate the selection of rates of separate supply through the anodic and cathodic zones which would be matched with the intensities of external electric and magnetic fields so that minimum power consumption is ensured in the absence of packing of activated carbon in the cathodic zone of the apparatus. (The apparatus selected as a prototype does not enable proper selection of such conditions and accomplishment of the objects of the invention.) Since the cathodic space is separated from the anodic one, the apparatus acts as a generator of hydroxyl ions in the cathodic space and hydroxyl ions are combined, by way of a chemical reaction, with metal ions from the leaching liquor with the formation of sparingly-soluble metal hydroxides which are precipitated.These metal hydroxides are continuously carried, in the form of a suspension, through the cathodic space and are subjected to the effect of the external electric and magnetic fields. The suspension particles, while moving in the stream of the solvent, acquire a sliding potential under the action of friction and get charged. These charged macroscopic particles, while interacting with the electric and magnetic fields during their movement, are displaced towards the walls of the apparatus, thus resulting in an increased rate of intermixing of the particles and coagulation thereof.

This movement of the suspension to the walls is especially intensive in the presence, in the liquor, of a considerable amount of silica particles with a highly developed surface area and a great amount of iron ions, forming a magnetic suspension which is coagulated under the influence of weak magnetic fields. At a considerable concentration of the suspended particles in the liquor, the moving suspension owing to the sliding potential creates a field of the medium formed by the total of the moving particles and the solvent. This field is combined with the external fields so that the movement of the medium takes place in a certain effective field influencing the medium movement and the processes of exchange with charges and heat in the medium.As a result, owing to the above-mentioned phenomena, conditions are formed which minimize code position of metals with the hydrate-formation pH values which are close to one another.

Furthermore, these conditions make it possible to successively recover, in accordance with their pH of hydrate-formation, different metals selectively. At the same time useful by-products are obtained such as hydrogen, oxygen, commercial sulphuric acid solution, and purified water containing readily soluble sulphates.

These by-products can be utilized in industry for any purpose, thus eliminating the formation of production wastes.

Furthermore, owing to simultaneous passing of the processed anolyte and catholyte through the anodic and cathodic zones, the possibility of penetration of the (acidic) anolyte into the catholyte is avoided, reducing the expenditure for the selective recovery of metals.

In one procedure, the leaching liquor is simultaneously passed through both the cathodic and anodic zones. This results in equalization of pH through the entire vessel. At the same time, the excess of the acidic anolyte is withdrawn from the anodic zone and the possibility of penetration of the anolyte into the catholyte through the membrane is eliminated. This results in lower consumption of energy and improved selectivity of metal recovery.

In another procedure, the leaching liquor be passed through the cathodic zone simultaneously with passing an aqueous solution of one or more chlorides through the anodic zone. This makes it possible, first of all, to increase the electrical conductivity in the anodic zone; secondly, on the anode gaseous chlorine is evolved which is partly dissolved in the anolyte with consumption of heat, thus improving thermal conditions and avoiding heat loss. Thirdly, carbon or graphite can be used as the anodes, which are not substantially broken down and have an extended service life; fourthly, the rate of anolyte consumption is drastically lowered. All this in combination results in lowered power consumption and renders the process economically more efficient.

It is desirable for a solution of sylvinite to be used as the aqueous solution of chlorides. This substantially lowers the cost of production and improves selectivity of the process, since sylvinite is a cheap naturally-occurring product.

The use of a solution of sylvinite makes it possible to considerably lower the rate of consumption of the anolyte, reduce power consumption, and increase productivity.

Alternatively, an aqueous solution of one or more sulphates may be passed through the anodic zone. This makes it possible to increase electrical conductivity in the anodic zone, which contributes to reducing heat losses, increases productivity, and decreases power consumption as well. Use may conveniently be made of an aqueous solution of sodium sulphate. The latter is well soluble in water and a most inexpensive naturally-occurring sulphate, thus rendering the process of selective recovery of metals from the leaching liquor less expensive.

It is preferable that the treated solutions be under the effect of an electromagnetic field. Owing to this fact the suspension particles are moved towards the vessel walls, coagulation is accelerated, the time of the process completion is reduced, power consumption is lowered, and the productivity of the process is increased.

In cases where gold is present in the leaching liquor, it is desirable for the cathodic zone to be filled with activated carbon. Owing to this feature, gold is adsorbed by the carbon before precipitation of iron hydroxide. In this case the current yield is above 100%, since the activated carbon particles behave as an additional electrode with a very developed surface area.

Furthermore, the present invention provides apparatus for selectively recovering metals from leaching liquors which comprises a reactor with coaxially positioned therein a cathode and an anode; a cylindrical manifold located in the upper section of the reactor and provided with socket pipes and holes for introduction and discharge of the leaching liquor and having electrically insulated upper and lower chambers made so that in the lower chamber a membrane is coaxially mounted between the cathode and anode which partitions the working space of the reactor into the cathodic and anodic zones; an electromagnetic coagulator intended for acceleration of the formation of the solid phase which communicates with a recycling pump and the reactor and a unit for measuring pH of the medium which is connected with the electromagnetic coagulator, reactor and a settling tank which communicates with a pump for recycling the iiquid from the settling tank back into the reactor.

Owing to the presence of the membrane the cathodic space is separated from the anodic one and the apparatus works as a generator of hydroxyl ions in the cathodic space.

Furthermore, the processes in the cathodic and anodic zones occur separately and the anolyte is not intermixed with the catholyte. As a result there is ensured the possibility of selective recovery of metals.

Owing to the fact that the anodic and cathodic space of the reactor are separated from each other by means of a membrane, the anodic and cathodic gases are collected by means of a manifold. These gases are not lost and do not pollute the environment. These gases can be further used for various industrial needs.

The presence of a membrane separating the anodic space from the cathodic one and the presence of a manifold makes it possible to effect such selection of rates of a separate supply of solutions into the cathodic and anodic spaces and such intensity of external electric and magnetic fields as to ensure the highest rate of variation pH and smallest power consumption.

The presence of an electromagnetic coagulator results in accelerated formation of the solid phase circulating through the cathodic space, which facilitates the progress of electrochemical processes on the cathode and lowers power consumption.

It is advisable that for fixation of the membrane coaxially in the centre of the upper and lower chambers of the manifold openings be provided. Owing to this arrangement, the anode is mounted relative to the cathode in such a manner that the electric potential is uniformly distributed over the cathode surface. This also eliminates side processes necessitating additional consumption of electric power.

It is advisable that the membrane be fixed by means of a sealing gasket impermeable to the leaching liquor and gases formed upon recovery of metals from the opening of the lower chamber of the manifold. This makes it possible to avoid the opportunity for overflowing of the more acidic anolyte into the less acidic catholyte, whereby power consumption is decreased; the possibility of intermixing of cathodic and anodic gases is also avoided, thus making it possible to obtain them in a more pure form.

It is also advisable for the cathode to be fixed to the lower chamber of the manifold provided with an outlet pipe for withdrawal of the gas from the cathodic zone of the reactor and the anode to be fixed to the upper chamber of the manifold provided with pipe for discharging and introduction of the gas from the anodic zone of the reactor. This provides for the opportunity of separate collection of the gases from the anodic and cathodic zones; avoids loss of these gases for industry; and eliminates contamination of the environment.

It is also advisable that the anode be secured to the upper chamber of the manifold by means of a sealing gasket to avoid leakage of the anode gases.

For the treatment of the leaching liquors having a low concentration of dissolved metals, to ensure communication of the electromagnetic coagulator with the reactor, it is advisable that it be fixed directly to the lower section thereof, whereby the whole apparatus for a selective recovery of metals becomes more compact. Furthermore, the speed of formation of the solid phase is increased, thus facilitating the course of electrochemical processes on the cathode and lowering power consumption.

For the treatment of leaching liquors with a high concentration of dissolved metals it is desirable for the electromagnetic coagulator to be connected to the lower section of the reactor to ensure communication therebetween. This eliminates the possibility of clogging of the coagulator and increases productivity of the apparatus for a selective recovery of metals at a high concentration thereof in the leaching liquor.

It is also desirable for the cathode positioned coaxially with the anode and the membrane to be made of the same material as the reactor and electrically connected thereto. This is favourable for acceleration of the deposition of the solid phase and facilitates the progress of electrochemical processes on the cathode, thus resulting in a reduced power consumption.

It is advisable for the cathode to be made perforated. This facilitates rapid equalization of pH and temperature within the entire volume of the apparatus.

In those cases where through the anodic zone a leaching liquor or a solution of sulphates is passed it is desirable for the anode to be provided with a vibrator. Owing to the vibrator there occurs an intensive separation of bubbles of the anode gas from the anode surface. As a result, the speed of chemical processes on the anode is increased and power consumption is lowered.

The electromagnetic coagulator may be made as a helical tube of a dielectric material positioned between terminals of a source of magnetic field; this contributers to a higher speed of coagulation.

In the recovery of metals from leaching liquors with a small concentration of dissolved metals, it is advisable for the electromagnetic coagulator to be made as a box of a dielectric material packed with a magnetic material positioned between magnetic field source terminals. The leaching liquor while passing through the packing, is subjected to an intensive effect not only by the external magnetic field, but by the magnetic field of the packing per se. Under the action of these fields in the liquor moving relative to the packing there occurs variation of concentrations of the dissolved compounds and the suspension formed as a result of the process of recovery of metals. Directly in the vicinity of the packing the concentration is increased; conversely, it decreases with increasing distances therefrom.As a result of increasing concentration about the packing the speed of coagulation is also increased.

The present invention provides for a mechanized and automated process for a selective recovery of metals from leaching liquors; it makes it possible to eliminate the production wastes and neutralization stages; and closed-circuit non-waste production is ensured which overcomes pollution of the environments. Furthermore, at the same time as selective recovery of metals from leaching liquors there is formed a great amount of pure water which can be used for industrial needs.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 schematically shows an apparatus for selective recovery of metals from leaching liquors; Figure 2 is a schematic general view of the reactor in the apparatus, partly in axial section; Figure 3 is a schematic side view of the magnetic coagulator at the bottom of the reactor, partly in section, on an enlarged scale; Figure 4 is a schematic view of a modification of the reactor, wherein the anode is provided with a vibrator; Figure 5 is a schematic part-sectioned side view of a helical magnetic coagulator which can be connected to the lower section of the reactor; and Figure 6 is a plan view of the helical magnetic coagulator.

The illustrated apparatus for the selective recovery of metals from leaching liquors comprises a reactor 1 in which a cathode 2 and an anode 3 are coaxially positioned along the reactor axis a-a (Figure 2). Between the cathode 2 and anode 3 a membrane 4 is coaxially secured along the same axis a-a and divides the working space 5 of the reactor 1 into an anodic zone 6 and a cathodic zone 7.

Owing to the presence of the membrane 4 the reactor works as a generator of hydroxyl ions in the cathodic zone 7, in which, upon reaching a pH for hydrate formation, the hydroxyl ions are combined by a chemical reaction with metal ions from the leaching liquor with the formation of a sparingly soluble hydroxide. As a result, in accordance with the hydrate-formation pH in the cathodic zone 7 there are formed precipitates of hydroxides of different metals present in the leaching liquor. The precipitates of metal hydroxides are separated from other metals remaining in the solution at a certain pH value, whereby selective recovery of metals from the leaching liquor is ensured. The resulting precipitates are employed in industry; simultaneously there are obtained useful products and pure water.

The reactor 1 has a two-part stepped cylindrical manifold 8 mounted in the upper section of the reactor coaxially therewith.

This manifold 8 is divided, by means of an insulation spacer 9, into an upper chamber 10 and a lower chamber 1 The manifold 8 and upper 9 prevent intermixing of gases formed during recovery of metals from the leaching liquor, ensures their separate collection and permitting further utilization in industry: pollution of the environment is avoided.

The casing 12 of the lower chamber 11 of the manifold 8 is screwed on the body of the reactor 1 by means of threading 13. A sealing gasket 14 between the lower chamber 11 of the manifold 8 and the reactor 1 eliminates leakage of the cathodic gases and the leaching liquor from the cathodic zone 7 of the reactor 1. In the casing 1 2 there are openings in which pipes 1 5 for collection of cathodic gases from the cathodic zone 7 of the reactor 1 are mounted.

In the same casing 12 there is an opening along the axis a-a, into which the cylindrical hollow cathode 2 is placed. The cathode 2 and casing 12 are rigidly connected together and are made of the same metal. Inside the cylindrical cathode 2 the insulation spacer 9 is rigidly fixed coaxially therewith.

To this spacer 9 the membrane 4 is fixed by means of a sealing gasket 1 0. The central opening of the upper part of this spacer 9 has threading 1 7 by means of which a clamping ring 1 8 connected with a cylinder 1 9 is secured to the spacer.

By means of this clamping or locking ring 18 secured to the cylinder 1 9, sealing of the gasket 16 is effected, thus avoiding the possibility of intermixing of the anolyte with the catholyte and the possibility of penetration of the cathode gases from the cathodic zone 7 of the reactor 1 into the anodic zone 6, as well as improving selectivity of recovery of metals from leaching liquors and reducing power consumption.

To the casing 12 of the lower chamber 11 of the manifold 8 the casing 21 of the upper chamber 10 is fastened by means of threading 20. Between the casing 12 and 21 an insulation gasket 22 is provided which is impermeable to gases, thus avoiding the possibility of leakage of the anode gases to the atmosphere.

In the casing 21 of the upper chamber 10 an opening is provided along the axis a-a, receiving a shaped washer 23 which is secured by means of screws 24. The washer 23 has a threaded opening 25, into which the cylindrical anode 3 is inserted. The anode 3 is secured to the washer 23 by means of a sealing gasket 26 and a nut 27 and is mounted along the axis a-a coaxially with the cathode 2 and the membrane 4, thus ensuring a uniform distribution of the electric potential over the entire surface of the cathode 2 and improving selectivity of metal recovery. The anode 3 has a central hole 28 along its entire length, which hole is intended for the supply of the anolyte into the anodic zone 6 of the reactor 1. The sealing gasket 26 is impermeable to gases formed in the anodic zone 6 of the reactor 1 in the process of metal recovery.

In the casing 21 of the upper chamber 10 of the manifold 8 there are openings in which pipes 29 are mounted. These pipes 29 are intended for collection of the anodic gases and withdrawal thereof from the anodic zone 6 of the reactor 1. This minimizes loss of the anode gases and prevents pollution of the environment. The anode gases can be further used in industry for various purposes. In the casing 21 there is also a hole 30 for the removal of the anolyte from the anodic zone 6 of the reactor 1.

In the upper part of the reactor 1, below the threading 13 but above the upper edge of the effective cathode, openings are provided for pipes 31 intended for the removal of the liquor from the cathodic zone 7 of the reactor 1.

An electromagnetic coagulator 34 is fixed directly to the lower section of the reactor 1 by means of threading 32 and a sealing gasket 33 impermeable to the leaching liquor.

To the outside surface of the casing 35 of the electromagnetic coagulator 34 a cylindrical permanent magnet 39 is secured by means of a plate 36, a thrust ring 37, both being made of nonmagnetic materials, and screws 38. Inside the cylindrical magnet 39 a coil 40 is provided with its carcass 41 wound of wire 42. By means of terminals not shown in the drawings, the coil 40 is connected to an AC voltage source (not shown).

In the inner face of the casing 35 of the electromagnetic coagulator 34 a recess 43 is provided, into which a ring 44 is inserted with a screen 45 mounted thereon which is permeable to the leaching liquor and the suspension of metals, but impermeable to particles of activated carbon.

in the lower section of the casing 35 of the electromagnetic coagulator 34 below the plate 36 and on the inner surface of the casing 35 of the electromagnetic coagulator 34 in a recess 46 a ring 47 is rigidly secured to which a screen partition 48 is rigidly fastened. In the lower section 35 of the electromagnetic coagulator 34 below the screen partition 48 a pipe 49 is provided which is made integrally with the casing 35 of the electromagnetic coagulator 34 and serving for the supply of the liquor into the inside space 50 of the electromagnetic coagulator 34 and into the cathodic zone 7 of the reactor 1.

The electromagnetic coagulator 34 is mounted, by means of the threading 32 and sealing gasket 33, on the lower section of the casting 51 of a unit 52 for the measurement of pH of the reaction medium and is connected, by means of the pipe 49, with a recycling pump 54 (Figure 1), the pump being connected, by means of a line 53 and a control valve 55, with the reactor 1.

The cathode 2 positioned coaxially with the anode 3 and membrane 4 can (as shown) be made perforated; for this purpose, openings 57 are uniformly positioned over the entire surface of the cathode 2, which openings make it possible to accelerate the process of equalization of pH in the reactor 1, accelerate the process of recovery of metals as hydroxides, improve exchange of the heat evolving during recovery of metals from the liquor, and reduce power consumption.

A vibrator 58 (Figure 4) and an anodic adaptor lead 59 can be secured to the anode 3 above tne nut 27, while on the external side of the casing 12 (Figure 2) of the lower chamber 11 of the manifold 8 a cathode lead 60 is welded at the centre between the pipes 1 5 (Figure 4).

The electromagnetic coagulator 34 described above is positioned in the lower section of the reactor 1; however, an electromagnetic coagulator 61 can be positioned outside the reactor 1. This electromagnetic coagulator 61 (Figure 5) consists of two U-shaped magnets 62, an insert 63 of a magnetically soft material, and a helical tube 64 of a dielectric material. An upper pipe 65 (Figure 5) of the electromagnetic coagulator 61 is connected with the line 53 (Figure 1) and through the unit 52, for measurement of pH of the medium, with the reactor 1. A lower pipe 66 (Figure 6) of the electromagnetic coagulator 61 is connected with the reactor 1 through a recycling pump 54 (Figure 1) and control valve 55.

The electromagnetic coagulator for recovery of metals from solutions is provided with a system 68 (Figure 1) for replacement of the anolyte. This system 68 comprises valves 69 and 70, a drain valve 71, and a pump 72 providing a controlled reduced pressure in the anodic zone 6 of the reactor 1. Between the reactor 1 and the unit 52 for measuring pH of the medium there is mounted a water pressure gauge 73.

The part of the line 53 between the recycling pump 54 and the electromagnetic coagulator 61 is connected with inlet valves 74, 75 and an outlet valve 76 which, in turn, is connected with a settling tank 77. The settling tank 77 is connected, through a pump 78, with the valve 75 and has in its bottom a valve 79 for draining the suspension into a vessel 80.

The apparatus has an inlet pipe 81 for admission of the liquor into the system and pipes 82, 83 which are connected with the pipes 1 5 (Figure 2) and 29 via gas manifolds (not shown).

The apparatus for selective recovery of metals from leaching liquors operates in the following manner.

Through the pipe 81 and open valve 74 (the valves 75 and 76 being closed) the liquor is admitted into the line 53 and fills the recycling pump 54. Through the control valve 55 it is fed into the reactor 1 and simultaneously it is fed, via the line 53, into the electromagnetic coagulator 61 and the unit 52 for measuring pH of the medium. When the predetermined mark on the pressure gauge 73 is reached, the valve 74 is closed.

By means of the system 68 for replacement of the anolyte the anodic space 6 of the reactor 1 is filled with the liquor. To this end, the valves 69 and 70 are opened and the liquor is fed into the anodic zone 6 of the reactor 1. The excess of the anolyte from the anodic zone 6 of the reactor 1 is removed by means of the pump 72 creating a certain reduced pressure in the anodic zone 6 of the reactor 1.

Thereafter the recycling pump 54 is switched on and by means of the control valve 55 the rate of circulation of the liquor in the reactor 1, the line 53, the pH measuring unit 52, and the electromagnetic coagulator 61 is adjusted.

When recorders (not shown) with their sensing members located in the unit 52 for the measurement of pH of the medium start to indicate the stationary values corresponding to the initial characteristics of the circulating liquor, voltage from a controlled DC source (not shown) is applied to the anodic adaptor lead 59 to establish electrical tension between the cathode 2 and the anode 3 of the reactor lithe values of voltage, current, and temperature in the reactor 1 are recorded by means of control instruments.

Under the stationary operation conditions of the apparatus the relationship of pH in the reactor vs.

time has a S-shaped curve with three different regions: initial, main working, and final.

The final region of pH vs. time relationship corresponds to the speed of pH variation in the reactor far from the pH of the metal hydrate formation. If the leaching liquor is used as the anolyte, or a solution of sulphates or a solution of sodium sulphate, the following processes take place: In the cathodic zone 7: In the anodic zone 6: 2H20 + 2e e H2t + 20H- 2H20 e 02t + 4H+ + 4e 2 2 + H20 + 28 o 20H- If as the anolyte use is made of a solution of chlorides or a solution of sylvinite, the following processes occur: In the cathodic zone:In the anodic zone: 2H2O + 28 -, H,t + 20H- 2CI- o Cl2t + 2e Cl2 + H20 = HCl + HOCI When in the cathodic zone of the reactor 1 the pH value of hydrate formation of a metal is reached, the speed of variation of pH is decreased and a flat region is observed on the curve of the relationship of pH vs. time; this flat region corresponds to binding of hydroxyi ions with metal ions with the formation of hardly soluble hydroxide forming a suspension, owing to the circulation of the liquor.

Therefore, the apparatus works as a generator of hydroxyl ions in the reactor 1, while hydroxyl ions are combined with the metal ions with the formation of a hardly soluble hydroxide.

The suspension particles circulating in the liquor become charged owing to the friction between the particles and the solvent molecules, in particular water molecules, and acquire the sliding charge.

For this reason, upon increasing concentration of the suspension in the liquor the whole of the suspension particles, solvent molecules as well as solute substances acquire the sliding potential and their own magnetic moment characterising this combination as a certain material medium moving relative to the external electric and magnetic fields. The fields originated in this material medium under the effect of circulation are combined with the external fields and form a certain effective field influencing the movement of the medium per se and the processes occurring on the cathode. Such effective fields are most significant in the leaching liquors owing to the content, in these liquors, of iron, suspended silica, and humic acid in considerable amounts. The intensity of such fields is increased with increasing concentration of the substances in the leaching liquor.

Upon circulation of the charged medium relative to the electromagnetic and magnetic fields the density of the medium at the walls on the interphase faces increases, and decreases with increasing distance therefrom. Therefore, in the electromagnetic coagulator 34 and 61 there occurs an intensive formation of the solid phase, which becomes more dense by the interphase faces, thus facilitating the course of the electrochemical processes on the cathode 2.

After the moment when the flat region of the S-shaped curves of the pH-vs.- time relationship is passed, the process in the reactor 1 is discontinued by switching off the voltage applied to the anode 3 and the recycling pump is switched off along with the system 68 for replacement of the anolyte. Then, with the valves 74 and 75 closed, the valve 76 is opened and the suspension from the reactor 1, the line 53, the recycling pump 54, the unit 52 for measuring pH of the medium, and the electromagnetic coagulator 61 is drained into the settling tank 77, whereafter the valve 76 is closed. By means of the pipe 81 and the valve 74 the apparatus is filled with water and rinsed. The washing water from the apparatus are drained through the valve 74 and pipe 81 into a receiving vessel (not shown), wherefrom water is periodically taken for the preparation of a solution of acid for leaching. The settled suspension is drained through the valve 79 into the vessel 80 and the clarified solution from the settling tank 77 is pumped by means of the pump 78 through the open valve 75 into the reactor 1, the line 53, the electromagnetic coagulator 61, and the unit 52 for measuring pH of the medium. Thereafter, the recovery of another metal from the liquor is started using the above-described procedure.

To attain the effect of the highest selectivity at minimal rates of consumption of the anolyte and minimal power consumption, the following operations are performed.

By means of the recycling pump 54, the control valve 75, and the pressure gauge 73 a certain rate of circulation of the liquor in the apparatus is set. Using the unit 52 for measurement of pH of the medium the speed of pH variation in the medium is recorded vs. time over the initial region of the pHtime curve at a certain arbitrary voltage applied to the anode 3. Then, using the anolyte replacement system 68 and the pump 72, in the anodic zone 6 of the reactor 1 such a reduced pressure is created that under the effect of higher pressure in the cathodic zone 5 of the reactor 1 the catholyte would be pushed through pores of the membrane 4 from the cathodic zone 5 into the anodic zone 6 of the reactor 1 at such a rate that no voltage increase on the anode 3 would be observed.Varying the voltage applied to the anode 3, the value of current through the reactor 1 is determined at which the rate of temperature variation in the reactor 1 is minimal. Thereafter, by means of the anolyte replacement system 68 the anolyte supply rate is adjusted so as to ensure the maximum rate of pH variation in the cathodic zone of the reactor 1.

EXAMPLE 1 A leaching liquor containing 0.832 kg/m3 of iron, 0.096 kg/m3 of copper, 0.3 kg/m3 of aluminium, and 0.676 kg/m3 of zinc, with an initial pH of 2.65 and an initial electrical conductivity of 0.51 7 Ohm/m, was treated in the apparatus. In the apparatus selective recovery of the metals as hydroxides was effected. As the anolyte use was made of the same leaching liquor. It was found that for comprehensive recovery of iron, aluminium, copper, and zinc with pH variation in the apparatus from 2.65 to 8, it was necessary to consume 138.2 kW. h of electric power per m3 of processed liquor.

EXAMPLE 2 A leaching liquor containing 0.73 kg/m3 of iron, 0.082 kg/m3 of copper, 0.35 kg/m3 of aluminium, and 0.52 kg/m3 of zinc with an initial pH of 3.05 and an initial electrical conductivity of 0.51 Ohm/m, was treated in the apparatus. Selective recovery of metals in the form of hydroxides was effected. The anolyte was a 20% solution of sodium chloride and potassium chloride in a ratio therebetween of 1:1.

For recovery of all metals as hydroxides at a pH within the range of from 3.05 to 8 the power consumption was 12.4 kW. h/m3. There were also obtained as by-products: 3kg/m3 of chlorine, 0.08 kg/m3 of hydrogen, 0.07 m3/m3 of commercial hypochlorite solution, and 0.85 m3/m3 of water containing 5.2 kg/m2 of soluble sulphates. The rate of consumption of the anolyte was 0.7 m3/m3; no consumption of the anode material was detected.

EXAMPLE 3 A leaching liquor containing 0.832 kg/m3 of iron, 0.096 kg/m3 of copper, 0.3 kg/m3 of aluminium, and 0.676 kg/m3 of zinc, with an initial electrical conductivity of 0.51 7 Ohm/m and an initial pH of 2.65, was treated in the apparatus. The anolyte was a solution of sodium sulphate with the concentration of 300 kg/m3. It was found that for recovery of all the metals as hydroxides at a pH within the range of from 2.8 to 8 it was necessary to consume 30 kW.h/m3 and the rate of anolyte consumption was 0.5 m3/m3.

EXAMPLE4 A leaching liquor containing 0.73 kg/m3 of iron, 0.082 kg/m3 of copper, 0.3 kg/m3 of aluminium, and 0.52 kg/m3 of zinc, with an initial electrical conductivity of 0.517 Ohm/m and an initial pH of 3.05, was treated in the apparatus and selective recovery of all the metals was effected at a pH within the range of from 3.05 to 8; the rate of electric power consumption was 18.5 kW . h/m3, and 0.1 5 m3/m3 of the anolyte (a 30% solution of sodium sulphate) was consumed.These fractions were obtained as dry solids having the following composition: 1 2 3 Recovery pH range 3.05-4 4-5.6 5.6-8 Iron, wt.% 42 2.8 4.4 Copper, wt.% 0.14 3.0 0.34 Zinc, wt.% 0.008 4.2 53.8 Electric power consumption for 4,200 7,300 3,600 recovery of dry solids, kW. h/t The by-products were: hydrogen, oxygen, 0.85 m3im3 of pure water, and 0.15 m3im3 of commercial sulphuric acid. The anode material wear was equal to 0.15 t per tonne of dry solids.

EXAMPLE 5 A leaching liquor containing 0.81 kg/m3 of iron, 0.29 kg/m3 of copper, 0.3 kg/m3 of aluminium, and 0.73 kg/m3 of zinc, with an initial pH of 3.0, was treated in the apparatus and selective recovery of all the metals as hydroxides was effected at a pH within the range of from 3 to 8; the rate of electric power consumption was 39.1 kW/h/m3: the rate of consumption of anolyte (a 30% solution of sodium sulphate) was 0.15 mum3. Three fractions were obtained as dry solids having the following composition: 1 2 3 Recovery pH range 3-3.8 3.8-5.8 5.8-8 Iron, wt.% 40 8.7 3.6 Copper, wt.% 0.04 9.3 1.4 Zinc, wt.% 0.75 2.9 45.4 Electric power consumption for 8,100 7,900 4,600 recovery of dry solids, kW.hlt The by-products were: hydrogen, oxygen, 0.15 m3/m3 of commercial sulphuric acid, and 0.85 m3/m3 of pure water. The rate of anode material consumption was 0.1 5 t/t of dry solids.

EXAMPLE 6 A leaching liquor containing 0.02 kg/m3 of copper and 7.7 kg/m3 of zinc with an initial pH of 5 was treated in the apparatus; recovery of one fraction was effected with the use of a 20% solution of sodium chloride and potassium chloride in the ratio of 1:1 as the anolyte, in a pH interval of from 5 to 8.

The resulting precipitate was dried and found to have the composition: 0.16% of copper and 64% of zinc. For the recovery there were consumed 4,100 kW. h/t dry solids and 0.07 m3im3 of the anolyte; the by-products were: hydrogen, chlorine, a solution of commercial hypochlorite, and pure water.

Claims

1. A process for selective recovery of a metal from leaching liquor, comprising passing a catholyte consisting of the liquor through a cathodic zone, passing an anolyte through an anodic zone, and simultaneously applying a constant dielectric field to the said zones, the pH of the catholyte in the cathodic zone being increased within the range of 1 to 14 by application of external electric and magnetic fields and selection of appropriate rates of supply of the anolyte and catholyte and a resultant rate of pH variation such that in the cathodic zone conditions are created for selective recovery of an oxide or hydroxide of the metal at a corresponding pH of deposition within the said range.

2. A process as claimed in claim 1, in which the anolyte consists of leaching liquor.

3. A process as claimed in claim 1, in which the anolyte consists of an aqueous solution of at least one chloride.

4. A process as claimed in claim 3, in which the anolyte consists of a solution of sylvinite.

5. A process as claimed in claim 1, in which the anolyte consists of an aqueous solution of at least one sulphate.

6. A process as claimed in claim 5, in which the anolyte consists of a solution of sodium sulphate.

7. A process as claimed in any preceding claim, in which the catholyte is subjected to the effect of an electromagnetic field.

8. A process as claimed in any preceding claim, in which the liquor contains gold and the cathodic zone is filled with activated carbon.

9. Apparatus for selective recovery of a metal from leaching liquor, comprising a reactor having separate outlets and inlets for a catholyte consisting of the liquor and an anolyte; a cathode and an anode coaxially positioned inside the reactor; a cylindrical manifold for the collection of gases located in the upper section of the reactor and having electrically insulated from each other an upper chamber and a lower chamber; a membrane coaxially secured in the lower chamber between the cathode and the anode and partitioning the working space of the reactor into a cathodic zone and an anodic zone; an electromagnetic coagulator, intended for acceleration of the formation of a solid phase, connected in series with a catholyte recycling pump and the reactor; and a unit for measuring pH of the catholyte.

10. Apparatus as claimed in claim 9, in which the reactor communicates, by way of valve means, with a settling tank and a pump for pumping the catholyte from the settling tank back into the reactor.

11. Apparatus as claimed in claim 9 or 10, wherein openings are provided at the centre of the upper and lower chambers of the manifold, for coaxially securing the membrane.

12. Apparatus as claimed in claim 11, in which the membrane is fixed by means of a sealing gasket, impermeable to the leaching liquor and to gases formed in the reactor in the opening of the lower chamber of the manifold.

1 3. Apparatus as claimed in any of claims 9 to 12, in which the cathode is secured to the lower chamber of the manifold, having a pipe or pipes for the removal of gases from the cathodic zone of the reactor, and the anode is fixed to the upper chamber of the manifold, having a pipe or pipes for removing gases from the anodic zone of the reactor.

14. Apparatus as claimed in any of claims 9 to 13, in which the anode is fixed to the upper chamber of the manifold by means of a sealing gasket.

1 5. Apparatus as claimed in any of claims 9 to 14, in which a said electromagnetic coagulator is fixed directly to the lower section of the reactor.

1 6. Apparatus as claimed in any of claims 9 to 15, in which a said electromagnetic coagulator is connected between the catholyte outlet and the catholyte inlet of the reactor.

1 7. Apparatus as claimed in any of claims 9 to 16, in which the cathode is connected to a part of the reactor made of the same material as the cathode.

18. Apparatus as claimed in any of claims 9 to 17, in which the cathode is perforated.

1 9. Apparatus as claimed in any of claims 9 to 18, in which the anode is provided with a vibrator.

20. Apparatus as claimed in any of claims 9 to 19, in which the electromagnetic coagulator comprises a helical tube of a dielectric material positioned in the field of a magnetic field source.

21. Apparatus as claimed in any of claims 9 to 19, in which the electromagnetic coagulator comprises a box made of a dielectric material filled with a packing of a magnetic material and positioned in the field of a magnetic field source.

22. Apparatus for selective recovery of a metal from leaching liquor, substantially as described with reference to, and as illustrated in, the accompanying drawings.