FI63444B - PROCEDURE FOR CHARACTERIZATION OF A CRYSTALLINE PRODUCT FROM A PARTICULAR FORM OF A CRYSTALLINE PRODUCT AND AN ELECTRICAL SYSTEM - Google Patents

Description

ESF * 1 M (11) MONTHLY PUBLICATION £ .34 4 4

I l ° J v 'UTLÄGGNINOSSKIUFT

C Patent granted on June 10, 1933

Patent ceddclat ^ T ^ (St) K ».ik.3 / fc« t.a.3 C 25 C 5/02 SUOMI-FINLAND (21) Pfottlhilcmu · - Ρμμκμι8ΙμιΙβ | 771107 • (22) Hihuiltpklvl —-Am6ta> lnpd «f 06.0H.77 '^ (Ö) Alkupihrt — GJUftwadag 06. OH. 77 (41) The public kiwifruit off «Mli (07.10.78

National Board of Patents and Registration (44) Date of publication and issue. - oft 02

Patent and Register AmMun utiifd odi utUkrtfun publkvnd ^ ou ^ .oj (32) (33) (31) Pnr4 * «y xuoikuui - iugtH prtorlt ·» (71) Duval Corporation, 700 Milam Street, Pennzoll Place, Houston, Texas 77002, USA (72) Melvin S. Cook, Tucson, Arizona, George E. Atwood, Tucson, Arizona, USA (7Π) Qy Kolster Ab (5Π) Method and apparatus for recovering a particulate crystalline product from an electrolysis system - For example and for the supply of particulate crystalline products to an electrolytic system

The invention relates generally to a crystallization process and, more particularly, to a method and apparatus for continuously recovering a crystalline product from an electrolysis system capable of producing a particulate product, wherein continuous recovery and removal of the product from production units is achieved without substantial contamination.

This invention relates to a method for continuously recovering a particulate crystalline product, such as copper, from an electrolysis system comprising cathode surfaces, anode surfaces and an electrolyte in a container, wherein the product has limited adhesion to the cathode surfaces, separating the product from the cathode surfaces and removing it from the electrolytic cell container. precipitating the dendritic crystalline product on the cathode surfaces, adjusting the size and density of the crystalline product and the structure of the dendrites and limiting crystal overgrowth on the cathode surfaces with a mechanical electrolyte fluid agitator at the bottom, continuously removing the particulate crystalline product from the electrolytic cell tank by means of a belt-conveyor system and ethane particulate crystalline product prior to its removal from the electrolytic cell tank through the wash zone to displace the electrolyte liquid from the particulate crystalline product.

The invention further relates to an apparatus for use in the above method for recovering a particulate crystalline product from an electrolysis system comprising cathode surfaces, anode surfaces and an electrolyte in a reservoir, the article having limited adhesion to cathode surfaces, characterized in that it comprises a flexible arm on each cathode. , the arms being fixed to a horizontal axis about which they oscillate and fixed to the electrolytic cell tank, an inclined channel extending upwards from the bottom of the electrolytic cell tank at an angle of not more than 45 ° to at least the height of the cathodes and anodes, and a belt conveyor system through to remove the particulate crystalline product from the electrolysis system.

The present invention provides an advantageous way to overcome the limitations of conventional electroplating methods, including: (1) the required product "starting plates", including their manufacture and processing for installation to begin production, followed by removal to recover the product, and (2) required process control to achieve production electroplating; which is flat, tightly crystalline, and strongly adhesive, while lacking cavities and electrolyte inclusions. This latter requirement imposes a severe limitation on the production current density, even by means of excipients which are colloquially referred to as "electroplating excipients".

The use of this invention in an electrolysis system capable of producing a particulate, crystalline product is generally feasible with respect to transition metals and Group IB and IIB metals, as conventionally located in the Periodic Table of the Elements. Such use is most likely to be made for iron, cobalt, nickel, copper, silver, gold, palladium, zinc, platinum and cadmium.

k 3 63444 EN application 2753/72 (approved on 14 March 1980) discloses a hydrometallurgical process for the recovery of copper, in which copper-containing substances are chemically treated in a chloride system, in which the copper is finally recovered as an electrolyte pair. It shows that the electrolysis of a metal chloride precipitates on the metal cathode while the chloride ion is released at the anode. By introducing the metal chloride in the lower valence state for electrolysis (as copper chloride in the case of copper) by limiting the electrolytic precipitation at the cathode so that it does not exceed half of the lower valence metal chloride in the electrolyte feed Thus, electrolysis performed in a chloride system in this manner reduces the detrimental polarizing effect of the gas released at the anode that plagues the electrolysis, for example in a sulfate system. This significant avoidance of gas polarization and the associated highly detrimental effect on electrical efficiency allows the chloride system to operate at phenomenally high electric current densities. As a result of such action, the increasing current density has a corresponding increasing tendency to change the crystalline form of the cathode-deposited metal: from a smooth, densely crystalline form at lower current densities to rough surfaces, dendritic and finally loosely adhered "dendritic" groups. This forms an electrolysis system capable of producing a crystalline, particulate product with limited adhesion to the cathode surface and designed for use in this invention. The main advantage of such a high current density electrolysis system is the higher productivity per unit area of the cathode, with relatively significant economic advantages in terms of reduced capital requirements for the electrolysis equipment and the product stock retained by the process.

In the accompanying drawings, Fig. 1 is a vertical sectional view of a series of electrolyte cells along their longitudinal axes, Fig. 2 is a vertical sectional view of the electrolyte cell, and shows an anode 4 63444 and a porous septum outline.

Figure 3 is a vertical section of the electrolyte cell and shows the appearance of the cathode and mixer.

Figure 4 is a vertical section of the electrolyte cell showing the relative position of the cathode, anode, agitator and septum components.

A series of electrode cells are used in the electrolysis of the copper chloride solution to recover metallic copper, as shown in Figure 1. The cells are located in a rectangular container 1 and are supported by an electrically non-conductive and corrosion-resistant inner conductor. Each cell comprises an inert anode 2, a porous partition 3 surrounding the anode and a cathode 4.

The metal-containing electrolyte feed solution 5, consisting mainly of copper chloride and a small amount of copper chloride in aqueous solution, is introduced into the catholyte 6. After the electrolyte (catholyte) has been recycled to the cathodes, it is discharged through the pipeline 12 and discharged into the anolyte compartment formed by the partition 3.

The anolyte solution in the anolyte compartment flows through the anolyte level control overflow 13 and the raffinate 14 (spent electrolyte) discharges from the electrolyte cells via line 15.

Electrolysis in the system, as described above, results in the transfer of copper ions to the cathode deposited on it as metallic copper and, at the same time, the transfer of chloride ions to the anode in the presence of an anolyte solution, thereby oxidizing the copper chloride to copper chloride.

The relative levels of catholyte and anolyte in their respective compartments are adjusted by overflow-type arrangements to maintain a positive hydraulic gradient from the catholyte compartment to the anolyte compartment. To prevent counterflow of anolyte into the catholyte compartment, the anolyte overflow 13 is kept lower than the catholyte overflow 8. If the anolyte solution containing copper chloride were allowed to flow into the catholyte compartment, it would tend to redissolve the copper in the catholyte compartment.

In Figure 2, the anolyte flow in the anolyte compartment formed by the septum 3 is directed using spacers 16 to provide complete flow contact and mixing on the anode surface. The spacers are attached to and support the porous septum while forming flow channels for the anolyte solution.

5 63444

The current density of the electrolysis is adjusted to such a level that the copper deposited on the cathodes is loosely adhered to them in the form of crystalline copper. To ensure the removal of crystalline copper from the cathodes, as shown in Figure 1, flexible agitators 17 are mounted on each side of each cathode 4 to pass across the active surfaces at a constant distance therefrom. The agitators are attached to a shaft 18 which is made to oscillate by means of a motor 20 shown in Fig. 3. Each agitator arm comprises a fiberglass tube 19 to which a rubber rope 17 is connected. An additional fiberglass tube 21 can be hung on the end of the rubber rope if desired.

Crystalline copper 22 is assembled on a flexible conveyor belt 23 as it drips from cathodes. As shown in Figures 2 and 3, a conveyor belt 23 forms a concave trough extending over the entire width of the electro-cell tanks to collect all the copper dripped from the cathodes 4. The conveyor belt 23 is inserted and guided in the electrolyte cell tank by means of wheels 24.

At the bottom of the container 1, the conveyor belt 23 then passes upwards through an oblique rectangular channel or horn 25 which is approximately the width of the container. In the relative "insulating portion" of the inclined channel 25, a displacement-washing zone 27 is maintained at its upper end, in which liquids are set to be deposited according to their relative characteristics. The interface of the displacement solution with the acatholyte solution is given in point 28.

As the crystalline copper product passes through the washing zone, the catholyte solution adhering to it is forced to leave under the effect of displacement. Thus, the washed crystalline copper is then discharged into a funnel or other collecting device, not shown, as the conveyor belt 23 passes over the traction sheave 26. The conveyor belt is then guided by means of return rollers 29 to a wheel 30, from which the belt then returns to the opposite end of the container 1.

In contrast to the operation of conventional electrolyte cells, which typically operate at relatively low current densities to improve the galvanization of metallic copper at the cathodes, this embodiment of the present invention allows current densities between about 800 A / m2 to about 4000 A / m2 to be used. The purpose of the work at these higher current densities is to produce copper in a form normally avoided in the operation of conventional electrolyte cells, i.e. to form dendritic crystalline copper loosely adhered to the cathodes.

6 63444

By being able to operate at higher current densities, the number of electrolyte cells required to produce metallic copper is relatively smaller. In this case, the cost of capital for electrolyte cells is clearly significantly reduced. Although operating costs increase due to the higher voltage associated with the use of higher current densities, this is partially offset by reduced maintenance costs resulting from the use of fewer Jennas as well as the benefits of using permanent cathodes instead of replaceable cathodes.

It has been found that crystalline copper, which loosely adheres to cathodes, can be removed from them by stirring the catholyte. Flexible mixers are used on each side of the cathode plate to mix the catholyte. These mixers also ensure thorough mixing of the catholyte so that the copper content in it is essentially homogeneous. It has also been found that the intensity of the agitation thus obtained can have a beneficial effect and help to control the size and density as well as the structural suitability of the crystal growth at the cathode. The increasing intensity of the mixture tends to promote the formation of a structurally valid dendritic crystalline product.

In addition, the agitators provide a secure means of limiting the extent of crystal growth from the cathode surface, thus preventing intrusion into the porous septum and short-circuit between adjacent cathodes and anodes, since the agitators are designed to completely sweep over the entire electrically active surface between each pair.

Although no special construction is required, mixers should be flexible rather than rigid. Orientation problems that result in repeated cracking or tearing of porous partitions can be caused by the use of rigid mixers. In addition, mixers wear faster than flexible ones and are usually more expensive.

A preferred embodiment of the present invention requires that the agitator array comprises flexible vertical arms attached to a horizontal axis located above the electrolyte cells. Each agitator arm comprises a fiberglass tube to which a rubber rope is connected. It has been found advantageous to connect an additional piece of fiberglass tube, which can be provided with a weight, to the lower end of the rubber rope. Each flexible arm, which is set to ensure toimintavälyk, it extends sufficiently below the entire length of the cathode plate, so that the arm swinging motion to cover the second side of the cathode's active surface.

7 63444

It is to be understood that the function of the sd devices, as set forth herein, is primarily to generate flow energy into solution in conjunction with agitation and agitation in the immediate vicinity of the cathode surfaces, thereby releasing the loosely adhered particulate crystalline product. Another task is to precisely limit the overgrowth of crystals at the cathode. This is ensured by the impact applied to it by the stirrer, which is limited by the standard operating clearance. At the same time, direct abrasive contact of the mixer with the surface of the porous partition wall with a constant operating clearance therefrom is avoided.

To reduce the electrical resistance of the electrolysis system, the distance between the electrodes should be reduced. This fact affects the setting of the operating clearances of the mixer arms. In this regard, Figure 4 shows a series of state measurements between adjacent electrodes in practical operation.

The flexible arm mixers are made to oscillate at a frequency of about 8 to about 24 times per minute. In general, the velocity increases with higher current densities. Above 24 oscillations / minute, undesired oxidation of cuprous chloride to cupric chloride has been observed. Preferably, the oscillation is made to occur about 10-14 times per minute.

A conveyor located at the bottom of the electrolyte cell tank is used to collect crystalline copper that drips from the cathodes and transport it from the tank. The conveyor, which may be of any suitable construction, preferably comprises a resilient belt concavely curved to form a trough with its edges closed below the rubber edge on the longitudinal sides of the container and the center of the belt contacting and resting on a plastic reading device located on the container bottom centerline. This arrangement reduces the amount of crystalline copper that penetrates below the belt.

The conveyor according to the invention is designed so that maintenance can be performed without interrupting the electrolysis process. The submerged lazy wheels for the conveyor are mounted in a frame that protrudes from the electrolyte fluid and are thus easily replaceable.

The conveyor carrying the crystalline copper leaves the container along a suitably inclined channel which extends upwards from the bottom of the electrolyte cell container at an angle of at most about 45 °. The width of the inclined channel is dimensioned to allow the surface of the conveyor to change shape from a concave tray to collect the crystalline product within the container into a relatively wide flattened belt surface for transport through the washing zone to the top of the inclined channel.

In the copper chloride electrolysis system of this preferred embodiment, the catholyte adhered to the collected and transported 8,644,44 crystalline product comprises residual copper chloride in solution substantially saturated with one or more molten metal chlorides, such as sodium chloride, potassium chloride, potassium chloride. Displacement of the accompanying residual liquid can be achieved according to the invention by a liquid of lower specific gravity or by liquids which are "floated" in a layered order on the surface of the catholyte-electrolyte. The composition of these lower specific gravity fluids may advantageously be proportional to the replenishment needs to maintain the fluid balance of the overall process. For example, an aqueous liquid containing one or more saline metal chlorides which are useful for supplementing the aneta balance and necessary to avoid precipitation of cuprous chloride and whose specific gravity is set as the chloride content by their to displace the copper-containing electrolyte from the copper product exiting the electrolyte cell tank. Such a layer can be maintained intermittently or continuously by injecting with refill fluid at the edges needed to maintain the material balance of the process. This fluid supply results in positive hydraulic displacement as opposed to the tendency for mixing contamination associated with the solid product moving up the conveyor. In addition, and equally useful for the process equilibrium requirements of the process, a liquid layer of water can be "floated" and maintained on top of the saline metal chloride layer, resulting in a similar displacing washing effect and removal of the copper product substantially free of soluble contaminants. This unique approach to these pollutants with respect to the purity of the product is maintained in this manner as valuable as ingredients in the process fluid, together with the need for replenishment of the process fluid system to maintain the material balance, forms an important aspect of the teaching of this invention.

By repeating the main points, the invention makes it possible to achieve the following: a. A chemically suitable liquid or liquids having a lower specific gravity than a given electrolyte can be "floated" as a layer or layers on the surface of the electrolyte.

b. The particulate crystalline product is transported upward from and through the main body of the electrolyte "mother liquor" to a layer of lower specific gravity liquid.

9 63444 c. the gravitational movement of the entrained heavier electrolyte solution is directed downward relative to the movement of the lower specific gravity fluid, thereby displacing the electrolyte from the cracks and surfaces of the particulate crystalline product as it is transported upwardly through the top layer.

d. The interface between the layered liquid layers can remain virtually unchanged for longer periods of time by limiting the linear speed of the product transport system.

An important new concept of the present invention is the detection of the importance of the relationship between the rate of electrolyte settling in the washing liquid due to the gravity of the electrolyte fluid and the reaction of the rate of rise of the conveyor. This explains the unexpected positive, apical, displacement washing performance achieved in conjunction with acceptable and usable product transport capacity in accordance with the teachings of this invention.

e. Some mixing of the deposited liquids necessarily occurs, however, the time prior to this occurrence may be extended, as described herein, to provide practical operating cycles before unacceptable contamination of the washing liquid or liquids occurs, necessitating replacement.

f. When material balance over the entire process allows, a liquid or liquids of suitable composition and required specific gravity can be established for replenishment as components of a layered washing system into which suitable replenishments are injected intermittently or continuously to maintain process balance, thereby counteracting hydraulics. -contamination effort associated with an upward solid product. In this way, unwanted contamination of the liquid or binders can be delayed virtually indefinitely.

The conveying speed of the conveyor is preferably kept as low as possible in order to implement the displacement washing. For the preferred embodiment described herein, experimental development tests designed and performed to investigate the relationship between conveyor travel speed, product loading on the conveyor, and the performance of the displacement wash have shown fully valid limits within which acceptable performance results can be achieved.

10 63444

table 1

Dual interface displacement washing with cell conveyor

Test Product load Conveyor speed Relative percentage of residual catalyst No. kg / h cm / min of product x 1 266 10.2 1.73 2 7.6 1.68 3 "5.1 1.19 4" 2.5 0, 37 5 134 10.2 2.70 6 7.6 1.86 7 5 1.63 8 2.5 0.36 9 "0.22

Lower solution - saturated aqueous sodium chloride solution, vertical depth 45.7 cm,

Upper solution - pure water, vertical depth 50.2 cm,

Production - copper crystals.

x calculated on the basis of potassium by dividing the potassium concentration in the dried final product by the potassium concentration in the catholyte.

The tabulation of the numerical values shows that the displacement of the electrolyte from the solid product in the washing system is a function of the speed of the conveyor and is mainly independent of the product load. The numerical values were obtained during the operation of the experimental prototype cell transport mechanism with an inclination angle of the inclined wash channel of 25 ° from the horizontal.

The displacement phenomenon described in the previous test result applies to alternative systems in which the actual washing efficiency is affected by the prevailing viscosity, solid product, structure and surface structure, and solution concentration as parameters. In other words, for a given alternative system, the abnormal decrease in electrolyte transferred with the product involves a reduction in the speed of the conveyor below an experimentally established critical value.

Claims (18)

A process for the continuous recovery of a particulate crystalline product, e.g. copper from an electrolysis system comprising cathode surfaces, anode surfaces and an electrolyte in a container, the product having a limited adhesion to the cathode surfaces, in which process the product is separated from the cathode surfaces and removed from the electrolytic cell container, characterized in that precipitates the dendritic crystalline product, regulates the size and density of the crystalline product, and the structure of the dendrites, and restricts the excessive growth of crystals on the cathode surfaces by a mechanical mixing device for the electrolyte liquid, which mixing device operates at a definite distance from the cathode surfaces, the crystalline product, separated from the cathode surfaces, on a belt conveyor system located in the bottom portion of the electrolytic cell container, continuously removes the particulate crystalline product from the electrolytic cell container by means of the belt transport system and transports the particulate crystalline product n before it is removed from the electrolytic cell container through a wash zone to displace the electrolyte liquid from the particulate crystalline product. 2. A method according to claim 1, characterized in that at least one liquid of less specific weight than the specific weight of the electrolyte is brought into the wash zone as a layer on the surface of the electrolyte to effect the displacing washing effect. Method according to claim 2, characterized in that the liquid is used to maintain the material balance in the system, whereby the level of the layer is maintained by the system supplying liquid, and the washing in the washing zone is carried out by hydraulic displacement of the electrolyte. 4. A process according to claim 1 or 3, characterized in that several liquids having consecutively lower specific gravity than the electrolyte are brought as successive layers on the surface of the electrolyte. Method according to any of claims 1-4, characterized in that the washing zone is located in the upper part of a sloping chute extending from the bottom of the electrolytic cell container at an angle not exceeding 45 degrees in relation to the horizontal plane. 15 63444 6. A method according to claim 5, characterized in that the conveying system comprises a flexible conveyor belt which runs continuously through the electrolytic cell container near the bottom and through the sloping channel which extends therefrom, and through the washing zone, the belt forming a concave collecting and transport surface within the container. a flat transport surface in the sloping gutter. Process according to any of the preceding claims, characterized in that the speed of movement of the transport system is regulated so that the electrolyte liquid is effectively displaced from the product and that minimal physical mixing of the liquids in the washing zone is caused. Method according to claim 7, characterized in that the speed of the conveying system is below 5 cm / min. Method according to any of the preceding claims, characterized in that the current density of the electrolysis is 800-4000 A / m2. Method according to any of the preceding claims, characterized in that the electrolyte fluid is agitated with a flexible arm on both sides of each cathode, these arms oscillating over a path which sweeps over the entire electrically active surface of each cathode at a certain distance from this . 11. A method according to claim 10, characterized in that the flexible arm agitators are caused to oscillate at a frequency of 8-24 turns per minute. 12. A method according to claim 10 or 11, characterized in that the flexible arm agitators are caused to oscillate at a frequency of 10-14 turns per minute and the conveying system comprises a belt operated at a speed of 2.5 cm / min. Process according to any of the preceding claims, characterized in that the liquid supplied to the washing zone contains a metal chloride which prevents the precipitation of copper (I) chloride, and the density of the liquid is adjusted to a value which deviates from the density of the electrolyte in a desired manner. by concentration of the chloride contained in the liquid. Process according to Claim 13, characterized in that the metal chloride is selected from a group consisting of sodium chloride, potassium chloride, magnesium chloride, calcium chloride and mixtures thereof.