EP0255451B1 - Process for shutting down and restarting an electrolytic refining plant - Google Patents

Abstract

The present invention concerns a process for stopping for a prolonged period and restarting a series of tanks for the electrolytic refining of copper. The process comprises preparing for the stoppage by reducing the proportion of Cu2+ ions in the electrolyte, controlling the additive agents, regulating the level of the electrolyte, and slow crystallization of CuSO4 in the form of very fine crystals. Subsequent restarting comprises restoration of the circulation of the electrolyte with progressive heating, a progressive increase in the electrolysis current strength, and resumption of the addition of additives. Use of the invention makes it possible to obtain deposits of refined copper of commercial quality as from the first electrolysis cycle.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a process for prolonged shutdown and subsequent restarting of copper electrolytic refining tanks, which process makes it possible to obtain commercial grade metal from the first cycle after restarting.

STATE OF THE ART

Most of the copper intended for the electrical and electronic industries is subjected to refining intended to bring its purity to a level at least equal to 99.90% (so-called HC quality: high conductivity). This purification, which makes it possible to eliminate the usual impurities such as: Ag, As, Au, Pb, Ni, Co, Sn, Se, Te, Zn, Bi, Fe, is carried out by electrolysis with soluble anode, in an electrolyte with base of copper sulphate and sulfuric acid, maintained at around 60 _° C, by auxiliary heating, at a current density of the order of 300 A / m2. Certain impurities pass into the sludge (Ag, Au, Pb, Sn, Se, Te, etc.), others, such as Ni, As, Co remain dissolved in the electrolyte, only the copper depositing at the cathode, at a purity which can reach 99.95%. The quality of the cathodic deposit is appreciably improved by a continuous supply in the electrolyte, of organic substances, and in particular of gelatin and thiourea, as well as chlorine, (introduced in the form of HCl).

The raw copper to be refined is introduced into the tanks in the form of anode plates several centimeters thick, the life of which can be, for example, of the order of about twenty days.

Refined copper is deposited on thin cathode sheets called "starting sheets" in the form of a massive, compact deposit, the thickness of which gradually increases. When the anode is at the middle of its lifetime (eg 10 days), the cathodes are harvested for the first time, and the starting cathode sheets are renewed. Used anodes are recycled in the foundry.

The cathode primers, or starting sheets, are obtained in special electrolysis sections (so-called "stripper" sections) in which the cathodes are laminated copper plates (mother plates) on both sides of which a thin deposit is caused. copper (0.8 mm).

After around twenty hours in the tank, this deposit is torn off (stripping) and thin sheets are obtained which are planed and stapled for their suspension in the tank.

The electrolyte is kept in circulation in the tanks. The liquors arrive at the head of the tank and at the bottom, the exit at the bottom of the tank and at the top. Maintaining the temperature is ensured by steam reheating because the Joule effect, due to the low electrolysis voltage (approx. 0.3 volts), is insufficient to maintain the bath at the optimum temperature, l '' from 50 to 60 _° C.

In addition, a number of so-called "de-cuving" tanks are provided.

Indeed, as the electrolysis continues, the electrolyte is enriched in soluble impurities (Ni and As) and is concentrated in copper sulfate. Proper electrolysis involves maintaining the copper content of the bath at a given level (40-45 g / I of Cu) and keeping the concentrations of impurities below a certain limit (10 g / I of As and Ni). We are therefore permanently led to purify the electrolyte, and to adjust its Cu content.

For this, a certain proportion is taken daily, for example 2 / 100th of the total volume, from which a purification is carried out by sequence.

In a first series of tanks, the copper is extracted by electrolysis in an insoluble anode (lead anode with 6% antimony). It is de-coppering. Cathodes are obtained, of non-commercial quality, which are recycled in the foundry to obtain anode plates.

In other tanks, the arsenic, then nickel, is removed.

An electrolytic copper refining plant operates continuously. However, it can be subject to shutdowns, of more or less long duration, either scheduled or accidental: Breakage of the electrical supply lines, breakdown of a rectifier, or other technical or human failure.

It is well known that, after a prolonged, total shutdown, the restarting of an electrolytic refining installation poses serious problems and that, whatever the precautions taken, the production corresponding to the first "cathode cycle" is of a quality poor and must necessarily be recycled in the foundry, which results in a significant loss for the operator.

OBJECT OF THE INVENTION

The subject of the present invention is precisely a process for prolonged shutdown and subsequent restarting of the electrolytic cells, making it possible to obtain refined copper of commercial quality from the first cathode cycle, and this in complete safety for the personnel. and for equipment.

The method is more precisely defined in the claims.

The method is more precisely defined in the claims. This process is characterized by the following steps.

A - SHUTDOWN

• 1. If shutdown has been programmed, it is preferable, in the days preceding, to carry out a slight reduction in the copper content of the electrolyte. The normal content being, for example, 45 g of Cu ²⁺ per liter, it is lowered to approximately 40 g / I (either by dilution, or by passage through a few tanks operating with an anode insoluble in lead with antimony for example ), the copper thus extracted being deposited on cathodes where it can be recovered, and the H ₂ S0 ₄ content is adjusted to approximately 180 grams per liter. On the other hand, the additions of additives (gelatin, thiourea, chlorine) are maintained at the normal level until stopping.
• 2. The electrolysis current, the heating and the electrolyte circulation are stopped at the same time.
• 3. The tanks are partially siphoned so that the level of electrolyte in each tank is slightly below the upper edge of the cathodes. The cathode bars, which support and connect all the cathodes of a tank are then washed with water and all the tanks are covered with a plastic Nylon (R) film playing the role of thermal insulator. The electrolyte is then allowed to crystallize in the tanks. In this way, crystallization takes place in the form of a slurry of very fine CuS0 ₄ crystals which do not cause any damage and will quickly go back into solution when restarted.
• 4. The flying de-cuving tanks are removed from the circuit so that there are none in service at the time of restart.
• 5. The circulation pumps are flushed with water.
• 6. The starting cathode sheet forming tanks (called "stripping tanks") are stopped, with copper deposit on the mother plates. The mother plates with their deposit (not stripped) are washed with hot water and stored without electrolyte for the duration of the shutdown.
• 7. During the entire shutdown period, care is taken to ensure that the anodes are well immersed in the electrolyte and all tanks where this would not have been the case are excluded from starting by short-circuiting. . These provisions allow a shutdown of approximately one month to six weeks without any risk for all of the installations.

B-RESTART

• 1. La remise en route des circulations de l'électrolyte, qui s'étale sur environ 24 heures, sans chauffage, et permet de "casser la cristallisation".
• 2. La remise en route du réchauffage de l'électrolyte, qui permet d'atteindre 50_°C environ en 48 heures.
• 3. La mise à niveau des compositions visées pour l'électrolyte, par vérification analytique et apport des éventuelles corrections.
• 4. La remise sous tension électrique, avec montée progressive en intensité de façon à atteindre l'intensité nominale en 48 heures environ. Différentes dispositions techniques accompagnent ces quatre phases successives du démarrage :
  • - les apports de thiourée + chlore sont repris au taux normal en même temps que la remise en route du réchauffage.
  • - les apports de gélatine sont repris à taux normal en même temps que la remise du courant électrique.
  • - les sections où les anodes n'ont pas baigné en permanence dans l'électrolyte sont exclues du démarrage. Elles sont réintroduites progressivement après que soit atteint le régime d'équilibre.
  • - Préalablement à la remise du courant électrique, tous les contacts électriques sont refaits par lavage à l'eau chaude.
  • - Le mise sous tension électrique ne s'effectue que lorsque les deux conditions suivantes sont simultanément réalisées :
  • - électrolyte parfaitement homogénéisé en composition,
  • - électrolyte à 45_° Celsius. L'intensité initiale est fixée à moins de 10% et par exemple de 5 à 6% du nominal, soit 500 ampères si l'intensité normale est de 9 à 10 KA.
  • - La remontée en intensité est linéaire par paliers de 500A, quelques heures séparant chaque changement de palier.
  • - Les cuves de décuivrage peuvent être réintroduites dans le circuit, si nécessaire dès que la tension des redresseurs le permet.
  • - Les plaques mères sont dépouillées de leur dépôt et remises en exploitation dès que les équilibres électrolytiques et électriques sont atteints.
  • - Pendant toute la période de remontée en intensité, des contrôles visuels systématiques des dépôts sont effectués. Il peut être procédé, si nécessaire, au lavage de certaines cathodes,qui présentent des dépôts blanchâtres.

The restart is spread over time and lasts between 4 and 6 days. The successive phases are in order:

• 1. Restarting the circulation of the electrolyte, which is spread over approximately 24 hours, without heating, and makes it possible to "break the crystallization".
• 2. Restarting the reheating of the electrolyte, which makes it possible to reach approximately 50 _° C in 48 hours.
• 3. Upgrading the targeted compositions for the electrolyte, by analytical verification and making any corrections.
• 4. Restoring electrical power, with gradual increase in intensity so as to reach the nominal intensity in approximately 48 hours. Different technical provisions accompany these four successive phases of start-up:
  • - the contributions of thiourea + chlorine are taken back at the normal rate at the same time as the restarting of the reheating.
  • - the intakes of gelatin are resumed at the normal rate at the same time as the return of the electric current.
  • - the sections where the anodes have not been permanently immersed in the electrolyte are excluded from starting. They are gradually reintroduced after reaching the equilibrium regime.
  • - Before the electrical power is restored, all the electrical contacts are replaced by washing with hot water.
  • - The electric power is only applied when the following two conditions are simultaneously met:
  • - electrolyte perfectly homogenized in composition,
  • - electrolyte at 45 _° Celsius. The initial intensity is set at less than 10% and for example from 5 to 6% of the nominal, or 500 amps if the normal intensity is from 9 to 10 KA.
  • - The rise in intensity is linear in stages of 500A, a few hours separating each change of stage.
  • - The de-curing tanks can be reintroduced into the circuit, if necessary as soon as the voltage of the rectifiers allows.
  • - The mother plates are stripped of their deposit and returned to operation as soon as the electrolytic and electrical balances are reached.
  • - Throughout the ramp-up period, systematic visual checks of deposits are carried out. It is possible, if necessary, to wash certain cathodes, which have whitish deposits.

We can thus from the 5th day, and at the latest, during the 6th day after starting, obtain cathodes of commercial quality which do not have to be recycled in foundry, as it was always the case according to the processes earlier.

This long shutdown and restart process can be simplified for short shutdowns not exceeding two weeks.

In such a case:

FOR STOPPING:

• - Les apports d'agents d'addition (thiourée + chlore + gélatine) sont maintenus à leur niveau normal jusqu'à l'arrêt électrique et repris au taux normal avec la remise en intensité.
• - Pendant la phase d'arrêt les apports de gélatine sont suspendus et les apports de thiourée + chlore sont maintenus sur base de 2/3 de la valeur normale.
• - Dès le début de l'arrêt les trains de cathodes sont remontés sur cale de façon que le niveau de l'électrolyte soit au-dessous des empreintes de poinçonnage de la cathode, c'est-à-dire des fixations des plaques cathodiques proprement dites sur les barres cathodiques horizontales qui les supportent et assurent l'alimentation en courant.
• - Les cuves de stripping (fabrication de plaques cathodiques de départ) sont arrêtées avec dépôt de cuivre sur les plaques mères. Les plaques mères avec leur dépôt (non dépouillées) sont lavées à l'eau chaude et stockées, hors électrolyte, pendant toute la durée de l'arrêt. Lors du redémarrage électrique les plaques mères sont dépouillées de leur dépôt et remises en exploitation.

An electrical shutdown is carried out and the electrolyte is maintained in circulation, in composition and in temperature.

• - Additions of additives (thiourea + chlorine + gelatin) are maintained at their normal level until the electrical shutdown and resumed at the normal rate with the resumption.
• - During the shutdown phase, the gelatin intake is suspended and the thiourea + chlorine intake is maintained on the basis of 2/3 of the normal value.
• - From the start of the shutdown, the cathode trains are reassembled on the block so that the level of the electrolyte is below the punching marks of the cathode, that is to say the fastenings of the cathode plates properly say on the horizontal cathode bars which support them and ensure the current supply.
• - The stripping tanks (manufacture of starting cathode plates) are stopped with copper deposition on the mother plates. The mother plates with their deposit (not stripped) are washed with hot water and stored, without electrolyte, for for the entire duration of the stop. During the electrical restart, the mother plates are stripped of their deposit and returned to operation.

ON RESTART:

• - The rise in intensity is linear in stages of 500 A, (for a nominal intensity of 9 to 10 K.A.), a few hours separating each change of stage. The de-cuving tanks are neutralized during the ramp-up period.

Throughout the ramp-up period, systematic visual checks of deposits are carried out. It is possible, if necessary, to wash certain cathodes, which have a whitish deposit.

The implementation of the process also ensures the production of commercial quality cathodes from the first cathode cycle, when the duration of the shutdown is limited to only a few days.

Claims (4)

1. A process for the prolonged stoppage and restarting of an installation for the electrolytic refining of copper comprising soluble anodes of copper to be refined, cathodic plates on which the purified copper is deposited, an aqueous electrolyte based on copper sulphate and sulphuric acid, and additive agents, which is maintained at a temperature of 50 to 60°C by means of auxiliary heating, and continuously circulated, the installation further comprising tanks for the formation of cathodic starting sheets from mother plates, said process being characterised by the succession of the following steps: a) for stopping:

- the proportion of copper in the electrolyte is progressively reduced to 40 grams per litre, while maintaining the additions of additive agents which are gelatine, thiourea and chlorine. The composition of the electrolyte is to be regulated so that in addition the H₂S0₄ content is of the order of 180 g/l,

- the electrolysis current, heating and circulation of the electrolyte are simultaneously interrupted,

- the level of the electrolyte is lowered to a little below the top edge of the cathodic plates, and

- the tanks are covered with a thermal insulating lining and the electrolyte is left to crystallize in the tanks by the formation of fine crystals of Cu-S04; b) for restarting:

- the circulation of the electrolyte is restored for 24 hours,

- heating of the electrolyte is restored to attain a temperature of 50°C in 48 hours while resuming the additions of thiourea and chlorine at the normal rate,

- the composition and the homogeneity of the electrolyte bath are checked and corrections are made if necessary;

- the additions of additive agents which are thiourea, chlorine and gelatine are maintained at their normal level until the electrical stoppage occurs and are resumed at the normal rate when restarting is effected,

- during the stoppage phase, the additions of gelatine are suspended and the additions of thiourea + chlorine are maintained on the basis of two thirds of the normal value,

- as from the beginning of the stoppage, the trains of cathodes are raised on supports so that the level of the electrolyte is below the punching impressions of the cathode,

- the tanks for the formation of cathodic sheets are stopped with the deposit of copper; the cathodic sheets are washed with hot water and stored out of electrolyte throughout the entire duration of the stoppage, and

- on restarting, the increase in current strength is linear in steps of 500 A (for a nominal strength of 9 to 10 KA), a few hours separating each change in level, so as to attain the nominal strength.

- the electrolysis current is restored at an initial strength which is lower than 10% of the nominal strength and at the same time the additions of gelatine are resumed,

- the strength of the electrolysis current is progressively increased with a linear increase in strength in steps of 500A, a few hours separating each change of step, so as to attain the nominal strength in about 48 hours. The sections in which the anodes have not bathed permanently in the electrolyte are excluded from the restarting operation and are progressively re-introduced after the steady operating state has been reached.

2. A process according to claim 1 characterised in that, for a prolonged stoppage, the tanks for the formation of cathodic starting sheets (mother plates) are stopped, with the deposit of copper on the mother sheets which are washed with hot water and stored out of the electrolyte throughout the entire duration of the stoppage.

3. A process according to claim 1 characterised in that for restarting the electrolysis current is restored at an initial strength which is between 5 and 6% of the nominal strength.

4. A process for the stoppage and restarting of an installation for the electrolytic refining of copper comprising suluble anodes of copper to be refined, cathodic plates on which the purified copper is deposited, an aqueous electrolyte based on copper sulphate and sulphuric acid, and additive agents, which is maintained at a temperature of 50 to 60_°C by means of auxiliary heating, and continuously circulated, the installation further comprising tanks for the formation of cathodic starting sheets from mother plates, said process being characterised in that, for a stoppage which does not exceed two weeks, the electrical feed is stopped and the electrolyte is kept circulating and is maintained in regard to composition and temperature.