Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/16—Regeneration of process solutions
  • C25D21/22—Regeneration of process solutions by ion-exchange

Definitions

• the present invention relates to a process for treating an effluent from a process of electro-zinc plating with a soluble anode and in a chloride medium as well as a process of electro-zinc plating comprising application.
• the electrozincing is carried out continuously in lines successively implementing the operations of preparing the sheets (alkaline degreasing and acid brightening), of electrozincing proper and of finishes (passivating finishes or organic coatings and rinses).
• electro-zinc plating leads to a certain number of losses and discharges which it is necessary to treat in order to satisfy the requirements of the environment.
• Conventional methods for treating various pollutant flows use methods for destroying effluents by insolubilizing metals (neutralization) with, on the one hand, a large production of cakes of metal hydroxides which are difficult to recover, and on the other hand hand, a fatal contamination liquid discharges by high salt concentrations.
• the present invention aims in particular to provide a "clean" process for treating rejects adapted to the electrozincing process in chloride medium.
• cleaning process is meant a process which allows both: a - to minimize the various releases and losses, b - to continuously regenerate the maximum of releases with recovery of by-products (water, salts, metals) and more generally, to reduce operating costs while improving the consequences for the environment.
• the * present invention aims very particularly to provide an electrogalvanizing process in which there is practically no rejection of zinc.
• electrozinc electrolytes are adaptable to market demands and can, in addition to zinc alone, lead to codepositions of zinc with other metals (Fe, Ni ...), in order to improve the properties of 'appearance or anti-corrosion of the sheets.
• the electrolytes then contain concentrations of chlorides in these addition metals.
• a typical composition of electrolytic electrolysis in chloride medium is as follows:
• Electrolytes of the same type can also be used, which also contain nickel ions.
• the Zn content is maintained in the concentration range targeted by periodic purging of electrolyte and reconsti ⁇ tution of new electrolyte.
• the present invention aims to completely eliminate the consequences of these rejected surpluses by regenerating the electrolyte by selective extraction of the excess zinc and recovery of the latter.
• the present invention thus relates to a process for the treatment of an aqueous effluent derived from an electrozincing process with a soluble anode and in a chloride medium, characterized in that the effluent is subjected to extraction by a phase organic practically insoluble in water, containing an organic anion exchanger.
• It also relates to an electrozincing process with an anode soluble in an aqueous electrolyte containing chlorides, characterized in that an electrolyte current is drawn off, this current is subjected to an extraction with a practically insoluble organic phase in water containing an organic anion exchanger and the extracted current is recycled.
• the organic anion exchanger can be advantageously constituted by an amine salt, in particular a salt formed with hydrochloric acid.
• the organic amine can in particular be a tertiary amine of formula R 3 N in which R is in particular a C 1 to C 1 alkyl group ? , for example an isooctyle group.
• the salts of organic amines allow a selective extraction of zinc in the form of an anionic complex ZnCl. 2- which is present in the bath due to the high chloride concentration.
• the organic phase advantageously contains an organic diluent insoluble in water and of low density which facilitates the separation operations (which allows for example the separation by decantation of the aqueous phase).
• it advantageously contains an alcohol insoluble in water which contributes to the stability (non-demixing) of the organic phase.
• the amine is preferably used in a proportion by volume of 5 to 50 °., Preferably from 15 to 35%.
• the organic phase can have the following composition: amine (in the form of a salt) ... 30% by volume alcohol (isodecanol) 20% by volume diluent (kerosene) 50% by volume.
• the extraction can be generally performed at a temperature from 15 to 70 * C. prati ⁇ that is performed at a temperature close to that of 1'electrozingage.
• Zinc can be re-extracted from the organic phase with an aqueous phase.
• This phase can be a concentrated alkaline aqueous phase (preferably a concentrated KOH solution) leading to the obtaining of an alkaline zincate or water leading to the production of pure zinc chloride.
• ZnCl 4 " 4- 2R 3 NH + C1 ⁇ ⁇ ZnCl 4 , 2R 3 NH + 2C1 ⁇ > and the re-extraction reaction with water: ZnCl 4 , 2R 3 NH ⁇ 2R 3 NH + C1 " + ZnCl 2
• the organic phase is advantageously washed in order to remove the fine aqueous droplets possibly entrained by the organic phase and thus improve the purity of the zinc re-extracted in the next step.
• the number of stages and the ratio of the phases present are chosen as a function of the isothermal equilibrium curves.
• the isothermal equilibrium curves during extraction and during re-extraction with as organic phase that consisting of 30% by volume of triisoctylamine (hydrochloride), 20% by volume of isodecanol and 50% by volume of kerosene.
• this quantity of zinc is the product of the flow rate treated by the difference in concentrations between that of the electrolyte to be regenerated and that of the regenerated electrolyte (extraction raffinate).
• the flexibility thus lies in the fact that by playing at the same time on:
• This remark can advantageously be used to obtain from an electrolyte to be regenerated, a saline solution practically free of zinc ( ⁇ 100 mg / 1) usable in watering sheets or rolls before restoring to electrozincing cells.
• Electrolyte flow to re-regulated -near rrreerr (m3 / h) (100 g / 1 Zn) 0.5
• the excess water in the electrolyte can be removed by evaporation under vacuum. We then take advantage of the excess calories produced by the Joule effect in the electrozincing cell. For this purpose, it is possible to provide a closed loop at high flow where the evaporation under vacuum of the electrolyte takes place at the electrogalvanizing temperature. This evaporation has very little effect on the concentration of the electrolyte, given the low ratio between the water removed and the circulation rate (1 to 2). According to the general thermal balance a thermal reheating of the electrolyte can be carried out before evaporation. The condensation of water vapor leads, depending on the technology selected, by mixing or by surface, to recover a purge of deconcentration water or a condensate usable for rinsing of brightening.
• Excess water in the electrolyte can also be removed by other techniques such as reverse osmosis. It should be noted that in the conventional technique, there is also a loss of electrolyte by entrainment by the electro-galvanized strip at the outlet of the electrolysis cells.
• the quantity of electrolyte purged to keep the zinc concentration constant results from the difference in balance between the excess zinc formed in the electrolysis cell and the zinc eliminated by the entrainments. Reducing the latter necessarily means increasing the quantity to be purged. It is therefore only a transfer between two treatments of rejections. One could therefore wonder about the interest of reducing training.
• the rinsing of the strip can be ensured in the following manner, making it possible to recycle at a low cost from 40 to 90% of this reduced flow.
• a rinsing and brushing station is created after the last electrolysis cell supplied with a low flow of make-up water.
• the resulting diluted effluent which collects a high percentage of the entrained initial flow is returned to the electrolyte evaporation loop at the cost of a modest increase in its capacity, the equivalent of additional operating cost of evaporation being largely compensated by the subsequent savings made on the reduction of the effluent treatment station.
• the first brushing rinsing is supplied with an additional water of V 1 / h.
• the rinsing brushing is watered by a current flowing in a closed circuit to ensure the hydraulic asper ⁇ sion. Under these conditions, it is withdrawn V 1 / h of diluted rinse having the composition C g / 1 Zn.
• the electrolyte entrainment by the strip towards the demineralization loop of the subsequent rinses proposed in accordance with the invention is, in g / h Zn: 150 x C.
• V therefore of C, for a given training, is done by comparing the cost of evaporation of V and the cost of demineralization of the pollutant load 150 x C.
• the final rinsing of the strip is therefore economically feasible after the rinsing-brushing described above, by a closed water circuit on a demineralization unit by ion exchangers (a cation exchanger and an anion exchanger).
• the rinsing tanks are advantageously arranged in cascade with supply of demineralized water against the current of the strip.
• FIG. 3 represents a diagram of such an installation.
• a raw sheet arrives at 1 in a degreasing station 2. It then passes successively through a station 3 for rinsing with water, a station 4 for acidic living, a station 5 for rinsing with water, a station 6 for electrozincing, a station 7 for rinsing-brushing, and finally in a station 8 for rinsing with demineralized water.
• the installation further comprises a station 9 for evaporation of the electrolyte under vacuum, a station 10 and extraction of the electrolyte in an organic phase, a station 11 for washing the organic phase and a station 12 of re-extraction with water and a station 13 for concentrating the ZnCl 3 product.
• the flows are as follows: from the degreasing station 2 it is discharged periodically through a conduit 21 from the spent degreasing bath to an installation 22 for treating effluents. From the rinsing station 3, the rinsing water is discharged through a conduit 23 to the installation 22 for treating effluents.
• From the acid brightening station 4 is periodically removed via a conduit 24 from the spent acid brightening bath to the installation 22 for treating effluents.
• sprinkling water is supplied via a pipe 25. From the electrozincing station 6, the electrolyte is permanently drawn off through a conduit 26 towards the evaporation station 9. The electrolyte is brought back to the electrozincing station 6 by a conduit 27.
• the condensates of the evaporation are evacuated from the station 9 by a conduit 28 which brings part of it by a current 28a to the rinsing station 5 and another part by a conduit 28b at station 7 of rinse-bros ⁇ sage.
• the rinsing water from station 5 is returned via a line 29 as rinsing water supplying the rinsing station 3.
• Electrozincing station 6 is also continuously withdrawn via a conduit 30 from the electrolyte to bring it to the extraction station 10 with an organic phase 15 containing an amine salt.
• This station 10 comprises for example two stages of mixer-settlers.
• the electrolyte having undergone the extraction is returned by a conduit 31 to the station 6 of electro-zinc plating.
• the organic phase enriched in zinc in the extraction station 10 undergoes washing in the washing station 11 comprising for example 3 stages of mixer-settlers.
• the washing solution is returned via a line 32 to the electro-zincing station 6.
• the washed organic phase is then sent to station 12 for re-extraction with water.
• the washing water is constituted on the one hand by water supplied by a conduit 33 coming from the station 8 for rinsing with demineralized water and on the other hand, by condensed water brought by a conduit 34 from the ZnCl- concentration station 13.
• the aqueous solution of ZnCl 4 obtained by re-extraction is sent via a conduit 35 to the concentration station 13. Part of this solution is taken through a conduit 36 to constitute the washing solution for the washing station 11.
• the concentrated solution of ZnCl ? is evacuated via a conduit 37 to a use 38 allowing the ZnCl 2 to be efficientlyzed
• the rinsing-brushing station 7 is supplied as indicated above by a conduit 28b bringing water leaving the evaporation station 9.
• the effluent is recycled through a pipe 39 to the loop of the evaporation circuit.
• the station 8 for rinsing with demineralized water is supplied with water in a closed circuit coming from a station 14 for demineralization via a conduit 40.
• the rinsing water is returned by a conduit 41 to the station 14.
• a part is withdrawn. through the conduit 33 for the supply of the station 12 for re-extraction.
• the resins used in the post; e- 14 are periodically eluted and rinsed, the effluents leaving the anionic resin are discharged to an installation 42 for treating effluents while the effluents leaving the cationic resin are returned via a conduit 43 towards the duct 26 of the evaporation loop.
• the re-extraction is partly fed with the condensate from the pure ZnCl evaporation.
• ZnCl 2 Concentrated solution (evacuated via line 37): 0.33 m 3 / h at 150 g / 1 Zn, i.e. 313.8 g / 1 ZnCl 2 .

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Metals (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Water Treatment By Electricity Or Magnetism (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=9402530

Family Applications (1)

Country Status (7)

Cited By (5)

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• 1990
  • 1990-11-23 FR FR9014657A patent/FR2669646A1/fr active Granted
• 1991
  • 1991-11-12 PL PL29554891A patent/PL295548A1/xx unknown
  • 1991-11-12 EP EP91920764A patent/EP0512097A1/de not_active Withdrawn
  • 1991-11-12 KR KR1019920701718A patent/KR927003887A/ko not_active Application Discontinuation
  • 1991-11-12 JP JP92501182A patent/JPH05505425A/ja active Pending
  • 1991-11-12 WO PCT/FR1991/000885 patent/WO1992009725A1/fr not_active Application Discontinuation
• 1992
  • 1992-07-21 CS CS922273A patent/CS227392A3/cs unknown

Non-Patent Citations (1)

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