DE3321451A1 - DEVICE AND METHOD FOR REMOVING COPPERIONS FROM AQUEOUS SOLUTIONS - Google Patents

Description

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The invention relates generally to a device and a method for extracting copper ions from aqueous solutions, particularly on the treatment iron solutions containing copper ions to reduce the copper ion concentration to a point at which the drained drain can be safely discharged as waste water.

The legal disposal of various UtnweltschutzbestimnruTigen, in particular those aimed at improving dei "Tiasserqualität _parked? Has made it imperative to reduce or discharging certain present in industrial effluents metal ions into the Abwassersystein eliminate. Copper is one such Hetallionj the fjich as environmental pollutants Many techniques have therefore been used and proposed to reduce the amount of contaminating copper ions or to remove them altogether so that the solution can be discharged into the wastewater as harmless, one such method is disclosed in US Pat In other techniques, various chemical reagents are used in industrial drainage of supferions, or ion exchange resins are used to extract the copper ion and other harmful ions from the aqueous solutions.

Certain industrial effluents such as those _from} the stamracn dor rinsing water after electroless deposition of copper contained _s

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Copper ion concentrations that are above the permissible range and in which the ions are kept in solution by various complexing agents. For example, common complexing agents, such as substituted allylamines, prevent the removal of copper ions from the solution by the customary methods, such as cases as copper hydroxide by adding sodium hydroxide solution.S5.ch has also proven to be ineffective to extract the copper ions from the use of ion exchange resins, because the anionic complexing agents have too strong a complex binding effect. When lime is used to treat the dex * solution, its pH rises to about 12, and the copper concentration can be lowered to a very low level, below about 1 mg / l, but this treatment fills in to form a large amount of voluminous sludge, which must also be eliminated; the treatment and cleaning of the treatment system is accordingly time-consuming and costly.

The invention is based on the object of specifying a device and a method with which the copper content in Industrial drains, the copper ions also in very strong complex-bound Form contained, can be reduced to a value of about 1 mg / l (1 ppm) and below. The system should be economical, be easy to operate and flexible to use.

The object is achieved by the device of claim 1 and the method of claim ΛK . Preferred embodiments are specified in the subclaims.

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The Vox parts, which performs the Erfindxing, Verden, seen from the aspect of the apparatus of by a system reaches the _s
contains a tajik or a container to which the copper-containing aqueous solution is fed at a controlled rate
vix-d and a pH monitoring device for the automatic
Adjustment of the pH value within a predetermined
Area by adding acidic or alkaline material
is incorporated. The pH adjustment tank is also provided with a stirrer and a level sensor for optionally switching on and off a pump that pumps the pH-adjusted solution through a large number of canisters arranged in series, each of which has a removable cartridge
made of steel wool, which, when combined with the copper ions in
Contact comes, is able to pull this out. The capacity
the pump -is- set to a size that is larger
as the inflow of the copper-containing solution into the tank, so
that the flow of the pH adjusted solution through
the canister is atis dissolved when a predetermined maximum solution level is reached in the tank and, terminated, vexni a predetermined lowest level is reached
The device may also have a copper ion probe on the drain
of the downstream canister to monitor the concentration of residual copper ions in the drain. Three-way halves can be provided in the device to selectively reverse the flow of the pH-adjusted solution and the inflow and outflow directions of the plurality of canisters
in accordance with the degree of saturation and effectiveness

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to be able to reverse the patx-ons contained therein.

According to the method of the invention, an aqueous copper ion containing solution is first adjusted to a pH value within a predetermined range at which any present complexes in their complex binding strength be reduced, after which the solution is passed through one or more canisters, the fine-grade steel wool, for example of grade "0" and can extract copper ions to a value of 1 ppm or less. In the Treatment of flushing solutions from the electroless deposition of copper can be an effective treatment by setting the IiH value can be achieved in the range from about 2 to about 6; optimal process conditions occur at a pH of about 4.0 a.

Further features and advantages to which the invention leads will become apparent from the following description of preferred embodiments, which are made in connection with the attached figures emerge.

Fig. 1 is a perspective picture of the device made in accordance with the preferred embodiments of the invention is built in modular construction.

FIG. 2 is a fragmentary top plan view of the tank portion of the apparatus shown in FIG. 1.

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Figure 3 is a fragmentary side view of the tank section the device shown in Figs.

Fig, h is a vertical cross-sectional view through a canister of the apparatus shown in Fig. 1 _s mid

Fig. 5 is a fragmentary schematic picture of a alternative valve arrangement for regulating the Flow through the two canisters of the device shown in FIG.

As best seen in Figure 1, the apparatus is shown in a modular design which can be installed as a unit for treating and removing copper ions in waste solutions and the like. As shown, the apparatus includes a base or baseplate 10 on which a rectangular tank or container 12 is mounted at one corner. A canister '] k and a second canister 16 are carried by the Gx "undplatte 10, do atifisiinahmen solution to be treated and extracting the copper ions therein, Sine, electric control panel 18 is on the base plate 10 by means of a pair of legs 20 and Stutζstreben. 22, with which the various operating components are electrically connected and controlled.

Dio line Zh, which is equipped with a valve 26, such as

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As seen in Fig. 1, the aqueous solution contaminated with copper ions leads to tank 12. The contaminated solution may be the overflow of a rinse solution resulting from rinsing of parts treated with a copper immersion bath and in which the copper ions are replaced by organic complexing agents such as ethylenediaminetetraacetic acid or the like, are co-plexj-bound. The solution containing copper ions can come directly from the flushing overflow or from an intermediate pump or a quay tank for such a flushing solution, from which it flows into the line Zh by means of a pump or the action of gravity.

The tank 12, as best seen in Figures 1 to 3, is provided with an automatic pH control unit 28 which extends downward and is in constant contact with the solution to sense its pH and monitor. In optimizing the removal of copper ions from such drains, it has been found that optimal results at selected pH values, depending on the concentration of the copper ions and the type or types of complexing agents present in the solution, and also on other contaminating constituents in the . ζχχ treating solution can be obtained. Accordingly, the pli-value control unit 28 is preset so that the loading in the tank 12 is kept within a preselected optimum range, and a metering pump 32 which is mounted on a flange 30 which runs around the upper edge of the tank 12,

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supplies acidic or alkaline material if this is necessary to maintain the appropriate pH. A supply tank 'century, is to this end, as shown in Fig. 2 gezeigtj, is provided which is connected by a line 36 to the metering pump in the drain in the tank 12 solution.

Crude solution drains from the electroless copper deposition are usually alkaline. It has been found to be functional is to acidify such drains because the binding force the chelating agent that uses KoiapXex to bind the copper ions such as the tetrasodium salt of Ethylenediaminetetraacetic acid at relatively low pH animal oils is significantly reduced »The results are particularly good by adjusting the pH of such solutions atif an ¥ ert below about 0, preferably about 2 to about 'f · have been obtained. The specific selected pH value is also determined by the amount of iron, those in the drains which are drained off after the treatment, the iron ion content dex * drained drains as a result of the increasing dissolution of iron in the treatment canisters when the pH value rises »

In any case, the pH control unit 28 causes the connection to the dex * metering pump 32 by constant or periodic introduction of acidic or basic material when the solution to be boliandolndo is continuously fed into the tank 12 through the feed line 2h that the pH -Value of the solution in de: n Taiiic 12 s üäudig within do-j above iorge ^

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Eoreiclies aufx ^ real is preserved. .The uplifting of a uniform mixture in the tank 12 is achieved by a mechanical stirrer ensured that an Anfcz'iebsmotoi-33 includes, which is mounted on the upper tank pad 30 and a shaft 40 and at the lower end one Has propeller 42, as best shown in FIGS. 2 and 3 you can see.

The level of the set at the pH of the solution in the tank 12 is constantly monitored • \ 6 of any known type by means of a water level control unit as to the solution within a maximum level prior k8 and hold a Niedrigebpogelstands 50 hu. The level control device h6 is connected through the electrical control plate 18 to a pump hh in order to switch on the pump 44 when the solution in the tank approaches the maximum level 48 and to activate a signaling device (not shown) when the maximum level 48 is reached, and to turn off the pump 44 before the solution flows to the lowest level 50 . The output of the pump 44 is selected so that it is greater than the flow rate or the rate at which the solution containing the copper ion is introduced into the tank 12 through the supply line 24. In this way, the solution from the tank 12 is prevented from overflowing.

As best seen in FIG. 2, the pump 44 is provided with a

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Outflow line 52 is provided which is connected to a Reguliox-veiitiX 'jh . This recirculating valve $ k is connected by a supply line 56, as shown in FIG. 2, to a flow control valve 5§, which in turn is in connection with a Stx'öi: TUxigsmesser 60, which carries a pressure gauge 62 at its upper end to feel the flow rate and the pressure of the pH-adjusted solution which is fed to the canisters 1'1 and 16. The pressure gauge 62 is connected by a line 64 to an inlet 66 at the bottom of the canister and an outlet 68 from the canister 1 · '+. The outlet 68 is preferably provided with a Probecntnahmehahn JO ¹ to obtain samples from the drain of the canister lh withdraw and to be able to analyze the concentration of copper ions. Alternatively, an automatic ICupferion sensor can be used to continuously measure and display the ICtipferions in the canister outlet »

The sampling tap 70 is connected by a cross line "J2" to an inlet 7 ^ at the bottom of the canister 16 and the solution flows out through an outlet 76 in the upper toilet of the canister 16, the outlet J6 having a sampling stalk as in the case of the canister 14 78 or an automatic copper measuring sensor. The sampling cock 78 is connected by means of a line 80 to a T-Fibbing 82, which in turn is connected to a drain line 8h , through which the treated aqueous solution to the final water! " treatment that includes neutralization and the like is derived "

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At the point in time when it becomes necessary to replace the cartridges in one or both canisters 14, 16 (for reasons that will be discussed in more detail below), the operating components are switched off by the control plate 18 and the flow of the material containing copper ions is stopped Closing the valve 26 (in Fig. 1) turned off. A vent line 86 is connected to the inlet of canister 14 and a second vent line 88 is connected to inlet "h of canister 16 is also opened, after which the solution flows through lines 86, 88 and valves 90, 92 to a T-fitting 9h , from where it flows through a drain line 96 which is connected to the drain line 84 by the T-fitting 82 .

To the canisters and the associated lines in preparation pulling out and replacing the cartridges clean is one with a fresh water connection, like one ! Thousand swas ser line to the connec tion connected tias s er feed Ic i tion 98 is provided which, as FIG. 1 shows, includes valve 100, that on a T-fitting 102 at the bottom of the Strönran knife 60 is connected. While cleaning the The canister with fresh water is the flow control valve 58 closed at the pump outlet, causing the water to go up through the flow meter 60, the manometer 62, the feed x -

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le.iti.ing 64 and into the inlet 66 of the canister 14, through which the cross-connecting line J2 and the canister 16 flows, from which it is drained through the line 80 into the drain line 84. The withdrawal of the remaining water from the canisters 14, 16 through the drainage system is evacuated by removable covers 97> which are removably secured to the upper edge of each canister to allow air to flow out in the canister. Alternatively, additional air voids can be provided in the covers 97 for the same purpose.

Reference is now made to FIG. 4, which shows a cross section through the canister 14. In the canister 14 a removable and disposable cartridge 14 is inserted. The description <les KcUiisters * [k is in the same way on the canister '! 6 portable j the canisters are actually borrowed of the same design and working method. As shown in Fig. 4, the oboro edge dor cylindrical side wall of the! Formed Canisters with a radial flange 106 on which a sealing ring is arranged .108 _e The peripheral portion of the circular cover 97 is adapted to sealingly against the sealing ring 108 abuts Sine series of Schraubbefesbigungcn 110 are fixedly connected to the radial flange 106 removably secure the cover 97 on the sealing ring 108 again va \.

The interior of the canister lh is provided with a round perforated plate 112, which is supported by a plurality of support bodies. 11 'carried I

which will also cause the flow entering the chamber tint of the plate 112 to be evenly distributed. The arrangement described above and shown in FIG. 4 delimits a chimney which is arranged following the inlet 66 , into which the solution to be treated, adjusted to the pH value, enters. A solid rod 16 is secured to the top of the plate 112 and is provided at its upper end with a button or handle 118 which is removably and screwably attached to it.

The removable cartridge 104 essentially contains one liquid impermeable tubular cylindrical core 120, which is adapted to the circumference of the rod 116, slidable on it sits. Fine sized steel wool 122 surrounds don the circumference of the grain 120 in the form of a cylindrical mass, which extends into circumferential contact with the inner surface of the canister i4. The steel wool is preferred xjj shape of a continuous cushion spiraling around the Wrapped with a core 120, around a circumferential cylindrical, cylindrical, axial Hate to form of desired height and diameter. The tubular core 120 and the mass 122 of steel wool therefore, by the clamping action of the handle 113 in dor position as shown in Fig. 4, held.

To get the maximum efficiency in terms of pulling out of copper ions from the solution adjusted to the pH value, which passes the pati'one 104 from bottom to top, zvt achieve,

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fine steel wool, for example a size grade "0", is preferably used, so that the surface contact and the deposition of copper ions on the surface is maximized. Replace the cartridge, which may be required from time to time, after the canister is emptied and is cleaned with fresh water, easily allows to that in Fig, k shown arrangement, by loosening the threaded fasteners 110, and removing the cover 97th The cartridge 104 and perforated plate 112 are removed as a unit by pulling upwardly on the handle 118, which is then removed to enable the cartridge 10 ^ to be withdrawn from the rod ii6. A fresh cartridge of the same construction is pushed onto the rod and the handle 118 is screwed tight again, after which the Gofuge is installed in the canister and the cover plate is reattached. Because of the economy of the cartridge, it can be discarded (disposable cartridge) or it can, if. desired, be subjected to extraction to recover the copper.

In accordance with the arrangement shown in FIG the replacement of the cartridge in the canister i'i- before the replacement of the Cartridges are required in the canister 16, which is arranged in the series downstream and exposed to a solution, from which in part the contaminating copper ions already are away. It is therefore to be considered that for Replacement of the cartridge in the canister 1 ^ the cartridge in the canister onhfornt and In Kani; jtei '1 * l · can be inserted, while in

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Canister 16 a fresh cartridge is inserted, the "recovery enabling the copper recovery operation.

According to an alternative embodiment of the invention, the Is shown fragmentarily and schematically in Fig. 5, flow switching valves in the supply line ^ system to be built into the canisters, whereby the upflow and .Abs Lröm position following the replacement of a cartridge in one or the other canister can be changed. With this arrangement, the canister, which is the upstream and whose cartridge had to be changed was functional following the replacement of the cartridge when the trading process is resumed be the downstream side. With this arrangement one achieves the same effect as described in connection with FIG. 1 when the cartridge of the AufströmiAiitlgen Canister is replaced by that of the downstream side and a fresh cartridge is inserted into this.

If the arrangement shown in FIG. 5, the solution set to the pll-iort occurs through the line 6k into a multi ^{-way valve 12 1} I- which is directed in FIG. 5 to the inlet 66 of the canister ^} 1 , after which the solution passes through the outlet 68 into a second multiway valve 126. In the illustrated position of the multi-way valve 126, the solution returns through a transverse line 128 to the Mohrwegeveutxl 12 ^, through which it is directed into the inlet fh of the canister 16 and dux-ch its outlet 76 at the upper end it is delivered . The outflowing

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Solution is in turn directed to multi-way valve 126 through which it enters drain line Qh as described in connection with FIG. When turning the Jlehrwegoventile 12h, 126 by 90 °, a reversal of the flow scheme just described occurs, whereby the supplied solution first passes the canister 16 and then enters the canister 1h , from which it passes through the multiway valve 126 is delivered to the drainage line 8h .

The operation of the device is started by opening the valve which allows the entry of the solution containing copper ions into the tank 12. The Kentrollpj atte 18 is stale bet to the veröchiedenen Überv / achungs- and set Ectriebslcomponenten of the system in activity "1 / lösuiig omi the lcupferionenhaltige Zufülix" the Tanlc begins to fill 12, 28 feeds the pH-control unit periodically or continuously the dosing pump 32, in order to keep the solution within the suitable pH range by constant agitation by means of the mechanical stirring device ^ JO, 42 Pump hh driven to cause u :: i flows dcT to the pH-adjusted solution through canisters 1'l- and 16. Since the capacity of the pump kk to a flow rate which is higher than that of the solution containing the copper, which the Tank Kugefülix't is selectively controlled, the solution level in tank 12 slowly sinks

down to the lowest level 50, vas through, the level control device 46 is displayed. At this time the pump kh- is switched off and remains switched off until the level control device h6 again shows the maximum level and the cycle described above is repeated.The size of the cartridges and the number of canisters is determined by the amount of Iorpferionen in the solution to be treated and the allowable copper ion concentration for the final solution drained from the device. Typically, the size of the cartridges and the number of canisters used will be chosen in view of the solution to be treated so as to provide for replacement of a cartridge on the upstream canister at various convenient times, depending on the concentration of copper ions in the treated drained solution to a value of about 1 ppm or less.

For example, flush water effluent from the electroless copper plating was treated by the Udique 820 process as described below to illustrate the process of the invention. Before the treatment, the effluent contained 58 mg / l copper ion and had a pII ratio of about 10.5. The effluent was treated at room temperature after adjusting the pH to about 1.0 by adding sulfuric acid by successively was passed through the first and the second canister \ h, i6 of the construction described above. Each canister contained 10.9 kg of grade "0" steel wool. The flow rate of the drain through the canisters was 18.925 3 / min. To

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8 hours each time the drainage was stopped and the kaiis tor was stopped rinsed with fresh water. The analysis of the discharge ex-gave For the total copper and total senions included at the beginning: after your first canister: 0.5 nig / l copper, 60 nig / l iron after the second canister: 0.05 m-j / l copper, 60 mg / l iron.

After the drain has passed through the canisters for ten hours; flows Aiar, about 2.633 ^ S of copper had been removed from the drain. The analysis values of the discharge were:

after the first canister: 1j5 nig / l copper, 60 nig / l iron after the second canister: 0.10 mg / l copper, ö0 cig / l iron.

This shows that the present invention can be used effectively and economical removal of copper ions from a drain can be applied

If desired, the iron-ion-containing drain can be used for Removal of iron will be treated, typically the Outflow calcium chloride or calcium oxide in about lr.olaron amounts, based on the iron present. Then the pH-1 / crt the runoff is increased to a "value of about 7 to 9" by adding caustic soda. Iron is precipitated and can chrrch Filbrieron to be removed. If desired, one can suitable flocculants, such as polyacrylamide, are added, to allow the formation of a Lesser filterable precipitate favor.

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The invention is attached above, more preferred embodiments been boscled. Yet it is usual that numerous modifications are possible that are still in the frame fall of the invention.

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Claims (1)

Claims j 1, device for removing copper ions from an aqueous solution contained therein, marked by a tank (12) for receiving the solution containing copper ions; first supply means (24, ZS ₉ 36) 213111 introducing the solution containing copper ions into the. Tank (i2) j a pH-Wort-Kontrollgei-ät (28) in the tank (12) for sensing the pH of the solution contained therein; second supply means (32 ₃ 3k, 36) for supplying at least one acidic or alkaline material to the tank (12) and adjusting the pH , / 2 Ouutache I'iitcmt Atlorno} · »Zi AG IIambuf &, No. O5 / 284OT VorlPv'ior holm K \ jrojjU! Hclioi »F * atf> iienmt 7000) ·:> us (»cl»> ck Humhui ·); 2842-206 ι α »
• · ■ the solution therein within a predetermined range, said supply means (32, 34, 36) being operative in response to the pH control device (28); Means (40, 42) for stirring the solution in the tank (12); a level sensor (46) in the tank (12) for sensing a predetermined minimum and maximum level (50, 48) of the solution in the tank (12); a pump (44) operable in response to the level sensor (46) to draw the pH adjusted solution from the tank (12) one or more canisters (i4, 16) connected in series, of which each containing a removable steel wool cartridge (ΐθ4), the upstream canister having an inlet (66) and the downstream canister (16) having an outlet (76) ; a conduit (64) for connecting the pump (44) to the inlet (66) of the canister (14) on the upstream side; and means for cleaning (84 to 96), which are in communication with the line (64) and the canisters (14, 16), for introducing water for the purpose of flushing out residual solution in preparation for removal and replacement of a cartridge (1O4). 2. Apparatus according to claim 1, characterized in that the pH control device (28) to a pH value below about 6 can be preset and the second supply means (32, 34, 36) can be actuated to acidic Feed material. * DO Q 3β Device according to claim 1, characterized in that the pH value control device (28) is operatively connected to the second supply means (32, 3k, 36) to keep the pH value of the solution in the tank (12) between about 2 and hold about zn. k. Device according to Claim 1, characterized in that it has a flow sensor (60) outside the line (56, 64) for monitoring the flow rate of the pH-adjusted solution to the canisters (1h, 16). 5 «, device according to. Claim 1, characterized in that it also has a manometer (62) in the line (6k) for monitoring the solution contained therein. Device according to claim 1, characterized in that the Pegelstandsmeßfühler (46) at lowering of the solution level in the tank (12) (44) switches off at or tinter the lowest water level (50) oil pump ^e. 7ο device according to claim 1, characterized in that the level sensor (46) at the maximum level (48) of the solution in the tank (12) turns on the pump (44) and drives until the lowest level (50) is reached. 8. Device: according to claim 1, characterized in that they flow control valves (58) in the first supply line (24, 26, 56) in order to increase the flow of the solution containing copper ions in the tank (12) to a value which is below the drain capacity of the pump (44). 9. Apparatus according to claim I ₁ characterized by a copper ion sensor connected to the drain line (84) for detecting the KupTerionenkonzent ration in the solution drained from the device. 10. Apparatus according to claim 1, characterized in that it also has valves (124, 126) by means of which the canister (i4) which is external to the flow in the downstream side Canister (16) and the downstream canister (16) in the upstream canister (i4) can be changed. 11. The device according to claim 1, characterized in that each canister (i4, 16) for removal and insertion of the cartridge (104) has a removable cover (97). 12. The apparatus of claim 1, characterized in that each canister (i4, 16) contains: a container, a perforated plate (112) spaced from the bottom of the container, a cartridge (104) over the perforated plate ( 112), an inlet (66) with Inside or the container in a position below the perforated plate (112) communicates, and © inen Outlet (68) in the container in a position above the cartridge (104). 13. The apparatus according to claim 12, characterized in that the canister (14, 16) additionally has a in the middle of the pex-forierten plate (l12) and in the container upwardly extending rod (II6) irnd a removable in the upper part of the Rod (116) has attached retainer or button (II8); and in that the canister (i4 ₉ 16) radially includes a mass of steel wool around a central tubular core (12o) and said core (12o) at least a portion of the rod (116) around, removable from it and carried by the PEX-perforated Plate (112) is arranged. lh _{o A} method for removing copper ions from an aqueous solution, characterized by the following steps: sensing the pH of the solution supplied, admixing at least one acidic or alkaline material to the solution supplied to adjust its pH within a predetermined range; Passing the pH-adjusted solution through one or more canisters connected in series and bringing the solution into contact with steel wool that is in the canisters so that at least some of the «Ο β / 6 holding copper ions, is pulled out and on the Steel wool separates, so that the concentration of the remaining Reduced copper ions in the solution flowing out of the downstream canister to a desired value will. 15. The method according to claim 14, characterized in that acidic material is added to the pH value below
bring about 6. 16. The method according to claim 15 »characterized in that the pH is brought to about 2 to k . 17. The method according to claim i4, characterized in that the pH is brought to about 4.0. 18. The method according to claim 14, characterized in that the flow rate of the pH-adjusted solution through the canisters is controlled. 19. The method according to claim 1 * f, characterized in that the solution adjusted to the desired pH value is passed through several canisters until the copper ion concentration is reached has dropped below about 1 ppm in the drain. • 9 · · φ 6 a λ * "ft" * " β β ο ο * * 332U51 20ο procedure according to. Claim 1 ^ ₉ characterized * that the steel wool cartridge in each canister is periodically renewed. 21, The method of claim 14, characterized in that the residual ₉ Kupferioiienlconaentration is sensed in the effluent β 22ο Method according to Claim Ih _3, characterized in that the direction of flow of the solution through the plurality of canisters is periodically reversed tdrd. 23ο Method according to Claim 20, characterized in that the canisters are removed before the steel wool cartridge is replaced
become gex · some fc. 2't ·. Method according to Claim 14, characterized in that the pressure and the flow rate of the on the
pH-adjusted solution when running through the Ilimdux
the canisters are sensed " 25, a method for removing supferions from an aqueous feed solution, characterized in that the feed solution at a pH ¥ ert below about 6 by
Full of steel is passed through, which has a sufficiently large surface to remove at least some of the copper ions from the solution and thereby the remaining »0/8 • · Copper ion concentration in the solution on the downstream side to reduce the steel wool. 26. The method according to claim 14, characterized in that the pH of the feed solution is adjusted to about 2 to h. 27. The method according to claim lh, characterized in that the solution is sent through a plurality of steel wool containing canisters connected in series with one another. 28. The method according to claim 1h, characterized in that the outflow of the downstream canister is subjected to the following further treatment to remove iron ions: a) adding CaCl ₂ or -CaO to the drain j b) Adjusting the pH to about 7 to 9 and c) Filtration of the effluent to remove the ferrous formed precipitate. 29. The method according to claim 251, characterized in that the Solution on the side of the steel wool to remove Iron ions are subjected to the following further treatment: a) adding CaCl ₂ or CaO to the drain} b) Adjusting the pH to about 7 to 9 and c) filtering the effluent to remove the ferrous precipitate formed.