EP0465822B1 - Recovery of sodium hydroxide and aluminium hydroxide from etching waste - Google Patents

Recovery of sodium hydroxide and aluminium hydroxide from etching waste Download PDF

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Publication number
EP0465822B1
EP0465822B1 EP91109027A EP91109027A EP0465822B1 EP 0465822 B1 EP0465822 B1 EP 0465822B1 EP 91109027 A EP91109027 A EP 91109027A EP 91109027 A EP91109027 A EP 91109027A EP 0465822 B1 EP0465822 B1 EP 0465822B1
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EP
European Patent Office
Prior art keywords
dialyzer
water
stream
sodium hydroxide
membrane
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP91109027A
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German (de)
English (en)
French (fr)
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EP0465822A1 (en
Inventor
Thomas A. Davis
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Graver Water Systems LLC
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Graver Co
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Publication date
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F1/00—Etching metallic material by chemical means
    • C23F1/46—Regeneration of etching compositions

Definitions

  • This invention relates to the treatment of the waste stream from aluminum dissolution operations and, more particularly, to an improved method for regenerating the alkali etch solution and recovering aluminum hydroxide.
  • reaction (1) there is an increase in the concentration of the NaAlO2 and a decrease in the concentration of the alkali as the aluminum metal dissolves.
  • the aluminate is not stable in water and, depending on existing conditions of temperature, concentrations and time, reacts with the water according to the following equilibrium equation: (2) NaAlO2 + 2H2O ⁇ NaOH + Al(OH)3
  • the present invention provides an improved method of recovering sodium hydroxide from etch waste solutions that substantially eliminates the above described problems inherent in the prior art methods.
  • the sodium hydroxide recovered is sufficiently concentrated for recycling and use in the etching operations and is also substantially free of contamination by dissolved aluminum present in the waste solution being treated.
  • the method of the invention also permits the recovery of substantial amounts of aluminum hydroxide which is a commercially useful product.
  • the invention comprises a departure from the prior art methods which add water to the etch waste solution in order to induce aluminum hydroxide precipitation and sodium hydroxide formation. Instead, the inventive method removes sodium hydroxide initially from the waste solution and recycles it directly back into the etching tank. The remaining aluminum-containing solution is treated in a particle-contacting crystallizer where solid aluminum hydroxide is recovered.
  • the inventive method of recovering sodium hydroxide from an etch tank waste solution containing dissolved aluminum comprises the steps of directing a stream of the wast solution into a diffusion dialyzer containing permeable membrane means that is permeable to sodium hydroxide and substantially less permeable to dissolved aluminum on one side of the membrane means, simultaneously directing a stream of water into the dialyzer on the opposite side of the membrane means whereby sodium hydroxide migrates through said membrane means from the waste solution stream into the water stream and recycling the sodium hydroxide-containing stream back into the etch tank.
  • the dialyzer includes one or more ion exchange membranes which are substantially permeable to sodium hydroxide but substantially less permeable to aluminum salts.
  • the etch waste solution is fed into a diffusion dialyzer stack on one side of the ion exchange membrane. Water is simultaneously fed into the stack on the opposite side of the membrane and countercurrent to the flow of the waste solution.
  • Sodium hydroxide diffuses across the membrane into the receiving water stream which is returned to the etching tank. Since this addition of sodium hydroxide would tend to precipitate many multi-valent cations present in tap water, it is beneficial to feed soft water into the diffusion dialyzer.
  • the waste solution exiting from the dialyzer is directed into settling vessel means to precipitate aluminum hydroxide therefrom, and preferably the waste solution exiting from the dialyzer is cooled to a temperature between 18.33 °C (65 °F) and 46.11 °C (115 °F) before being directed into the settling vessel means.
  • the remaining dilute waste solution may be discarded or treated further for the recovery of what small amounts of alkali remain therein.
  • the inventive method can further comprise the steps of directing a stream of the overflow liquid from the settling vessel means into a second diffusion dialyzer containing permeable membrane means that is permeable to sodium hydroxide and substantially less permeable to dissolved aluminum on one side of the membrane means, simultaneously directing a stream of deionized water into the second dialyzer on the opposite side of the membrane means and directing the water stream into the etch tank.
  • the overflow from the crystallizer in the present method contains useful components of the bath, i.e., NaOH and other bath additives, it is a preferred source of make-up water for the etch bath. Moreover, return of the overflow to the bath eliminates the need for disposal or further treatment of the overflow.
  • a high utilization of the crystallizer overflow as makeup water would eliminate a means of purge or blowdown of impurities that enter with makeup water. In such a case it is beneficial to deionize the make-up water and the feed water to the diffusion dialyzer.
  • the method is simple and efficient and does not require the use of many sophisticated controls.
  • the inventive method is carried out with an apparatus for recovering sodium hydroxide and aluminum hydroxide from an etch tank waste solution comprising diffusion dialysis means having channels on opposite sides of permeable membrane means that is permeable to sodium hydroxide and substantially less permeable to dissolved aluminum for receiving respectively a stream of the waste solution and a stream of water, pumping means for directing said two streams in opposite directions through the dialysis means on opposite sides of said membrane means and settling vessel means for receiving the waste solution exiting from the diffusion dialysis means and collecting aluminum hydroxide precipitating therein.
  • Such an apparatus can comprise deionizing and degassing means for treating the water before pumping into the diffusion dialysis means.
  • the method comprises the steps of directing a stream of sodium aluminate solution into a diffusion dialyzer containing permeable membrane means that is permeable to sodium hydroxide and substantially less permeable to sodium aluminate on one side of the membrane means, simultaneously directing a stream of water into the dialyzer on the opposite side of the membrane means whereby sodium hydroxide migrates through said membrane means from the sodium aluminate solution stream into the water stream, directing the water stream exiting from the dialyzer into a sodium hydroxide storage vessel and directing the sodium aluminate stream exiting the dialyzer into settling vessel means to precipitate aluminum hydroxide therefrom.
  • the streams of sodium aluminate solution and water can flow countercurrently through the dialyzer.
  • the water directed into the dialyzer can be first softened and degassed.
  • the softened and degassed water is heated to a temperature between 40.5 °C (105 °F) and 54.44 °C (130 °F).
  • the sodium aluminate solution exiting from the dialyzer can be cooled to a temperature between 18.33 °C (65 °F) and 46.11 °C (115 °F) before being directed into the settling vessel means.
  • FIG. 1 there is shown a method of recovering and recycling sodium hydroxide and also recovering useful aluminum hydroxide.
  • the embodiment shown is employed in connection with a conventional aluminum etching operation wherein aluminum articles are immersed for relatively short periods in an etch tank 10 containing a bath of sodium hydroxide and water. Dissolution of the aluminum takes place as indicated in equation (1) above.
  • Waste solution is pumped from the tank 10 through line 12 and into a diffusion dialyzer 15.
  • Diffusion dialyzer 15 comprises a liquid flow vessel 16 divided into chambers or channels 18 and 20 on opposite sides of an ion-exchange membrane 22. As shown, the waste solution is pumped into and flows upwardly through channel 18. Simultaneously, a stream of warm water, which has been softened and degassed by boiling, is pumped into and flows downwardly through channel 20.
  • the water and waste solution are here supplied to the dialyzer 15 at substantially equal rates.
  • Membrane 22 is substantially permeable to sodium hydroxide and substantially less permeable to the dissolved aluminum or aluminum salts. Such membranes are of a type commonly available and manufactured by companies like Pall/RAI under the trade designation BDM and Tokuyama Soda under the trade designation Neosepta CR-2. Inside the dialyzer column 15, sodium hydroxide migrates across the membrane 22 and into the water stream and the recovered sodium hydroxide is discharged back into the etch tank 10 as indicated through line 24. The recycled sodium hydroxide is sufficiently concentrated to be useful in carrying on the basic etching operation.
  • the alkali-depleted waste stream exits from the top of channel 18 through line 26 and is cooled, preferably by a water jacket heat exchanger or the like, and then pumped into a crystallizer vessel 28.
  • the waste solution exiting from the dialyzer column 15 is believed to be supersaturated in aluminum hydroxide, which is known to be extremely slow to precipitate from aqueous solution under normal conditions.
  • the crystallizer vessel 28 is of known construction and provides nucleation sites for enhancing the formation and precipitation of aluminum hydroxide which is removable from the bottom of the vessel as illustrated.
  • the overflow from vessel 28 is a dilute waste solution 30 low in remaining sodium hydroxide and/or aluminum hydroxide and may be disposed of as waste or in some cases used as make-up water for the etch tank. However, if desired, the waste solution 30 may be further treated as before in a second diffusion dialyzer for recovery of any remaining usable components.
  • the water temperature should be preferably between 40.5 °C (105 °F) and 54.4 °C (130 °F), and most preferably about 48.9 °C (120 °F).
  • the ratio of water flow rate to waste solution flow rate also affects the results achieved. That ratio is preferably in the range of 0.5 and 4.0 to 1 and most preferably about 2 to 1.
  • the diffusion dialyzer may comprise a plurality of diffusion membranes properly spaced to provide a stack with waste solution and water channels on opposite sides of each membrane.
  • the nature of the operation will also determine if certain temperature and/or filtration controls of the waste solution being fed into the dialyzer are required. For example, in a simple etching operation of the type already described, the temperature of the etch bath is not raised substantially above ambient.
  • chemical milling operations which dissolve larger amounts of metal produce bath temperatures at or near the boiling point of water and also significant amounts of other metals, such as copper.
  • waste solution temperatures approaching 99.9 °C (212 °F) would be destructive of the membranes in the dialyzer, it is desirable to first cool the waste solution to temperatures near ambient.
  • a precipitating agent like Na2S to the bath for precipitating out the dissolved copper and other metals.
  • the precipitated sulfides form a sludge which desirably is filtered from the waste solution before feeding into the dialyzer.
  • the milling operation comprises multiple etch tanks 50, 52, 54, from which the waste solution is fed first into settling tanks 56, 58, 60, for removal of sulfide precipitates. The supernatant solution is then pumped through filter means 62, 64, to remove any remaining sludge. The temperature of the clear waste solution is regulated in suitable temperature control means 66 to approximately ambient, and then pumped into a diffusion dialyzer stack 75 to flow upwardly therethrough.
  • a water tank 68 is provided having associated hot air or steam means for degassing the water.
  • the degassed water is pumped through suitable temperature control means 70 to reach a preferred temperature of around 48.89 °C (120 °F) and then into the top of the dialyzer 75 to flow downwardly therethrough.
  • the dialyzer 75 comprises multiple diffusion membranes and includes vent means 76 for periodically purging any air bubbles from the flow channels in the dialyzer.
  • Storage tanks 78 and 80 are provided for respectively receiving the sodium hydroxide and the alkali-depleted salt solution. Sodium hydroxide from tank 78 is recycled and fed back into the etch tanks 50, 52, 54, as desired.
  • the salt solution from tank 80 is fed into conventional crystallizing or precipitating means, in this embodiment, a mixing tank 82, where the solution may contact previously precipitated Al(OH)3, and settling tank 84 from which precipitated aluminum hydroxide is removed.
  • the supernatant liquid from the settling tank 84 is, in this operation, also recycled back into the etch tanks, for recapture of the remaining sodium hydroxide and also to replace the water which is being evaporated from the hot etch tanks.
  • etch waste solution containing about 8% sodium hydroxide was fed into a dialyzer column comprising a single BDM ion-exchange membrane with about 2dm2 of exposed area.
  • the waste solution and water were fed to the dialyzer by a dual head, size 13 Masterflex pump operating at 28.5 rpm to supply the solutions at equal rates.
  • the system was operated overnight and samples taken the following day.
  • the measured output flow rates were 0.44 ml/min. for the recovered base and 1.22 ml/min. for the treated etching solution.
  • a diffusion dialysis stack was assembled with ten sheets of Neosepta CR-2 membrane separated by Vexar-type spacers about 0.75 mm thick. Each membrane sheet had about 175 cm2 of its surface exposed to the solutions. Alternate solution compartments were fed with water flowing downward and a spent aluminum chemical milling etchant flowing upward. The water, which had been demineralized and boiled, was warmed to about 43.33 °C (110 °F) by passing it through a heating coil before it entered the stack. Analysis was by titration with H2SO4. In an experiment of 450 min duration, a 2371 ml batch of etchant was treated in the stack.
  • the etchant contained 144 g/l of free NaOH, and 476 g/li of NaAlO2.
  • a 2644 ml batch of base was recovered composed of 109 g/l of free NaOH, and 15 g/l of NaAlO2.
  • the 4060 ml batch of base-depleted salt solution contained 12 g/l of free NaOH, and 272 g/l of NaAlO2. Upon standing at room temperature, a voluminous white precipitate of Al(OH)3 formed in the base-depleted salt solution.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)
  • Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)
  • ing And Chemical Polishing (AREA)
  • Removal Of Specific Substances (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
  • Processing Of Solid Wastes (AREA)
  • Heat Treatment Of Water, Waste Water Or Sewage (AREA)
  • Physical Water Treatments (AREA)
EP91109027A 1990-07-06 1991-06-03 Recovery of sodium hydroxide and aluminium hydroxide from etching waste Expired - Lifetime EP0465822B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US54939690A 1990-07-06 1990-07-06
US549396 1990-07-06

Publications (2)

Publication Number Publication Date
EP0465822A1 EP0465822A1 (en) 1992-01-15
EP0465822B1 true EP0465822B1 (en) 1994-08-17

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EP91109027A Expired - Lifetime EP0465822B1 (en) 1990-07-06 1991-06-03 Recovery of sodium hydroxide and aluminium hydroxide from etching waste

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EP (1) EP0465822B1 (es)
JP (1) JPH05115871A (es)
AT (1) ATE110123T1 (es)
AU (1) AU634661B2 (es)
CA (1) CA2043717A1 (es)
DE (1) DE69103486T2 (es)
ES (1) ES2057668T3 (es)
MX (1) MX9100096A (es)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19710563C2 (de) 1997-03-14 2003-10-02 Daimler Chrysler Ag Verfahren und Vorrichtung zum Betreiben von Aluminium-Fräsbädern
CN1298637C (zh) * 2005-08-08 2007-02-07 南京工业大学 含色素废碱液中回收氢氧化钠的方法
JP5016973B2 (ja) * 2007-05-21 2012-09-05 株式会社野坂電機 アルカリエッチング液のアルカリ回収方法及び装置
EP2352859B1 (de) * 2008-11-03 2018-06-27 Thomas König Beizverfahren und beizanlage
CN101928948A (zh) * 2010-09-02 2010-12-29 吉林麦达斯铝业有限公司 铝型材挤压模具碱洗残液的回收工艺
DE102013105177A1 (de) * 2013-05-21 2014-11-27 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Verfahren zur Gewinnung metallischer Anteile sowie von metallabgereichertem Material aus metallhaltigen Materialien
CN104626453A (zh) * 2014-12-05 2015-05-20 博罗县东明化工有限公司 铝合金树脂复合体的制备方法及铝合金树脂复合体

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3607482A (en) * 1969-08-11 1971-09-21 Wilson & Co Process of regeneration of metal treating solutions
US4136026A (en) * 1977-11-23 1979-01-23 Aluminum Company Of America Caustic solution having controlled dissolved aluminum content
JPS5827984A (ja) * 1981-08-10 1983-02-18 Kurisutaru Eng Kk アルミニウム及びその合金のアルカリエツチング液の再生方法
GB8612627D0 (en) * 1986-05-23 1986-07-02 Ici Plc Dechlorination of aqueous alkali metal chloride solution
US4826605A (en) * 1986-11-03 1989-05-02 Caspian International, Inc. Process for depleted chemical milling solutions

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Publication number Publication date
EP0465822A1 (en) 1992-01-15
ATE110123T1 (de) 1994-09-15
MX9100096A (es) 1992-02-28
JPH05115871A (ja) 1993-05-14
DE69103486D1 (de) 1994-09-22
AU7948091A (en) 1992-01-09
CA2043717A1 (en) 1992-01-07
AU634661B2 (en) 1993-02-25
ES2057668T3 (es) 1994-10-16
DE69103486T2 (de) 1994-12-08

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