Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Treating process fluid by means other than agitation or...
Reexamination Certificate
2001-01-23
2003-08-19
King, Roy (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Treating process fluid by means other than agitation or...
C204SDIG004, C205S101000, C210S673000, C210S720000, C210S724000, C210S726000, C210S912000, C210S913000
Reexamination Certificate
active
06607651
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process and apparatus for treating an aqueous flushing solution discharged from an ion exchanger containing various impurities from an electroplating bath, such as, metal ions from the structures being electroplated, metal ions from the anodes used in the electroplating bath and metal ions from the plating metal.
BACKGROUND OF THE INVENTION
In general, an ion exchanger for treating liquid from an electroplating bath has columns filled with resin beads and is loaded with hydrogen ions. Liquid from the electroplating bath, which contains metal ions from the electrodes used in the bath, metal ions from the structures which have been plated in the bath and metal ions from the plating metal is flushed through the ion exchanger. The metal ions in the plating bath liquid replace the hydrogen ions in the ion exchange columns. The water discharged from the ion exchanger include hydrogen ions and the unabsorbed metal ions from the plating metal that are then supplied back to the plating bath. An example of such an exchanger is the chromapure exchanger commercially available from Ecotech located in Pickering, Ontario, Canada.
Because the ion exchange columns become loaded with metal ions over a period of use, it becomes necessary to periodically flush the apparatus to raise the hydrogen ion content in the ion exchange columns. In order to “reload” the columns with hydrogen ions, the apparatus is flushed with an acidic aqueous solution, preferably including sulfuric acid. The pH of this flushing solution is usually about 2 and preferably as close to zero as possible. As a result of such flushing, the metal ions in the columns are displaced by hydrogen ions in the solution and the stream discharged from the apparatus is an aqueous solution that contains sulfuric acid, metal ions from the electrodes, metal ions from the structures being plated, metal ions from the plating metal, sulfate ions and hydrogen ions. The pH of this discharge stream is approximately 1-3 and normally about 2.
This discharge stream must be disposed of properly and cannot simply be flushed into the sewer system or waterways due to its heavy metal content. Most heavy metals are toxic and in chrome plating operations this problem becomes more acute because chromium (VI) ions are recognized as being carcinogenic to humans. Regardless of the metal content in the aqueous discharge stream, the discharge stream must be handled appropriately and in an environmentally safe manner. One option is to simply barrel the discharged water and ship it to a hazardous materials waste site. This option is not cost-effective because the costs associated with barreling and shipping can become extremely expensive at the high volumes handled by a typical electroplater. Moreover, it is not an environmentally friendly solution permitting the recycling of the water or metals from the discharge stream.
One known method of treating this discharge stream in chrome plating operations is to direct the stream into a large container and add a reducing agent, such as elemental iron powder, to the solution. The iron reacts with the chromium (VI) ions to reduce them to chromium (III) ions. Then, in the same container, sodium hydroxide is added to the solution to raise its pH to about 10. As the solution pH reaches this point, the chromium (III) ions and the metal ions from both the structures being plated and the electrodes used in the plating bath bond with hydroxyl ions in the solution and precipitate out from the solution. Then, these precipitates are separated from the solution in a single separating step, thereby producing a semi-solid or solid sludge that has the chromium and both metals all mixed together. The resulting discharge stream after the separation step is not suitable for reuse in the electroplating process and cannot be discharged into the environment as potable water. Specifically, the sodium hydroxide is not readily removed from the discharge stream and it cannot be recycled for use in the treatment of the flushing stream. In an ever increasingly environmentally conscious world, it is always desirable to recycle products that have recycling potential.
SUMMARY OF THE INVENTION
To address the above problem, the present invention provides both a method and a system for treating an aqueous solution discharged during flushing of an ion exchanger wherein the resulting discharge solution, after treatment, consists essentially of water.
Specifically, the present invention provides a method for treating an aqueous solution discharged from an ion exchanger during a flushing thereof wherein an aqueous flushing solution, preferably comprising sulfuric acid, is caused to flow through the apparatus and the resulting aqueous discharge solution is acidic and comprises metal ions from structures being plated in an electroplating bath, metal ions from electrodes used in the electroplating bath, and the metal ions being electroplated.
The solution's pH is raised by a pH raising agent having a cation with a valence of at least 2. The pH is raised such that hydroxyl ions in the solution bond with (i) the metal ions from the structures being plated in the electroplating bath to form a first precipitate; (ii) the metal ions from the electrodes to form a second precipitate; and (iii) the plating metal to form a third precipitate.
Next, the first, second and third precipitates are removed from discharge solution. This separation can occur by co-precipitation wherein the first, second and third precipitates are removed as group or by selective precipitation wherein they may be selectively precipitated out of solution.
The discharge solution is aerated with carbon dioxide such that the cations from the pH raising agent react with carbon dioxide to form a carbonate precipitate. The calcium carbonate precipitate is then separated from the discharge solution such that the solution consists essentially of water.
The advantage of the present invention is that the discharge stream consists essentially of water and can be recycled for use within the electroplating plant or discharged back into the environment.
Other objects, features and advantages will become apparent from the following detailed description, the accompanying drawings and the appended claims.
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CWS Parts Company
King Roy
Leader William T.
Pillsbury & Winthrop LLP
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