Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G3/00—Compounds of copper
  • C01G3/02—Oxides; Hydroxides
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/02—Treatment of water, waste water, or sewage by heating
  • C02F1/025—Thermal hydrolysis
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/20—Heavy metals or heavy metal compounds

Definitions

• This invention relates to the treatment of waste or spent copper-containing solutions, such as spent ammonium persulfate copper etching solutions, to make them suit-able for discarding, for example, into a sewage system in form of non-toxic Waste.
• ammonium persulfate solution is used as an effective and fast etchant for copper and brass at temperatures from room temperature to 150 -F.
• the active ammonium persulfate is consumed by the etching process and when the solution becomes saturated with copper, the etchant solution has to be discarded.
• Such an etching solution is highly toxic even at a very low concentration, due essentially to its copper salt content and is thus a proper subject for waste treatment.
• Neutralization of the free acid in the spent solution constitutes an insuflicient treatment, since the copper salts are soluble in the ammonia compounds remaining therein.
• the presently accepted and employed method of treatment involves a two-stage process. In the first stage, the copper is progressively removed from the solution by electrodepositing it on cathode sheets employed with insoluble anodes. When the copper is as completely as possible removed by electrolysis, the second stage of the treatment is performed and involves neutralization of the free acids in the remaining solution with alkali metal hydroxides of carbonates.
• Another object of my invention has been to provide a method of treating such a toxic solution as to minimize the equipment involved, the tedious controls and tests heretofore required, and to do so by an entirely new approach to the problem;
• a further object of my invention has been to devise a treatment for a copper-containing toxic waste solution of an improved, more effective and complete type
• the invention relates to a process for the treatment of a used etching solution containing toxic copper salts and ammonium persulfate to convert the solution from a toxic to a non-toxic condition for freely discarding as non-toxic Waste. It involves adding an excess of caustic soda to the toxic solution and heating the solution, to convert the ammonium and copper content into ammonia gas and copper oxide, and to drive off the ammonia gas and precipitate out or remove the copper oxide from the solution to form a copper-free and ammonia-free supernatant liquid.
• I entirely eliminate the need for plating-out the copper content of a spent ammonium pers-ulfate etchant solution by first adding an excess of a strong neutralizing alkali, such as caustic soda, preferably in solution form, to the spent etchant to provide a solution having a minimum pH of 12.
• a strong neutralizing alkali such as caustic soda
• the thus-treated solution is then conditioned or heated and preferably brought to a boiling temperature to drive-out its ammonia content.
• the caustic soda is employed to convert the ammonium sulfate compounds into ammonium hydroxide which is then driven-out of the solution by the heating operation in the form of ammonia gas.
• caustic soda additions may be made to maintain the excess caustic soda needed, since some caustic soda is consumed for the neutralization and precipitation of the copper as the ammonia is driven out.
• the vapor pressure of the ammonia gas is sufiiciently high to complete the reaction in about one hour at the boiling temperature of the solution, for example, in the neighborhood of C. Heating, however, may be effected at a lower temperature for a slightly longer time, depending on the temperature of the solution.
• a good indication that all the ammonium compounds are converted into ammonium hydroxide is the fact that free caustic soda is available.
• the pH of a solution containing about .4 gram per liter of NaOH is 12, thus a pH of 12 indicates complete conversion.
• As the copper is precipitated some further caustic soda may be needed, as indicated by a pH test, but my usual procedure is to add a suflicient excess at the beginning of the treatment. The quantity of this excess will depend on the usual copper concentration of the solution and will be determined by the user in an empirical manner. It is thus apparent that free caustic soda should be available throughout the treatment.
• NH is a gas that, when dissolved in water, forms ammonium hydroxide
• the vapor pressure of ammonia gas at 25 C. is sufficiently low that the aqueous tension is in balance with the vapor pressure of the gas up to the maximum solubility limit or" 480 grams per liter of ammonia.
• the commercial available concentration is only 280 grams per liter.
• the lower the concentration the greater the tendency of the aqueous tension to overcome the vapor pressure of the ammonia gas which is considerable, even at room temperature. As the solution temperature is increased, the vapor pressure increases and thus, the solubility of the ammonia in water becomes less and less.
• the vapor pressures of ammonia at different temperatures are about atmospheres at C., about 31 atmospheres at 68 C., about 41 atmospheres at 80 C., and about 62 atmospheres at 100 C.
• the practical result is that at a boiling temperature, the ammonia gas may be driven out of solution in about one hour. At 80 C., the time required will increase by about 50 to 100%.
• Equations 2 et seq. A further consideration is that dehydration of the precipitated copper hydroxide to oxide, see Equations 2 et seq., is effected by heating the solution above room temperature, and while this reaction will proceed at a temperature lower than required for boiling, optimum results are obtained by boiling or by the use of a boiling temperature.
• cupric hydroxide While the ammonium compound, namely, ammonia gas, is being removed from the solution due to vaporization-01f, the copper salts become insoluble and precipitate as cupric hydroxide.
• the maintenance of the heated or boiling solution causes the cupric hydroxide, itself, to decompose due to dehydration, so that cupric oxide is precipitated.
• cupric oxide Since cupric oxide is a relatively heavy compound having a specific gravity of 6.4 to 6.45, it settles rapidly and can be easily removed from the solution by settling, filtration or centrifuging.
• the remaining supernatant liquid consists essentially of sodium sulfate and sodium hydroxide which may be neutralized with a suitable acid, such as sulphuric acid, so that the solution can now be fully discarded as fully-treated non-toxic waste. 7
• etching reaction of an ammonium persulfate solution as heretofore employed in etching copper or copper in brass, is represented as follows:
• Equation 1 the ammonium persulfate solution i substantially consumed by the reaction, in that its content is decreased from about 240 grams per liter to about 10 grams per liter. It will be further noted that, in accordance with heretofore employed conventional treatment, in which copper is removed by electrolysis, essentially only remains. However, in accordance with my treatment, procedure or method, ammonia gas is driven oif after neu- 4. tralization with caustic soda, such that Na SO +CuO (precipitated) still remains, as follows:
• the spent etchant solution need only be drawn 01f into a suitable heating tank or vessel, that the caustic soda solution can then be added to the solution of the tank and the solution heated to complete the process.
• the treated solution can be withdrawn from an intermediate level of the tank and the precipitated copper oxide may be removed after it has settled to the bottom of the tank.
• a process for the treatment of a used etching solution containing copper salts including a copper ammonium compound and a minor amount of ammonium persulfate to free the solution from its toxic ammonia and copper content for discarding the treated solution as Waste comprises, adding an excess of a strong neutralizing alkali of the nature of caustic soda to the solution, maintaining an excess of the alkali in the solution throughout the treat-ment in an amount sufiicient to provide a minimum pH of about 12; heating the solution to an elevated temperature above room temperature and maintaining the excess of the alkali and the elevated temperature while converting its ammonium content into ammonia gas and driving-01f the ammonia gas, and while progressively with the driving-oil of the ammonia gas, freeing its copper con tent from its ammonium compound and converting its freed copper content into and precipitating it out of the solution as copper oxide; and continuing the defined treatment until the solution is essentially fully freed of its toxic ammonia and copper content.
• a process for the treatment of a used etching solution containing copper salts including a copper ammonium compound and a minor amount of ammonium persulfate to free the solution of its toxic ammonia and copper content for discarding the treated solution as waste comprises, adding an excess of a strong neutralizing alkali of the nature of caustic soda to the solution; heating the solution to an elevated temperature above room temperature and agitating it and maintaining the excess of the alkali to provide the solution with a minimum pH of about 12, while converting its ammonium content into ammonia gas and vaporizing-oft" the ammonia gas, and while progressively with the vaporizing-oil of the ammonia gas, freeing its copper content from its ammonium compound and precipitating its copper content out of the solution; and continuing the defined treatment until the solution is essentially fully freed of its toxic ammonia and copper content.
• a process for the treatment of a used etching solution containing copper ammonium sulfate, copper sulfate, ammonium sulfate, sulphuric acid and a minor amount of ammonium persulfate in solution to essentially fully free the solution from its toxic ammonia and copper content for discarding the treated solution as waste which comprises, reacting the ammonium sulfate with a strong neutralizing alkali hydroxide and forming an alkaline sulfate and ammonium hydroxide, applying heat and agitation to the ammonium hydroxide to convert it to ammonia gas, and driving the ammonia gas out of the solution; reacting the copper ammonium sulfate with the alkali hydroxide to form an alkali sulfate, copper hydroxide and ammonia gas, and driving off the ammonia gas from the solution; applying heat to convert the copper hydroxide into copper oxide and water, and precipitating the copper oxide out of the solution; progressively with the driving oil

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Hydrology & Water Resources (AREA)
• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Water Supply & Treatment (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Inorganic Chemistry (AREA)
• Removal Of Specific Substances (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Citations (2)

• 0
  • NL NL121499D patent/NL121499C/xx active
  • NL NL262660D patent/NL262660A/xx unknown
• 1961
  • 1961-02-02 GB GB4017/61A patent/GB905615A/en not_active Expired
  • 1961-02-04 DE DE19611517681 patent/DE1517681A1/de active Pending
  • 1961-02-14 CH CH174461A patent/CH409799A/fr unknown
  • 1961-02-17 FR FR853014A patent/FR1295376A/fr not_active Expired
• 1962
  • 1962-11-20 US US239091A patent/US3218254A/en not_active Expired - Lifetime

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