Classifications

• • 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
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/40—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using liquids, e.g. salt baths, liquid suspensions
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/34—Methods of heating
  • C21D1/44—Methods of heating in heat-treatment baths
  • C21D1/46—Salt baths
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
  • C21D1/607—Molten salts
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the salts added for this purpose generally include alkali chlorides, e.g., sodium chloride and potassium chloride, alkali cyanides, e.g., sodium cyanide and potassium cyanide, alkali cyanates, e.g., sodium cyanate and potassium cyanate, alkali nitrites, e.g., sodium nitrite and potassium nitrite, alkali nitrates, e.g., sodium nitrate and potassium nitrate, alkali carbonates, e.g., sodium carbonate and potassium carbonate and alkaline earth salts such as barium carbonate, strontium chloride, barium chloride, strontium carbonate, calcium carbonate, magnesium carbonate, calcium chloride, and magnesium chloride.
• alkali carbonates e.g., sodium carbonate and potassium carbonate and alkaline earth salts
• the cyanide salts for example are converted into hydrocyanic acid and this is then burned catalytically.
• the barium and cyanide components of hardening bath residues can be recovered if the salt residue which has been broken down in normal size pieces and slurried in water is treated with an aqueous iron (II) chloride solution at a pH of 7 to 14 in an amount equivalent to the cyanide portion of the residue and in the presence of the least amount of alkali carbonate, e.g., sodium carbonate or potassium carbonate corresponding to alkathere can be used soda or-potash. Soda is preferred since it is frequently already present in the hardening I salt residue. It is preferably added in solid form.
• the concentration of iron (II) chloride in the water ist not critical. Conveniently it is employed as a 5 to 40 so lution.
• the resulting precipitate contains the alkaline earth carbonates, i.e., also magnesium carbonate; the filtrate on the contrary contains the alkali ferrocyanide formed as well as alkali cyanate and alkali chloride.
• the carbonate precipitate after washing with water is dissolved in a mineral acid, preferably hydrochloric acid, and by the addition of barium hydroxide the ,en-
• tire alkaline earth ions with the exception of barium ions were precipitated as hydroxide and separated from barium.
• the hydroxides can be deposited directly with suitable precautions or after conversion to thesulfates.
• the resulting, pure barium. chloride solution can be worked up in known manner, for example, in a spray drier or crystallizer.
• alkali cyanide e.g., sodium cyanide or potassium cyanide
• alkali ferrocyanide e.g., sodium fer rocyanide or potassium ferrocyanide
• the hardening bath residue is broken to the usual granule size, preferably to 2 to 5 mm. Finely divided material to be sure is more easily decomposed but requires higher grinding costs, while with coarse grained material long reaction times are needed in the decomposition.
• This pre-broken salt is then slurried, preferably in 2 /2 times its amount of water.
• the exact amount of water is not critical. For example it can be 1 to 10 times the amount of broken salt.
• the iron (II) salt solution can, if necessary also be added in a somewhat larger than the equivalent amount, namely in an excess up to about 10%.
• the individual concentrations of the iron (II) salt solution, the alkali carbonate solution and the mineral acid are those of commerce and preferably are about grams of material per liter of solution but can be varied widely.
• the industrial advantage of the process of the invention is not only the effective decontamination of the hardening salt residues but also, in the recovery of the main components, barium and cyanide.
• the precipitate was dissolved in l65 liters of 10 weight hydrochloric acid. By the addition of 3 kg of solid Ba(OH the excess acid was neutralized and all of the alkaline earth metals except the barium precipitated. The precipitate formed was filtered off and the filtrate neutralized with hydrochloric acid. The clear solution was evaporated in a spray drier.
• a process of decontaminating a hardening salt residue from treating steel with a hardening salt contain ing alkaline earth metal at least a part of which is barium and also containing cyanide and alkali chloride containing alkaline earth metal at least a part of which is barium and also containing cyanide comprising slurrying the coarsely broken pieces of salt residue in water and then treating said slurry with an amount of aqueous iron (ll) chloride at least sufficient to convert the cyanide portion of said residue to alkali ferrocyanide at a pH of 7-14 and in the presence of alkali carbonate in an amount at least sufficient to convert all of the alkaline earth metal present to the carbonate but not over 30% based on hardening salt residue to be decontaminated, and separating the cyanide containing solution from the carbonate containing precipitate.
• aqueous iron (ll) chloride at least sufficient to convert the cyanide portion of said residue to alkali ferrocyanide at a pH of 7-14 and in the presence
• a process according to claim 1 comprising dissolving the carbonate precipitate in mineral acid, adding barium hydroxide in an amount sufficient to precipitate all of the alkaline earth metals present except the barium as the corresponding hydroxides and separating the alkaline earth hydroxide precipitate from the barium containing filtrate.
• a process according to claim 1 including the steps of separating the cyanide in solution as iron (ll) ferrocyanide by acidifying the solution and adding iron (ll) chloride to precipitate the iron ferrocyanide.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Processing Of Solid Wastes (AREA)
• Removal Of Specific Substances (AREA)
• Manufacture And Refinement Of Metals (AREA)

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Cited By (5)

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Citations (5)

• 1972
  • 1972-06-30 DE DE2232123A patent/DE2232123C2/de not_active Expired
• 1973
  • 1973-06-19 US US37149873 patent/US3865921A/en not_active Expired - Lifetime
  • 1973-06-29 GB GB3120473A patent/GB1427574A/en not_active Expired

Patent Citations (5)

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