Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B15/00—Obtaining copper
  • C22B15/0026—Pyrometallurgy
  • C22B15/006—Pyrometallurgy working up of molten copper, e.g. refining

Definitions

• the present invention pertains to refining copper precipitated from solution, and more particularly to refining metallic copper precipitates by pyrometallurgical techniques.
• Metallic copper precipitates can also be obtained by hydrogen reduction of copper-containing process solutions at elevated pressures of 350 pounds per inch at 2- 90C. These. powders are generally finely divided and contain up to about 0.1% sulfur and 0.01% iron.
• metallic copper that contains up to about 5% iron, up to about oxygen, up to about 1% sulfur and at least one volatile impurity selected from the group consisting of arsenic, bismuth, lead, selenium, tellurium, tin, and zinc, after any preliminary beneficiation treatment, is melted in a free-oxygen-containing atmosphere to slag iron and to form a copper bath containing sulfur and oxygen, with the oxygen content being at least in excess of the sulfur content without producing a separate cuprous oxide phase, and at least one other volatile impurity selected from the group consisting of arsenic, bismuth, lead, selenium, tellurium, tin, and zinc.
• a purge gas which can contain free oxygen, is passed through the copper bath while the bath is maintained at subatmospheric pressures below about 0.001 atmosphere to rapidly lower the sulfur content to less than about 0.001%.
• the single phase copper bath contains at least about 0.1%
• the flow of the purge gas is terminated after the sulfur content of the copper bath is lowered to less than about 0.001%, and the bath is subjected to subatmospheric pressures of less than about 0.0002 atmosphere for further refining by volatilizing at least one impurity selected from the group consisting of arsenic, bismuth, lead, selenium, tellurium, tin and zinc from the bath.
• the copper bath is then deoxidized. Before casting, the copper bath can be optionally treated with phosphorus to produce oxygen-free copper.
• a solid reductant is added to the copper bath either during the entire deoxidation treatment or during the latter stages thereof, i.e., when the oxygen content of the bath falls to about 0.05% or less, to lower the oxygen content to about 0.01%, advantageously about 0.005%.
• the copper melt can optionally be completely deoxidized by phosphorus additions thereto.
• the deoxidation treatment with solid carbon is advantageously conducted at subatmospheric pressures less than about 0.01 atmosphere, e.g., between about 0.005 atmosphere and 0.0005 atmosphere.
• the bath is maintained in a state of turbulence by purging with a non-oxidizing gas, i.e., an inert or reducing gas.
• Inert gases such as nitrogen or argon, are advantageously employed as purge gases to minimize the problems associated with dissolved hydrogen at low oxygen contents.
• purge gas flow rates between about 1 and standard cubic feet per hour per square foot of bath surface area are employed to provide the re-.
• the copper bath is desulfurized, refined and deoxidized at temperatures of at least about l,200C. and advantageously at temperatures between about 1,250and 1,400C. to insure rapid and substantially complete desulfurization, refining, and deoxidation.
• the various operations can be conducted in any type of furnace but it has been found advantageous to use induction furnaces to take advantage of the stirring effect of these furnaces. Induction furnaces have the additional advantages of completely eliminating the possibility of contaminating the copper by combustion products of the fuel. An even further advantage of induction furnaces is that they can be readily equipped with appropriate vacuum equipment.
• Cement copper which was derived from the precipitation of copper from sulfate leach solutions on shredded, detinned cans and which contained 0.7% sulfur, 6% oxygen, 1.2% iron, 0.029% arsenic, 0.038% lead, 0.0023% selenium, 0.0007% tellurium and minor amounts of calcium oxide, silica and alumina, was melted in air in an induction furnace, which furnace was equipped with a vacuum unit, to slag the iron, calcium oxide, silica and alumina and to form a copper bath which contains 0.01% iron, 0.30% sulfur, and 1.49% oxygen.
• the surface of the bath was cleared of the slag, and the pressure within the vacuum unit was then lowered to 0.0003 atmosphere while nitrogen at a rate of 15 standard cubic feet per hour per square foot of bath surface area is passed through the bath to lower the sulfur'content to 0.0005%. Purging of the bath with nitrogen is then terminated, and the pressure within the furnace is lowered to 0.0001 atmosphere to further refine the bath. During this stage of the refining operation, the levels of arsenic, lead, selenium, and tellurium are lowered to 0.01%, less than 0.002%, 0.001%, and 0.0003%, respectively. Carbon is then added to the bath, and the bath is again purged with nitrogen at a flow rate of 12 standard cubic feet per square foot of melt surface per hour to lower the oxygen content of the bath to 0.02%. The bath is then cast.
• EXAMPLE I This example confirms thatmolten copper is more readily desulfurized by a simultaneous inert gas purge and vacuum treatment than by a vacuum treatment alone, even with pressures of one-tenth or less of that employed with an inert gas purge.
• the bath initially containing ppm sulfur was simultaneously subjected to subatmospheric pressures and a nitrogen purge at a rate of about 15 standard cubic feet per square foot of surface melt per hour.
• EXAMPLE III Although an inert gas purge greatly improves subatmospheric pressure desulfurization, this example confirms that the inert gas purge interferes with other refining reactions by precluding the attainment of the necessary low pressures and that two-stage subatmospheric pressure treatments are advantageous in providing an overall refining operation.
• Two copper baths one containing 19 ppm selenium and 13 ppm tellurium and the other containing 29 ppm selenium and 11.5 ppm tellurium, were established by heating cement copper to 2,300F. Both baths were oxidizing in that oxygen was present in amounts of more than 1%.
• the bath containing 19 ppm selenium was simultaneously purged with nitrogen at a rate of 15 standard cubic feet per square foot of melt surface area per hour and subjected to subatmospheric pressure between 200 and 250 microns. Samples were taken at various intervals and analyzed for selenium and tellurium contents with the results being shown in Table 2A.
• the bath initially containing 29 ppm selenium was merely subjected to subatmospheric pressures between 15 and 32 microns. Again, samples were periodically taken and analyzed for selenium and tellurium, and the results are reported in Table 2B.
• EXAMPLE IV This example confirms that molten copper is more effectively deoxidized by carbon at subatmospheric pressures with a simultaneous inert gas purge than by hdyrogen bubbled through molten copper.
• a copper bath containing 0.26% oxygen was established, and a hydrogen-nitrogen gaseous mixture containing 75% hydrogen was bubbled through the bath at a rate of 6.9 standard cubic feet per hour which was equivalent to 100 standard cubic feet per square foot of melt surface area per hour, which flow rate insured vigorous agitation of the bath.
• the oxygen content of the bath was determined at various intervals wtih the results being reported in Table 3A.
• the present invention provides a pyrometallurgical process for refining metallic copper precipitated from aqueous solutions.
• the present invention has been described in conjunction with the treatment of cement copper, those skilled in the art will appreciate that the process can be employed to refine melts of electrorefined or electrowon copper that are contaminated with sulfur during melting operations or contain objectionably high quantities of arsenic, bismuth, lead, selenium, tellurium, tin, and zinc.
• a process for refining metallic copper that contains up to about 5% iron, up to about 10% oxygen, up to about 1% sulfur and at least one volatile impurity selected from the group consisting of arsenic, bismuth, lead, selenium, tellurium, tin, and zinc which comprises: melting the metallic copper precipitate in a free-oxygen-containing atmosphere to slag the iron and to form a copper bath containing sulfur, oxygen, and at least one other volatile impurity selected from the group consisting of arsenic, bismuth, lead, selenium, tellurium, tin and zinc, the oxygen content being at least in excess of the sulfur content without forming a separate cuprous oxide phase; removing the slag from the copper bath; then passing a purge gas, which can contain free oxygen, through the copper bath while maintaining the bath at a subatmospheric pressure below about 0.01 atmosphere to rapidly lower the sulfur content of the bath to less than about 0.001%; then terminating the flow of the purge gas and lowering the pressure above the copper
• the purge gas is at least one member selected from the group consisting of nitrogen, argon, air and oxygen.
• the purge gas is at least one member selected from the group consisting of nitrogen, argon, air and oxygen and is passed through the copper bath at a rate between about 1 and 20 standard cubic feet per hour per square foot of bath surface area.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Logic Circuits (AREA)

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Citations (24)

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  • BE BE791287D patent/BE791287A/xx unknown
• 1971
  • 1971-11-15 US US00198984A patent/US3767383A/en not_active Expired - Lifetime
• 1972
  • 1972-10-02 CA CA153,029A patent/CA973720A/en not_active Expired
  • 1972-11-09 ZA ZA727948A patent/ZA727948B/xx unknown
  • 1972-11-10 PH PH14073A patent/PH9937A/en unknown
  • 1972-11-10 ZM ZM177/72*UA patent/ZM17772A1/xx unknown
  • 1972-11-14 SE SE7214758A patent/SE396770B/sv unknown
  • 1972-11-14 NO NO4123/72A patent/NO131550C/no unknown
  • 1972-11-14 FR FR7240335A patent/FR2160439B1/fr not_active Expired
  • 1972-11-14 GB GB5256972A patent/GB1351089A/en not_active Expired
  • 1972-11-14 FI FI3184/72A patent/FI60239C/fi active
  • 1972-11-15 JP JP47114630A patent/JPS524250B2/ja not_active Expired
  • 1972-11-15 DE DE2255977A patent/DE2255977C3/de not_active Expired
  • 1972-11-15 NL NL7215477A patent/NL7215477A/xx not_active Application Discontinuation
  • 1972-11-17 ES ES408574A patent/ES408574A1/es not_active Expired

Patent Citations (24)

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