Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F7/00—Compounds of aluminium
  • C01F7/48—Halides, with or without other cations besides aluminium
  • C01F7/50—Fluorides
  • C01F7/54—Double compounds containing both aluminium and alkali metals or alkaline-earth metals

Definitions

• This invention relates to the recovery of valuable fluorine, aluminum and sodium compounds from aluminum electrolytic furnace wastes.
• the furnace wastes are leached with a solution of alkali. for example alkali metal hydroxides and cryoill) Reissu-ed Aug. 19, 1969 ree lite is precipitated from this solution in two separate and distinct steps, first in an alkaline pH by contact with a hydrogen fluoridecontaining liquid and then in an acid pH by Contact with an aluminum trifluoridc-containing liquid.
• alkali for example alkali metal hydroxides and cryoill
• the liquor may be immediately pumped to the second precipitation step and the quantity of aluminum trifluoride solution r quired will be known immediately.
• the supply of aluminum trifluoride solution can alternatively be controlled. in the second precipitation step, by testing samples of the mother liquor from the first precipitation to determine at what point addition of a further increment of tritluo ride solution will not cause further precipitation to occur. In either case, long storage periods and the requirement for storage capacities are eliminated and the entire process may be carried on continuously. Furthermore.
• the furnace wastes such as furnace pot bottoms and linings and other perishable elements of the funrace which absorb aluminum. fluorine and sodium compounds. are preferably crushed to small particles so as to increase the efficiency of the leaching operation, for example, to an average particle diameter of 3 mm. or less.
• an aqueous solution of alkali for example, sodium hydroxide in a concentration of 0.66% by weight is mixed with the crushed furnace wastes, preferably with agitation so that the fluorine, aluminum and sodium compounds may be extracted from the furnace wastes.
• the leaching liquid can be the recycled liquor from which cryolite has already been precipitated in accordance with the invention and to which have been added the required amount of sodium hydroxide.
• the leach liquor is subjected to precipitation in an alkaline pH in the range of 7.5 to 13, and preferably at it) to H.
• the precipitation is carried out by contacting the alkaline leach liquor with a hydrogen fluoride-containing aqueous liquid, for example, tower acid or an aqueous solution of hydrogen fluodide.
• tower acid is the aqueous liquid absorbent obtained in the gas scrubbers which are connected to the aluminum electrolytic furnace. In these scrubbers, the OE gases from the furnace are washed with water to remove volatile fluorides and other noxious materials.
• the hydrogen fluoridecontaining liquid is supplied in such proportions that from 5.0 to 6 equivalent Weights of hydrogen fluoride are added for each equivalent weight of aluminum in the alkaline leach liquor.
• the concentration of hydrogen fluoride in the aqueous liquid. by which it is to be supplied, may vary considerably from about 2% to about 20% or more and generally speaking as the concentration of HF increases less of the liquid may be mixed with the alkaline leach liquor to supply the required number of equivalents of hydrogen fluoride.
• the hydrogen fluoride-containing liquid is supplied to the alkaline leach liquor preferably while the entire liquid is being agitated and precipitation of so-called basic aluminum takes place.
• the mother liquor together with the precipitated cryolite is then subjected to a second precipitation, this time in an acid medium.
• the liquor is contacted with an aqueous solution of aluminum trifluoride formed by dissolving aluminum hydroxide in the same hydrogen fluoride-containing liquid as used in the first precipitation step or in any other hydrogen fluoride-containing liquid.
• the quantity of aluminum hydroxide dissolved in the hydrogen fluoride-containing liquid will be stoichiometric as required to form aluminum trifluoride in accordance with the equation:
• the remaining leach liquor may be desirably recycled so that additional sodium hydroxide may be added for leaching additional crushed furnace wastes in accordance with the process, Before the liquid is so recycled, it is preferable to remove any residual amounts of carbon dioxide contained in the liquid since otherwise a portion of the sodium hydroxide to be added will be reacted to sodium carbonate and thereby wasted. This will increase the cost of the process and in time result in excessive consumption of sodium hydroxide. For this reason.
• the leach liquors to be recycled usually contain small quantities of dissolved sodium fluoride which are unavoidable as the precipitation following in the alkaline and acid stages is not 100% complete. However, this small quantity of dissolved sodium fluoride does not in any way interfere with the operation of the process.
• Example 1 1055 kgs. of furnace bottoms containing substantial i quantities of sodium, aluminum and fluorine compounds were crushed to particles averaging about 3 mm. in diameter or less. The crushed furnace bottoms were leached with 12,850 liters of a recycle liquor which contained approximately 8 kgs. of sodium fluoride and to which had been separately added 151 liters of a 40% (by weight) aqueous sodium hydroxide solution. After removal of the insolubles by filtration and washing, 13,000 liters of leach liquor was obtained which contained 90.3 kgs. of fluorine, 21.3 kgs. of aluminum and 155.5 kgs. of sodium. Thus. approximately 86.8 kgs. of fluorine, 21.3 kgs. of aluminum and 101.5 kgs. of sodium, all economically valuable materials, were extracted from the furnace bot toms by the leach liquor.
• the leach liquor was subjected to a first precipitation step by mixing it at a pH between 10 and 11 with approximately 2.660 liters of tower acid which contained 3% by weight of hydrogen fluoride and small amounts of sodium and aluminum.
• the tower acid was obtained from gas scrubbers connected to the aluminum electrolytic furnaces in which scrubbers the furnace waste gases are washed with water to remove volatile fluorides and other noxious materials.
• the tower acid supplied slightly more than 80 kgs. of hydrogen fluoride or a little more than 5.0 kgs. of equivalents for kg. equivalent of aluminum contained in the leach liquor.
• a major proportion of the aluminum in the leach liquor was precipitated as cryolite.
• the mother liquor together with the precipitated cryolite was subjected to a second precipitation step by mixing it at a pH between 4 and 5 with 2.840 liters of a weakly acidic aqueous solution of aluminum trifluoride. This solution was formed by dissolving 101 kgs. of aluminum hydroxide in 2,840 liters of the previouslymentioned tower acid containing 3% by weight of hydrogen fluoride. On mixing of the two liquids at acid pH. additional cryolite precipitated and a total of 470 kgs. of cryolite was recovered from both precipitations. This represents approximately 75% of the total original amount of fluorine that was contained in the crushed furnace bottoms and in the tower acid, and substantially 100% of the sodium, fluorine and aluminium that was contained in the leach liquor and in the first and second precipitating liquids.
• the method of recovering fluorine. aluminum and sodium compounds from aluminum electrolytic furnace wastes which comprises leaching said furnace wastes with an aqueous solution of alkali to extract said fluorine, aluminum and sodium compounds, mixing with the leach liquor at a pH from 7.5 to 13 a liquid containing hydrogen fiuoride to form a precipitate of said fluorine, aluminum and sodium compounds without determining in advance the precise quantities of said compounds that are dissolved in said leach liquor, then mixing with the resulting precipitate-containing liquor at a pH from 2.0 to 5 a liquid containing aluminum trifiuoride to form a further precipitate of said fluorine, aluminum and sodium compounds again without determining in advance the precise quantities of said compounds that are still dissolved in said precipitate-containing liquor, whereby substantially all of the fluorine, aluminum and sodium in said leach liquor and in said first and second liquids is recovered.
• a method as in claim 1 which includes the step of crushing said furnace wastes to small particles prior to the leaching thereof.
• a method as in claim 1 which includes the step of recycling the mother liquor remaining after formation of the second precipitate for use in leaching additional furnace wastes.
• a method as in claim 3 which includes the step of removing any residual carbon dioxide which may be contained in said mother liquor prior to the recycling thereof.
• liquid containing hydrogen fluoride is obtained from gas scrubbers connected to aluminum electrolytic furnaces and contains about 3% by weight of hydrogen fluoride.
• a method as in claim 1 wherein said liquid containing aluminum trifluoride is obtained by dissolving aluminum hydroxide in a liquid containing about 3% by weight of hydrogen fluoride.
• a method of recovering fluorine, aluminum and sodium compounds from aluminum electrolytic furnace wastes which comprises leaching said furnace wastes with an aqueous solution of alkali to extract said fluorine, aluminum and sodium compounds, mixing with the leach liquor at a pH from about to about 11 a liquid containing hydrogen fluoride to form a precipitate of said fluorine, aluminum and sodium compounds without determining in advance the precise quantities of said compounds that are dissolved in said leach liquor, mixing with the resulting precipitate-containing liquor at a pH from about 4 to about 5 a liquid containing aluminum trifluoride to form a further prepicitate of said fluorine, aluminum and sodium compounds again without determining in advance the precise quantities of said compounds that are still dissolved in said precipitate-containing liquor, separating said precipitates from the liquor and recycling said liquor for use in leaching additional furnace wastes, whereby substantially all of the fluorine, aluminum and sodium in said leach liquor and in said first and second liquids is recovered.
• the method of recovering fluorine, aluminum and sodium compounds for aluminum electrolytic furnace wastes which comprises leaching said furnace wastes with an aqueous solution of alkali to extract said fluorine, aluminum and sodium compounds, mixing with the leach liquor at a pH from 7.5 to 13 a liquid containing hydrogen fluoride to form a precipitate of said fluorine, aluminum and sodium compounds without determining in advance the precise quantities of said compounds, that are dissolved in said leach liquor, then mixing With the resulting precipitate-containing liquor at a pH from 2.0 to 6.0 a liquid containing aluminum trifluoride to form a further precipitate of said fluorine, aluminum and sodium compounds again without determining in advance the previse quantities of said compounds that are still dissolved in said precipitate-containing liquor, whereby substantially all of the fluorine, aluminum and sodium in said leach liquor and in said first and second liquids is recovered.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Inorganic Chemistry (AREA)
• Processing Of Solid Wastes (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
• Removal Of Specific Substances (AREA)
• Electrolytic Production Of Metals (AREA)
• Manufacture And Refinement Of Metals (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=19908710

Family Applications (1)

Country Status (6)

Cited By (2)

Families Citing this family (2)

• 1963
  • 1963-09-11 ES ES291558A patent/ES291558A1/es not_active Expired
  • 1963-09-12 DE DE19631467265 patent/DE1467265A1/de active Pending
  • 1963-09-26 GB GB37995/63A patent/GB1027362A/en not_active Expired
  • 1963-09-27 CH CH1192763A patent/CH428687A/de unknown
  • 1963-10-11 FR FR950347A patent/FR1371110A/fr not_active Expired
• 1968
  • 1968-11-29 US US26645D patent/USRE26645E/en not_active Expired

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