US 5,723,097 AGranted

Method of treating spent potliner material from aluminum reduction cells

AssigneeGoldendale Aluminum Company

InventorsRobert J. Barnett, Michael B. Mezner

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Abstract

A method of treating spent potliner material from aluminum reduction cells is disclosed. The spent potliner material is introduced into a sulfuric acid digester to produce a gas component including hydrogen fluoride and hydrogen cyanide and a slurry component including carbon, silica, alumina, sodium sulfate, iron, calcium and magnesium. The gas component is recovered and heated an effective amount to eliminate hydrogen cyanide and produce a remaining gas component including CO.sub.2, H.sub.2 O, nitrogen oxides and HF. The remaining gas component is directed through a water scrubber to form hydrofluoric acid, and the hydrofluoric acid is admixed with aluminum hydroxide to create aluminum fluoride. The slurry component is rinsed with water to separate a first solid fraction containing carbon, alumina and silica from a second liquid faction. The pH of the liquid fraction is adjusted to first create and separate aluminum hydroxide and then to separate sodium sulfate. Finally, the solid fraction is admixed with an alumina/silica mix and then subjected to an elevated temperature in an oxygen-rich atmosphere to oxidize the carbon and vitrify the alumina and silica into refractory material.

Claims31

Dependent claims

A method of treating spent potliner material from aluminum reduction cells, which spent potliner material may include fluoride compositions, cyanide compositions, iron compositions, calcium compositions, magnesium compositions, alumina, carbon, silica and sodium sulfate, said method comprising the steps of:

introducing said spent potliner material into a sulfuric acid digester to produce a gas component which may include hydrogen fluoride and hydrogen cyanide, and a slurry component including carbon, silica, alumina, sodium sulfate, iron sulfate, calcium sulfate and magnesium sulfate;
recovering said gas component from said digester and heating it to a temperature which is sufficient to decompose any hydrogen cyanide which has been produced, and thereby produce a gas component which is substantially cyanide free, and including CO.sub.2, H.sub.2 O, nitrogen oxides and HF;
combining said gas component with water to form hydrofluoric acid;
admixing said hydrofluoric acid with aluminum hydroxide to create aluminum fluoride;
rinsing said slurry component with water to separate a first solid fraction including carbon, alumina and silica from a second liquid fraction;
adjusting said second liquid fraction to a first pH in the range of about 12.0-12.5 to create sodium aluminate in solution while precipitating impurities including Ca, Fe and Mg and then filtering the impurities from the liquid to produce a filtered liquid fraction;
adjusting the filtered liquid fraction to a second pH in the range of about 7.0-8.0 to precipitate and form aluminum hydroxide from the filtered liquid fraction;
admixing said first solid fraction with an alumina/silica mix to form an admixture;
and
subjecting said admixture to an elevated temperature in an oxygen-rich atmosphere to oxidize said carbon and vitrify said alumina and silica into refractory material.

7 more elements

A process for recovering fluoride, aluminum, sodium and brick material from spent aluminum potliner (SPL) material said SPL material further including cyanide, carbon, silica, calcium, iron and magnesium, said process comprising the steps of:

crushing said SPL material into a particulate feed;
introducing said particulate feed into a heated sulfuric acid digester to produce a gas component including hydrogen fluoride and hydrogen cyanide, and a slurry component comprising a residual solid fraction and a liquid fraction, said liquid fraction having an acid pH and said solid fraction including carbon, silica, alumina, sodium sulfate, calcium, iron and magnesium;
recovering said gas component from said digester and heating it to a temperature effective to convert said hydrogen cyanide and hydrogen fluoride to a residual gas component including carbon dioxide, steam, nitrogen oxides and hydrogen fluoride;
directing said residual gas component through a water scrubber to form hydrofluoric acid and then reacting said hydrofluoric acid with aluminum hydroxide to form a first end product of aluminum fluoride;
rinsing said slurry component with a water rinse to first remove salts therefrom and then polish the solids in said solid fraction to form the liquid fraction containing said salts and the solid fraction containing said carbon, alumina and silica;
adjusting the pH of said slurry component liquid fraction to a first pH in the range of about 12.0-12.5 to create and separate an intermediary product of sodium aluminate in solution while precipitating calcium hydroxide, iron hydroxide and magnesium hydroxide as impurities;
adjusting the pH of said intermediary product solution to a second pH in the range of about 7.0-8.0 to precipitate aluminum hydroxide for use in reacting with said hydrofluoric acid to form said first end product, while forming a resultant liquid stream containing soluble sodium sulfate;
mixing said resultant liquid stream with alcohol to precipitate a second product of sodium sulfate;
rinsing said slurry component solid fraction with an ammonium chloride solution to react with calcium sulfate therein to form an intermediary solution containing soluble ammonium sulfate and calcium chloride, and then admixing said intermediary solution with said residual solid fraction;
and
admixing said slurry component solid fraction with an alumina/silica mix to obtain a 70/30 alumina/silica ratio, by weight, drying said 70/30 mix, and then subjecting said 70/30 mix to temperatures of greater than about 1500.degree. C. in an oxygen-rich environment to produce carbon dioxide and heat as by-products and create a third end product comprising refractory material.

8 more elements

A process for recycling spent potliner (SPL) material from aluminum reduction cells into refractory material for reforming furnace brick, aluminum fluoride for reuse in an aluminum reduction cell, sodium sulfate for use in commercial applications, atmospheric gases and ammonium sulfate, said process comprising the steps of:

crushing said SPL material into a particulate feed;
introducing said particulate feed into a screw auger digester containing concentrated sulfuric acid heated to a temperature in the range of about 135.degree. to about 160.degree. C. to produce a gas component including hydrogen fluoride and hydrogen cyanide, and a slurry component comprising solid and liquid fractions, said liquid fraction having an acid pH, and said solid fraction including carbon, silica, alumina, sodium sulfate, calcium, iron and magnesium;
recovering said gas component from said digester and heating it to greater than about 800.degree. C. to convert said hydrogen cyanide and hydrogen fluoride to a residual gas component including carbon dioxide, steam, nitrogen oxides and hydrogen fluoride;
directing said residual gas component through a water scrubber to form a liquid portion containing hydrofluoric acid and a gaseous portion, and then reacting said hydrofluoric acid in an aluminum hydroxide reactor to form a first end product of aluminum fluoride, said gas portion being directed to a caustic scrubber utilizing sodium hydroxide to adjust the pH to the range of about 7.0-8.0 prior to releasing it to the atmosphere;
rinsing said slurry component with a first water rinse to remove soluble salts therefrom and then a second water rinse to polish the solids in said slurry to form a liquid fraction containing said soluble salts and a solid fraction containing carbon, alumina and silica;
mixing said liquid fraction with alcohol to remove excess sulfuric acid and precipitate water soluble salts;
redissolving said salts with water to reform a liquid fraction;
adjusting the pH of said reformed liquid fraction to a pH in the range of about 12.0-12.5 to create and separate an intermediary product of sodium aluminate in solution while precipitating calcium hydroxide, iron hydroxide, and magnesium hydroxide impurities;
adjusting the pH of said intermediary product solution to a second pH of about 7.0-8.0 to precipitate a second end product while forming a resultant liquid stream containing soluble sodium sulfate;
mixing said resultant liquid stream with alcohol to precipitate a second end product of sodium sulfate;
rinsing said solid fraction with an ammonium chloride solution to react with calcium sulfate to form an intermediary solution containing soluble aluminum sulfate and calcium chloride, and then admixing said intermediary solution with said solid fraction to form a solution from which ammonium sulfate is removed;
and
admixing said solid fraction with an alumina/silica mix to obtain an approximately 70/30 alumina/silica ratio, drying said alumina/silica mix, and then subjecting said mix to temperatures of greater than approximately 1500.degree. C. in an oxygen-rich environment to create a third end product comprising refractory material and produce carbon dioxide and heat as by-products utilized to heat said gas component from said digester.

10 more elements

Dependencies are inferred from the claim text.