Method for spent potliner processing separating and recycling the products therefrom

Abstract

A method is provided for efficient processing of spent potliner, separating and recycling/utilizing the liquid and solid products generated during processing. The method includes the steps of crushing and screening the potliner freed from metal debris, pulverizing the potliner suspended in a hot aqueous slurry by autogenous grinding in a tumbler in the presence of air, subjecting the potliner to a series of leaching, thickening and filtering steps followed by separation of the potliner into Bayer Liquor, solid sodium fluoride, quality carbon product and mineral matter characterized by low cyanide and fluoride leachability. About 85% of the water required for potliner processing is recovered and recycled into the process.

What is claimed is:  
     
         1 . A method for processing fine particles of spent potliner suspended in aqueous slurries containing caustic soda, separating and recovering from said aqueous slurries metallic aluminum, Bayer Liquor, solid sodium fluoride, carbon fuel and mineral matter; the method comprising the steps: 
 a) separating large pieces of metallic aluminum and steel/iron debris from the potlining material by a combination of magnetic separation and manual sorting, crushing so obtained potlining material so the product of crushing passes 100 mm screen;    b) tumbling so prescreened potlining material in hot aqueous slurry containing caustic soda, in presence of air, under conditions of autogenous grinding;    c) screening the hot slurry exiting the tumbler using 0.5 mm or less trommel screen, washing oversize particles with hot, fresh water, separating residual metallic aluminum from washed oversize particles and recycling the oversize particles for tumbling;    d) diluting the slurry that passed the trommel screen with fresh water and agitating the hot fine slurry in a first battery of extracting/leaching mixers supplied, from the bottom with steam and air;    e) thickening (in a thickener) the hot fine slurry that exits the first battery, separating the clarified extract/leachate, pumping the thickened slurry and diluting it with fresh water prior to agitating it again in a second battery of extracting/leaching mixers supplied with steam;    f) thickening the slurry exiting the second battery, separating the clarified extract/leachate, filtering the thickened slurry using horizontal vacuum belt filter or other filtering device, washing the particles with hot, fresh water and dewatering the particles on the belt filter;    g) suspending the dewatered particles in fresh water to form a slurry, agitating and heating so obtained slurry with steam in a third battery of extracting/leaching mixers thus forming primary hot fine slurry;    h) thickening the primary hot fine slurry exiting the third battery, separating the clarified extract/leachate, pumping the thickened slurry for gravity/size separation and separating the thickened slurry into two streams: one stream of slurry containing mineral particles with size 0.05 mm and larger and one stream of slurry containing all carbon particles and mineral particles with size 0.05 mm and smaller;    i) adding small quantities of suitable mineral oil to the stream of slurry containing all carbon particles and mineral particles with size 0.05 mm and smaller, passing so obtained oil containing stream through a commercial high shear agitator and separating by flotation or other techniques the oil agglomerated carbon particles from the residual slurry containing the mineral particles with size 0.05 mm and smaller;    j) filtering the oil agglomerated carbon particles using horizontal vacuum belt filter or other filtering device, washing the agglomerated carbon particles with fresh water and dewatering them on the belt filter thus producing carbon fuel product;    k) combining the stream of slurry containing mineral particles with size 0.05 mm and larger with the stream of residual slurry containing the mineral particles with size 0.05 mm and smaller, filtering the combined streams using horizontal vacuum belt filter or other filtering device, washing the mineral particles with hot fresh water and dewatering the particles on the belt filter thus producing mineral matter product;    l) combining all streams of produced clarified extracts/leachates and filtrates and processing them in a commercial water treatment and distillation system thus generating distilled water that is recycled for spent potliner processing and non-distillable liquid;    m) separating by filtration the non-distillable liquid containing precipitated sodium fluoride (NaF) into solid NaF product and Bayer Liquor product;    n) subjecting, if required, the mineral matter product to thermal treatment/calcination within the temperature range of 300-850° C.    
     
     
         2 . A method according to  claim 1 , where in step a) spent potlining material, freed of steel/iron debris and large pieces (>20 mm) of metallic aluminum is crushed and prescreened to reduce the size of the largest particles of the potlining material to less than 200 mm.  
     
     
         3 . A method according to  claim 1 , where in step b) crushed and prescreened potlining material, suspended in a hot (50° C. up to boiling point) aqueous slurry containing sodium hydroxide in concentrations 0-10 g/L or 60-200 g/L, is pulverized under autogenous grinding conditions (rpm: 3 and over; solids mass flow: over 1.0 tph; solids concentration in a slurry: about 50-65 w/w %) in a tumbler (equipped with lifters) through which fresh air is flowing at volumetric flow rates of 1-60 m 3 /1 ton potlining material/min.  
     
     
         4 . A method according to  claim 1 , where in step c) oversize particles separated on the screen, at the exit from the tumbler and freed of metallic aluminum are subjected to size reduction, prior to recycling them for tumbling.  
     
     
         5 . A method according to  claim 1 , where in step c) hot slurry after exiting the tumbler is passed through the screen with openings of not less than 0.15 mm and not more than 1.0 mm.  
     
     
         6 . A method according to  claim 1 , where in step d) hot slurry after exiting the tumbler and passing the 0.15-1.0 mm screen is diluted with fresh water to solids concentration of about 15-30 w/w %.  
     
     
         7 . A method according to  claim 1 , where in step e) the about 15-30 w/w % solids concentration hot fine slurry, exiting the battery of mixers, is separated in a thickener into two streams: a stream of clarified, solid particles free, extract/leachate and a stream of thickened slurry with about 40-50 w/w % solids concentration.  
     
     
         8 . A method according to  claim 1 , where in a step h) the stream of thickened slurry with about 40-50 w/w % solids concentration is subjected to separation using spiral separator into two streams: the first stream containing all carbon particles and mineral particles of 0.1 mm and smaller and the second stream containing mineral particles of 0. 1 mm and larger.  
     
     
         9 . A method according to  claim 1 , where in step i) suitable mineral oil to be added to the stream of slurry containing carbon particles is defined as any commercial mineral light oil (like Diesel oil, naphta, kerosene, jet fuel or others), or any blend of commercial mineral light oils, or a blend of any commercial mineral light oils with heavy oils/bitumen (API Gravity below 16) where the heavy oil/bitumen component accounts for up to 70 w/w % of the total blend.  
     
     
         10 . A method according to  claim 1 , where in step i) the oil agglomerated carbon particles are separated using any suitable system (like flotation, cycloning or other methods), from the residual slurry containing mineral particles of 0.05 mm and smaller.  
     
     
         11 . A method according to  claim 7 , where the thickened slurry with about 40-50 w/w % solids concentration is either diluted with fresh water to about 15-30 w/w % solids concentration and treated in a battery of mixers, or is subjected to filtration and the solid particles deposited on a filter are thoroughly washed with hot (50-95° C.) fresh water, dewatered and suspended in fresh water to form slurry with about 15-30 w/w % solids concentration that is agitated in a battery of mixers.  
     
     
         12 . A method according to  claim 9 , where suitable light mineral oil, or a blend of light mineral oils, or a blend of light mineral oils with heavy oil/bitumen to be added to the stream of slurry containing carbon particles is, prior to addition, emulsified with water using any commercially available emulsification system.  
     
     
         13 . A method according to  claim 9 , where quantities of suitable light mineral oil, or a blend of light mineral oils, or a blend of light mineral oils with heavy oil/bitumen to be added to the stream of slurry containing carbon particles are in the range of 0.1-10.0 w/w % based on mass of carbon particles in the slurry stream.  
     
     
         14 . A method according to  claim 11 , where the slurry diluted to about 15-30 w/w % solids concentration is agitated at such agitation intensity that the concentration of solid particles in the slurry, at any location in the mixer, is essentially the same.  
     
     
         15 . A method according to  claim 11 , where the slurry diluted to about 15-30 w/w % solids concentration is extracted/leached in a battery of mixers (one to five mixers per battery), where each mixer is heated with steam to keep the temperature of the slurry from 50° C. up to its boiling point.  
     
     
         16 . A method according to  claim 15 , where the slurry is also supplied with air at volumetric flow rates from 0.5-5.0 m 3 /mixer/min.