Method for extracting gallium from fly ash

Abstract

Disclosed is a method for extracting gallium from fly ash, which comprises the following steps: crushing the fly ash and removing Fe by magnetic separation; then dissolving it by using hydrochloride acid ( 2 ) to obtain hydrochloric acid leachate; adsorbing gallium in the hydrochloric acid leachate with macro-porous cationic resin, followed by eluting to obtain the eluent ( 5 ) containing gallium; adding sodium hydroxide ( 6 ) solution into the eluent containing gallium to react and obtaining sodium metaaluminate solution containing gallium ( 8 ); introducing CO 2 into the sodium metaaluminate solution containing gallium ( 8 ) for carbonation, followed by separating gallium from aluminum and obtaining aluminum-gallium double salt ( 15 ) with the gallium to alumina mass ratio being more than 1:340; adding the aluminum-gallium double salt ( 15 ) into sodium hydroxide ( 17 ) to react, followed by alkalinity-adjustment concentration to obtain alkali solution containing gallium and aluminum; electrolyzing ( 10 ) the alkali solution containing gallium and aluminum to obtain metal gallium ( 11 ). The method simplifies the process and improves extraction efficiency of gallium.

1 . A method for extracting gallium from fly ash, comprising the following steps:
 a) crushing the fly ash to a size of 100 mesh or smaller, removing iron by wet magnetic separation, such that the ferric oxides content in the fly ash is reduced to 1.0 wt % or less, then adding hydrochloride acid into the de-ironed fly ash to perform an acid-leaching reaction, and subjecting the reaction product to solid-liquid separation to yield a hydrochloric leachate having a pH value in the range of 1-3;   b) adsorbing gallium in the hydrochloric leachate by passing the same through a column loading with a macro-porous cationic resin; eluting the column with water or hydrochloride acid as an eluting agent when the adsorption reaches saturation to obtain a gallium-containing eluent;   c) adding sodium hydroxide solution into the gallium-containing eluent to react, separating precipitates after reaction by filtration to obtain a gallium-containing sodium metaaluminate solution;   d) subjecting the gallium-containing sodium metaaluminate solution to carbonation by introducing carbon dioxide therein, and then separating gallium from most aluminum to obtain a gallium-aluminum double salt with the mass ratio of gallium to alumina being more than 1:340; and   e) adding the gallium-aluminum double salt into a sodium hydroxide solution, subjecting the reactant to evaporation and concentration to obtain a base solution containing gallium and aluminum with the contents of gallium and alumina being μmol/l or more respectively, and then electrolyzing the base solution to obtain metal gallium,   wherein in the acid leaching reaction of step a), the reaction temperature is 100-200° C., the reaction pressure is 0.1-2.5 MPa, and   in step b), the macro-porous cationic resin is selected from any one of D001, 732 and 742.   
     
     
         2 . The method according to  claim 1 , wherein, in step a), the concentration of the hydrochloride acid is 20-37 wt %; the molar ration of HCl contained in the hydrochloride acid to alumina contained in the fly ash is 4:1-9:1. 
     
     
         3 . The method according to  claim 2 , wherein, in the acid-leaching reaction of step a), reaction time is 0.5-4.0 hours. 
     
     
         4 . (canceled) 
     
     
         5 . (canceled) 
     
     
         6 . The method according to  claim 3 , wherein, in step b), adsorbing gallium in the hydrochloric leachate by passing the hydrochloric leachate through the column from the bottom to top with a volume flux of 1-4 times over resin volume per hour at 20-90° C. 
     
     
         7 . The method according to  claim 6 , wherein, in step b), eluting said macro-porous cationic resin with 2-10 wt % hydrochloride acid as an eluting agent, and preferably, the eluting temperature is 20-60° C., the amount of the eluting agent used is 1-3 times over the volume of the resin, and the eluting rate is 1-3 times over resin volume per hour. 
     
     
         8 . The method according to  claim 1 , wherein, in step c), the concentration of sodium hydroxide solution is 180-240 g/l; preferably, the reaction temperature is 20-100° C. 
     
     
         9 . The method according to  claim 1 , wherein, in step d), the carbonation by introducing carbon dioxide into the gallium-containing sodium metaaluminate solution comprises the steps of:
 performing a primary carbonation: introducing carbon dioxide into the gallium-containing sodium metaaluminate mother solution obtained in step c), in which the flow rate of carbon dioxide is in the range of 80-160 ml/min, the reaction temperature is controlled in the range of 40-90° C., the carbonation time is in the range of 4-10 h, the pH value at the end of the reaction is in the range of 10.6-9.7, then separating the precipitates from the solution by filtration, so as to separate gallium from aluminum for the first time;   performing a secondary carbonation: further introducing carbon dioxide into the solution obtain from the primary carbonation after the separation of the aluminum hydroxide precipitates, in which the flow rate of carbon dioxide is in the range of 100-160 ml/min the reaction temperature is controlled in the range of 30-60° C., the carbonation time is in the range of 3-7 h, the pH value at the end of the reaction is in the range of 9.8-9.0, so as to precipitate all aluminum and most gallium; subjecting the reactant to filtration to obtain gallium-aluminum double salt; then crystallizing sodium carbonate in the filtrate obtained from the filtration by evaporization and concentration and separating the crystallized sodium carbonate from the solution; and then recycling the filtrate containing a small amount of gallium obtained after the separation of sodium carbonate to the beginning of the secondary carbonation for further carbonation.   
     
     
         10 . The method according to  claim 9 , wherein, in step d), when the mass ratio of gallium to alumina in the gallium-aluminum double salt obtained after the primary carbonation and secondary carbonation is equal to or less than 1:340, dissolving the double salt in a sodium hydroxide solution or the sodium metaaluminate mother solution and repeating the primary carbonation and the secondary carbonation until the mass ratio of gallium to alumina in the last gallium-aluminum double salt is more than 1:340. 
     
     
         11 . The method according to  claim 1 , wherein, in step e), the concentration of sodium hydroxide solution is 180-245 g/l; preferably, the reaction temperature in step e) is 20-100° C. 
     
     
         12 . The method according to  claim 1 , wherein, in step e), when the base solution containing aluminum and gallium is electrolyzed, platinum electrodes are used as the negative and positive electrodes, electrolysis current is in the range of 180-200 mA/l, electrolysis voltage is in the range of 4V and electrolytic bath temperature is in the range of 35-45° C. 
     
     
         13 . The method according to any  claim 1 , wherein, in step a), the apparatus used for de-ironing by wet magnetic separation is a vertical ring magnetic separator which comprises a rotating ring, an inductive medium, an upper iron yoke, a lower iron yoke, a magnetic exciting coil, a feeding opening, a tailing bucket and a water washing device, wherein the feeding opening is used for feeding the coal ash to be de-ironed, the tailing bucket is used for discharging the non-magnetic particles after de-ironing, the upper iron yoke and the lower iron yoke are respectively arranged at the inner and outer sides of the lower portion of the rotating ring, the water washing device is arranged above the rotating ring, the inductive medium is arranged in the rotating ring, the magnetic exciting coil is arranged at the periphery of the upper iron yoke and the lower iron yoke so as to make the upper iron yoke and the lower iron yoke to be a pair of magnetic poles for generating a magnetic field in the vertical direction, and wherein the inductive medium is layers of steel plate meshes, each steel plate mesh is woven by wires, and the edges of the wires have prismatic sharp angles. 
     
     
         14 . (canceled) 
     
     
         15 . The method according to  claim 13 , wherein the vertical ring magnetic separator further comprises a pressure balance chamber water jacket disposed adjacent to the magnetic exciting coil. 
     
     
         16 . The method according to  claim 15 , wherein the steel plate mesh has a medium layer spacing of 2-5 mm, preferably 3 mm; and the steel plate mesh is made of 1Cr17. 
     
     
         17 . The method according to  claim 16 , wherein the steel plate mesh has a thickness of 0.8-1.5 mm, a mesh grid size of 3 mm×8 mm-8 mm×15 mm, and a wire width of 1-2 mm, preferably, the steel plate mesh has a thickness of 1 mm, a mesh grid size of 5 mm×10 mm, and a wire width of 1.6 mm. 
     
     
         18 . The method according to  claim 17 , wherein the vertical ring magnetic separator further comprises a pulsating mechanism, which is coupled with the tailing bucket via a rubber plate. 
     
     
         19 . The method according to  claim 18 , wherein the inductive medium is provided in the entire circle of the rotating ring. 
     
     
         20 . The method according to  claim 19 , wherein the magnetic exciting coil is a flat wire solenoid coil which is double glass envelope enamelled aluminum. 
     
     
         21 . The method according to  claim 20 , wherein the magnetic field strength of the vertical ring magnetic separator is 15,000 Gs or more, preferably 15,000-20,000 Gs, further preferably 15,000-17,500 Gs. 
     
     
         22 . A method for extracting gallium from fly ash, comprising the following steps:
 a) crushing the fly ash to a size of 100 mesh or smaller, removing iron by wet magnetic separation, such that the ferric oxides content in the fly ash is reduced to 1.0 wt % or less, then adding hydrochloride acid into the de-ironed fly ash to perform an acid-leaching reaction, and subjecting the reaction product to solid-liquid separation to yield a hydrochloric leachate having a pH value in the range of 1-3;   b) cooling the hydrochloric leachate till its temperature is 90° C., then pumping the hydrochloric leachate into a column loaded with JK008 Resin to enrich gallium, wherein the flow flux of the hydrochloric leachate is 4 times over resin volume per hour; and when the adsorption reached saturation, eluting the column with 2 wt % hydrochloride acid as an eluting agent at 60° C. to obtain a gallium-rich eluent, wherein the flow flux of the hydrochloride acid is 1 time over resin volume per hour, and the total amount of the eluting agent used for elution is 2 times over the volume of the resin;   c) adding sodium hydroxide solution into the gallium-containing eluent to react, separating precipitates after reaction by filtration to obtain a gallium-containing sodium metaaluminate solution;   d) subjecting the gallium-containing sodium metaaluminate solution to carbonation by introducing carbon dioxide therein, and then separating gallium from most aluminum to obtain a gallium-aluminum double salt with the mass ratio of gallium to alumina being more than 1:340; and   e) adding the gallium-aluminum double salt into a sodium hydroxide solution, subjecting the reactant to evaporation and concentration to obtain a base solution containing gallium and aluminum with the contents of gallium and alumina being 1 mol/l or more respectively, and then electrolyzing the base solution to obtain metal gallium,   wherein in the acid-leaching reaction of step a), the reaction temperature is 100-200° C., the reaction pressure is 0.1-2.5 MPa.   
     
     
         23 . A method for extracting gallium from fly ash, comprising the following steps:
 a) crushing the fly ash to a size of 100 mesh or smaller, removing iron by wet magnetic separation, such that the ferric oxides content in the fly ash is reduced to 1.0 wt % or less, then adding hydrochloride acid into the de-ironed fly ash to perform an acid-leaching reaction, and subjecting the reaction product to solid-liquid separation to yield a hydrochloric leachate having a pH value in the range of 1-3;   b) cooling the hydrochloric leachate till its temperature is 40° C., then pumping the hydrochloric leachate into a column loaded with SPC-1 Resin to enrich gallium, wherein the flow flux of the hydrochloric leachate is 1 time over resin volume per hour; and when the adsorption reached saturation, eluting the column with 10 wt % hydrochloride acid as an eluting agent at 30° C. to obtain a gallium-rich eluent, wherein the flow flux of the hydrochloride acid is 3 times over resin volume per hour, and the total amount of the eluting agent used for elution is 1 time over the volume of the resin;   c) adding sodium hydroxide solution into the gallium-containing eluent to react, separating precipitates after reaction by filtration to obtain a gallium-containing sodium metaaluminate solution;   d) subjecting the gallium-containing sodium metaaluminate solution to carbonation by introducing carbon dioxide therein, and then separating gallium from most aluminum to obtain a gallium-aluminum double salt with the mass ratio of gallium to alumina being more than 1:340; and   e) adding the gallium-aluminum double salt into a sodium hydroxide solution, subjecting the reactant to evaporation and concentration to obtain a base solution containing gallium and aluminum with the contents of gallium and alumina being μmol/l or more respectively, and then electrolyzing the base solution to obtain metal gallium,   wherein in the acid-leaching reaction of step a), the reaction temperature is 100-200° C., the reaction pressure is 0.1-2.5 MPa.