Process for the recovery of soda ash

Abstract

A process for the production of soda ash by withdrawing an aqueous mining solution containing dissolved sodium carbonate and at least about 1 wt % sodium bicarbonate from an underground alkali source; stripping CO 2 gas from the withdrawn aqueous mining solution, to convert sodium bicarbonate dissolved therein to sodium carbonate; co-crystallizing sodium carbonate monohydrate and sodium sesquicarbonate by evaporation of water from the CO 2 -stripped aqueous mining solution, without co-crystallization of anhydrous sodium carbonate, to form a slurry of crystalline solids in an aqueous liquor; recovering crystalline solids from the slurry; and calcining the recovered crystalline solids to produce soda ash.

What is claimed is:  
     
         1 . A process for the production of sodium carbonate-containing crystalline solids comprising: 
 (i) providing an aqueous solution containing sodium bicarbonate;    (ii) converting a portion of the sodium bicarbonate in the aqueous solution to sodium carbonate to provide a sodium carbonate concentration in the bicarbonate-depleted solution such that a resulting crystallization step provides crystals of both sodium carbonate monohydrate and sodium sesquicarbonate;    (iii) co-crystallizing sodium carbonate monohydrate and sodium sesquicarbonate crystalline solids from the bicarbonate-depleted solution, to avoid co-crystallization of anhydrous sodium carbonate, by evaporation of water at a temperature of at least about 50° C. and below the invariant point of the bicarbonate-depleted solution to form a slurry of crystalline solids in an aqueous liquor; and    (iv) recovering the sodium carbonate monohydrate and sodium sesquicarbonate crystalline solids from the slurry.    
     
     
         2 . The process of  claim 1 , wherein the crystalline solids are in bimodal form with at least a portion of the sodium carbonate monohydrate crystals being larger than the sodium sesquicarbonate crystals.  
     
     
         3 . The process of  claim 2 , further comprising separating large sodium carbonate monohydrate crystals from smaller sodium carbonate monohydrate crystals and from essentially all of the sodium sesquicarbonate crystals in the crystalline solids recovered from said slurry.  
     
     
         4 . The process of  claim 1 , further comprising, calcining the crystalline solids to produce soda ash.  
     
     
         5 . The process of  claim 4 , further comprising: introducing the soda ash into an aqueous medium to recrystallize the soda ash as sodium carbonate 
 monohydrate in a sodium carbonate monohydrate crystallization step; recovering the crystalline sodium carbonate monohydrate; and calcining the recovered sodium carbonate monohydrate to produce a dense soda ash.    
     
     
         6 . The process of  claim 4 , further comprising, introducing the soda ash into an aqueous suspension containing crystalline sodium carbonate 
 monohydrate to effect solubilization and conversion of the soda ash into crystalline sodium    carbonate monohydrate in a sodium carbonate monohydrate crystallization step; recovering crystalline sodium carbonate monohydrate from the suspension; and calcining the recovered sodium carbonate monohydrate to produce a dense soda ash.    
     
     
         7 . The process of  claim 4 , which further comprises: converting the soda ash to sodium carbonate monohydrate in a hydrator; and calcining the sodium carbonate monohydrate to produce a dense soda ash.  
     
     
         8 . The process of  claim 1 , wherein the aqueous solution contains a total alkali content, expressed as Na 2 CO 3 , of sodium carbonate and sodium bicarbonate of at least about 8 wt %.  
     
     
         9 . The process of  claim 8 , wherein the aqueous solution contains at least about 6 wt % sodium carbonate and from about 2 wt % to about 8 wt % sodium bicarbonate.  
     
     
         10 . The process of  claim 9 , wherein the aqueous solution further contains sodium chloride in an amount of up to about 8 wt %.  
     
     
         11 . The process of  claim 1 , wherein the converting of a portion ofthe sodium bicarbonate in the aqueous solution to sodium carbonate , comprises stripping CO 2  from the aqueous solution at a temperature between about 50° C. and about 140° C.  
     
     
         12 . The process of  claim 11 , wherein CO 2  gas is stripped from the aqueous solution by countercurrent multistage contact of the aqueous solution with a water vapor gas stream.  
     
     
         13 . The process of  claim 12 , which further comprises condensing and separating water from a CO 2 -containing exit gas stream from the CO 2  stripping step to recover a CO 2  rich gas.  
     
     
         14 . The process of  claim 1 , which further comprises concentrating the aqueous solution, prior to the co-crystallization step, by evaporating water at a temperature of at least about 50° C., without causing crystallization of any crystal species.  
     
     
         15 . The process of  claim 14 , further comprising stripping CO 2  from the aqueous solution prior to the concentration of the aqueous solution.  
     
     
         16 . The process of  claim 15 , wherein CO 2  gas is stripped by countercurrent multistage contact of the aqueous solution with a water vapor gas stream from the concentration step.  
     
     
         17 . The process of  claim 15 , wherein concentrating the aqueous solution and stripping CO 2  from the aqueous solution are carried out as a single step.  
     
     
         18 . The process of  claim 1   1 , wherein stripping CO 2  from the aqueous solution and co-crystallizing sodium carbonate monohydrate and sodium sesquicarbonate crystalline solids are carried out as a single operation.  
     
     
         19 . The process of  claim 1 , wherein the co-crystallization of sodium carbonate monohydrate and sodium sesquicarbonate crystalline solids from the bicarbonate depleted solution is carried out at a temperature between about 70° C. and about 100° C., provided that the about 100° C. temperature is below the invariant point for the stripped solution.  
     
     
         20 . The process of  claim 1 , wherein the slurry of crystalline sodium carbonate monohydrate and crystalline sodium sesquicarbonate has a total alkali content in which sodium carbonate monohydrate is at least about one-fourth of the total alkali content of the crystallized solids.  
     
     
         21 . The process of  claim 12 , wherein sufficient CO 2 is stripped from the aqueous solution to convert at least about 10% of the sodium bicarbonate in the aqueous solution to sodium carbonate prior to the co-crystallization of sodium carbonate monohydrate and sodium sesquicarbonate crystalline solids.  
     
     
         22 . The process of  claim 12 , wherein sufficient CO 2 is stripped from the aqueous solution to convert at least about 20% of the sodium bicarbonate in the aqueous solution to sodium carbonate prior to the co-crystallization of sodium carbonate monohydrate and sodium sesquicarbonate crystalline solids.  
     
     
         23 . The process of  claim 4 , further comprising separating sodium carbonate monohydrate crystals having a larger size from smaller sodium carbonate monohydrate crystals.  
     
     
         24 . A process for the production of sodium carbonate containing crystalline solids, comprising: 
 (i) obtaining an aqueous solution containing at least about 1 wt % sodium bicarbonate from an alkali source;    (ii) converting at least a portion of the sodium bicarbonate in the aqueous solution to sodium carbonate by removing CO 2  from the aqueous solution to provide a modified solution containing increased sodium carbonate content in relation to the remaining sodium bicarbonate content in the modified solution, such that upon evaporative crystallization ofthe modified solution, crystals of sodium carbonate monohydrate and crystals of sodium sesquicarbonate precipitate;    (iii) co-crystallizing sodium carbonate monohydrate crystals and sodium sesquicarbonate crystals in bimodal form from the modified solution containing increased sodium carbonate content below an invariant point of the modified solution to avoid co-crystallization of anhydrous sodium carbonate, by evaporation of water at a temperature of at least about 50° C. and below the invariant point of the modified solution to form a slurry of crystalline solids in an aqueous mother liquor; and    (iv) separating the crystalline solids from the mother liquor to recover the crystalline solids.    
     
     
         25 . The process of  claim 24 , wherein converting at least a portion of the sodium bicarbonate in the aqueous solution to sodium carbonate by removing CO 2  from the sodium bicarbonate in the aqueous solution comprises stripping CO 2  from the sodium bicarbonate in the aqueous solution.  
     
     
         26 . The process of  claim 24 , wherein converting at least a portion of the sodium bicarbonate in the aqueous solution to sodium carbonate by removing CO 2  from the sodium bicarbonate in the aqueous solution comprises removing CO 2  from the sodium bicarbonate by evaporating and/or concentrating the aqueous solution.  
     
     
         27 . The process of  claim 24 , wherein the concentration of sodium bicarbonate in the aqueous solution is greater than approximately 3% by weight.  
     
     
         28 . The process of  claim 24 , wherein mother liquor from step (iv) is admixed with the aqueous solution.  
     
     
         29 . In an in situ solution mining process of a sodium bicarbonate containing ore wherein the resulting mine brine is treated to convert at least a portion of the sodium bicarbonate content to sodium carbonate to produce a process stream having significant sodium carbonate content and sodium bicarbonate content, comprising carrying out a conversion step on the mine brine to produce a process stream with a sodium carbonate content and a sodium bicarbonate content such that a resulting crystallization step at a temperature below the invariant point provides crystals of both sodium carbonate monohydrate and sodium sesquicarbonate.  
     
     
         30 . The process of  claim 29 , wherein the conversion step includes stripping the mine brine to remove at least some CO 2  from the bicarbonate content of the mine brine.  
     
     
         31 . The process of  claim 29 , wherein the conversion step is carried to a point wherein the sodium carbonate content in the process stream is sufficient that upon co-crystallization of sodium carbonate monohydrate crystals and sodium sesquicarbonate crystals, the sodium carbonate monohydrate crystals constitute at least about one-fourth of the alkalinity of the total crystalline solids.