Process for treating a sodium carbonate purge

Abstract

Concentrated aqueous sodium hydroxide solution comprising: at least 25% by weight of NaOH, sodium chloride (NaCl) and/or sodium sulfate (Na 2 SO 4 ), and one soluble impurity from a sodium carbonate or bicarbonate ore deposit, said soluble impurity being selected among: As, Ba, B, Ca, Co, K, Li, Mg, Mo, P, Pb, Se, Si, Sr, Te, Tl, Ti, V, W, and the soluble impurity being in specific concentrations ranges. And process for producing such concentrated aqueous sodium hydroxide solution by treating a purge stream comprising sodium carbonate or bicarbonate.

1 . A concentrated aqueous sodium hydroxide solution comprising:
 at least 25% by weight of NaOH,   sodium chloride (NaCl) and/or sodium sulfate (Na 2 SO 4 ),   and at least one soluble salt or one soluble impurity from a sodium carbonate or bicarbonate ore deposit,   said soluble salt or soluble impurity comprising at least one of the following elements selected from the group consisting of: As, Ba, B, Ca, Co, K, Li, Mg, Mo, P, Pb, Se, Si, Sr, Te, Tl, Ti, V, and W,   
       wherein:
 the at least one element is at a concentration expressed in mg of element per kilogram of the aqueous sodium hydroxide solution, in the following ranges: 
 As at least 18 and at most 31.4, 
 Ba at least 0.04 and less than 0.17, 
 B at least 560 and at most 1160, 
 Ca at least 5.9 and at most 21.7, 
 Co at least 0.52 and at most 1.24, 
 K at least 6187 and at most 12360, 
 Li at least 29.0 and at most 47.4, 
 Mg at least 2.4 and at most 3.4, 
 Mo at least 64 and at most 74.1, 
 P at least 114 and at most 460 expressed as PO4, 
 Pb at least 1.2 and at most 2.4, 
 Se at least 1.1 and at most 9.2, 
 Si at least 187 and at most 1970, 
 Sr at least 0.06 and at most 0.17, 
 Te at least 0.7 and at most 6.2, 
 Tl at least 0.5 and at most 0.6, 
 Ti at least 0.34 and at most 0.74, 
 V at least 21 and at most 26.1, 
 W at least 2.6 and at most 2.7. 
 
     
     
         2 . The concentrated aqueous sodium hydroxide solution according to  claim 1 , comprising at least one soluble impurity from ore deposits, said soluble impurity comprising at least one of the following elements selected from the group consisting of: Be, Bi, Cu, and Sn,
 and said aqueous sodium hydroxide solution comprising 2.4 mg Be/kg, or less than 0.8 mg Bi/kg, or less than 0.24 mg Cu/kg, or at most 4.2 mg Sn/kg.   
     
     
         3 . The concentrated aqueous sodium hydroxide solution according to  claim 1 , comprising at least 560 and at most 1160 mg B/kg. 
     
     
         4 . The concentrated aqueous sodium hydroxide solution according to  claim 1 , comprising at least 6187 and at most 12 360 mg K/kg. 
     
     
         5 . The concentrated aqueous sodium hydroxide solution according to  claim 1 , comprising at least 114 and at most 460 mg P expressed as PO4/kg. 
     
     
         6 . The concentrated aqueous sodium hydroxide solution according to  claim 1 , comprising at least 187 and at most 1970 mg Si/kg. 
     
     
         7 . The concentrated aqueous sodium hydroxide solution according to  claim 1 , comprising at least 3200 and at most 6684 mg S expressed as SO4/kg. 
     
     
         8 . The concentrated aqueous sodium hydroxide solution according to  claim 1 , wherein the ore deposit is a trona ore deposit. 
     
     
         9 . The concentrated aqueous sodium hydroxide solution according to  claim 1 , obtainable by causticizing a purge stream derived from an anhydrous sodium carbonate crystallizer, or a sodium carbonate monohydrate crystallizer, or a sodium carbonate decahydrate crystallizer, or a sodium sesquicarbonate crystallizer, or a wegsheiderite crystallizer, or a sodium bicarbonate crystallizer, said purge stream comprising sodium carbonate and/or sodium bicarbonate and at least 1% by weight of a sodium salt selected from the group consisting of sodium chloride, sodium sulfate and mixtures thereof. 
     
     
         10 . A method for producing the concentrated aqueous sodium hydroxide solution according to  claim 1  from a purge stream, said purge stream deriving from an anhydrous sodium carbonate crystallizer, or a sodium carbonate monohydrate crystallizer, or a sodium carbonate decahydrate crystallizer, or a sodium sesquicarbonate crystallizer, or a wegsheiderite crystallizer, or a sodium bicarbonate crystallizer,
 said purge stream comprising sodium carbonate and/or sodium bicarbonate from a sodium carbonate or bicarbonate ore deposit, and 
 said purge stream comprising at least 1% by weight of a sodium salt selected from the group consisting of sodium chloride, sodium sulfate and mixtures thereof, and 
 said method comprising the following steps:
 f) adding lime to the purge stream, in presence of water, so that to causticize at least 50 mol. % of the sodium from sodium carbonate and/or sodium bicarbonate, 
 into an aqueous sodium hydroxide solution and 
 into a calcium carbonate mud; 
 g) separating the calcium carbonate mud from the aqueous sodium hydroxide solution; 
 h) concentrating the aqueous sodium hydroxide solution by removing part of the water in order to obtain: 
 the concentrated aqueous sodium hydroxide solution comprising at least 25% NaOH, and 
 to crystallize a solid comprising sodium carbonate and comprising sodium chloride and/or sulfate, 
 wherein lime added at step f) and water removed at step h) are controlled so that the weight ratio of sodium carbonate to the sum of the sodium chloride and/or sodium sulfate in crystallized solid is at most 2, 
 i) separating the crystallized solid comprising sodium carbonate and sodium chloride and/or sulfate from the concentrated aqueous sodium hydroxide solution. 
 
 
     
     
         11 . The method according to  claim 10 , further comprising:
 j) recycling at least one part of the concentrated aqueous sodium hydroxide solution to the anhydrous sodium carbonate crystallizer, or to the sodium carbonate monohydrate crystallizer, or to the sodium carbonate decahydrate crystallizer, or to the sodium sesquicarbonate crystallizer, or to the bicarbonate crystallizer, or to processes upstream of the anhydrous sodium carbonate crystallizer, or of the sodium carbonate monohydrate crystallizer, or of the sodium carbonate decahydrate crystallizer, or of the sodium sesquicarbonate crystallizer, or of the bicarbonate crystallizer.   
     
     
         12 . The method according to  claim 10 , wherein the purge stream is a purge derived from a decahydrate sodium carbonate crystallizer, or from a sodium sesquicarbonate crystallizer. 
     
     
         13 . The method according to  claim 10 , wherein the decahydrate sodium carbonate crystallizer, or the sodium sesquicarbonate crystallizer are crystallizers, and wherein a purge from a sodium carbonate monohydrate crystallizer is treated in order to control the sodium chloride and/or the sodium sulfate of the sodium monohydrate crystallizer. 
     
     
         14 . The method according to  claim 10 , wherein the purge stream comprises at least one impurity of a soluble salt or at least one soluble impurity from ore deposits selected from the group consisting of: trona, nahcolite, and wegscheiderite ore, said soluble salt or soluble impurity comprising at least one element from the group consisting of: As, Ba, Be, Bi, B, Ca, Co, Cu, F, K, Li, Mg, Mo, P, Pb, Se, Si, Sn, Sr, Te, Tl, Ti, V, and W,
 and wherein said soluble salt or soluble impurity is at least partially removed at step f) to i) from the purge stream.   
     
     
         15 . A method for producing a sodium carbonate salt or a sodium bicarbonate salt from a sodium carbonate/bicarbonate solution derived from a sodium carbonate/bicarbonate ore such as trona, nahcolite, and wegsheiderite ores, or from a sodium carbonate/bicarbonate lake water, or from a reclaimed solid, or from a mine water, said ores, waters or solid comprising sodium carbonate/bicarbonate,
 comprising the following steps:
 a) optionally pre-treating the sodium carbonate/bicarbonate solution in removing part of organics and/or changing the carbonate/bicarbonate molar ratio in order to obtain an optional pre-treated sodium carbonate/bicarbonate solution; 
 b) crystallizing from the sodium carbonate/bicarbonate solution, or from the optionally pre-treated sodium carbonate/bicarbonate solution, 
 a sodium carbonate salt or a sodium bicarbonate salt with one of the mean selected from the list of: evaporation crystallization, cooling evaporation, carbonation crystallization and combinations thereof, 
 said crystallization step of the sodium carbonate salt or the sodium bicarbonate salt generating a mother liquor, said mother liquor comprising sodium carbonate or bicarbonate, sodium chloride or sodium sulfate, and water; 
 c) separating the sodium carbonate salt or the sodium bicarbonate salt from the mother liquor; 
 d) recycling part of the mother liquor back into one of the step a), or step b) and removing part of the mother liquor in order to generate a purge stream to control the sodium chloride and/or the sodium sulfate concentration in the mother liquor of the crystallization step b), 
 e) treating the purge stream and producing the concentrated aqueous sodium hydroxide solution according to the method of  claim 10 . 
   
     
     
         16 . The method according to  claim 15 , wherein the sodium carbonate salt is sodium carbonate monohydrate,
 and wherein the carbonate/bicarbonate solution is a trona ore solution mining solution and/or a trona ore mine water and/or a reclaimed solid comprising sodium carbonate,   said carbonate/bicarbonate solution comprising at least 10% total alkalinity expressed as sodium carbonate and comprising sodium chloride and/or sodium sulfate,   wherein:
 step a) comprises:
 a wet calcination in one or several steps for partly decarbonating the carbonate/bicarbonate solution to a sodium bicarbonate content of less than 5 w % NaHCO 3 , and 
 a water evaporation operation to increase the total alkalinity of the carbonate/bicarbonate solution exiting step a) to at least 20% expressed as sodium carbonate, and 
 a caustic calcination for further partly decarbonating the carbonate/bicarbonate solution to a sodium bicarbonate content of the carbonate/bicarbonate solution exiting step a) to less than 4 w % NaHCO 3 , using at least partly the sodium hydroxide from the concentrated aqueous sodium hydroxide solution; 
 
 step b) comprises crystallizing from the carbonate/bicarbonate solution exiting step a), a carbonate salt in the form of sodium carbonate monohydrate salt or a sodium carbonate anhydrous salt with one of the mean selected from the list of: evaporation crystallization, cooling evaporation; and 
 step c) comprises separating the sodium carbonate (monohydrate or anhydrous) salt from the mother liquor of step b), and drying/calcining the sodium carbonate (monohydrate or anhydrous) salt into dried anhydrous sodium carbonate.