Method of increasing the stability of a Bayer process liquor
Methods, and related products and compositions, of increasing the stability of a Bayer process liquor are described. A method of increasing the stability of a Bayer process liquor includes contacting the Bayer process liquor with a ppm quantity of a low molecular weight dextran. Also described are methods, and related products and compositions, for controlling the precipitation of aluminum-containing compounds from a Bayer process liquor.
1. A method of increasing the stability of a Bayer process liquor by controlling the precipitation of aluminum-containing compounds therefrom, the method comprising: contacting the Bayer process liquor with a ppm quantity of a low molecular weight dextran to suppress or reduce precipitation of aluminum-containing compounds from the Bayer process liquor prior to and/or during filtration of the Bayer process liquor, wherein the ppm quantity of the low molecular weight dextran is less than about 15 ppm of active dextran and the dextran has a molecular weight less than about 500,000 Daltons; wherein the low molecular weight dextran is added to thickener overflow liquor, surge tanks, or D-tank liquor, thereby to increase the liquor stability prior to filtration.
2. A method according to claim 1 , wherein the dextran has a molecular weight less than about 200,000 Daltons.
3. A method according to claim 1 , wherein the dextran has a molecular weight between about 1,000 to 200,000 Daltons.
4. A method according to claim 1 , wherein the dextran has a molecular weight between about 10,000 to 200,000 Daltons.
5. A method according to claim 1 , wherein the dextran has a molecular weight between about 100,000 to 200,000 Daltons.
6. A method according to claim 1 , wherein the method further comprises: filtering the Bayer process liquor; and precipitating the aluminum-containing compounds.
7. A method according to claim 6 , wherein the low molecular weight dextran is added in ppm quantities sufficient to suppress precipitation of the aluminum-containing compounds upstream of and through the liquor filtration step, while allowing for the controlled precipitation of the aluminum-containing compounds at a further step downstream of the filtration step.
8. A method according to claim 1 , wherein the contacting the Bayer process liquor with a ppm quantity of a low molecular weight dextran is conducted for a time period sufficient to increase the stability of the Bayer process liquor.
9. A method according to claim 8 , wherein the Bayer process liquor is contacted with the low molecular weight dextran for a period of between about 0.01 and 24 hours.
10. A method according to claim 1 , wherein the method further comprises adding more than one quantity of low molecular weight dextran or dextrans to the Bayer Process liquor.
11. A method according to claim 1 , wherein the amount of low molecular weight dextran added is between about 0.15 ppm and 15 ppm.
12. A method according to claim 1 , wherein the amount of low molecular weight dextran added is between about 0.15 ppm and 7.5 ppm.
13. A method according to claim 1 , wherein the amount of low molecular weight dextran added is between about 0.15 ppm and 3 ppm.
14. A method according to claim 1 , wherein the amount of low molecular weight dextran added is between about 0.15 ppm and 1.5 ppm.
15. A method according to claim 1 , wherein the low molecular weight dextran is added to liquor which is at a temperature of about 50° C. and above.
16. A method according to claim 15 , wherein the temperature of the liquor is about 80-110° C.