FR2614623A1 - SULPHONE STARCH COMPOSITIONS AND THEIR USE AS FLOCCULATING AGENTS FOR BAUXITE RESIDUES - Google Patents

Abstract

COMPOSITIONS OF STARCH SULFONE AND THEIR USE TO FLOCCULATE MINERAL PROCESSING RESIDUES, IN PARTICULAR RED SLUDGE FROM BAUXITE RESIDUES. THE USE OF MODIFIED STARCH INCLUDES THE ADDITION, TO AN ALUMINA LIQUOR FROM A BAUXITE TREATMENT, A FLOCCULATING AMOUNT OF A SULFONE STARCH, POSSIBLE HYDROLYSIS, OR OF A SULFON STARCH, ALSO METHYL , AND POSSIBLE HYDROLYSIS. PREFERREDLY, SULFONE STARCH COMPOSITIONS ARE DERIVATIVES OF POTATO STARCH OR DASHEEN PREPARED AT TEMPERATURES OF ABOUT 50 CA 150 C, OR, IF THEY ARE THEN METHYL, AT TEMPERATURES OF ABOUT 50 CA 85 C.

Description

The invention relates to new agents

  of flocculation for the aqueous dispersion of mineral wastes

  , their preparation and their method of use,

  especially for the flocculation of bauxite residues in the production of alumina (red mud). The production of alumina from bauxite is carried out by the well-known Bayer process.

  the Bayer process is a hydrometallurgical process of ex-

  alkaline traction, which involves the dissolution of oxy-

  aluminum hydroxides, gibbsite (AlOH) 3), boeh-

  moth and / or diaspore (A1203.H20) present in the bau-

  xite, using caustic soda at elevated temperatures and pressures. The process is based on the variation

  solubility of gibbsite, boehmite and diaspo-

  re, with the increased concentration of soda

  tick. In practice, bauxite is diluted in a solution of caustic soda, and digested at temperatures ranging between 140 and 250 C. This treatment results in the formation of a suspension, consisting of a liquid phase saturated with aluminate sodium (NaAl (OH) 4), and a caustic residue of insoluble bauxite, commonly known as red mud and "ferrosilt". The rest of the process involves the separation of the saturated sodium aluminate liquor by means of decantation or

  other techniques. The liquid phase is then clarified.

  filtered by filtration to remove the last traces of red mud, and is finally transferred to the precipitation or decomposition section, in which

  add gibbsite seeds (crystals) previously

  in order to cause precipitation. The gibbsite obtained is washed and calcined at a temperature between 1000 and 1200 C in order to remove the free moisture and the water of crystallization. The calcined alumina is cooled,

  stored and transported to melting furnaces.

  The red mud produced is washed in a counter-settling system (DCC), in order to recover the valuable dissolved compounds it contains. It is finally discharged from the tail of the alumina plant unit, in spreading zones which can be natural depressions, cavities of old bauxite mines or artificial lakes, depending on the zones available.

  Residues of red mud produced in the pro-

  aluminum recovery, include parts

  very fine cules, very difficult to remove. In addition, and in order to ensure the efficiency of the process, these red mud, which represents approximately 5 to 30% of the ore, must be

  quickly and carefully removed from the a- liquor

  solubilized lumine. According to US Patent 3,390,959, it is known in the industry to accelerate the separation of red mud from alumina liquors by adding different

  flocculating agents, such as starch or derivatives of a-

  midon, homopolymers of acrylic acid or acrylates,

  acrylamide derivatives, imidazoles or various other

  very agents. However, these agents are not fully acceptable for one or more reasons, for example their cost, their effectiveness, or the difficulties they

create in the rest of the process.

  The invention relates to a new flocculation agent.

  tion of red mud in alumina liquors or others

  aqueous systems of high dispersion, which leads to a se-

  significantly improved paration of dispersed particles,

  and thus provides a more efficient process.

  The invention relates to starch compositions.

  sulfonated and their use as flocculent compositions

  lantes. These flocculants are derived from starch, which is modified to contain sulfonic acid groups;

  the sulfonated starch can be further processed by hydro-

  lysis, by methylation, or by methylation followed by hy-

26 1 4623

  drolysis. Although some of the flocculants of the invention can be used to flocculate various other types

  of mineral waste dispersions, the detailed description

  The invention illustrates, in the following, an application

  cation with red mud from the treatment of the bau-

  xite by flocculants based on modified starch.

  As indicated above, the flocculants used in the process of the invention are derived from starch, which can be any quality of starch, such as that of wheat, potato, corn, of different

  yams, including the many species of yams

  caines, cassava, dasheen (Colocasia esculenta) or the like.

  Preferably wheat starches, corn starches,

  potatoes, dasheen, cassava and yams

  1 5 maicaines, and preferably wheat starch and

  potato. Other pro-

  starch-like products, such as different gums,

  for example guar, acacia, ghatti, traga-

canthe and the like.

  As indicated, the starch is modified by sulfona-

  tion. However, the sulfonated starch can then be treated by methylation, and the sulfonated or sulfonated-methylated starch.

can be hydrolyzed.

  Sulphonation and methylation of starch

  are known and can be achieved by different methods

  thodes. Although we can generally use the techniques

  sulfonation and methylation of the prior art, we de-

  write some favorite techniques and illustrate them with

  examples. Also the sulfonation is preferably carried out

  - used by means of a product capable of generating sulfur trioxide, for example sodium bisulfite in the presence of lime or another base. Starch methylation is,

  preferably carried out with methyl iodide as a pre-

  silver oxide. The sulfonation process fixes a sulfonic acid group (-SO2OH) on the starch, and the

  methylation reaction introduced on the starch of the groups-

  acetal (-CH2OH) and ether (-OCH3). Although the sulfo-

  nation and methylation can be carried out at temperatures of about 50 C to 150 C, it is preferred to apply temperatures of about 50 C to 85 C for the sulfonation-methylation reactions, because the starch flocculants

  sulfonated-methylated obtained at these temperatures have generally-

  better flocculating power for bale residues

  xite, than those produced at 150 C.

  When the starch is only sulfonated (i.e.

  say not methylated later) the sulfonation carried out from 50 ° C. to 150 ° C. gives substantially equivalent results. It should also be understood that the effectiveness of the flocculants varies to a certain extent with the different parameters of their manufacture. So, for example, a higher preparation temperature has a more pronounced harmful effect with potato starch than with dasheen starch. The dosage is also a factor in the effectiveness of starch derivatives , and the appropriate dosages will be easily determined by

one skilled in the art.

  Preparation of sulfonated starch The starch is first dispersed in water at a concentration

  0.5% starch, and the pH is adjusted to about 2.5 per ad-

  edition of hydrochloric acid or alesolution. The dispersion is then heated to a temperature of 80 C at boiling point, until a slightly milky starch suspension is formed. The same result can be obtained by heating the dispersion of starch in water to around 150 ° C.,

  under pressure, for at least 2.5 hours.

  The sulfonation of the starch dispersion is carried out by adding sodium bisulfite and a small amount

  of lime, followed by heating, with stirring, to a tem-

  high temperature (from 50 C to 150 C approximately), for approximately

1 hour.

  Once the sulfonation reaction is complete, the product

  of the reaction is usually treated by a small quan-

  lime to reduce the acidity of the product to a pH of about 7.0. Preparation of sulfonated-methylated starch

  The methylation of the sulfonated starch is carried out, preferably

  by heating the starch dispersion with

  methyl iodide in the presence of silver oxide at a time

  temperature between 500C and 85 C approximately during

about 2 hours.

  It is understood that other conventional techniques-

  starch sulfonation and methylation

  also be used to prepare flocculants used

read in the invention.

  Hydrolysis of methylated sulfonated starch As indicated above, it is possible to carry out a step

  hydrolysis, which often increases the efficiency

  cited methylated sulfonated starch. In this hydro-

  lysis, the aqueous suspension of modified starch is heated, with stirring, to a temperature of approximately 50 ° C. to 150 ° C. for approximately 1 hour in the presence of trisodium phosphate.

  (Na3PO4) and sodium aluminate (Na2A1204).

  As the flocculants used in the invention are

  extremely effective, they are added to bau-

  xite at a very low level of concentration. Usual-

  A dispersion of flocculant based on modified starch, containing approximately from 0.5% to 2% by weight of flocculant, is added to the residues in the proportion of approximately 15 to 200 ppm, and preferably approximately 25 to 100 ppm. , compared to the residues. However, the amount of flocculating agent to use varies with each particular flocculant, and a small amount is often more effective than an amount

bigger.

  In order to better illustrate the invention, we give below

26 1 4623

  specific examples of preparation and use of flocculants.

EXAMPLES

  1. Dispersion of starch A. The pH of 400 ml of tap water is adjusted to 2.5, and

  add 2 g of powdered potato starch. We heat-

  fe with stirring until boiling. The product obtained is a colloidal solution of dispersed starch slightly opalescent. 2. Dispersion of starch B. In a similar manner to the previous procedure, 400 ml of tap water and 2 g of powdered potato starch are placed in an inert, closed reactor (preferably in

  Teflon), and heated to 150 C for about 2.5 hours.

  3. Sulfonation of Dispersion A. A volume of 400 ml of Dispersion A is poured into a flask with a small magnetic stirrer and a thermometer. This flask is maintained in a water bath at C and it is connected to a reflux condenser. When the temperature of the solution reaches 50 C, add

  0.6 g of sodium bisulfite and the mixture is stirred for

  for a minute. Then 0.18 g of lime is added. The so-

  - lution is stirred in the water bath at 50 C for 2 hours -

res to carry out the sulfonation.

  The product is designated by "0.5% PSA 50" which means

  that it is dispersion A at 0.5% of potato starch

re, which was sulfonated at 50 C.

4. Methylation of dispersion A.

  200 ml of "0.5% PSA 50" are taken and 5 ml of ion is added.

  hard methyl and 0.1g silver oxide. The solution is heated to 50 ° C. with stirring and in a water bath for one hour. The product obtained is designated by "0.5% PSMA 500 ,.

  5. Another methylation process, with dimer sulfate

  thyle at 50 C. A 4% dispersion of potato starch in 400 ml of tap water is heated to 50 C. 1.52 g of lime are added and the mixture is stirred for one minute. 2.4 ml of dimethyl sulphate are then added. The contents are then stirred and heated at 50 ° C. for 2 hours to carry out the methylation.

  6. Hydrolysis of dispersion A of methylated sulfonated starch.

  100 ml of "0.5% PSMA 50 are taken and 0.075 g of trisodium phosphate and 0.05 g of sodium aluminate are added.

  mixture is heated at 50 C for 1 hour.

  The hydrolyzed product is designated by "0.5% PSMHA 50".

  The sulfonation, methylation and hydrolysis of the starch dispersion B, are carried out in the same way, the products obtained are designated as above, except that the letter B replaces the letter A. The sulfonation reactions, of methylation and hydrolysis are also carried out at 85 C and 150 C and

  the products obtained are designated accordingly.

  The above processes are also applied

  to modify dasheen starch, and these starches modify

  are designated by the same code, except that the letter P (for potato starch) is replaced by the letter

D (for dasheen starch).

Evaluation of modified starches

  The modified starches of the invention are tested for

  complete their ability to flocculate digested residues pro-

  coming from bauxite treatments. Flocculation tests are sedimentation tests analyzed by the Kynch method, which provides a sedimentation time-called

  "ultimate time" (You). Tu is an indicator of the duration

  quise so that the sediment reaches near the final height. This parameter is used to assess the effectiveness of sedimentation aids in suspensions. The more

  the lower the value of Tu, the better the sedimentation.

  Another parameter to express the effectiveness of sediment

  mentation is called "unit area"; it is defined as follows: unit surface: Tu / (C x H) formula in which C: Initial solid concentration (ton / m3) o H: Initial height (m) o Tu: Ultimate time (days) The unit surface is expressed in m2 / ton / day. It represents the surface necessary to deposit a ton

  of solid per day. A small value of this uni-

  silence indicates effective sedimentation.

  To perform these tests, bauxite residues

  are mixed and quickly poured into large cylinders

  100 ml bottles. Residues in the cylinders are processed

  ted with 0.1 ml of a 4% solution of aluminum sulfonate, and the contents of the cylinders are mixed by inverting them three times. This is immediately followed by treatment

  per 100 ppm of the dispersion tested containing 0.5% of flo-

  culant. The contents of the cylinders are mixed in the return-

  five times. Immediately afterwards, we measure and record

  records the sedimentation height at regular intervals

as a function of time.

  The following table illustrates typical values of Tu and unit area for control tests and for the starch flocculants used in the process.

of the invention.

TABLE I

  Digested Jamaican bauxite residues flocculated by sulphonated potato starch derivatives prepared at 50 C ppm Tu (mn) unit area (m2 / ton / day Untreated 0 195.00 9.42 Ex.N Modified starch

1. 0.5% PSA 50 100 52.50 2.54

2. 0.5% PSHA 50 100 61.50 2.97

3. 0.5% PSA 50 25 80.00 3.86

4. 0.5% PSHA 50 25 58.00 2.80

5. 0.5% PSMA 50 100 62.30 2.97

6. 0.5% PSMHA 50 100 62.50 3.01

7. 0.5% PSMA 50 25 55.00 2.66

8. 0.5% PSMHA 50 25 45.00 2.17

9. 0.5% PSB 50 100 44.00 2.13

10. 0.5% PSHB 50 100 64.00 3.09

11. 0.5% PSB 50 25 62.00 2.99

12. 0.5% PSHB 50 25 48.00 2.32

13. 0.5% PSMB 50 100 55.00 2.66

14. 0.5% PSMHB 50 100 49.00 2.37

15. 0.5% PSMB 50 25 43.00 2.07

16. 0.5% PSMHB 50 25 48.00 2.80

  As can be seen from the above data, the sulfonated-methylated potato starches, which they

  whether hydrolyzed or not, are very effective flocculants

these for bauxite residue.

  The following Table II gives similar results when

  that the sulfonated starch derivatives are prepared at 85 C.

TABLE II

  Digested Jamaican bauxite residues flocculated by sulphonated potato starch derivatives prepared at 85 C ppm Tu (mn) unit area (m2 / ton / ____ ________ day Untreated 0 195.00 9.88 Ex. N Starch amended

17. 0.5% PSA 85 100 41.50 2.01

18. 0.5% PSHA 85 100 56.50 2.73

19. 0.5% PSMA 85 100 58.70 2.83

20. 0.5% PSMHA 85 100 53.00 2.56

21. 0.5% PSB 85 100 108.00 5.24

22. 0.5% PSHB 85 100 59.00 2.85

23. 0.5% PSMB 85 100 45.00 2.17

24. 0.5% PSMHB 85 100 90.00 4.35

25. 0.5% PSMB 85 25 70.00 3.38

  It is also clear from the above results that the sulfonated potato starch derivatives are

very good flocculating agents.

  Table III gives the results for the amino derivatives.

sulfonated donation prepared at 150 C.

/

TABLE III

  Digested Jamaican bauxite residues, flocculated by sulphonated potato starch derivatives prepared at 150 C ppm Tu (mn) unit area (m2 / ton / ______ ___ day) Untreated 0 195.00 9.88 Ex. N Starch amended

26. 0.5% PSA 150 100 83.00 4.01

27. 0.5% PSHA 150 100 71.00 2.03

28. 0.5% PSMA 150 100 352.00 17.00

  29. 0.5% PSMHA 150 100 330.00 15.88

30. 0.5% PSB 150 100 48.50 2.34

31. 0.5% PSHB 150 100 45.00 2.17

32. 0.5% PSMB 150 100 110.00 5.21

33 0.5% PSMHB 150 100 105.00 5.07

  The above results show that the potato starch derivatives, prepared at 150 ° C., only sulfonated

  or sulfonated and hydrolyzed, give better performance

  that these same sulfonated and methylated derivatives after the sul-

  foundation. Thus, if a sulphonated starch is prepared at 150 ° C., methylation must be avoided, since it tends to decrease significantly or destroy the flocculating power of the product. The tables which follow show the results obtained with

  similar preparations, in which starch is used

lisé is a dasheen starch.

  Dasheen starch is easily obtained from the dasheen plant, which is the common name for Colocasia

  esculenta - including the variety antiquorum (Taro) -

  plants are among the few varieties consumed

  wheat of the aroid family (Ayaceae), and are nati-

  from Southeast Asia and Malaysia. Consumable tubers (underground stems), from which

  starch is obtained, bear an aggregate of large leaves

  1 to 2 m long, often called elephant ears

  phantom. The isolation of dasheen starch from the root is well known, and it is not necessary to

remember here in detail.

TABLE IV

  Digested Jamaican bauxite residues flocculated by

  derivatives of sulfonated dasheen starch prepared at 50 C.

  ppm Tu (mn) unit area (m2 / ton / day) Untreated 0 195.00 9.88 Ex. n Modified starch

34. * 0.5% DSA 50 100 12.00 2.08

35. * 0.5% DSHA 50 100 117.00 8.21

36. * 0.5% DSMA 50 100 40.00 1.92

37. * 0.5% DSMHA 50 100 29.00 1.40

38. 0.5% DSB 50 100 30.00 1.45

39. 0.5% DSHB 50 100 115.00 5.57

40. 0.5% DSMB 50 100 35.00 1.69

41. 0.5% DSMHB 50 100 36.00 1.74

  * Prepared from starch dispersion "A" with adjuster-

pH 4.0.

  The results clearly show that the starch derivatives

  sulfonated dasheen prepared at 50 C are also floccu-

very effective gloves.

TABLE V

  Residues digested from Jamaican bauxite, flocculated by

  sulfonated dasheen starch derivatives prepared at 85 C.

  ppm Tu (mn) unit area (m2 / ton / day) Untreated 0 195.00 9.88 Ex. n Modified starch

42. * 0.5% DSA 85 100 145.00 3.53

43. * 0.5% DSHA 85 100 23.50 1.13

44. * 0.5% DSMA 85 100 22.00 1.06

* 45. * 0.5% DSMHA 85 100 29.00 1.40

46. 0.5% DSB 85 100 22.00 1.06

47. 0.5% DSHB 85 100 120.00 5.80

48. 0.5% DSMB 85 100 30.00 1.45

49. 0.5% DSMHB 85 100 25.00 1.21

  * Prepared from starch dispersion "A" after

adjustment of pH to 4.0.

  The results of Table V show that the amino derivatives

  donated sulfonated dasheen prepared at 85 C are also

  effective flocculants for bauxite residues.

/

TABLE VI

  Digested Jamaican bauxite residues flocculated by

  sulfonated dasheen starch derivatives, prepared at 150 C.

  ppm Tu (mn) unit area (m2 / ton / day) Untreated 0 195.00 9.88 Ex. n Modified starch

50. * 0.5% DSA 150 100 21.50 1.04

51. * 0.5% DSHA 1500 100 26.00 1.25

52. * 0.5% DSMA 150 100 200.00 9.66

  53. * 0.5% DSMHA 150 100 200.00 9.66

54. 0.5% DSB 1500 100 25.00 1.21

55. 0.5% DSHB 1500 100 50.00 2.42

56. 0.5% DSMB 150 100 235.00 11.33

  57. 0.5% DSMHB 150 100 235.00 11.33

  * Prepared from starch dispersion "A" whose pH

has been adjusted to 4.0.

  As can be seen from the results in Table VI, the flocculating efficacy of the sulfonated dasheen starch on the bauxite residues is destroyed, when the sulfonated product is subsequently methylated. This result agrees with those of Table III, and also, if a sulfonated starch is prepared at temperatures above 85 C, the

  methylation of the product is not recommended.

  The starch composition of the invention allows better clarification of the liquor and a higher density of

  sedimentation which until then had not been possible.

  As a result, fewer washing steps are required in the

  counter-current settling system for red sludge

  ges, and the resulting process is more economical, both

  in cost and duration of treatment.

Claims (10)

Claims   1. Flocculating composition comprising a starch which has been modified by sulfonation to contain sulfonic acid groups, and where appropriate, subsequently methylated to   contain methoxy and acetal groups.   2. Flocculating composition, in accordance with the claim   cation 1, in which the modified starch was then hy- drolysed.   3. Flocculating composition, in accordance with the claim   cation 1 or 2, in which the starch is derived from wheat, potato, corn, yam, cassava or dasheen.   4. Flocculating composition according to one of the resales   dications 1 to 3, characterized in that the starch has been sul-   dark at a temperature of around 500C to 85 C.   5. Process for the flocculation of dispersions a-   diggers of mineral waste, characterized in that one adds   in the dispersion a flocculating amount of a sulfonated starch   born. 6. Method according to claim 5, in   which the sulfonated starch has been hydrolyzed.   7. The method of claim 5, wherein the starch was sulfonated at a temperature between 50 C and 85 C approximately, and wherein the sulfonated starch was then methylated at a temperature between 5 C and 85 C approximately.   8. Method according to claim 7, in   which the sulfonated starch is methylated and hydrolyzed.   9. Method according to one of claims 5 to 8,   applied to the flocculation of red mud from residues of alumina liquors.   10. Method according to one of claims 7 to   9, in which the amount of flocculant is approximately 25 to ppm compared to the residues.