SU1838237A3 - Method to recover aluminium oxide of a bauxite - Google Patents

Description

UNION OF SOVIET

SOCIALIST

REPUBLIC

... SU. ,,, 1838237 AZ (51) 5 C 01 F 7/06

STATE PATENT

DEPARTMENT OF THE USSR (ROSPATENT USSR)

DESCRIPTION OF THE INVENTION

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TO THE PATENT (21) 4742492/26 ¢ 2) 11/09/89 (46) 08/30/93. Bull. No. 32 (71) Ellide Colloid Limited (GB) (72) Gillian Mary Moody and Christina Ann Rushfort (73) Ellide Colloid Limited (GB) (56) US Patent No. 3,575,868. C 01 F 7/36. 1968.

(54) METHOD FOR EXTRACTION OF ALUMINUM OXIDE FROM BOXITE (57) Use: in the production of alumina. Essence: bauxite is leached with an aqueous alkaline solution, the resulting suspension is treated with a flocculant, the red mud is separated from the resulting solution in the first stage. Part of the settled solution from the first stage is fed to the second stage of clarification. A flocculant is introduced into the solution and the red mud particles of the ot solution are separated. The red mud from the first stage is subjected to multi-stage washing and, if present, partially from the second stage of clarification. After washing, the washing solution is treated with a flocculant and the precipitate is separated from the washing solution. The flocculant is administered in at least one of the stages selected from the first stage of separation; the second stage of clarification and stage washing. As a flocculant, dextran and a synthetic polymer flocculant are used; containing 50-100% anionic monomer and 0-50% acrylamide. 8 s.p. f-ly., 7 tab.

The invention can be used in the production of alumina.

The purpose of the invention is to increase the efficiency of the process.

In the Bayer process, the extraction of aluminum oxide according to the invention, bauxite is boiled in a single alkaline solution, the resulting red mud is flocculated by a flocculating agent and separated from the cooking solution in the first separation stage, the settled solution from this stage is partially fed to the secondary clarification stage, in which the newly suspended particles red mud is flocculated and separated from the solution, then the red mud from the first separation stage and, if present, is washed partially and in the second clarification stage in many successive washing stages, in each of which the sludge is washed with a washing solution, it is flocculated by a flocculating agent and separated from the washing solution, and the flocculating agent in at least one stage selected from the first separation stage, the second clarification stage and the washing stages, contains two components, and the method is characterized in that these two components are: a) dextran and b) synthetic anionic polymer flocculant.

Preferably, _{4, the} components a and b are added sequentially, although good results can sometimes be obtained. if they are pre-mixed and then added to the solution.

Although dextran can be mixed with a solution that is treated with a synthetic polymer, it is preferred that the polysaccharide be mixed with the solution until

SU <„. 1838237 AZ of how a synthetic polymer flocculant will be added to a solution. Between these two methods of administration there may be a small interval, immediately after completion of the stage of mixing the polysaccharide, mixing with a solution of a synthetic polymer flocculant begins. It was found that better results are achieved if the dextran is mixed more intensively with the solution and the synthetic polymer is less intense. It is possible that the polysaccharide acts as a coagulant.

Dextrin should be soluble in water and have a molecular weight of at least 5000, although values from 500,000 to 10 million are preferred. Dextran is preferably a microbially prepared polysaccharide and has glucose residues linked by glucosidic bonds 1: 6. Dextran sulfates can also be used. Dextran can be supplied in the form of dry solid particles, for example, which have been recovered from a microbial suspension. Often, the final purification step may be a spray drying step at which other components may be added in order to aid processing. In general, such auxiliaries should not be removed from dextran prior to its use as a flocculant. Typically, dextran is soluble in water or an alkaline solution before being added to the solution used in the inventive method.

A synthetic polymer flocculant is a generally high molecular weight water soluble polymer formed from an anionic ethylenically unsaturated monomer partially with a nonionic ethylenically unsaturated monomer.

The anionic monomer is mainly a monoethylenically unsaturated carboxylic or sulfonic acid, which is usually acrylic acid, but may be, for example, methacrylic acid (meth / allyl sulfonic acid, vinyl sulfonic acid or

2-acrylamidomethyl propane sulfonic acid. The anionic polymer is mainly present in the form of a sodium salt or other alkali metal or ammonium salt.

The non-ionic monomer, if present, is usually acrylamide, but other immiscible monomers can be incorporated in a known manner. For example, a small amount of a methylolacrylamide particle may be included.

The optimal amount of anionic particles depends in part on the total alkalinity of the solution, and as indicated above, it is generally desirable to use a polymer with a high anionic content (for example, 100% or lower to 80% or 90% by weight) in the first separation step, and polymers with possibly lower alkalinity, for example, up to 20% in the last stage, with intermediate values in the intermediate stages. Depending on the alkalinity of the particular solution and other process conditions, the polymer is mainly used polymer with 20-100% anionic monomer, usually from 50 to 100% anionic monomer (usually sodium acrylate) and the rest is acrylamide. At the first separation stage and at the first washing stage, a polymer is formed containing from 80 to 100% anionic monomer, but at the last stage it can be formed, for example, from 40 - 75% anionic monomer and the rest is acrylamide.

The synthetic polymer may be supplied as a return phase dispersion, but preferably it comes in the form of a gel or a granular polymer, for example, in powder water, which dissolves in water or a vegetable solution before use.

Although the introduction of a flocculant, mainly by pretreatment with a mixture comprising dextran, gives advantages at least at one stage in a number of processes, we have found that it gives great advantages at a stage where the effect of the flocculant is worse than suggested, taking into account the alkalinity of the solution and anionic polymer content. We found that the action of the flocculant does not depend, despite previous statements, on total alkalinity, and together it strongly depends on the chemical type of alkalinity, as well as on general alkalinity. In particular, we found that the presence of significant amounts of sodium carbonate adversely affects the effect exerted by the flocculant, especially when only a synthetic anionic polymer flocculant is a flocculant. However, this detrimental effect can be reduced or overcome by treatment with dextran or polysaccharide, in particular by pretreatment with dextran. Thus, the invention is of great importance when a dextran or polysaccharide is added to a solution having a relatively high content of sodium carbonate,

This solution may be a solution from the first precipitation step. Lime can be added to this solution for regeneration from a sodium hydroxide solution in order to prepare the solution for reuse in the cooking process. Most preferably, the presence of dextran in a highly alkaline solution that prevails in the first precipitation step, in combination with a homopolymer, for example sodium acrylate.

Alternatively or additionally, the solution may be used from the second clarification step. Lime can be added before this stage.

In other stages of the methods, dextran and a synthetic polymer are added to the washing solution in one or more washing stages and, if necessary, they can be added in two or more stages, which include a first separation stage, a second clarification stage and a washing stage. If required, they can be included in the washing solution at each washing stage.

Regardless of the specific stage, an improvement in flocculation is manifested, for example, in improving transparency and, as a result, reducing the amount of suspended solids in the purified solution and / or improving the deposition rate, and / or improving the density of red mud at any dose of synthetic flocculant and anionic contents of the synthetic polymer .

The amount of dextran that is added to the solution is usually 0.2 to 10, preferably 0.5 to 5 mg / L, and the amount of synthetic polymer is usually from 10 to 150%, preferably from 25 to 100%. The amount of the synthetic polymer depends on its anion content and molecular weight (which is usually above 0.5 million and preferably above 1 million) but is usually in the range of 0.5 to 20, preferably 1 10 mg / L.

The alkalinity of the washing solution may be in the range of, for example, from 10 to 300 g / l, expressed in sodium hydroxide. When the indicated combination, as the most preferred, is used For more alkaline solutions, the alkalinity of which is in the range of 100-300, often 200-300 g / l, expressed in sodium hydroxide. The invention is especially valuable when the sodium carbonate content in the solution is at least 10 g / l, often at least 20 g / l, and especially when it is more than 50 g / l. The carbonate content can be up to 100 g / l or even towers, but usually less than 200 g / l.

The solid red mud content in the solution (in the cooking liquor or in the washing solution) that undergoes flocculation is generally higher than 10 g / l, but lower than 100 g / l. Often it is in the range of 20-50 g / l.

The method, regardless of the addition of flocculant, may be conventional. Cooking is usually carried out using a hot (100 ° C) alkaline cooking solution, usually with an alkalinity of 150 to 250 g / l NgO, to form a solution containing sodium aluminate, from which aluminum hydroxide precipitates. To convert sodium carbonate to sodium hydroxide, lime may be added to the solution, and the resulting solution may be returned to the process. Separation of the solution from insoluble components at any stage where a combination of dextran is not used (synthetic polymer is carried out by including a flocculant, which can be used as a polysaccharide, but usually sodium acrylate polymer (or other anionic ethylenically unsaturated monomers) with 0 - 20% weight, usually 0 to 10% by weight of acrylamide.

As was briefly described above, the red mud from the first precipitation stage is fed to the first washing stage, where it is washed with a washing solution, flocculated with a flocculating agent and separated from the washing solution, and then proceeds to the second washing stage. The washing solution from the first washing stage usually enters the cooking stage, and the washing solution used in the first stage is usually a solution that is recovered from the second stage. The process is repeated several times, in the total number of washing stages is from 4 to 10. often from 5 to 7, to the last stage described above. The washed sludge from this stage is deposited in a stack, lagoon or other known apparatus, and the purified solution from the precipitant is usually recycled as part of the total amount of the last washing solution.

To improve flocculation, lime may be added to the cooking or washing solution in any amount of the amount of dextran or synthetic polymer, for example, in the first separation stage or in the washing solution.

Example 1. In each experiment, the suspension consisted of 25 g / l of solid particles of red mud in an aqueous solution, sodium hydroxide or sodium hydroxide and sodium carbonate, and then the suspension was flocculated

Ί by adding a high molecular weight homopolymer of sodium polyacrylate in the indicated doses and partially after preliminary treatment with dextran in the indicated doses. Doses are indicated in mg / L. The deposition rates are indicated in cm / min, preferably the highest speed; transparency is indicated on a scale on which a higher value indicates improved transparency; Settled solids are indicated as a percentage, where the highest value corresponds to improved values.

The results are presented in table 1.

From table 1, the advantage of using dextran is clearly visible.

PRI me R 2. The synthetic solution for the first stage of deposition contained 25 g / l of red mud and 200 g / l of sodium hydroxide. In each experiment, 500 ml of the suspension was placed in a measuring cylinder with a volume of 500 ml, which was placed in a water bath at 80 ° C. A certain dose of diluted flocculant (0.1 M sodium hydroxide solution) was added to the suspension, the resulting mixture was mixed a predetermined number of times with a stainless plunger. When using a two-component flocculant, each component was added separately; after each addition, the same number of times was mixed.

The order of additions is given in Table 2.

The rate of deposition of solid particles was recorded between two fixed points of the cylinder. After 10 min, a sample of the settled solution was removed and its transparency was checked. The test was carried out by placing the sample in a wedge-shaped transparent vessel, which is pointed downwards at the narrower end, and whose vertical rear surface is marked in a certain sequence, and the numbers in this sequence increase with the thickness of the wedge and therefore with the distance through the liquid in the horizontal plane. The highest values that can be read when the back wall of the vessel is viewed horizontally through the liquid are shown in the table. Higher values correspond to greater transparency, which is more desirable.

Dextrin was added with an equal amount of sodium tripolyphosphate. A high molecular weight homopolymer of sodium acrylate (PAN) was used as a synthetic polymer.

The results show that for a suspension whose alkalinity is determined by the presence of sodium hydroxide, the combination of dextrin with poly (sodium acetate) gives an unexpectedly high sedimentation rate. When the components are added separately and the first component is mixed before the second component is added, the sedimentation rate increases more, especially when the dextrin is added first. Higher dextran content gives good transparency.

Example Z. Repeat the techniques described in example 3, but using a suspension containing 205 g / l sodium hydroxide and 50 g / l sodium carbonate.

The results are shown in table.Z.

The results show that for high carbonate suspensions, it is preferred that dextran be added first. In all experiments, both transparency and sedimentation rate are improved.

PRI me R 4, Example 3 was repeated, but the effect obtained from the degree of mixing of each component was determined, which was achieved by changing the number of immersion after each addition.

The results are shown in table 4.

The results show that it is much better if the dextran is mixed in suspension more vigorously than polyacrylate. Increased mixing of dextran leads to improved subsidence and transparency. On the other hand, increased mixing of the polyacrylate leads to a decrease in the settling rate, although inadequate mixing gives a fuzzy sludge line, which is an advantage in itself.

PRI me R 5. Repeat example 2, but using a suspension containing 205 g / l of sodium hydroxide and 50 g / l of sodium carbonate. When using a two-component flocculant, dextran is always added first, mixed, and then a synthetic polymer is added. In this example, lime was added to some suspensions.

The results are shown in table 5.

These results show that for suspensions with a high carbonate content, neither dextran nor sodium psiacrylate give adequate results when used separately, in particular, the synthetic polymer gives a very poor sedimentation rate. In each case, the addition of lime improves the results to some extent, although even significant amounts of lime do not provide sufficiently good transparency or settling rate.

The combination of dextran and poly / sodium acrylate / gives a significant increase in the deposition rates and transparency of the clarified solution, and large amounts of dextran give better results for both 5 indicators. The introduction of lime provides a further improvement in transparency, especially when using large amounts of dextran, although there is a slight decrease in the deposition rate.

Example 6. Experiments were conducted to study the effect of changes in the amount of carbonate, which affects alkalinity, using suspensions with constant total alkalinity (210 g / l, measured for sodium hydroxide), but with a varying amount of sodium hydroxide and sodium carbonate, which also affect the alkalinity of the solution. In the case where a combination of flocculant was used, dextran was added by the can.

The results are shown in table.6.

The results show that for suspensions with a high carbonate content, the use of only one synthetic 25 polymer does not allow satisfactory flocculation. The introduction of dextran improves the deposition rate and transparency even for these suspensions.

PRI me R 7. Repeat example 6, but 30 change the total alkalinity by maintaining a constant concentration of sodium hydroxide (at the two indicated levels) and changing the amount of sodium carbonate used. 35

The results are shown in table.7.

The results again show that for suspensions with a high carbonate content, where the synthetic polymer alone gives inadequate flocculation, 40 using it in combination with dextran allows for a satisfactory deposition rate and transparency.

An example. Example 3 is repeated using the same suspension as in Example

3. but instead of dextran, other polysaccharides are used, including those that have been used or have been proposed for use in the Bayer process. In each experiment, the polysaccharide was added first and mixed, then 3 mg / L PAN was added and even mixed. Polysaccharides were used in amounts up to 50 mg / l, but not one gave positive results. The test materials were low and high molecular weight dextrins, cationic and anionic starches, alginates, carboxymethyl cellulose, hydroxyethyl cellulose, amylopectin (waxy corn starch), amylose and guar gum.

Claims (8)

Claim 1. The method of extraction of alumina from bauxite, including leaching of bauxite with an aqueous alkaline solution, processing the resulting suspension with a flocculant, separation of red in the first stage 10 sludge from the resulting solution, supplying part of the settled solution from the first stage to the second clarification stage, introducing a flocculant into the solution and separating the red mud particles from the solution, multi-stage washing of the red mud from the first separation stage and, if available, partially from the second clarification stage, after washing, the washing solution is treated with a flocculant and the precipitate is separated from the washing solution and the flocculant is introduced in at least one of the stages selected from the first separation stage, the second separation stage and the stage myvki, and used as a flocculant two components, characterized in that, in order to increase efficiency of the process, are used as components dextran and synthetic polymer flocculant comprising 50 - 100% anionic monomer with 0 - 50% acrylamide. 2. The method according to claim 1, characterized in that the dextran and the polymer flocculant are administered separately. 3. The method according to claim 1, characterized in that the dextran is added to the pulp before the polymer flocculant is added. 4. The method according to claims 1 to 3, characterized in that the dextran and the polymer flocculant are introduced into the first stage of sedimentation of the sludge. 5. The method according to claim 1, characterized in that the dextran is used with a pier. May. 5 x 10 ⁵ - 10 10 ^th. 6. The method according to claim 1, characterized in that in the quality of the synthetic polymer flocculant use homopolymer of sodium polyacrylate. 7. The method according to claim 1, characterized in that the dextran is administered in an amount of 0.2 - 50 10 mg / l, preferably 0.5 to 5 mg / l. 8. The method according to claim 1, with the fact that the synthetic polymer flocculant is added in an amount of 0.5 to 20 mg / l, preferably 1 to 10 mg / l. 55 9. The method according to claim 1, with the fact that at the stage of introducing the flocculant, the content of sodium carbonate is at least 10 g / l, mainly at least 20 g / l and more predominantly 50 g / l. Table 1 NaOH, hl No. gCOz Dextran, mg / L Polymer, mg / L Precipitation rate Transparency Solid particles,% 243 - -  3 36.3 Bad 243 - - 4 65,4 Beautiful 243 - - 5 80.0 Also 243 - 6 88.8 243 - 3 3 78.1 Good 200 fifty - 3 10 approx. 3 18.1 200 fifty - 3 20 3 18.7 200 fifty - 5 thirty 3 19,4 200 fifty 1 3 32.6 8 21,2 200 fifty 2 3 62.5 fifteen 22.3 200 fifty 3 3 68.5 18 22.3 200 fifty 4 3 78.9 22 22.3 200 fifty 1 4 58.8 eleven 23.1 200 fifty 2 4 64.8 16 23.1 200 fifty 3 4 81.1 19 22.7 200 fifty 4 4 78.9 20 21.92 table 2 Flocculant / order of administration / Dose, mg / g Settling speed, cm / min Transparency PAN 1 1 2 2 21 3 3 44 5 4 57 6 Dextran 0.5 2 6 1,0 6 8 1,5 eleven 6 2.0 thirteen 6 PAN / Dextran 0.75 1 4 2: 1 mixture 1,5 9 4 2.25 26 5.5 3.0 29th 5 PAN + Dextran 2 + 1 39 5.5 2 + 1 40 17 Dextran + PAN ί + 1 40 8 2 + 2 60 27 Table 3 Flocculant administration Dose, mg / L Stirring (number of dives) Settling speed, cm / min Transparency Dextran + PAN 0.5 + 3 3 + 3 52 5 1,0 + 5 3 + 3 68 8 1,5 + 3 3 + 3 71 eleven 2.0 + 3 3 + 3 69 9 PAN + Dextran 3 + 0.5 3 + 3 51 5 3 + 1,0 3 + 3 51 5 3 + 1,5 3 + 3 55 6 3 + 2.0 3 + 3 60 6 Table 4 Flocculant and order of administration Dose, mg / L Stirring (number of dives) Settling speed, cm / min Transparency Dextran + PAN 1,5 + 3 3 + 1 84 ^x 9 1.5 + 3 3 + 3 62 8 1.5 + 3 3 + 6 48 9 PAN + Dextran 3 + 1,5 3 + 1 51 4 3 + 1.5 3 + 3 59 6 3 + 1,5 3 + 6 59 12 ^x Slurry line does not differ Table 5 Dextran Dose, mg / L PAN dose, mg / l Lime, g / l Settling speed, cm / min Transparency 1.5 - - 8 8 2  - - 10 8 1,5 - 5 8 12 2 - 5 10 14 - 3 - 10 ^x 3 - 4 - 20 ^x 3 - 3 2 18 ^x 6 -. 4 2 21 ^x 6 - 3 5 thirty 7 - 4 5 49 7 1 3 - 63 fifteen 2 3 - 79 22 1 4 - 65 16 2 _e 4 - 79 20 1 3 1 57 16 2 3 1 60 27 15 1838237 16 Continuation of the table. 5 Dextran Dose, mg / L PAN dose, mg / l Lime, g / l Settling speed, cm / min Transparency 1 3 2 55 17 2 3 .... 2 60 24 . 1 4 2 63 fifteen 2 4 2 79 25 ^x no differences in the lines of sludge, the formation of which is very undesirable. Table 6) NaOH, g / l / MagSOz, g / l Dextran, mg / L PAN, mg / l The deposition rate, cm / min Transparency ί 200 thirteen - 2 I ABOUT 10 200 thirteen - 3 76 fifteen 200 thirteen - 4 90 fifteen 200 thirteen 1.0 3 85 35 200 thirteen 1.5 3 93 38 200 thirteen 2.0 3 96 40 180 40 - 2 21 ^x 6 180 40 - 3 44 ^x 6 180 40 - 4 50 ^x 7 180 40 1.0 3 77 fifteen 180 40 1.5 3 78 20 180 40 2.0 3 94 23 160 66 - 2 14 ^x 5 160 66 - 3 X 5 160 66  - . 4 X 5 160 66 1.0 3 54 9 160 66 1.5 3 56 12 160 66 2.0 3 69 14 ^x Fuzzy sludge line. Table 7 NaOH, hl IAGCO3, g / l Dextran, mg / L PAN, mg / l The deposition rate, cm / min Transparency 150 fifty - . 3 67 8 fifty 1 3 64 14 55 - 3 49 6 55 1 3 69 thirteen 60 - 3 X 5 60 1 3 68 12 65 - 3 X 4 65 1 3 56 9 Continuation of the table. 7 NaOH, hl IAGCO3 g '/ l Dextran, mg / L PAN, mg / l The deposition rate, cm / min Transparency 128.5 28 - 3 91 32 28 1.5 3 125 46 48 - 3 67 16 48 1,5 3 83 42 68 - 3 47 ^x eleven 68 1.5 3 70 thirty 88 3 30 ^x 6 88 1.5 3 77 24 108 - 3 X 5 108 1.5 3 fifty 10 ^x The sludge line is indistinguishable. Editor S. Kulakova Compiled by N. Tselikova Tehred M. Morgenthal Corrector O. Mandzic Order 2897 Circulation Subscription VNIIIPI of the State Committee for Inventions and Discoveries under the State Committee for Science and Technology of the USSR 113035, Moscow, Zh-35, Raushskaya nab., 4/5 Production and Publishing Plant Patent, Uzhhorod, st., Gagarina, 101