CA1275889C

CA1275889C - Surfactant compositions in alumina precipitation in the bayer process

Info

Publication number: CA1275889C
Application number: CA000615584A
Authority: CA
Inventors: David O. Owen; David C. Davis
Original assignee: Nalco Chemical Co
Current assignee: ChampionX LLC
Priority date: 1987-04-09
Filing date: 1989-12-27
Publication date: 1990-11-06
Anticipated expiration: 2008-04-08
Also published as: AU593987B2; YU71088A; HU202789B; DE286034T1; ES2010966B3; AU1401788A; DE3862052D1; CN1016866B; US4737352A; ES2010966A4; BR8801621A; YU46453B; CN88101926A; CA1266365A; JPS6414111A; EP0286034B1; HUT46597A; EP0286034A1

Abstract

ABSTRACT
The invention relates to a composition for use in a method of reducing the percent of small size alumina trihydrate crystals produced during crystallization of alumina trihydrate from a hot, caustic pregnant Bayer process liquor, the composi-tion comprising (A) a surfactant which will not degrade to anything less than a tall oil equivalent in the presence of a hot strong caustic solution, together with (B) an oil carrier or solvent vehicle for the surfactant that has a boiling point safely above that of hot Bayer green liquor undergoing precipitation.

Description

~L275889 66530-44~D

The invention is concerned with treatment of a Bayer process green liquor from which aluminum values are precipitated.
This divisional application is divided out of parent application Serial Number 563,608 filed on ~pril 8, 1988. The parent application relates to a method of reducing the percent of small size alumina trihydrate crystals produced during cry-stallization of alumina trihydrate from a hot, caustic pregnant Bayer process liquor, thereby to increase the yield of coarse crystals subsequently to be processed to yield aluminum, which comprises adding to-the pregnant liquor, after red mud separation and prior to crystallization of alumina trihydrate, an effective amount of two mutually soluble components (A) and (B), component (A) being a surfactant which will disperse component (B) in the pregnant liquor and component (B) being an oil in which the surfactant is dissolved and having a boiling point above the temperature prevailing during alumina hydrate crystallization.
In the Bayer process for Bauxite ore beneficiation, crystallization and precipitation of solubilized alumina tri-hydrate values from caustic liquors, referred to herein as Bayer process liquor, is a critical step towards the economic recovery of alumina values. Bayer process operators optimize their precipitation methods so as to produce the greatest pos-sible yield from the Bayer process liquors while trying to achieve a given crystal size distribution. It is desirable in most instances to obtain relatively large crystal size since this is beneficial in subsequent processing steps required to produce aluminum metal. Production is often limited by pro-cessing conditions under which the crystallization and precipitation is conducted. These processing conditions vary from one plant to the next and include, but are not limited ~758~9 to, temperature profiles, seed charge, seed crystal surface area, liquor loading, liquor purity, and the like.
It is an extremely well known fact that organic impurities in the Bayer process liquors, which are normally derived from organics present in the Bauxite ore, can haYe a devasting effect on Bayer process crystallization practice.
In addition to humate chemicals derived frorn the impure Bauxite ores, another primary organic contaminant is sodium oxalate, thought to be produced during the high temperature digestion of the raw material Bauxite ore in highly concentrated caustic solutions. Regardless of the source of sodium oxalate, its presence in Bayer process liquors is undesirable for a number of reasons, as explained - la -in U.S. Patent No. 4,608,237. 1 2 ~ 5 8 8 9 Sodium oxalate often crystalizes and co-precip1tates from solu~ion over essentially the same temperature profiles as does the desired alumina trihydrate crystals. Fine oxalate particles act as secondary nucleation sites for alumina trihydrate, thereby increasing the total number of alumina crystals during the alumina trihydrate precipitation. This has an effect of causing a shift to smaller alumina trihydrate crystal size distribution and the production of very finely divided materials which for the most part are not wanted.
However, some of the smaller ~ize alumina trihydrate is needed, as will be explained. The general criterion is not to produce any more o~ the Eine particle crystal than is needed for reseeding.
15The oxalate crystals, which are extremely finely divided and have an extremely large surface area, adhere to the surfaces of growing alumina trihydrate agglomerates. Thi~
adhesion of the oxalate crystalite~ interferes with both alumina trihydrate unit crystal growth and the agglomeration of alumina hydrate crystals. Occlusion of sodium oxalate crystalites within the growing alumina trihydrate mult~crystal al~o results in the weakening of the final crystal structure.
noted abovev this is very unde~irable since it leads to the development of excessive amount~ of extremely f inely divided alumina trihydrate both during the precipitation process as well as in the alumina trihydra~e calcina~ion processes which ollow.

PRIOR ART: OBJECTIVES OF
THE INVENTION
30The di~closure in U.S. Patent No. 4,608,237 i~ the prior art we addres~. According to the disclosure in that ~L~75~389 patent,the precipitation of alumina hydrate crystals of coarse or large size from a Bayer process green liquor is aided ~y employing certain latex polymers. Being in the latex form, these polymers are expensive to produce. Our ob~ect is to achieve yields of coarse alumina trihydrate particles at least quantitatively equal to the achievement under Patent No.
4,608,237 but achieved merely by blending a fatty acid ~or equivalent surfactant) and an oil, the two being soluble in one another, so that the treatment (a mere blend) can be a matter of having the two liquids available at the plant and intro-ducing them into the precipitation tank in-line with introduc-tion of the green liquor charged into the precipitating tank.
Another object of the invention is to present an economic alternative to the polymeric treatment of United States Patent No. 4,608,237 by which to meet the general criterion of fine particle crystal size mentioned above.
THE INVENTION IN PRACTICE: EXAMPLES
In one aspect, the invention of the parent application provides a method of reducing the percent of small size alumina trihydrate crystals produced during crystallization of-alumina trihydrate from a hot, caustic pregnant Bayer process liquor, thereby to increase the yield of coarse cry-stals subsequently to be processed to yield aluminum, which comprises adding to the pregnant liquor, after red mud separa-tion and prior to crystallization of alumina trihydrate, an effective amount of two mutually soluble components (A) and (B), component (A) being a surfactant which will disperse component (B) in the pregnant liquor and component (B) being an oil in which the surfactant is dissolved and having a boiling point above the temperature prevailing during alumina ~75889 66530-449D

hydrate crystallization.
The invention of the present divisional applica-tion provides a composition for use in the method above, which composition comprises (A) a surfactant which will not degrade to anything less than a tall oil equivalent in the presence of a hot strong caustic solution, together with (B) an oil carrier or solvent vehicle for the surfactant that has a boiling point safely above that of hot Bayer green liquor undergoing precipitation.
In the examples to follow, Bayer process pregnant or green liquors at different plants (Plant A, Plant B, and so on) were employed to determine if the invention was in any way limited by variations in precipitation parameters employed by different producers of aluminum, known only to them. These parameters include the nature of the ore, the amount of impurities whether organic or inorganic, caustic concentrations, and especially the conditions inside the precipitation tank which include the form and purity of the seed crystals (small particles of alumina trihydrate), the degree of agitation, time, temperature, and so on. While the details of the pre-cipitation techniques at the various plants are not known, it is known that they do vary widely.

- 3a -~2~S88~
We found the invention in practice is unaffected by different proprietary precipitation techniques lnvolving proce~s parameter~ unknown to us. This fact is of great .significance because it establishes that regardless of the proprietary ~unpublished) processing parameters maintained inside the precipitating tank, the present invention for actual practice only requires blending and in-line injection of ~he two-constituent solution which composes the treatment.
These constituents are (A) a surfactant which will not degrade to anything less than a tall oil equivalent in the presence of a hot (up to 180-190F) strong caustic ~olution (e.g., 200 g/l alkalinity) together with (B) an oil carrler or solvent vehicle for the fatty acid. The oil need only be a solvent for the ~urfactant and have a boiling point safely above that of hot Bayer green liquor undergoing precipitation.
The preferred surfactant is tall oil fatty acid, but there are a host of equivalents. Thu~, the fatty acid is one having at least a saturated or unsaturated four carbon alkyl backbone, with or without one or more carboxylic acid, ester, anhydride or sulf~te surfactant functional groups attached directly or by a succinic alkyl linkage. Advantageously the fatty acid may contain at least an eight carbon backbone with at least one of the above functional groups attached.
The oil carrier may vary widely; the surfactants are oil soluble and there are many oils with a hoiling point above say 200F. ThU~ the oil may be a fatty alcohol-ether-ester complex derived from Clo alcohol distillation; it may be one selected from the paraffinic serie3, it may b~ an aromatic oii ~e.g. naphthenic oil) or it may be any mixture of these.
The oil specie~ that are possible, a~ equivalents, would __, , . . _ . .

1~751~89 represent an almost endless list and our broad-based examples, though few in number, are intended to emphasize this feature of the invention.
The most preferred embodiment is a solution of tall oil fatty acid in a C10 alcohol distillation residue as the oil carrier, in the weight proportion of about 15:85, the dosage being about 20 mg/l. The next preferred embodiment is tall oil fatty acid (surfactant) in naphthenic oil as the oil carrier, in the weight proportion of 15:85 and the dosage being about 20 mg/l. The preferred oil carrier (fatty acid solvent) is the C10 alcohol distillation residue having a boiling point of about 250C (482F). It is light yellow to yellowish brown in color and has a specific gravity of 0.862, OH number 90, SAP No. 50, weight percent acetic 0.07 and carbonyl 0.5. Its main source (and commercial description) is the distallation bottoms or resident from distilling a C10 alcohol. Chemically, it is 57-73 weight percent of primary branched chain C10-C22 alcohols (classed as fatty alcohols) and 29-41 weight percent of mixed long chain esters and ethers (C18 C33 ester; C18-C22 ether).
In all examples, the green or pregnan-t liquor (charge~ employed for alumina trihydrate precipitation is the hot caustic solution obtained after elimination of the red mud in the Eayer process. It is not necessary to an understanding to outline the whole Bayer process to those having skill in that art. The green liquor, after red mud separation, is a hot, caustic filtrate, the commercial production green liquor containing the aluminum values as dissolved sodium aluminate.
This liquor and recirculated fine ~ L2~5~38~3 particle alumina trihydrate seed~ are charged into a suitable precipitatlng tank or a series of connecting tanks. Here, the charge is cooled under agitation to stress the contents, causing precipitation of alumina hydrate crystals on the seeds which constitute growth site3.
Complete elimination oE the fine particle material (e.g. -325 mesh or smaller) is not wanted. There need~ to be a r~mnant source of seeds, following precipitation, for recirculation to serve the next generation of repea~ed growth in a continuous proces~.
In brief~ the precipitation proces~ involve~
nucleation followed by (a) initial crystal growth and ~b) agglomeration of those crystal~ into a coarse or sandlike alumina trihydrate particle which will later be dried, and often calcined to obtain A1203 a~ the commercial product of value~
Also, in the example~ to follow, the "oil carrier,"
unless otherwise noted, is the alcohol distillation residue identified above, and the "fatty acid" is tall oil. Percents are weight percent.
The object of Example~ lA, lB and lC wa~ to determine th~ response using d;fferent dosages of fatty acid/oil blend with diferent seed charge~ imposed on the green liquor of Plant ~. Response in all examplas is the percent reduction to a -325 mesh fraction of the aluminum hydrate cry~tal, equivalent to 44 or 45 microns. The greater ~he reduction, up to a limit, the better the performance in producing the large size crystals for calcination. The "blank" in all examples i~ an undosed green liquor from the plant 9 ite.

., ~

~2~7~i813~
Example lA
Charge: Plant A green liquor; washed fine ~eed.
Treatment: 15% fatty acid ~refined tall oil) 85~ oil carrier Dose ~mg/l)_ Reduction Blank o.o +5.1 +17.2 +31.4 100 ~43.8 200 ~63.0 ~00 +65.0 Example lB
Charge:Plant A green liquor Unwa~hed fine seed Treatment: 15% fatty acid (refined tall oil) 85~ oil carrier Dose ~m~/l)% Reduction Blank 0.5 ~15.7 +31.2 100 ~50.0 Comparing lA and lB it i~ seen that there is little difference in the effect of the treatment whether or not the (recirculated) fine seed i9 washed for more purity.
Example lC
Charge: Plant A
Coarse seed (wa~hed) Treatment: 15~ Fatty acid (tall oil, refined) 85~ Oil carrier 3 Reduction Blank o.o ~66.7 100 +66.7 Example lC shows a coarser seed particle has no adver~e effect on the pre~ent treatment; compare Example lA, "fine seed. n ~7S~
Example_lD
Charge: Plant B
Fine seed (washed) Treatment: 15~ Fatty acid ~unrefined tall oil) 85% oil carrier Dose (m~ Reduction Blank 0.0 ~29.0 2S ~24.0 ~26.0 Charge: Plant C
Fine seed ~unwashed) Treatment: 15~ Fatty acid (unrefined tall oil) 8S% Mineral seal oil ~carrler) Dose (mg/l) ~ Reduct _n Blank o.o sO +30.0 Example4 lD and lE verify that beneficial re~ults in percent reduction are achieved with different plant proce~ses for precipltation, different seed charge~ and different tall oil purity.
In Example lE, the oil carrier is paraffinic, (b.p 150C or higher), performing every bit aQ well as the Clo alcohol distillat~on re~idus.
The object of the following example (2A) was to determine the benefit, if any, using diEfexent ratio~ of fatty acid and oil carrier, compared to the ~atty acid employed by ltself a~ a treatment. The fatty acid in thi~ example wa~
unreined tall oil.

;889 Example 2A
Charge: Plant B
Fine seed (wa~hed~
Treatment Dose ~m~ Reduction Blank o o Fatty acid in oil carrier 15~ 50 ~23 3~% 50 +37 4~ 50 ~35 60~ 50 +21 75% 50 +18 Fatty acid alone 100~ 50 -25 From this example, a 30-45 weight percent ratio of fatty acid in oil is optimum. Negativ~ results are achieved without the oil carrier for the fatty acid.
The object of the following example is to determine if beneficial results are obtained regardless of the order in which the components are added. The fatty acid was refined tall oil.

Example 3A
Charge: Plant A
Fine seed 5washed) Treatment Dose ~m~ % Reduction Blan~ 0 0 ~atty acid (15~) in oil carrier 100 +33.6 Fatty acid followed by oil carrier 15+85 +43.4 Oil carrier followed by fatty acid 85+15 ~38.9 Desirable results were obtained regardless of the srder of addition.
The following two example~ were undertaken to ~7S88~
determine whether a fatty acid ~refined tall oil) dis~olved in an oil carrier perform3 better than an oiI carrier alone.
Al~o, whether there would be an appreciable difference between a petroleum-derlved (paraffin serie~) oil carrier and an aromatic oil employed a~ the carrier. In these two examples (4A, 4B) the fatty acid wa~ refined tall oil.

.

~xample 4A
Charge: Plant ~
~ine seed (washed) Treatment Dose tmg/l) ~ Reduction Blank 0 0 15~ fatty acid in oil carrier 100 ~30.0 Oil carrier only 85 +14.1 15% fatty acid in high aromatic oil(l) 100 +24.3 High aromatic oiltl)85 0 15% fatty acid in oil t~l5% aromatic oil)(2) 100 ~22.4 Oil (~15~ aroma~ic oll) alone~2) 85 + 4.4 15% fatty acid in low aromatic oil~3) 100 +34.6 Low aromatic oil alone 85 ~15.1 (1) Exxon*Aromatic 150 (98~) (2) VM&P*Naptha (3) Exxon low odor paraffinic oil (4~ aromatic) Example 4B
..
Charge: Plant B
Fine seed (washed) Treatment Does (mg/l) ~ Reduction Blank 0 0 15~ fatty acid in naphthenic oil 50 +36 15~ fatty acid in paraffinic oil 50 +27 15~ fatty acid in oil carrier 50 +28 15% fatty acid in mineral oil 50 ~25 The data of these two examples show inferior performance when an oil twhether alcoholic,aliphatic or aromatic) is used alone, withouk any fatty acid, but the *Trade Mark ~ 275~38~
rank of the oil carrier (aliphatic, alcoholic, aromatic or mixed) i~ immaterial.
Example 5A, which follow~, wa~ to determine any ~ynergistic effect of the fatty acid/oil blend compared to each ~eparate component by itself.
Example SA
Charge: Plant C
~ine seed (unwashed) ~ Reduction Treatment Do~e (mg/11 in -325 Me~h Blank 0 0 15% fatty acid in mineral seal oil 50 +30 100~ mineral seal oil 50 0 100% fatty acid S0 -41 The tall oil fatty acld by itself gives inferior performance compared to the paraffinic oil by it~elf (which gives nothing more than a nul re~ult, the ~ame a~ the Blan~) but a~ will be shown by Example~ 6A and 6B many different ~pecie~ of fatty acids are effective when combined with an oil carrier.
. 20 Example 6A
Charge: Plant A
Fine seed ~wa~hed) ~ Reductlon Treatment Do~e (m~/l) in -325 Me~h Blank o o 15~ refined tall oil in oil carrier 100 ~24.2 15% unxe~ined tall oil in oil carrier 100 ~ 7.0 ~2758~9 ExamPle 6B
Charge- Plant A
Fine seed (wa~hed) % Reduction Treatment DoRe (mq/l) in -325 Mesh 15% fatty acid (low rosi~) in an oil carxier 50 +29 15% atty acid ~ high ro~ln) in an oil carrier 50 ~25 f atty ac id (high pitch) in an oil carrier 50 ~24 15~ mixture of oleic and ~tear~c acid~ in an oil carrier 50 +31 15% ~tearic acid in an oil carrier 50 +34 15% oleic acid in an oil carrier 50 +20 15~ n-octenylsuccinic anhydride in an oil carrier 50 +12 15~
n-dodecenyl~uccinic - anhydride in an oil carrier 50 +16 15% isomerized dodecenylsuccinic anhydride in an oil carrier 50 ~19 In Example 6s, the fatty acids of the first three compositions tested were re~pectively a tall oil with low rosin content, one with high ro~ln content and one with a hl~h content of pitch, none of which made any appreciable or noteworthy diEference. In thi~ example t6B) all the acid~
are equated to the fatty acid cla~ becau3e the alkenyl succinic anhydrides hydrolyze in the Bayer pregnant liquor to alkenyl ~dicarboxylic) fatty acid.

~27~i8~9 The following th~ee examples demon~trate that surfactants other than a fatty acid may be successfully employed as an equivalent.
., Examvle 7A
Charge: Plant A
Fine seed (washed) Treatment Dose (mg/l) % Reduction Blank 0 15~ sodium lauryl sulfate in oil carrler lO0 +26.5 15~ complex ~l) phosphate ester in oil carrier 100 +31.4 Cl2 linear alkyl -amino butyric acid in oil carrier (2) lO0 +29.4 (1) GAFAC BH-650 ~GAF Company) (2) this carboxy acid is also known as betaine ExamDle 7B
Charge: Plant B
Fine seed (washed) Treatment Dose_(m~ Reduction .
Blank o o Sulfonated tall oil in oil carrier 50 +17 1~ methacrylic acid stearylmethacrylate copolymer in oil carrier 50 +18 15% att amide ~1) in mineral seal oil 50 +14 (l) amide of refined tall oil, which degrades to tall oil in the green oil Bayer liquor, trade mark.

~L~7S~3~9 Example 7C

Charge: Plant C
Fine ~eed ~washed) Dose ~ Reduction product ~mg/l) in -325 Mesh Blank o O
15% fatty amidell) 50 ~22 in mineral ~eal oil (1~ amide of refined tall oil which degrade~ to tall oil in the green Bayer liquor Example 8A
Thi~ example was to determine whether the fatty acid/oil treatment oE the pre~ent invention would be effective when coupled with a Bayer proce~s liquor at Plant X having no appreciable, if any, oxalate in the green liquor. The treatment remained effective, that i5, the absence of the oxalate made no difference:

~2758~
Wt.~ Dose (mg/l) ~ Reduction Tall Oil Amide 50 22 Mineral ~eal Oil Refined Tall Oil 50 30 Mineral Seal Oil Crude Tall Oil Amide 50 30 Oil Carrier 100 Refined Tall Oil 50 0 100 Mineral 5eal Oil 50 0 Blank __ o The example~ are intended to demon~trate that the useful ~urfactants cover a wide range of chemical variants with or without attached functional groups which may.
contribute more ~urface activity to the surfactant compound.
Therefore, many equivalents may be employed to supplant tall oil a~ long as the surfactant will disper~e the oil in the hot caustic Bayer green liquor. The oil, as noted, is a high boiling point solvent for the surfactant and again there is a wlde range oE equivalents for the preferred species which is the distillation bottoms from distilling a Clo alcohol by oxy processing. Hence while we have set forth a preferred embodiment of the invention it ls to be understood this is capable of variation and modification.

~7588~
It will be seen from the foregoing that under the present invention practiced with a hot caustic Bayer proces~
green liquor, the treatment to shift or bia~ precipitation of alumina trihydrate crystals toward the coarser size is a ~uractant combined with an oil. The oil itself i5 a solvent for the Rurfactant, with a boiling point well above the temperature prevailing during precipitation, while the surfactant in turn is a dispersant or emulsifier for the oil.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A composition for use in a method of reducing the percent of small size alumina trihydrate crystals produced dur-ing crystallization of alumina trihydrate from a hot, caustic pregnant Bayer process liquor, the composition comprising (A) a surfactant which will not degrade to anything less than a tall oil equivalent in the presence of a hot strong caustic solution, together with (B) an oil carrier or solvent vehicle for the surfactant that has a boiling point safely above that of hot Bayer green liquor undergoing precipitation.

2. A composition according to claim 1 in which compon-ent (B) is an oil selected from the group consisting of:
(1) paraffinic;
(2) naphthenic;
(3) mixed paraffinic and aromatic;
(4) the residue of C10 alcohol distillation.

3. A composition according to claim 2 in which the surfactant is a fatty acid that has at least a saturated or unsaturated four carbon alkyl backbone, with one or more car-boxylic acid, ester, anhydride or sulfate surfactant functional groups attached directly or by a succinic alkyl linkage.

4. A composition according to claim 3 in which the fatty acid has an at least eight carbon atom backbone.

5. A composition according to claim 1, 2 or 3 in which the ratio of the amount of component (A) to component (B) is in the range 15:85 to 45:55.

6. A composition according to claim 1 in which the surfactant is a tall oil fatty acid.

7. A composition according to claim 6 in which the oil is the residue of C10 alcohol distillation.

8. A composition according to claim 6 in which the oil is a naphthenic oil.

9. A composition according to claim 7 wherein the ratio of tall oil to residue is about 15:85 by weight.

10. A composition according to claim 8 wherein the ratio of tall oil to naphthenic oil is about 15:85 by weight.