Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2002-01-29
2003-09-09
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C524S005000, C524S008000, C524S071000, C524S272000, C524S276000, C210S733000, C210S732000
Reexamination Certificate
active
06617421
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a process for producing substantially dry water insoluble polymers from poly alkyl esters of vinylic monomers for improved flocculation of red mud in the Bayer process and for a process of clarification of the red mud-containing liquors generated in the Bayer process for the recovery of alumina from bauxite ore with high molecular weight emulsion polymers.
BACKGROUND OF THE INVENTION
The Bayer process for the production of alumina includes the basic steps of pulverizing a bauxite ore which is slurried in water and digested with caustic at elevated temperatures and pressures. The caustic solution dissolves oxides of aluminum to form an aqueous sodium aluminate solution that must be separated from the caustic-insolubles of bauxite ore (red mud). Separation typically occurs through the process of sedimentation and filtration, which are often aided by a flocculant. Once separated, alumina trihydrate can be precipitated out of the aqueous sodium aluminate solution and collected as product.
Specifically, the pulverized bauxite ore is fed into a slurry mixer where the slurry makeup water is typically spent liquor and added caustic. The bauxite ore slurry is then diluted and passed through a digester under high pressure and temperature conditions where about 98% of the total available alumina is released from the ore as caustic-soluble sodium aluminate. After digestion, the slurry passes through several flash tanks where the pressure of the digested slurry is reduced from several atmospheres to one atmosphere and the temperature of the slurry is reduced from about 200° C. to about 105° C.
The aluminate liquor leaving the flashing operation contains about 1 to 20 weight percent solids. The coarser solids may be removed from the aluminate liquor with “sand trap” cyclones. The finer solids are generally separated from the liquor first by settling aided by a flocculant and then filtration. The aluminate liquor slurry leaving the flash tank is diluted by a stream of recycled washer overflow liquor. Any Bayer process slurry taken from the digesters through a subsequent dilution of the slurry, including the flash tanks, but before the primary settler, is the primary settler feed.
Normally, the primary settler feed is fed to the primary settler where it is treated with a flocculant. As the mud settles, the clarified sodium aluminate solution (“green” or “pregnant” liquor) overflows to a weir and is collected. This overflow from the primary settling tank is then passed through subsequent process steps.
The clarity of the primary settler overflow is crucial to efficient processing of alumina trihydrate because further steps will be required if the overflow has not been properly clarified. An overflow liquor containing a concentration of suspended solids of about 10-500 mg suspended solids per liter is typically unacceptable and will require further processing in a secondary clarification stage to achieve the desired 10 mg suspended solids per liter.
A flocculant is often added to aid in the partial separation of the red mud solids from the pregnant liquor in the primary settler stage. Flocculating agents, such as inverse emulsion liquid polymers, dry polymers and polysaccharides including starch, improve the separation of insolubles. Flocculants are able to increase the rate at which solids settle by reducing the amount of residual solids suspended in the liquor and by decreasing the amount of liquor in the settled solids phase.
Flocculants are highly important in the primary settling stages. Red muds are comprised of iron oxides (about 50 weight percent), together with silicon oxides, calcium oxides, sodium alumino-silicates, titanium oxides and other material commonly comprise about 5 to about 50 weight percent of the bauxite ore. Generally, the muds are comprised of very fine particles, which hinder separation of red mud particles from the solubilized alumina liquor. If the rate of separation is too slow, output is diminished and the overall process efficiency is impaired. If the separation is not clean, a more extensive treatment to remove residual solids will be required.
Conventional treatments include the application of polysaccharides, such as starch and dextran. For instance, U.S. Pat. No. 3,085,853 to Lesinski et al. uses native dextrans to increase the rate of sedimentation of finely divided solids in aqueous suspensions. After polysaccharides were introduced, synthetic polymeric flocculants were developed which have became more popular for use in the Bayer process. Additional polymers include those formed from the polymerization of vinyl amine or vinyl formamide as disclosed in U.S. Pat. No. 5,346,628; phosphonic acid polymers as disclosed in U.S. Pat. No. 5,534,235; and polymers containing hydroxamic acid groups in U.S. Pat. No. 4,767,540.
Other Bayer process treatments include the combination of polysaccharides with synthetic polymeric flocculants. For example, U.S. Pat. No. 3,397,953 to Galvin et al. discloses that polyacrylic acid alone is not suitable as a flocculating agent, instead it teaches the use of a blend of starch and polyacrylic acid on red mud suspensions. The polyacrylic acids generally have molecular weights of less than 300,000. The flocculation and sedimentation activity of the blend is used in the primary settler stage of a bauxite process, and contains at least about 80 weight percent of the acrylic acid mer with a molecular weight in excess of 50,000 and preferably in excess of 100,000. Other starch/polymer combinations are disclosed in U.S. Pat. Nos. 3,397,953; 3,541,009; 3,681,012; and 5,008,089.
Emulsions of polymers formed of lower primary alkyl acrylate monomers for refining alumina are disclosed in U.S. Pat. No. 3,755,531. Moreover, unexamined Japanese Patent No. 4986-1979 discloses a process for producing an ultra high molecular weight acrylic acid copolymer salt. However, only lower molecular weight polymers which are less effective flocculants than higher weight polymers are disclosed in the Japanese Patent.
Disclosed in U.S. Pat. No. 5,286,391 is a process for improving the flocculation of suspended red mud solids in a Bayer process liquor comprising a water-continuous dispersion containing a polymer dispersed in the water of the continuous phase, wherein the polymer comprises at least 50 mole percent of mer units having pendant groups that hydrolyze to pendant carboxylic acid groups. However, this reference suggests that because the in-situ hydrolysis occurs over time and results in continuous activation, that the optimal polymer would be one containing 100 mole percent of mer units having pendant hydrolyzable groups. By contrast, this invention discloses that there is an optimal degree of hydrolysis (not 100%), that occurs in the range of 70-80%.
Oil continuous liquid flocculants (hereafter termed o/c flocculants) and powder flocculants are typically referred to as synthetic flocculants. Such flocculating agents are added to the primary settler, the mud washing circuit, mud-dewatering systems including centrifuges and vacuum filters and to enhance mud stacking in mud disposal sites.
High molecular weight synthetic polymers are often used in conjunction with starches. Starch is said to improve supernatant liquor clarity, the interface between the settled mud and the cleaner supernatant liquor, and reportedly helps to maintain the stability of the settled mud in settlers and washers. However, starch occasionally produces a red mud which has poor rheology and undesirable underflow characteristics. If not diluted, the underflow can occasionally become difficult to pump.
The oil continuous flocculants must be inverted prior to application to transfer the flocculant to the water phase of the emulsion. If o/c flocculants are added neat (non-inverted) the polymer flocculant will not disperse in the Bayer liquor, the oil phase containing the flocculant will plug the injection equipment, and poor activity will be encountered.
Oil continuous liquid flocculants of sodium or ammonium acrylate are larg
Allain Ronald J.
Phillips Everett C.
Breininger Thomas M.
Cummings Kelly L.
Martin Michael B.
Ondeo Nalco Company
Truong Duc
LandOfFree
Method for producing substantially dry water-insoluble... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing substantially dry water-insoluble..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing substantially dry water-insoluble... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3082807