Process for water based mineral material slurry surface whitening

Abstract

The present invention is directed to a process for surface whitening mineral matter in a slurry that includes the following steps: (a) preparing by dispersing and/or grinding at least one water based mineral matter slurry; and (b) adding during and/or after step a) 0.005 wt % to 0.5 wt %, based on dry weight of the mineral matter, of at least one alkylene oxide block co-polymer or at least one alkylene oxide random co-polymer.

Claims

1. A process for improving the whitening of a mineral matter slurry surface by reducing flotation of impurities to the slurry surface which cause darkening of the slurry surface, the process comprising the following steps: (a) preparing by dispersing and/or grinding at least one water based mineral matter slurry, wherein the mineral matter comprises calcium carbonate and impurities that can cause darkening of a slurry surface, wherein the impurities comprise one or more oxides, sulphides, silicates, and crystalline and/or amorphous carbon; and (b) adding to the slurry during and/or after step a), 0.005 wt % to 0.5 wt %, based on dry weight of the mineral matter, of at least one alkylene oxide block co-polymer or at least one alkylene oxide random co-polymer, to obtain a slurry of mineral matter in which the slurry surface has improved surface whiteness over the same slurry in which the at least one alkylene oxide block co-polymer or the at least one alkylene oxide random co-polymer is not added, wherein the whitening of the slurry surface is improved by reducing flotation of impurities to the slurry surface which cause darkening of the slurry surface.

2. The process according to claim 1, wherein the co-polymer added in step b) is at least one alkylene oxide block co-polymer.

3. The process according to claim 1, wherein 0.005 wt % to 5 wt %, based on dry weight of the mineral matter, of at least one dispersing and/or grinding aid is added during and/or after step a) and/or step b).

4. The process according to claim 1, wherein the at least one alkylene oxide block co-polymer is a bi-block copolymer.

5. The process according to claim 4, wherein the bi-block copolymer is an EO/PO block polymer.

6. The process according to claim 1, wherein the at least one alkylene oxide block co-polymer is a tri-block copolymer.

7. The process according to claim 6, wherein the tri-block copolymer is an EO/PO/EO or a PO/EO/PO block copolymer.

8. The process according to claim 6, wherein the tri-block copolymer has the general structure: ##STR00005## and wherein x, y, and z each independently represents any single integer between, or equal to 1 and 120, and wherein x and z are the same or different integer(s), or ##STR00006## in which a, b, or c each independently represent any single integer between, or equal to 1 and 120, and wherein a and c are the same or different integer(s), and wherein R and R in formulas (I) - (II) are alkyl residues and/or hydrogen.

9. The process according to claim 8, wherein x, y, and z each independently represent any single integer between, or equal to 1 and 80, and a, b, or c each independently represent any single integer between, or equal to 1 and 80.

10. The process according to claim 8, wherein x, y, and z each independently represent any single integer between, or equal to 3 and 70, and a, b, or c each independently represent any single integer between, or equal to 3 and 30.

11. The process according to claim 8, wherein x, y, and z each independently represent any single integer between, or equal to 5 and 34, and a, b, or c each independently represent any single integer between, or equal to 4 and 34.

12. The process according to claim 4, wherein the bi-block has the general structure: ##STR00007## or ##STR00008## wherein d, e, f or g each independently represent any single integer between, or equal to 1 and 120, d and e are the same or different integer(s), and for g are the same or different integer(s), and wherein R and R in formulae (III) - (IV) are alkyl residues and/or hydrogen.

13. The process according to claim 12, wherein d, e, for g each independently represent any single integer between, or equal to 1 and 80.

14. The process according to claim 12, wherein d, e, for g each independently represent any single integer between, or equal to 2 and 70.

15. The process according to claim 12, wherein d, e, for g each independently represent any single integer between, or equal to 4 and 40.

16. The process according to claim 3, wherein the at least one dispersing and/or grinding aid is an anionic dispersing and/or grinding aid.

17. The process according to claim 3, wherein the at least one anionic dispersing and/or grinding aid is selected from organic or inorganic dispersing and/or grinding aids.

18. The process according to claim 3, wherein the at least one anionic dispersing and/or grinding aid is an organic dispersing and/or grinding aid selected from the group consisting of sodium citrate, a sodium acrylate, a homo- or copolymer of sodium acrylate or sodium methacrylate, and any combination thereof.

19. The process according to claim 3, wherein the at least one anionic dispersing and/or grinding aid is an inorganic dispersing and/or grinding aid selected from the group consisting of sodium pyrophosphate, sodium polyphosphate, sodium hexametaphosphate and sodium tripolyphosphate.

20. The process according to claim 3, wherein the at least one anionic dispersing and/or grinding aid is an anionic polymeric dispersant selected from the group consisting of polymeric dispersants comprising at least one group chosen form a hydroxyl group, an amido group, a carboxyl group, a sulfo group and a phosphono group, and alkali, earth alkali metal and ammonium and/or amine salts thereof.

21. The process according to claim 20, wherein the anionic polymeric dispersant is a polymeric acrylic dispersant having a molecular weight from 1000 g/mol to 30000 g/mol.

22. The process according to claim 20, wherein the anionic polymeric dispersant is a polymeric acrylic dispersant having a molecular weight from 2500 g/mol to 16000g/mol.

23. The process according to claim 20, wherein the anionic polymeric dispersant is a polymeric acrylic dispersant having a molecular weight from 3200 g/mol to 13000 g/mol.

24. The process according to claim 20, wherein the anionic polymeric dispersant is a polymeric acrylic dispersant having a molecular weight from 3300 g/mol to 7500 g/mol.

25. The process according to claim 20, wherein the anionic polymeric dispersant has acid groups that are partially or fully neutralized, by at least one mono and/or bivalent and/or trivalent and/or tetravalent neutralizing agent.

26. The process according to claim 25, wherein the at least one mono- or bivalent neutralizing agent is lithium, sodium, potassium, magnesium, calcium, ammonium, or any combination thereof.

27. The process according to claim 1, wherein the mineral matter is natural calcium carbonate obtained from one or more of marble, limestone, chalk and calcite.

28. The process according to claim 1, wherein the mineral matter is precipitated calcium carbonate.

29. The process according to claim 1, wherein the mineral matter comprises calcium carbonate and one or more of kaolin, talc, mica, dolomite, bentonite, TiO.sub.2 and Al(OH).sub.3.

30. The process according to claim 1, wherein the oxides include iron oxides, the sulphides include iron sulphides and pyrite, and the carbon includes graphite.

Description

EXAMPLES

(1) The following non-limitative examples are intended to illustrate certain embodiments of the invention and should not be construed to limit the scope of the invention as set out in the claims.

(2) Experimental Set-Up

(3) TABLE-US-00001 Sample preparation 500 ml bottle Slurry quantity 500 g Shaken for (min) 5 min Container to make the surface Crystallising dish 60 mm 115 mm picture (height diameter)

(4) Illumination

(5) TABLE-US-00002 Eclectic lighting Kaiser Repro RB 5055HF Angle (in air relative to liquid 40 from liquid plane surface) Power Level 4 Distance to the slurry surface 40 cm

(6) Imaging

(7) TABLE-US-00003 Camera Canon PowerShot A640 ( 1/1.8 inch CCD sensor) Camera Objective Focal length 7.3-29.2 mm, aperture range 1:2.8-4.1 Resolution (pixel pixel bit depth) 2272 1704 24 Zoom (magnification) 1 Distance to slurry surface 11 cm Shutter speed 1/50 s Image format JPEG Image acquisition 90 (perpendicular) to the slurry surface plane

(8) Software

(9) TABLE-US-00004 Frame grabber ImageAccess Performance class: Enterprise, ver. 8, of Imagic Bildverarbeitung AG Image analysis analySIS ver. 3.1 (build 540) from Olympus SoftImageSolutions GmbH Image editing tool Corel X4 Photo-Paint Edited resolution 1500 1200 24 (pixel pixel bit depth)

(10) Material

(11) Additives

(12) Prior Art

(13) 1) Polyethylene glycol Mw 600, CAS 25322-68-3

(14) 2) 2-Amino-2-methyl-1-propanol, CAS 124-68-5

(15) Invention

(16) 3) Triblock PEG250-PPG1800-PEG250 (31PO/11EO)

(17) 4) Dowfax 63 N 30, DOW

(18) 5) Dowfax 63 N 40, DOW

(19) 6) Lumiten P-T, BASF

(20) 7) Triblock PEG 300PPG 1200PEG 300

(21) 8) Triblock PPG 2100PEG 600PPG 2100

(22) 9) Blend Lumiten P-T/Bevaloid 2565 (2:1 w/w):

(23) TABLE-US-00005 Additive Chemistry Properties 3) Triblock PEG250- produced by PPG1800-PEG250 polymerisation of EO and (31PO/11EO) PO; 4) Dowfax 63 N 30, DOW produced by Cloud point: 62 C. (10% polymerisation of EO and surfactant in a solution of PO 25% diethylene glycol butyl ether in water; Cloud Points: ASTM D 2024) Viscosity (ASTM 445/446): 441 cSt at 25 C. Theoretical Molecular Weight (Molecular Weight: calculated from the molecular weight of the initiator and oxide units in the molecule): 2400 g/mol 5) Dowfax 63 N 40, DOW produced by Cloud point: 72 C. (10% polymerisation of EO and surfactant in a solution of PO 25% diethylene glycol butyl ether in water; Cloud Points: ASTM D 2024) Viscosity (ASTM 445/446): 589 cSt at 25 C. Theoretical Molecular Weight (Molecular Weight: calculated from the molecular weight of the initiator and oxide units in the molecule): 2800 g/mol 6) Lumiten P-T, BASF produced by Viscosity (Contraves polymerisation of EO and Rheometer; DIN 53 019 PO STV, MS 45/II): ~500 mPa .Math. s 7) Triblock produced by polymerisation of EO and PO; PEG 300 - PPG 1200 - PEG 300 8) Triblock produced by polymerisation of EO and PO; PPG 2100-PEG 600- PPG 2100 9) Bevaloid 2565 produced by Cloud point: 33-37 C. polymerisation of EO and (10% surfactant in a PO solution of 25% diethylene glycol butyl ether in water; Cloud Points: ASTM D 2024) Brookfield viscosity at 20 C.: ~800 mPa .Math. s (viscosity measurement The Brookfield viscosity is measured after 1 minute of stirring by the use of a RV DV-III ultra Brookfield viscometer and a rotation speed of 100 rpm (revolutions per minute) with the appropriate disc spindle 4) *) PPG: polypropyleneglycol; PEG: polyethyleneglycol

(24) Minerals

(25) Blend of Chinese/Vietnamese/Malaysian Marble (approximately 50:25:25 in respect to dry weight)

(26) HCl insoluble part: 0.25 wt %

(27) Mineralogy of the HCl-insoluble part: Graphite, Muscovite, Chlorite, Feldspar, Talc, Amphibole, Quartz

(28) All size distribution values were measured with a Sedigraph 5100 particle size analyser from Micrometrics (USA) in an aqueous solution of 0.1 wt % Na.sub.4PO.sub.7, wherein the samples are dispersed using a high-speed stirrer and ultrasound. The d.sub.N value being defined as that equivalent spherical diameter under settling below which N % by weight of the material particles are finer. The d.sub.50 is thus taken to be the weight median particle size.

(29) Preparation of a Mineral Slurry

(30) Dry ground Marble blend, having a d.sub.50 of 45 m, is wet ground to a d.sub.50 of 1.4 m. The wet grinding is done at 78 wt % solids in tap water in a vertical attritor mill having a volume of 1500 litres in a continuous mode, using zircon silicate beads of 1-1.5 mm diameter and using 0.63 wt % of a sodium/calcium polyacrylate dispersant having a molecular weight (Mw) of 5500 and polydispersity of 2.7. The final product further had a d.sub.98 of 7 m and a BET specific surface area of 6.7 m.sup.2/g determined according to ISO standard 9277. The test method used was the static volumetric method, with multipoint determination. Degas conditions were 250 C./30 min. The fraction <2 m was 62 wt %, and the fraction <1 m was 37 wt %. The final solids was 77.4 wt %.

(31) Preparation of Samples 1-9

(32) For each sample, 500 g of slurry was introduced in an 500 ml PE bottle, 500 mg/kg of additive (additives 1-9) in respect to slurry was added and the closed bottle shaken for 5 min at ambient temperature (23 C.3 C.).

(33) Sample Measurements

(34) The degree of colour was measured pouring the slurry into a glass receptacle of 60 mm height and 115 mm diameter and taking a photograph of the slurry surface in between 5 to 15 min after pouring the slurry into the glass receptacle. Imaging was performed with a readily available digital camera device, e.g. Canon PowerShot A640 ( 1/1.8 inch CCD sensor). The picture was taken at a resolution of 22721704 pixels with a bit depth of 24, in colour mode, Zoom 1 at a distance of the objective to slurry surface at 11 cm and a shutter speed of 1/50 s. Light conditions were the following as set out in the table of the experimental set up. The photographing setup was protected from ambient light.

(35) Out of the image taken with 2272170424 resolution and bit depth, an image section of 1500120024 resolution was selected and submitted to computational calculation for determining the whiteness value. The zero whiteness value was determined from a picture taken with closed objective, i.e. with the protective light tight lid clamped on.

(36) As white standard an image section of a BaSO.sub.4 tablet (10 g of BaSO.sub.4 powder was used to press a tablet in an Omyapress 2000, said press being commercially available) was taken at a resolution of 22721704 pixels with a bit depth of 24, in colour mode, Zoom 1 (1 magnification) at a distance of the objective to slurry surface at 11 cm and a shutter speed of 1/50 s, an image section of 1500120024 resolution was selected and submitted to the same computational calculation for defining an arbitrary 100% whiteness definition.

(37) The wet surface colours of samples 1-9 where photographed and submitted to computational calculation. The BaSO.sub.4 standard having a computational value of 202 was set as 100% of whiteness, the zero whiteness value to 0. Non-treated wet slurry surface was photographed as a comparative example.

(38) The results of the images from samples 1-9, the image of non-treated slurry as well as zero whiteness and 100% whiteness are shown in Table 1, together with their computational value and normalized values.

(39) TABLE-US-00006 TABLE 1 wet surface colour of slurry surface Wet surface colour software calculated value normalized Black Standard*.sup.1 0 0 White standard (BaSO.sub.4 tablet)*.sup.2 202 100 Prior art Non treated slurry surface 194 96 1) Polyethylene glycol Mw 600 184 91 2) 2-Amino-2-methyl-1-propanol 187 93 Inventive samples 3) 201 100 4) 202 100 5) 202 100 6) 202 100 7) 202 100 8) 199 99 9) 198 98 *.sup.1picture with clamped lid on lens; *.sup.2Merck BaSO.sub.4 1.01748.0250 [CAS-No. 7727-43-7] for Brightness Standard DIN 5033 is used for calibration.

(40) The results of Table 1 clearly demonstrate that the inventive additives, the herein described alkyleneoxides, present at a concentration of 500 ppm, improve the surface whiteness of the wet slurry surface by 7-8 points over the prior art, and by at least 4 points over the untreated slurry. If the normalized value is set to 100%, the wet slurry surface values are then 7-8% of improved whiteness of the wet slurry, and 4% over the untreated slurry, respectively.

(41) Thus the wet surface whiteness of the slurry is at least 2% above the whiteness of the same slurry with no alkylene oxide present in the step b) of the above disclosed process. Preferably the wet surface whiteness is 3% above the whiteness of the same slurry with no alkylene oxide present in the step b), more preferably the wet surface whiteness is 4% above the whiteness of the same slurry with no alkylene oxide present in the step b).

(42) Thus the present invention provides for a water based mineral matter slurry with a wet slurry surface whiteness of more than 96%, preferably of 97%, more preferably of 98%, still more preferably of 99%, most preferably of 100%, compared to the BaSO.sub.4 standard, meaning thus that the wet slurry surface whiteness of the present invention comprises between more than 96% and less or equal 100% compared to the standard whiteness reference of BaSO4, representing 100% whiteness, when measured according to the measuring method of the present invention.

(43) Meaning thus that the wet slurry surface whiteness of the present in invention is comprised between more than 96% and equal or less than 100% compare to the standard whiteness reference of BaSO.sub.4, presenting 100% whiteness, when measured according to the measuring method of the present invention. Thus such values are absolute values in the scale of 0% to 100%.

(44) However, increased whiteness levels are not limited to 2%, 3% or 4%. It will be easily understood by the skilled person, that treated and untreated wet slurry surfaces of mineral materials can have whiteness levels below the mentioned 91% in table 1, compared to the standard whiteness reference of BaSO.sub.4. Thus the difference between the whiteness levels of treated and untreated mineral matter slurry can also exceed the 4%, for example 5%-10%.

(45) The method for measuring the wet mineral matter slurry surface whiteness according to the present invention comprises the steps of: (a) providing a wet mineral matter slurry of the present invention and a white standard (b) comparing computed digitalized surface images of the wet mineral matter slurry with the white standard

(46) The present embodiment for measuring the wet mineral matter slurry surface whiteness is however not to be construed to be of limiting character. It remains within the discretion of the skilled person to choose alternative imaging systems which provide for whiteness values for computational comparison, such as analogue imaging and subsequent digitalization of the images, video capturing and subsequent computational comparative analysis of whiteness values.

(47) Comparing in the context of the method of the invention means that a white standard is selected, which not necessarily has to be a specific one such as BaSO.sub.4, but can be any one known to the person skilled in the art to be suitable as standard white material, with the provision that the standard white is known and the same for any one of the samples to be compared with each other.

(48) With respect to the term whiteness, there are several whiteness definitions in the art, such as CIE whiteness, Tappi whiteness, etc., any one of which may be measured according to the method of the present invention, provided that the same whiteness is measured with respect to the samples to be compared with each other.

(49) A particular embodiment of the method for measuring the wet mineral matter slurry surface whiteness according to the present invention comprises the steps of: (a) preparing a wet mineral matter slurry (b) providing a suitable receptacle to carry the wet mineral matter slurry of step (a) (c) taking a photograph of the wet slurry surface (d) compute the whiteness value of the taken photograph or of a section of the photograph of the wet slurry surface (e) taking a photograph of a white standard (f) compute the whiteness value of the taken photograph or of a section of the photograph of the white standard (g) compute the value of zero-white (h) provide a scale wherein the computed value of the white standard is set to 100% whiteness and the value of zero-white is set to 0% whiteness (i) compare the computed whiteness value of step (d) with the provided scale of step (h)

(50) Further to this, it still lies in the discretion of the skilled person that the sequence of the steps of the present method be neither static nor mandatory. Of course, the steps (c) to (h) can be rearranged in such a way that first the white standard is photographed and computed, and the wet mineral matter slurry surface is photographed and computed, followed by comparison with the white standard.

(51) Still the method is not limited to doing the computational analysis subsequent to the imaging. It will be evident to the skilled person that imaging and computational analysis can be performed in different sequences separated in time and place, other than as herein described.

(52) Thus an alternative embodiment of the method for measuring the wet mineral matter slurry surface whiteness according to the present invention comprises the steps of: (a) preparing a wet mineral matter slurry (b) providing a suitable receptacle to carry the wet mineral matter slurry of step (a) (c) taking a photograph of the wet slurry surface and of a white standard (d) compute the whiteness value of the taken photograph or of a section of the photograph of (i) the wet slurry surface and of (ii) the white standard, wherein (ii) can also precede (i) (e) compute the value of zero-white, wherein (e) can precede the steps of (a)-(d) (f) provide a scale wherein the computed value of the white standard is set to 100% whiteness and the value of zero-white is set to 0% whiteness (g) compare the computed whiteness value (i) of the step (d) with the provided scale of step (h)