FI114723B - A process for preparing an aqueous calcium sulfate based suspension - Google Patents

Description

114723

The present invention relates to a process for preparing an aqueous calcium sulfate based suspension for use in particular as a filler or coating pigment in the manufacture of paper, comprising: forming a calcium sulfate suspension using of two different types of ethylene monomers, the first of which contains ethylene monomers having a phosphate or phosphonic function.

Phosphoric acid is produced using natural phosphate and sulfuric acid, which precipitates an aqueous calcium 15 sulphate, commonly called phospho-gypsum: over 4 tonnes of phospho-gypsum is produced per ton of P205. Today, the world's production of phosphoric acid produces over 100 million tonnes of phospho-gypsum each year.

At present, only a small part of this is utilized in the construction industry and agriculture, most of which has to be dumped or dumped in estuaries or the sea. This practice is ecologically damaging. As a result, there have been various attempts to find new areas where this product could be recycled.

· ;;; 25 In this sense, particularly in the paper industry, suspension of calcium sulphate in water is known. The paper industry requires stable suspensions, i.e., non-decanting and high solids contents, particularly due to transport costs. In addition, ': * 30 said aqueous suspensions must be sufficiently fluid, ** to facilitate handling and, if necessary, must be compatible with other excipient or coating pigment suspensions when used in papermaking; *.

114723 2

Numerous attempts have been made to increase the solids content of suspensions by keeping viscosity within a limited range.

It has been found that without the viscosity regulator 5, it is not possible to achieve the solids content of the suspensions required by the paper industry. It has also been found that the said suspensions are not sufficiently stable as the calcium sulphate is partially sedimented.

EP 366 569 recommends the use of a viscosity control complex, namely copolymers consisting of two or three ethylene monomers. The first type of monomer, which is required in the copolymer, contains ethylene monomers having a phosphate or phosphone function. The second or third type, at least one of which must be present in the copolymer, contains ethylene monomers having a carboxyl function and ester type or substituted ethylene monomers, respectively. These polymers can be used to make sufficiently stable calcium sulfate suspensions with a relatively high solids content. The disadvantage of using these expensive copolymers is that the amounts required are so large that the process is not economically • * · * feasible. In addition, one skilled in the art is well aware that the use of large quantities of N * copolymers adversely affects the brightness of the pigments. On the other hand, the disadvantage of using such copolymer amounts in calcium sulfate-based. it is in the fillers or coating pigments that such large quantities can disturb the overall balance of the papermaking process: on the other hand, the coating pigments are disturbed during the recycling of the old paper or of the wastes covered by such pigments. it is disturbed by the accumulation of copolymer-containing excipients therein. Therefore, it is problematic to combine the solids contents of these crystalline sulfate suspensions and the viscosities required by the papermakers.

The object of the invention is to solve this problem. For this purpose, according to the invention, in addition to the first 5 viscosity regulators, which in particular contain a copolymer according to European Patent Application No. 366 569, a second viscosity regulator containing an alkali metal phosphate or polyphosphate is added in an amount such that its viscosity is 10 250-2500 mPa.s, preferably 500-2000 mPa.s, and having a solids concentration of 60-77%, preferably 66-72%.

Thus, a combination of said first and second viscosity regulators provides complete control over viscosity and solids content during calcium sulfate treatment. On the other hand, a suspension with a higher solids content has a smaller amount of water, which reduces the transportation costs. The process also becomes cheaper because it consumes less viscosity weather-20 bogies.

According to a preferred embodiment of the invention, a third viscosity regulator is added containing cellulose ether, in particular carboxymethyl cellulose and / or hydroxyethyl cellulose.

;;; 25 The addition of cellulose ether also has the advantage that it does not cause misalignment ···! and, above all, it is ion-free and the subsequent recycling of the paper V 'can be carried out particularly conveniently.

The calcium sulphate suspensions thus obtained are of particular interest to the paper industry, which requires very fine particles in fillers and coating pigments to obtain satisfactory opacity, brightness and gloss and, where appropriate, good color retention. In addition, it has been discovered that without the viscosity regulator, the required fineness cannot be achieved, given the high viscosity of the suspensions, as described in U.S. Patent No. 4,310,360. Therefore, according to a preferred embodiment of the invention, said suspension is milled wet and at least part of said viscosity regulator is added during milling to obtain an average particle size of milled calcium sulfate of 0.8 to 10 μ. On the other hand, if the above-mentioned calcium sulphate is used as a filler, at least a portion of said viscosity regulator is added during wet milling so as to obtain an average particle size of 3 to 9 μm and preferably 5 to 7 μm. On the other hand, if the aforementioned calcium sulphate is used as a coating pigment, at least a portion of said viscosity regulator is added during wet milling so as to obtain an average particle size of milled calcium sulphate of 0.9-3 μm and preferably 1.3-2 μm. Thus, the grinding required can easily achieve the required fines. In addition, it can be stated that these fines have been achieved economically.

According to a preferred embodiment of the invention, said first viscosity regulator containing the copolymer is added several times according to the viscosity of the calcium sulphate suspension. This allows the viscosity to be maintained at an acceptable level throughout the whole; 25 during the grinding. In addition, the gradual addition of copoly '··' mer avoids over-consumption, which would adversely affect the pigment brightness. This effect is also obtained by addition of the aforementioned copolymer at different times than other viscosity regulators and especially at a different time than the other viscosity regulator, for example by adding the copolymer as late as possible during grinding. By doing this, the copolymer consumption is minimized and the process is thus cheaper.

5, 114723

The pH of the calcium sulfate suspension is preferably adjusted so that the pH of 7 to 12, preferably 5 to 7.5 to 10, more preferably 8-9, of the suspensions diluted with distilled water and adjusted to 10% by weight of solids can be measured. This minimizes the amount of viscosity regulator used for grinding.

According to a specific embodiment of the invention, the pH is adjusted by adding an alkali metal base, preferably sodium hydroxide, to the calcium sulfate suspension.

According to a particular embodiment of the invention, the grinding is carried out by means of balls, in particular in a mill, by means of glass balls in an amount of 50 to 90% by volume, preferably 75 to 85% by volume of the mill. This increases the efficiency of grinding by using inert balls 15 and avoids a change in brightness.

According to another embodiment of the invention, the calcium sulfate suspension is foamed, preferably before grinding. Foaming is known per se and does not provide sufficient brightness. However, when combined with the milling process, it can be used to remove the organic matter it enters, achieving a higher brightness after milling. This effect is further enhanced by the use of foam dispenser during foaming and. when the foam thus formed is collected using a foaming agent.

• »

In yet another embodiment of the invention, the ··· calcium sulfate suspension is introduced into the hydrocyclone, preferably before grinding and preferably before foaming.

Hydrocyclonization is known per se, providing a sufficient degree of brightness. Hydrocyclonization increases, however, the milling efficiency and narrows the particle size distribution, which also increases the brightness.

Other features and advantages of the present invention will become apparent in the following examples in order to implement the method of the invention: ': 35 by reference to the accompanying drawings.

6 114723

The letters refer to the various steps in the method.

The only drawing of the appendix is a functional diagram showing the sequential steps of the method of the invention.

The present invention relates to the preparation of a finely ground calcium sulphate suspension having a high solids content, which is derived from gypsum produced by industrial processes or natural gypsum, a process for their use as a filler or a pigment.

The process of the invention can be applied to calcium sulfates such as phosphokips, sulfoxips produced during desulphurisation of boilers, Titano-15 gypsum produced during titanium dioxide production, gypsum by-products formed from citric acid, boric acid and tartaric acid, gypsum, when it is desired to partially or completely remove certain inorganic or organic impurities contained in these calcium sulfates and to bleach them.

The following process of the invention is applicable to phospho-gypsum.

From this phosphoric acid production unit, fos - ;;; During the first step of the process, certain water-soluble impurities, such as free acidity, fluorinated compounds, v: inorganic salts and organic compounds, have been removed from the 25 gypsum. In fact, if the amount of impurities exceeds this particular concentration, these impurities make it impossible to use them as an inorganic filler and pigment, especially in the paper industry.

• * ·

Phospho gypsum, which comes from the phosphoric acid unit * ·; * 'as double crystallized hemihydrate dihydrate in the example 7114723 below, has the following chemical and physical properties: - pH of a 10% solids solution: 2-4% total P205: 0.2 0.5 to 5% water-soluble P205: 0.04 to 0.2% F: 0.2 to 0.6% Na2O: 0.1 to 0.3% SiO2: 1.0 to 1.8% total C: 0.2-0.4% - the weight percentages of these and the following particles are determined, for example, by a MALVERN MASTERSIZER-branded laser granule meter when ultrasonically dispersed in methanol for more than 212 microns for 15 minutes : 2 - 5% 15 over 150 microns: 10 - 25% over 106 microns: 25 - 40% over 45 microns: 55 - 70% over 20 microns: 80 - 90% - mean diameter, henceforth d50 : 50-80 microns.

- TAPPI Whiteness Index: 45-52, this and the following indices were measured on a Zeiss Elrepho instrument at 457 nanometer wavelength using barium sulfate as standard.

'. Phospho-gypsum pre-purification is first carried out by wet screening in the second step B of the process to separate the largest particle size particles, i.e. a fraction greater than 0.25 mm, and then in the third step C of the process, by hydrocyclonation, representing extreme particle sizes, i.e. Fractions of 120 micro-30n and fractions of less than 10-25 microns.

; : This results in purified gypsum having the following characteristics: pH of a 10% solids solution: 4-5% total P205: 0.1-0.4 L 35% in water soluble P205: 0.01 -0.02 8114723 -% F: 0.1 - 0.3 -% Na2O: 0.05 - 0.2 -% SiO2: 0.4 - 1.0 -% total C: 0.05 - 0.1 5 - particle size: over 212 microns: 0-1% over 150 microns: 3 - 10% over 106 microns: 10 - 20% over 45 microns: 45 - 65% 10 over 20 microns: 90-95% - <350: 40-60 microns.

- Loss Whiteness Index: 68-72 This gypsum is not suitable as such for papermaking, where the TAPPI-15 gypsum-based coating slurry must have a brightness index of more than 87 at the time of use and a particle fineness of less than 5 microns.

After the aforementioned hydrocycloning, the gypsum is bleached during the fourth stage D of the invention.

In the paper industry, calcium sulfate-based coating pigments require particles of greater than 90% less than 5 microns and 50% less than 2 microns, such as those measured by a MALVERN laser granule, to obtain particularly satisfactory paper; 25 opacity, brightness, gloss and good color fastness. For this purpose, the purified calcium sulphate in the above process steps is suspended in water, milled f * v v, respectively, in the fifth step E of the process and the sixth step F of the process. The balls, for example, have a diameter of 0.4 to 3 mm and are preferably of an inert material, for example glass. Selected balls are proportionally smaller than gypsum, which must be ground finer.

The process of the invention is described in the following examples: 9114723

EXAMPLE 1 The purpose of this example is to illustrate an object of the invention relating to purification and bleaching, namely: treatment of calcium sulfate with foaming D after hydrocyclo-5 C. It should be noted that, according to the invention, the flotation D can also be carried out prior to hydrocyclone-indium C. In the case of calcium sulphate obtained during the preparation of phosphoric acid using Kouribga phosphate as starting material, calcium sulphate (step A) has the following 10 characteristics: pH of the solution containing the substance: 2.8% total P205: 0.42% F: 0.34% Na20: 0.23 15% SiO2: 1.34% total C: 0, 27 - particle size: more than 212 microns: 3.6% more than 150 microns: 14.2% 20 more than 106 microns: 30.7% more than 45 microns: 63.2% ti>: more than 20 microns: 86.2% »* .. - d50: 62.8 microns.

• i · ', - Pin brightness index: 48.6.

· ;;; The above calcium sulfate has been removed by '<··' impurities and organic matter by filtration, hydrocyclonation and foaming (steps v 'B, C and D, respectively). Thus, the by-product of the phosphoric acid production unit, phospho-gypsum, is fed to a second aqueous suspension on a sieve to remove particles greater than 700 microns in diameter (Step B).

The passage passes through a hydrocyclone equipment (step 'C') consisting of two layers. Thus, the first layer of the hydrocyclone apparatus is fed; 35 to six tons per hour of calcium sulfate in suspension, 10 114723 with 25% solids, thereby separating particles greater than 100 microns in diameter. This yields 7.5 tonnes per hour of calcium sulphate in the form of a suspension of 16% solids, which is fed to the second layer of the hydrocyclone ionization apparatus, whereby particles smaller than 20 microns in diameter are separated. This will reduce the spectrum of particles to be refined later and thus make the refining more efficient. This yields 6.2 tonnes per hour of calcium sulphate having the following characteristics: - pH of a 10% solids solution: 4.6 -% total P205: 0.29 -% F: 0.23 -% Na 2 O: 0.12 15% SiO 2: 0.62% Total C: 0.07 ± 0.005 Particle size: over 212 microns: 0.6% over 150 microns: 4.6% 20 over 106 microns: 12 , 6% over 45 microns: 49.2% over 20 microns: 92.8%, - d50: 44.1 microns.

* - Loss Whiteness Index: 70.7.

* ·; · 25 The brightness index is here determined for calcium sulphate before grinding. This index rises by about 10 points during the milling process to the required level in the paper industry.

The hydrocycloned calcium sulfate is fed as a suspension of 40-45% solids in a flotation device. to a body of five 1500 liter flotation cell batteries, each of which operates with vigorous stirring and * · * injection of air so as to remove unwanted particles from the foam. During the flotation, 50 g of methyl isobutylcarbinol (MIBC) per 100 grams of calcium sulfate are added as a foam dipper. This removes 2-4% solids from the foam.

The calcium sulphate suspension 40 to 45% solids thus leaving the flotation apparatus is filtered in the fifth step E of the process as a filter, for example a drum filter under vacuum. This results in a filter cake containing 70-83% solids.

Purified phospho-gypsum has the following characteristics: pH of a 10 to 10% solids solution: 7 - Total carbon%: 0.01 ± 0.005 - TAPPI brightness index: 77.2

EXAMPLE 2 The purpose of this example is to illustrate the state of the art ti-15a for the preparation of calcium sulfate suspensions from various sources by dispersing. The characteristics and results obtained are summarized in Table 1 below.

I f »t f I · I ·

• * I

* I ♦ * * 4> l · ♦ I »t 1 * * * * * *»! *% I * I ·> 1 «

I I 1 • f I I

t I

! '* t 1> I »i k»> 12 114723

table 1

Calcium Suspen Particle CoAANA (**) A slight increase in the solids content of the Brook Sulfate Sion increases the concentration of the viscous agent (%) viscous (%) substance% s / sec. 10,100 rpra mPa · s

Phosphokips 68 44.9 0.1 900

Pre-ground 15 phospho gypsum 68 15.3 0.1 1.320

Sulfokipsis 68 43.5 0.1 820

Pre-ground phospho gypsum 68 15.6 0.1 1.250

Natural gypsum 68 43.7 0.1 620 20 Pre-ground natural gypsum 68 14.9 0.1 1.050: ·. (*) determined by drying to constant weight in an oven at 50 ° C.

»T * (**) CoAANa: ethylene copolymer neutralized with sodium hydroxide.

• *

Dispersion tests have been carried out in a laboratory in a '··' · liter beaker fitted with a lid to prevent evaporation during the test. The flask is equipped with a 65 mm diameter laboratory turbine that runs at, for example, 2000 rpm.

Pour water into the bottom of the dispersion vessel and add calcium sulfate.

> T \

A viscosity regulator, namely a copolymer,

I I

add 0.1% of active ingredient to raise the weight of calcium sulfate to the bottom of the vessel, finally add calcium sulfate.

13 114723

The pH of the suspension is adjusted by the addition of an alkali metal base, particularly sodium hydroxide, so that the pH remains at 8.5 ± 0.1 at a solids concentration of 10%. The duration of the dispergation is one hour. Table 5 1 below shows the fineness of each particle as the mean diameter represented by d50 and the viscosities of Brookfield as mPa.s at 100 rpm for each of the different types of calcium sulfate at a constant concentration of suspension expressed as a percentage and a constant concentration of which is neutralized with sodium hydroxide and is expressed as a% of the active ingredient and is designated in the table below and hereinafter referred to as CoAANa. By active substance is meant a pure copolymer.

EXAMPLE 3 The purpose of this example is to illustrate an object of the invention relating to the preparation of a purified and bleached calcium sulfate suspension prepared in Example 1 above by dispersion in polyphosphate followed by addition of a small amount of copolymer. This example is described in Table 2 below.

• * »• · • ♦« »·» · 14 114723 H M G P · PPG Ό 0) ft h a) e (1) P H -H e (4-1 n a x o ^ o o

o X CM CM

owo oooooooonoooo oo h -h o covocor-'Ocovoin v in cm co in - oo CD t> i — i t ^ ioiooo ^^^ coHOiio ^ n p vo A! a) G co <0 CO I +> \ 2> ιΡ G P X <Λ -rl P D dl

CO P M G M p p P p p P r-IP O 1 — I I — I I — I I — I iH rH

0 P 44 P P

U P G> G <#> ooooooooooooo oo X in in o in in 1 G <D incMPCMino-ocM cm cm cm M P M CM 12 »«. 2 s s 1 o p ra \ 'Oooooho o o o.

P G> iAi O

Ndffl dl CU A tm PU CU PU Oh CU CU CU

f — i c co co ocucuoncucucueucuocmocu o cm 00 Ή - S E- · E- <E- · E- <E- <E- · - E-i • E- ·> E- · cu p h dp οχωωωωωωωοωοω o co.

1 I

<u a) o x p m. X £ Ό ''! p

PCW CMCMCMCMCMCMCMCMCMCMCMCMCM P P

i, C- | {DG K V

: \, (O-HO inininininininininininininininin • cu H G p p

G G O

. . OOP

',,.' p c X P

, M 1Ö (0 ^ G 0) G G <#> .... Q) P 0) M - 'o. G a) p::: bp c c 3 P P <D cococooocococococooocooo coco

CO .V CO CO LOiOvOvOiOvOvOiOiOt ^ C ^ vOiO vDiO

1 1 P

3. . 3 P 1 G MO 3

',,, · CM P CO P P CO P P

. G P P CO P CO PCD

2 ... OlP 0) G CU CD P a) Oh: ·: Λ6Ρ p a: p c p a: jCp

.1 3 G <D M P A! O M M O X

3 P G G P G O P CD GO

.. P M P G Ό> P G β β -1-) P

3 P P O .GC0PPP PM

G G 3 3 3 G O O G M MO

EnfeiMP P, n P -n> dl CdP

15 114723 where the abbreviations used are explained here: d50: average particle weight distribution

CoAANa: ethylene copoly-5 mer neutralized with sodium hydroxide HMP: polyphosphate in the form of NaPO 3 (hexametaphosphate with a molar ratio Na / P = 1).

STTP: polyphosphate in the form Na5P3010 (sodium tripolyphosphate with a Na / P molar ratio of 1.66).

SAPP: polyphosphate in the form of Na2H2P207 (acidic sodium pyrophosphate with a molar ratio Na / P = 1).

Dispersion is carried out as described in Example 2. Table 2 above shows that using STPP up to 0.75% per tonne of dry phospho-gypsum under other conditions effectively reduces the viscosity of the suspensions. In addition, Table 2 shows that using HMP or SAPP, which are otherwise more expensive than STPP, does not achieve the same efficiency as using STPP under other conditions. On the other hand, it appears that when the solids content of the suspension is high or correspondingly low, the viscosity obtained is high or correspondingly low, all other conditions remaining the same.

• · '*! It is also noticed that without CoAANa, • · * ;;; under the same conditions, the viscosity obtained is significantly higher.

Example 4 The purpose of this example is to illustrate the state of the art and relates to the grinding of calcium sulphate suspensions from various sources without the addition of polyphosphate and with only one copolymer. The '1' feminine characteristics of the suspensions and the resulting fineness after grinding are as follows: · 35 summarized in Table 3 below.

16 114723

G I

Φ O

Ό h • H O AI Φ 00 ** φ ΙΓ) Ή Ή * H TJ E C "O 'OO 00 Φ X tfl

AI 3 I

HO O

+ J C H H {N O

μ Φ O AI <0 (0 -H ID -H -H 00 O 00 H J3 Ό E C * h rH Ή

OH

Φ {0 10 {OMI 4-> ^

2> i -H <0 -O AI

<»0 -H -μ 0) <D

{0 <10 4-> tO C tO O O O

10 0 -H Al -H -H

M U rl li> Hl # i-t rH rH

φ μ (0 i <d -μ c -he 0) -μ I -h to -ha to μ a) a: ό o -μ μ · μ x: oh ai -μ «H 3 O 0) t0 0). O Dj o O o

H (0 μ -H -H 0) O E O tN <N

Oh · -) 03 4-1> -µ rH CO VO

to AI

h a) {0 {0 {0 c <0 to i -μ '--s

. -H to 2> 1 -H <i -μ AI

··; E to <rt ή -μ φ a)

oa) <tO 4-> M C tO H H H

· (0 O · Η S Ή · Η * * ": ·. C -μ o ri ®> e # o o o

O -H

.:. -HO G

to O) i wj i o g μ c φ c c -h. . φ φ φ + J φ φ + J r-v · ... · Οι Oi Oi C C Φ CO «J <#> tO tD lOO-HCCtO'- '

': · 3 Ή 3 -H -H -H o μ 00 CO CO

top tOMAIfÖAI + J VO vO VO

(0 I -H Ov LO t> o AI G «» ,,; in -h O tji oo oo ό e μ: ···: -H i μ AI 10 μ Ai C 3 •, · · {0 -H Φ O (0

, {0 μ Ό G l-H [V {N CO

· '· Ν ^ μ-ΗΦΟΑΙΟ

n H «3Φ-Η in -H O 00 rH VO

3 A H X Ό E μ CO CO en o to i

• · X E -H

S3 Φ Cl

,.: 3 -H e O -H O -H I -H

• H CO C m to 4-t M G to 3 H O tOOiHOlOCOi

to (O 3 O -H 3 -H 3 O -H

& hai p (uaiwaipca: 17 114723 where d50: mean particle weight distribution d90: largest diameter found in 90% of particle weight distribution

The calcium sulfate suspension prepared according to Example 2 is added to a microsphere mill having a useful volume of 0.6 liters. It will be understood that the useful volume of the refiner means the volume remaining after subtracting the volumes of the parts of the refiner contained in its internal volume, such as the volume of the mixer. This means, for example, balls of inert material of glass having a diameter of 1.0 to 1.6 mm and a weight of about 1.2 kg and a volume of about 0.42 liters.

To separate the refining balls from the powdered calcium sulphate suspension, the refiner is equipped with a sieve of about 300 microns.

The grinding starts without a viscosity regulator. Its addition is only started when the suspension thickens; its addition is continued to 1% by weight of the active ingredient calcium sulfate. The pH of the suspension is adjusted with an alkali metal, such as NaOH, to maintain a pH of about 1; 8.4 ± 0.1 in 10% solids. Jauhanta ;;; 25 is stopped when the powdered calcium sulfate has a viscosity close to solidification.

Example 5 '' The purpose of this example is to illustrate the subject matter of the invention and relates to the grinding of the calcium sulfate suspensions obtained in Example 1. The polyphosphate is added to the dispersion and the copolymer is added to the pulp. The characteristics and results obtained are listed in Table 4 below.

18 114723 ra 3 o

G (O

Φ -rl

• H G

Λ O

M {NOOCOCMrHCOO ^ OrH {N

G O a: inoooovDr-iroincooo vo

φ LO -H V

Ό Ό E OOCSi — Ι (Ν0-ΐΓ0ι — LiHr-liH rH

B

a)

B

Φ (0

X -H

X G

• rl O

μ t-ι tTvcoinc ^ c ^ vovo ^ fOC "oo l-ι o Ai ^ ηΝΰΐηοσοΌη oo (0 LO · Η

fti Ό E {Ji ^ 'i4iN00Nn'i4i CO

<#>

I I

(0 G -H I O

W -H φ μ H

to -H G G

φ Ai Ή φ G i-li "" li-IrHi-li-IrHiHi-lrH ιΗ (0 tOtOO ---------- - μ GG οοοοοοοοοο Ρ 3 G oo φ a; -h + i + i + i + i + i + i + i + i + i + i + ix: v μ 3 - -HG to ^ 'f ^^^ ininininin in (0 3 Φ Φ 10 - »n {¾ μ ό p oinoc ^ ooooooooooo oo

C/O

> 1

XO

CO <0 h μ a: H CO φ

H (O CO 2)

«> Μ

Z -H μ X

<-H φ φ «ί μ c ra οοοοοοοοοο o o a: -h ---------- -

U (0 (Q dP r-l * Hr-lrHrHrHi — ΙγΗτ-ΗγΗ. — I

• ·: <d μ ra

φ CO CD

1 · * Φ> 1 3 • μ xo x h p ra φ <o: -h -h co

,,, · Η H 'v. G

:: o, Ai <o

... co CU Φ in in G

h Cu co ocNinooocNinoo w G

1! 1 φ Eh ---------- v {0 ·· 'Geo en <*> ooor-tc ^ oooi-tcs o .e,: ·, -h co 3 • · · E co λ 'o Φ -o

(0 I

e μ e co e o * H Φ (0 X0; · -H O Ό G P XÖ ra en -h φ μ - μ G P 0) Ό G <*> xo; Φ φ μ -h φ - ra a o. e φ ra -h ra ra -h e e o h, 3 -H -H -PO -H C0C0C0C0C0C0C000C0C0 00, * · en Ω * <0 Ai μ m ^ ominvovovovoiovo «neo

• * »Z

l · rtJ

... Hl * rfj eo ... o I -H {01 ox ε μ ihii -n co i -h * · 3 3 ίο Φ p ra *> ra -h ra ra o 3 -H {0C ΦΧΟ · Η3 · Η3100 & Ai h ra mee co ε μ ό μ aj <p -no 3 hho -h ra h μ £ μ ha: a; CO {033 {0 · Η {0Φ3Φ {03Ο k: mh 60Α:> μΛμ> μμ * 1U723 19

The table above shows that 1%

In each case, the addition of CoAANa with the additional addition of STPP results in a finer particle size and maximum fineness is achieved with an amount of STPP expressed as 5% sec / sec and close to 0.25-5%. It also appears that raising the pH, for example by adding sodium hydroxide, further improves the efficiency of the pulverizer while all other conditions remain the same. Dispersion and grinding are performed under the conditions described in Prep 10 and 2, respectively.

Example 6 The purpose of this example is to illustrate the subject matter of the invention and relates to the grinding of the purified and bleached calcium sulphate suspensions obtained in Example 1.

15 This example is described in Table 5 below.

• »• · t •» * · I | »

«I I

t 1 2 „1 1 4723 03

•B

o g σ. o

OS O VV

CO Ό M rH rH

3%

O P

d e ai

•B

** 03 d '2 O • «S' a) o 5 -

Ό Φ H CS

• h -d a

® -H

<D ® OP

X I

X C I o

H-H I -P H

P-H-h C

M J * 0) O) C> -1 rH

03 r CO 0 v * · Λ C -H d o o

3 (0 O 0

X X -H +1 +1

d ^ P

v a) c 03 m in 0) K Ό Q) (0 * · »

W a -H Ό P oo CO

CO a) 0) p

0) CO

P> 1 P «3 0) to x! -h. λ:

3 H ™ <D O O

03 p 03 CO

O) 03 CO p \ o Ή z p p x <> O) 0)

rt, P d CO

0 P -H

U P <0 <#> 03 Λί a)

C/O

s in m 1 10 X es es> i <D * · ·> {¾ ίο to o o

; H CO

: co -h <*>

P rH

; ·. a) •. a) m P> 1 h «3 Ä ,, -: -H CO Φ

• rl -H CO

:: a h \ ... CO I Ä. -H O 0) O Ή ': · 03 s to vv

d <0 U ^ rH O

, *; *. -h co <*> ... e co 'O <13

0) I

d p d o3 O -H <13 03 *; * -HO -O e 3h (0 tJI -H m P "" CU CD $ d <*>:; <D <D p -h o) ”* aa d cd co

*, CO CO -H C d O

. 3 -H -rl .J O -rl CO 00

', · * COQ «ΙοΛίΡ Ό ID

m d

O 1 -H CO I

X SP I H I I ·! -) CO I -H

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The table above shows that the addition of low molecular weight carboxymethylcellulose (CMC) during the dispersion of calcium sulfate, all other conditions remaining the same, further improves the mill efficiency; you only need to compare the average diameters denoted by d50, expressed in microns in Tables 4 and 5. Dispersion and grinding are performed as described in Examples 2 and 4, respectively.

Example 7 In this example, which is illustrated by tau number 6 below, hydroxyethyl cellulose is added during the dispersion of calcium sulfate. In this way, while all other conditions remain the same, the efficiency of the pulverizer can be improved, as shown by comparing the d50 values in Tables 5 and 6. Dispersion and grinding are carried out as described in Examples 2 and 4, respectively.

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Example 8 In contrast to the examples given so far and described in the laboratory tests, this example is carried out on a pilot scale. It is intended to illustrate the dispersion and grinding of the purified and bleached calcium sulfate of Example 1 according to the invention. Dispersion of calcium sulfate is carried out as described in Example 2 in a 350 liter CELLIER-branded Type C3 mixer dispersion vessel. The pulverization of the calcium sulphate suspension 10 is carried out continuously as described in Example 4 in a refiner having a total volume of 25 liters, containing glass beads having a diameter of 0.8 to 1.5 mm, a weight of about 48 kg and a volume of nearly 19 liters; the operating conditions are defined as follows; Dispersion: - NaOH addition: 0.2% sec / sec.

- STPP increment: 0.25% sec / sec.

- concentration of suspension: 69.6% - pH of suspension at 20 to 10% solids; 8.4 - dispersion time: one hour.

: Powdering: .. - suspension feed rate and copolymer addition are functions of the consumed energy set to 150 * ;;; 25 * Kwh / tonne of calcium sulphate.

* ··; * - 40 to 50 ° C

. - sodium hydroxide addition: 0.12% v - use of copolymer: 1.1% - pH of the suspension at a solids concentration of 10%: 8.4 ± 0.1

Characteristics of powdered calcium sulfate suspension: - solids concentration: 67.2% - particle size: d90: 4.25 microns t% d50: 1.88 microns 35 - viscosity: 1.060 mPa.s 24 114723

The volume fraction of the balls compared to the volume of the mill is 50-90%, preferably 75-85%.

On the other hand, it has also proved advantageous to add a biocide during the process of the invention.

It is self-evident that the invention is by no means limited to the examples described above, and that other modifications may be developed within the scope of this application. Thus, for example, filtration of the calcium sulfate suspension (step E of the figure) can be performed by treating the calcium sulfate suspension with ozone and / or oxidized water and / or oxygen. In the case of phospho-gypsum, ozone is added to 0.150 kg per tonne of gypsum in an aqueous solution having a pH equal to or greater than 3. This results in a degree of brightness after 82 millings.

On the other hand, the ozone treatment may be replaced or combined with an acidic solution with chlorine, chlorine oxides, particularly chlorine dioxide, or at a pH of less than 6, preferably less than 3, so that the colored organic impurities do not adhere to the calcium sulphate particles. .

In addition, a homopolymer, in particular polyacrylate, preferably 0.05 to 2% by weight, preferably 0.1 to 1% by weight, may also be used as an additional viscosity regulator.

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Claims (26)

A process for preparing an aqueous calcium sulfate-based suspension, especially for use as a filler or coating pigment in papermaking, forming a calcium sulfate slurry by a first viscosity-regulating additive containing a copolymer which has been obtained from various resins, types of ethylene monomers, the first of which contains ethylene monomers with phosphate or phosphonate function, characterized by the addition of another second viscosity regulating additive containing a phosphate or polyphosphate of an alkaline metal, and the amount added viscosity control additive is such that the viscosity is between 250 and 2,500 mPa.s, preferably between 500 and 2,000 mPa.s, and that the solids concentration is between 60 and 77%, preferably between 66 and 72 %. Process according to claim 1, characterized in that a third viscosity regulating additive is added which contains cellulose ether, especially carboxymethyl cellulose and / or hydroxyethyl cellulose. Process according to any one of claims 1 and 2, characterized in that said slurry 25 is subjected to a wet grinding and while it is being added, at least '!!! a portion of said viscosity regulating additive thus, obtaining an average particle size of the ground calcium sulfate between 0.8 and 10 µ, and, one side, if using said calcium sulfate as additive in the pulp, , preferably one obtains a genome; average particle size of the ground calcium sulphate flour. * ··. between 3 and 9 µ, more preferably between 5 and 7 µ, and / or, on the other hand, if the aforementioned calcium sulfate is used as a coating pigment, thus, to obtain preferably an average particle size of the ground calcium sulphate between 0.9 and 3 µ, more preferably between 1.3 and 2 µ. Method according to claim 3, characterized in that at least a part and preferably the total amount of the second viscosity-regulating additive is added to the grinding stage, especially in the slurry to form a dispersion. Process according to any one of claims 3 and 4, characterized in that at least part 10 and preferably the total amount of the first viscosity regulating additive is added during the grinding stage. Process according to claim 5, characterized in that said first viscosity controlling additive is added in several stages during the grinding stage together with the viscosity of the calcium sulfate slurry. Process according to any one of claims 1-6, characterized in that the second type of the ethylene monomers of the copolymer in the first viscosity regulating additive comprises ethylene monomers having carboxylic function and / or ethylene monomers of the esters or substituted type. Method according to any one of claims 1-7, characterized in that the pH of the calcium sulphate slurry is controlled so as to be between 7 and 12, preferably between 7.5 and 10, and more preferably between 8 and 10. 9, when the solids diluted with distilled water (1% water, weight% are adjusted to 10). 9. A process according to claim 8, characterized in that the pH is controlled by adding to the calcium sulfate slurry of an alkaline base, preferably sodium hydroxide. Process according to any one of claims 3-9, characterized in that the grinding is carried out by means of beads, especially glass beads, in a pulverizer using an amount between 50 and 90% by volume. , preferably between 75 and 85% by volume with respect to the utility volume of the pulverizer. 11. A method according to claim 10, characterized in that balls having a diameter of between 0.1 mm and 3.5 mm are used, preferably between 0.8 mm and 2.5 mm, and most preferably between 1.2 and 2 mm. , 2 mm. Process according to any one of claims 1 to 11, characterized in that sodium tripolyphosphate is added as an alkaline polyphosphate. 10 13. Process according to claim 12, characterized in that the sodium tripolyphosphate is added in a ratio of 0.05 - 1.0% by weight, preferably 0.2 - 0.6% by weight. Process according to any one of claims 1-13, characterized in that the ethylenic copolymer is added in a ratio 0.05 - 1.8% by weight, preferably 0.08 - 1.5% by weight and most preferably 0. 1 to 1.1% by weight of the active material. Process according to any of claims 1-14, characterized in that the carboxymethyl cellulose or hydroxyethyl cellulose is added in a ratio of 0.05 to 1% by weight, preferably 0.1 to 0.6% by weight. 3rd Process according to any one of claims 1 to 15, characterized in that sodium carboxymethyl cellulose having a viscosity of less than 100 mPa.s, when the weight weight of the solution is 4, is added at a temperature of 25 ° C. whose pH is 5-9, preferably 6 - 8.5, when the weight percent of the solution is 1. Method according to any one of claims 1-3, characterized in that hydroxyethyl cellulose is added in a ratio 0.05 - 1.8% by weight, preferably 0.1-1.5% by weight. , and more preferably 0.2 - 1.2% by weight. 18. A process according to any one of claims 1 to 17, characterized in that the calcium sulphate slurry is subjected to a flotation, preferably before the grinding thereof. 114723 19. A method according to claim 18, characterized in that during the flotation a foaming agent is intended to be used for producing foam and that the foam thus produced is collected using a foam collecting agent. 20. A process according to any one of claims 1 to 19, characterized in that the calcium sulphate slurry is subjected to a hydrocyclonation, preferably before the grinding thereof, more preferably before the flotation. 10 A process according to any one of claims 1-20 for the preparation of an aqueous calcium sulfate-based suspension, especially for use as a filler or coating pigment, characterized in that it is subjected to a calcium sulfate slurry as well as a hydrocyclone or a flotation, which is combined in a grinding process. Method according to claim 21, characterized in that the flotation is followed by a filtration of the calcium sulfate slurry, before the possible grinding process. Process according to any one of claims 21 and 22, characterized in that hydrocycloning is preceded by: salting. Process according to any of claims 22 and 23, characterized in that the filtration is preceded by a treatment with ozone and / or oxidized water and / or oxygen and / or chlorine, in particular with chlorine oxides, such as chlorine dioxide and / or chlorates and / or hydrochloric acid. '; · 25. A process according to any one of claims 21 to 24, 30 characterized in that the calcium sulphate slurry is subjected to a hydrocycloning step, thus removing the particles, the diameter of which is less than the threshold - (> \ value 5 - 40 µ, preferably 10 - 30 µ and of all heists: · * 18 - 22 µ. 1 1 472? Process according to any one of claims 21 to 25, characterized in that the calcium sulphate slurry is subjected to a hydrocycloning step, thus removing the particles, the diameter of which exceeds the threshold of 50 - 150 µ, preferably 80 - 120 µ and of all heists. 95 - 105 µ. > · • * '* * »>« ♦ · I · »