WO2000051941A1 - A composition of matter comprising high brightness calcium carbonate pigments and processes for making same - Google Patents

Abstract

High brightness, whiteness and opacity calcium carbonate pigments (44 and 58) may be produced by magnetic separation (34 and 50). A composition of matter comprising high brightness calcium carbonate pigments (44 and 58) produced by using magnetic separation (34 and 50) on a properly dispersed, minimum viscosity slurry to optimize contaminant liberation and removal, with the impurities being liberated by and during grinding (32 and 46) prior to magnetic separation (34 and 50) while maintaining said slurry temperatures at or above 50 degrees C. The magnetic separation (34 and 50) of a dispersed, minimum viscosity slurry separates coarse to ultra-fine particles in slurries ranging from 5 % to 65 % solids by, at least in part, removing and selectively separating dolomitic components from the calcium carbonate mineral systems.

Description

A COMPOSITION OF MATTER COMPRISING

HIGH BRIGHTNESS CALCIUM CARBONATE PIGMENTS

AND PROCESSES FOR MAKING SAME

U.S. PATENT APPLICATION OF MICHAEL W. GINN

FIELD OF THE INVENTION

The present invention relates generally to the field of the

production of high brightness pigments, and more particularly to a

composition of matter comprising high brightness calcium carbonate

pigments produced using magnetic separation and processes for making

the same. BACKGROUND OF THE INVENTION

A summary of the application of magnetic separation to various

mineral systems is found in Taggart, HANDBOOK OF MINERAL

DRESSING, Sec. 13, 1927. The development of the field in general may be

traced by reference to individuals and companies such as Frantz,1937;

Jones, 1955; Iannicelli, 1967; MEA 1969; PEM, 1971; Eriez 1986;

CARPCO, 1992; ACMI, 1993.

Specific patents of note are 2,331,769; 2,430,157; 2,329,893;

2,786,047; 3,471,011; 3,961,971; 3,985,646; 4,005,008; 4,087,004;

4,087,358; 4,147,632; 3,627,678; 4,157,954; 4,281,799; 4,356,093;

3,676,337; 4,424,124; 3,667,689; 3,567,026; 3,770,629; 3,819,515;

5,047,375; 5,697,220; 5,495,718; 5,237,738; 5,148,137; 5,019,247;

4,694,269; 4,680,936.

In the late 1960's, High Gradient Magnetic Separation was

applied to the beneficiation of kaolin clays. Product brightness was

enhanced without altering the composition of the clay.

The process was so effective that by 1990 every major kaolin

producer in the world was using High Gradient Magnetic Separation as a

part of their processing. Patents 3,980,240 and 3.990,642 issued to Nott in the 1970's

were directed to calcitic and dolomitic ores, respectively.

In 1980, A Survey-Beneficia on of Industrial Minerals, Ores,

and Coal By High Intensity Wet Magnetic Separation by Dr. Hayden

Murrary and Dr, Joe Iannicelli under Grant No. GT 44219 and NSF ISP

74-21921 for the National Science Foundation Directorate for Engineering

and Applied Science was published. At page 54 of that report, the authors

concluded- 'Calcium carbonate is the largest tonnage filler used. High

quality calcium carbonate is used in paper, paint, rubber and other filler

uses and must be very white and usually fine in particle size. The iron

percentage, even though very small to begin with, was significantly reduced

using HIMS. Figure 23 shows the brightness increase of the two samples

indicating a slight improvement in brightness can be achieved using HIMS.

HIMS should be studies further as a potential beneficiation process to

improve the color of certain calcium carbonates."

Whether the above conclusions in 1980 are read as an

encouragement for further work or, when taken with the slight increase in

brightness shown in Figure 23 of that report, to discourage work in this

area as a high priority, the facts are: since 1980 the need for high brightness ground calcium

carbonate to compete with precipitated calcium carbonate and titanium

dioxide has greatly increased, and

prior to the present invention no ground calcium carbonate

producer was employing high gradient, high intensity magnetic separation

to produce a commercial product.

The present invention makes possible the commercial

application of high gradient, high intensity magnetic separation to the

beneficiation of ground calcium carbonate by discovering a process that

significantly increases the whiteness, brightness, and opacity of ground

calcium carbonate.

The magnetic separation process is a contaminant removal

process. Minerals and mineral complexes have varying magnetic

susceptibilities and can be physically separated as a function of this

property. Common minerals removed from calcium carbonate slurries are:

Carbonates such as dolomite, ankerite, and siderite;

Sulfides such as pyrite, marcasite, bornite, and

pyrrhotite;

Oxides such as hematite, ilmenite, chromite, and rutile;

Silicates such as chlorite, biotite, muscovite, and amphiboles.

"Non-magnetic" minerals and mineral complexes that have Fe

substituted in their lattice are also separated.

Magnetic polymers are also used to increase the magnetic

susceptibilities of silicates such as quartz.

Magnetic separation may be used in calcium carbonate

applications to bring about brightness improvement, abrasion

improvement, cost reduction, reserve extension and to reduce

environmental concerns.

It has now been discovered and it is the subject matter of the

present invention and application that magnetic separation has a number of

processing advantages. It efficiently separates particles from coarse (<44

um, mean 20 um) to ultra-fine (100% < 2 um, mean 0.25 um). It efficiently

separates contaminants in slurries ranging from 5% to 65% solids. It does

not chemically or physically alter the mineral slurry other than to remove

magnetically susceptible contaminants. It efficiently functions in fully

dispersed mineral systems optimizing contaminant liberation and removal.

Magnetic separation when compared with flotation is more

controllable, more environmentally friendly, more selective as a separation

process, costs less and provides more consistent quality products. Conventional flotation is, in general, limited to less than 86%

<2um and can produce no more than a 96 GE brightness while the process

of the present invention may produce brightness of 98 and higher with up

to 100% <2 um. When combined with floatation the present invention

makes possible brightnesses as high as 98 and higher from 70 to 100% <

2um.

The present invention may reduce processing costs for

brightness and provide the opportunity to produce higher brightness and

lower abrasion products, creating added value for the customer.

SUMMARY OF THE INVENTION

The present invention produces a calcium carbonate with the

maximum product brightness with the highest recovery at the least cost by

proper (usually maximum) dispersion, with impurity liberation by grinding

and by employing elevated slurry temperatures during magnetic

separation.

It has now been discovered and it is the subject matter of the

present invention and application that magnetic separation has a number of

processing advantages. It efficiently separates particles from coarse (<44

um, mean 20 um) to ultra-fine (100% < 2 um, mean 0.25 um). It efficiently

separates contaminants in slurries ranging from 5% to 65% solids. It does

not chemically or physically alter the mineral slurry other than to remove

magnetically susceptible contaminants. It efficiently functions in fully

dispersed mineral systems optimizing contaminant liberation and removal.

The slurry solids may be run from 5% to 65% at temperatures of 50

degrees C and higher. In all cases, the slurry should be dispersed to

minimum viscosity and have its impurities liberated by grinding prior to

magnetic separation.

A composition of matter comprising a high brightness, whiteness, and opacity calcium carbonate pigment is produced by using

magnetic separation. Proper dispersion to minimum viscosity is employed

to optimize contaminant liberation and removal as a result of liberation of

the impurities by, and during grinding, prior to magnetic separation. The

slurry temperature is maintained at or above 50 degrees C.

Magnetic separation is applied to a dispersed mineral system to

efficiently separate particles from coarse to ultra-fine in slurries ranging

from 5% to 65% solids without chemically or physically altering the

mineral slurry other than to remove the magnetically susceptible

contaminants.

Another aspect of the present invention of great significance is

the removal of dolomitic components from calcium carbonate mineral

systems, separation of a dispersed mineral system to efficiently separate

particles from coarse to ultra-fine in slurries ranging from 5% to 65%

solids without chemically or physically altering the mineral slurry other

than to remove the magnetically susceptible contaminants is a part of the

present invention. The removal of a substantial portion of dolomitic

components from calcium carbonate systems is also an unexpected feature

of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

The drawings constitute a part of this specification and include

exemplary embodiments of the invention, which may be embodied in

various forms. In the drawings appended hereto:

Figure 1 is a schematic diagram of a superconducting high

intensity, high gradient magnetic separator of the type preferred in and as

the best mode of carrying out the present invention.

Figure 2 is a schematic flow diagram of low and high solid

options in accordance with the present invention.

Figure 3 illustrates the slurry dynamics of fine particle slurries.

Figure 4 illustrates the time vs. brightness relation for a typical

calcium carbonate magnetic separation.

Figure 5 illustrates the separation time vs. brightness relation

for a typical calcium carbonate magnetic separation.

Figure 6 illustrates the separation time vs. brightness data at a

5% solids magnetic separation of calcium carbonate.

Figure 7 illustrates the separation time vs. brightness data for a

0% solids magnetic separation of calcium carbonate. DETAILED DESCRIPTION OF THE PREFERRED

EMBODIMENTS

Detailed descriptions of the preferred embodiment are

provided herein. It is to be understood, however, that the present invention

may be embodied in various forms. Therefore, specific details disclosed

herein are not to be interpreted as limiting, but rather as a basis for the

claims and as a representative basis for teaching one skilled in the art to

employ the present invention in virtually any appropriately detailed system,

structure or manner.

The present invention produces a calcium carbonate with the

maximum product brightness and whiteness with the highest recovery at

the least cost by proper-usually maximum- dispersion, with impurity

liberation by grinding and employing elevated slurry temperatures during

high gradient magnetic separation.

The present invention may be carried out with any suitable

magnetic system.

The best mode of equipment for carrying out a magnetic

separation in accordance with the present invention is illustrated

schematically in Figure 1 which shows a cut away section of a typical

superconducting magnetic separation unit. Cryostat 20 and cryogen storage 8 serve to cool the superconducting coil 18 which surrounds the canister

volume 14 which is fed by slurry feed tube 16 while the slurry exits through

slurry exit tube 12. The magnetic field is effectively contained by the

magnetic flux return iron 10.

Typically such a magnetic separation unit will be run at 2 or 3

Tesla or higher and employ a matrix packing density of from 4 to 8 %. The

fiber or strand size of the matrix may be from 22 um to 75um, with 30 um

being generally preferred. In typical operations the slurry may be fed at

0.5 to 2 canister volumes per minute with a residence time in the field of the

canister of from 0.5 to 2.0 minutes.

The slurry solids may be run from 5-65% at temperatures of 50

degrees C.

In all cases the slurry should be dispersed to minimum viscosity

and have its impurities liberated by grinding prior to magnetic separation.

As shown in Fig. 2 there are several options available in the

processing of calcium carbonates by magnetic separation. The quarry stone

, marble , limestone, chalk or other form of calcium carbonate indicated at

22 is crushed and/or ground by dry processing in a cascade or ball mill at

24.

In following the low solids path at 26, a material is produced having a particle size diameter of d50 equal to approximately 10 to 15 um.

This material is made down in water and conditioned with a conventional

flotation reagent. The flotation product which is ground at 32 by ultra fine

wet grinding means with the particle size being from 50% to 98% < 2um.

The material is subjected to classification, if required, at 34 and passed

through a 325 mesh screen prior to magnetic separation at 36 in accordance

with the processing parameters set forth above. Following magnetic

separation at 36, the slurry is subjected to evaporation and dewatering at

38 . A high solids slurry is produced at 40 on the order of 70% to 76%

solids for slurry shipment, if desired. Otherwise, the slurry is further dried

at 42 to produce high brightness products 44.

In following the high solids option 28, which may , of course, be

used also for low solids processing the material is crushed and/or ground

by dry processing at 24 by means of a cascade mill or ball mill or other well

known means. It is made down in water and dispersed to minimum

viscosity for further grinding at 46 where a 25%-65% solids slurry is

subjected to ultrafine wet grinding to produce a slurry having a particle

size of from 50% to 98% < 2um. The material is subjected to classification,

if required, at 48 and the 50% to 98% < 2 um slurry is passed through a

325 mesh screen prior to being magnetically separated at 50 in accordance with the teachings set forth herein. The magnetically separated materials

are then subjected to evaporation and dewatering at 52. The high solids

slurry is established at 54. A 70% to 76% solids slurry may be prepared

for slurry shipment. Otherwise, the slurry is dried at 56 to produce a high

brightness/ low cost product 58.

As shown in Figure 3, the slurry dynamics of such fine particle

slurries as are the subject of the present invention are shown with the high

temperature resulting in a lower Brookfield viscosity, CPS, #1 spindle at

100 rpm from 15% to 65% solids and above of a dispersed calcium

carbonate slurry as shown by curves 62 and 60.

Figure 4 shows the time vs. brightness curve 64 for a sample

reaching a maximum brightness of 95.6.

Figure 5 shows the separation time vs. GE brightness on curve

66 which is drawn with respect to time in minutes where one minute is

equal to 2.0 canister volumes per minute.

Figure 6 shows separation time vs. GE., Tappi, Brightness in

which the brightness 68 is plotted against the magnet run time in minutes

for 2 canister volumes per minute. The integrated measured average at 2

canister volumes per minute is shown at 70 to be 97.65. The total run time

of 9.25 minutes at 2 canister volumes per minutes is equal to 12 Tonnes per hour.

The separation time vs. brightness data for a 40 % solids

separation is plotted for 1 and 2 canister volumes per minute in curves 74

and 72 respectively yielding an integrated measured average of 97.3 and

97.2 respectively. The 2 CVS/min is equal to a flow rate of 0.66 cm/sec and

the lCV/min to 0.33 cm/sec.

Practice of the present invention will now be illustrated by the

following Examples which are deemed illustrative of both the process

taught by the present invention and of the product yielded in accordance

with the invention.

The invention is further explained below. In these Examples, to

which the invention is not limited, the starting material was a calcium

carbonate sample.

Since calcium carbonate is a natural product, its composition is

subject to routine variations, and the entire disclosure herein is subject to

routine variations, depending on the material used as the starting material.

Here follows a brief description of some of the tests to which

reference will be made in discussion some of the properties of the products

of the present invention.

Brightness is measured by a well-known instruments made by the Techudyne Corp. , such as the TB 1-C. The value of brightness, as

measured by such an instrument, is conventionally designated as the "G.E.

or TAPP Brightness" value. The brightness of magnesium oxide, MgO, is

given a value of 100. Other brightnesses are described as a percentage of

the brightness of MgO. TAPPI Procedure T-646-os-75 is followed in

making this measurement. All brightness values of minerals and fillers as

used herein refer to block brightness values as determined in accordance

with the above cited TAPPI standard procedures with a G.E. reflectance

meter using light having a wavelength of about 457 nanometers or with

comparable equipment and techniques. Paper brightness was measures in

accordance with the Canadian Pulp and Paper Association Standard

Method E. J.

Diffuse opacity was measured in accordance with TAPPI

Standard Method T 519 o 86. Reflectance backing opacity was

measured in accordance with TAPPI Standard Method T 425 om 86.

Both the brightness characteristics of a given material and the

opacifying properties of the same when incorporated as a filler in paper,

may be quantitatively related to a property of the filler identified as the

"scattering coefficient, S" The scattering coefficient, S, of a given filler

pigment is a property well known and extensively utilized in the paper technologies and art and has been the subject of numerous technical papers.

An early exposition of such measurements was made by Kubelka and

Munk, and is reported in Z. Tech Physik 12:539(1931). Further citations to

the applicable measurement techniques and detailed definitions of the said

scattering coefficient are set forth at numerous places in the patent and

technical literature. Reference may usefully be had in this connection to

U.S. Patent Nos. 4,026,762 and 4,028,173. In addition, reference may

further be had to Pulp and Paper Science Technology, Vol. 2 "Paper",

Chapter 3, by H.C. Schwalbe (McGraw-Hill Book Company, New York).

Abrasion may be measured by the well-known Valley Abrasion

test method described in the Institute of Paper Chemistry Procedure 65 and

as described in U.S. Patent No. 3,014,836 to Proctor. It may also be

measured by the Breunig Abrasion test as set forth in U.S. Patent No.

4,678,517 to Dunaway or by the Einlehner Abrasion Test as set forth in U.

S. Patent 5,011,534 to Berube et al. In general, the measurements reported

herein have been made in accordance with TAPPI Standard Abrasion

techniques at 100,000 revolutions and at 15% solids.

Oil Absorption may be measured as set forth in ASTM D 281-

31.

Bulk density is measured as described in U.S. Patent No. 4,693,427 to Billmoria et al.

Particle size may be determined by sedimentations methods as

published November 1954 by the Technical Association of the Pulp and

Paper Industry as "T 649 SM-54".

"Strike-through" is defined as 100 minus the ratio (expressed as

a percent) of the reflectance of the back of the printed area to the

reflectance of the unprinted sheet while both are backed by a black body.

Unless otherwise noted, the magnet conditions in each example

were within the ranges set forth above.

In general , the examples show an improvement in GE

Brightness units of 1.5 -2.0% , although brightness increases of as much as

20 GE units have been obtained.

In the examples, unless otherwise noted the samples were fully

dispersed to minimum viscosity at approximately 90%< 2 um PSD: 50-90

degree C. in temperature and 5-65% solids. The present invention has

successfully separated calcium carbonates and their impurities in fully

dispersed slurries up to 65% solids.

The present invention has successfully separated calcium

carbonates with PSD's of from 300 mesh (-50 um) to 99%<2 um.

Substantially the same results have been obtained with 22 um, 30 um, 50 um, and 75 um matrix strand diameters.

The residence time was varied from 0.5 to 3 minutes with

substantially the same results-that is to say with the increasing residence

time yielding only limited or marginal improvements in the GE brightness

on the order of that which would be expected.

Example 1-A southeastern US calcium carbonate sample of

90% < 2 um and at 20% solids was processed at 3 Tesla with a matrix

density of 6% through a 30 um matrix at 2 canister volumes per minute

and a residence time of 30 seconds. Feeds of 96.0 and 94.8 GE brightness

yielded 97.6 and 96.6 GE brightnesses, respectively.

Example 2-A non-floated ground calcium carbonate sample showed

an improved brightness from ~ 91% GE brightness to 98% GE brightness

at 50 % solids with a dispersed 96% < 2um slurry.

Example 3-A southeastern US sample was processed at 3 Tesla,

65 degrees C. , 40 % solids, 6% packing density for the canister and a flow

rate of 2 canister volumes per minute. The GE brightness went from 95.4

to 97.2 with a significant improvement in whiteness.

Example 4-Shown below is the calcium carbonate product GE

(Tappi) incremental brightness for a material 90% <2um after fine

grinding from four geographic areas, southeastern(SE) and northwestern (NW) United States(US) where the top figure is the feed and the bottom

figure is the product of magnetic separation:

Example 5-The following GE brightnesses were obtained from

northwestern US feed materials as indicated with additional brightness

figures for the product ground to 90% < 2 um:

Example 6-The following GE brightnesses were obtained from

northwestern US feed materials after magnetic separation:

Example 7-A southeastern US calcium carbonate sample was

magnetically separated at various solids with the feed and product GE

brightness shown below:

Example 8-A northwestern US sample was magnetically

separated at the following solid with the GE brightnesses as shown:

Based upon the above observations, it is clear that the present

invention is a surprising and unexpectedly effective discovery of an

application for magnetic separation.

Other processing possibilities are also apparent, such as is

apparent and within the scope of the present invention.

In accordance with the present invention it is possible to apply

grinding both before and after magnetic separation. Other selective

separations may be used in lieu of flotation.

In summary, the present invention produces the maximum

product brightness with the highest recovery at the least cost by applying the proper, minimum viscosity dispersion with the impurities liberated

during grinding and the slurry temperatures being elevated usually above

50 degrees C. The optimization of these factors is particularly important in

the high solids option of the present invention.

The process of the present invention provides significant

quality and environmental advantages. For example, in the reduction of

flotation chemicals and their environmental effects.

Suitable equipment to carry out the grinding functions

includes ACM mills, CMT mills, classifiers, and the like. Equipment such

as that known as PPS— Powder Process Systems Ltd. of Essex England—

CMT air classification grinding mills are particularly effective at this stage.

The milling/pulverization/particle sizing processing stage at any

point in the process is employed to produce a dispersed, low residue feed

with desired particle size and abrasion. In general the pulverizing is

intended to refer to the deaglomeration of aggregates; the milling to the

reduction of residue and the particle sizing to the classification for an

optimized feed.

The pulverization and milling , in general, deagglomerates and

reduces the particle size of the products.

Suitable equipment includes ACM and CMT mills and various classifiers. In some cases all of these steps may be accomplished in a single

piece of equipment. In other cases it may be desirable to approach each

aspect of this stage as a separate unit operation in individual pieces of

equipment, all of which are conventional and well known.

The product may also be screened to remove residue.

The grinding stage may be required for various applications.

It may be accomplished in sand, bead or ball mills or in other suitable

grinding apparatus.

Blending of other minerals is also an option for this processing

step.

Products of the present invention may be used in a wide variety

of ways. For example the products may be tailored as pigments for use in

paper where their high brightness and whiteness as well as their low cost

will be see as major advantages. The pigments may also be used in paints

to the same advantage.

Further the products of the present invention may be used as

functional fillers in plastics, rubber, and in household and personal care

products.

It is to be noted that heat is of course generated in the grinding

process which is useful as a processing aid. When magnetic separation is used in lieu of flotation, oxidation

with ozone or other suitable agents may further improve brightness.

Organic polyaculate dispersants may be employed in the

present invention

In addition, magnetic polymers in the form of a magnetic

emulsion having a molecule with a hydrophobic end to attract graphite ,

carbon and similar impurities may be employed as may ferric and ferrous

chlorides and lauric acid. These agents may be used in an amount such as

40 ml/ 8 pounds of dry calcium carbonate or 0.5 -0.6 pounds/ ton of calcium

carbonate.

From 0.2-5 pounds / ton of seed material may also be used with

5 minutes of shear mixing to throughly admix such as 2-15 minutes for 1-10

HP-HR T of calcium carbonate.

Magnetic rejects may be used to add opacity in certain cases.

Analysis by x-ray diffraction, SEM and ED AX of the magnet

feed, reject and product surprisingly showed that the process of the present

invention removed substantially all of the dolomite. The removal of

dolomite by magnetic separation from calcium carbonate materials results

in significant brightness improvements and has not been previously

recognized as either a significant factor or even as a possibility. This discovery is applicable to all of the dolomite, ankerite and

siderite groups as well as to the rhodochrosite group as set forth in the

MANUAL OF MINERALOGY after Dana, thel9th edition edited by

Hurlbut and Klein at 301,302,307,and 308. The removal of these materials

from calcium carbonate by magnetic separation has not been previously

well recognized and may explain in part the totally unexpected nature of

the present invention. These materials will be referred to herein as the

dolomitic group of materials.

The present invention produces a calcium carbonate with the

maximum product brightness with the highest recovery at the least cost by

proper (usually maximum) dispersion, with impurity liberation by grinding

and employing elevated slurry temperatures during magnetic separation.

It has now been discovered and it is the subject matter of the

present invention and application that magnetic separation has a number of

processing advantages. It efficiently separates particles from coarse (<44

um, mean 20 um) to ultra-fine (100% < 2 um, mean 0.25 um). It efficiently

separates contaminants in slurries ranging from 5% to 65% solids. It does

not chemically or physically alter the mineral slurry other than to remove

magnetically susceptible contaminants. It efficiently functions in fully

dispersed mineral systems optimizing contaminant liberation and removal. The slurry solids may be run from 5% to 65% at temperatures of 50

degrees C and higher. In all cases, the slurry should be dispersed to

minimum viscosity and have its impurities liberated by grinding prior to

magnetic separation.

A composition of matter comprising high brightness and

whiteness calcium carbonate pigments and products by using magnetic

separation, proper dispersion to minimum viscosity to optimize

contaminant liberation and removal as a result of the liberation of the

impurities by, and during grinding, prior to magnetic separation, while the

slurry temperature is maintained at or above 50 degrees C. is a novel facet

of the present invention.

Magnetic separation is applied to a dispersed mineral system to

efficiently separate particles from coarse to ultra-fine in slurries ranging

from 5% to 65% solids without chemically or physically altering the

mineral slurry other than to remove the magnetically susceptible

contaminants.

Another aspect of the present invention of great significance is

the removal of dolomitic components from calcium carbonate mineral

systems.

The present invention also includes the processes for the production of high brightness calcium carbonate pigments by the use of

magnetic separation comprising the steps of providing the proper

dispersion to minimum viscosity, to optimize contaminant liberation and

removal, with liberation of the impurities by, and during, grinding prior to

magnetic separation, while maintaining slurry temperatures at or in excess

of 50 degrees C. The magnetic separation of a dispersed mineral system to

efficiently separate particles from coarse to ultra-fine in slurries ranging

from 5% to 65% solids without chemically or physically altering the

mineral slurry other than to remove the magnetically susceptible

contaminants is a part of the present invention. The removal of dolomitic

components from calcium carbonate systems is also an unexpected feature

of the present invention.

It has been discovered that by the selective separation of a

substantial portion of the dolomite mineral groups as defined herein that a

high brightness, whiteness, and opasity product having a whiteness as

defined by its "b" value of 0.5 or less, usually less than 0.0. For example, a

1.1 % Mg content sample reflecting a dolomite content on the order of 2-

3% may be reduced to 0,4% Mg with the magnetic rejects containing 13%

Mg.

It is to be further noted that the hich solid processing disclosed herein produces brightnes increases on the order of 3 G.E. units while the

full range of processing conditions produces brightness improvements on

the order and in excess of 3.5 units.

While the present invention has been particularly set forth in terms of

specific embodiments thereof, it will be understood in view of the instant

disclosure, that numerous variations upon the invention are now enabled to

those skilled in the art, which variations yet reside within the scope of the

present teachings. It is not intended to limit the scope of the invention to the

particular form or forms set forth, but on the contrary, it is intended to

cover such alternatives, modifications, and equivalents as may be included

within the spirit and scope of the invention. Accordingly, the invention is to

be broadly construed and is to be limited only by the scope and spirit of the

claims now appended hereto.

Claims

Claims:

Claim 1. A calcium carbonate product having high brightness,

whiteness and opacity with an increase of at least 1.0 GE brightness units

over the feed material and a whiteness, "b" value of less than 0.5, as a

result of magnetic separation.

Claim 2. The calcium carbonate of claim 1 having had

substantially all of any dolomitic group impurities originally present

removed by magnetic separation.

Claim 3. The calcium carbonate of claim 1 having increased

whiteness.

Claim 4. A high brightness calcium carbonate produced by

dispersing a slurry of said carbonate to minimum viscosity and grinding the

same prior to magnetically separating the dolomitic group and other

discoloring materials from said carbonate at a temperature in excess of 50

degrees C.

Claim 5. The product of claim 4 in which the separation is

aided by a magnetic polymer.

Claim 6. The product of claim 4 in which the separation is

aided by adding seed material.

Claim 7. The product of claim 4 wherein it comprises a composition of matter comprising high brightness calcium carbonate

pigments produced by using magnetic separation on a slurry dispersed to

maximum viscosity to optimize contaminant liberation and removal, said

impurities being liberated by and during grinding prior to magnetic

separation of said slurry maintained at a temperature of 50 degrees C. or

higher.

Claim 8. The product of claim 7 wherein said magnetic

separation of a dispersed system of course to ultra-fine slurries ranging

from 40% to 65% solids without chemically or physically altering the

mineral slurry other than to remove the magnetically susceptible

contaminant.

Claim 9. A method of magnetically separating dolomitic group

impurities and other discoloring impurities from calcium carbonate by:

(1) dispersing a slurry of calcium carbonate to minimum

viscosity;

(2) liberating any dolomitic impurities and other discoloring

impurities by grinding in the dispersed state prior to magnetic separation,

and

(3) maintaining the slurry temperature at 50 degrees C.

Claim 10. The method of claim 9 wherein the slurry is at a

solids in excess of 40%.

Claim 11. The method of claim 9 wherein the materials are

subjected to dry and wet grinding , followed by classification prior to

magnetic separation.

Claim 12. The method of claim 9 wherein flotation precedes

magnetic separation

Claim 13. The method of extraction of one or more members of

the dolomitic group from calcium carbonate by dispersing to minimum

viscosity, liberating impurities during grinding prior to magnetic

separation and maintaining the slurry temperatures at or above 50 degrees

C. and magnetically separating the dolomitic group materials from the

calcium carbonate.

Claim 14. The method of claim 13 wherein the process of

magnetic separation is applied to separated particles from coarse to ultra-

fine slurries ranging from 40% to 65% solids.