GB1602359A - Method of brightening natural calcitic ores - Google Patents

Description

(54) METHOD OF BRIGHTENING NATURAL CALCITIC ORES (71) We, ANGLO-AMERICAN CLAYS CORPORATION, a corporation organized under the laws of the State of Delaware, in the United States of America, of Kaolin Road, Sandersville, Georgia 31082, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to calcium carbonate-containing minerals and more particularly is concerned with a process for beneficiating calcium carbonate-containing minerals.

Pigments based on calcium carbonate find application in a wide variety of industrial and other environments. For example, such pigments are widely used as fillers in the manufacture of papers, rubber and various plastics materials, and as extenders in paint formulations. Such pigments furthermore, either alone or in combination with other pigments, are widely used in paper coating. In many of the aforementioned uses, and particularly where the pigments are used for paper coating, it is desirable that the calcium carbonate be as bright as possible.

High brightness calcium carbonate pigments have long been produced by chemical processes wherein the calcium carbonate pigments are prepared as precipitates. These processes, however, are comparatively complex and are unsuited to low cost operations.

Therefore interest has centered upon the possible use of naturally-occurring calcium carbonate-containing minerals, particularly since such minerals are extremely abundant in virtually all parts of the world, and therefore represent a ready source of inexpensive raw material. In practice, however, it is found that many of the natural deposits of such minerals are so highly contaminated with discolourants that, when comminuted in their natural state, they are unacceptable as pigments. Thus, in typical instances deposits which consist primarily of calcite may be contaminated with pyrites and with mica, both of which in varying degrees contribute to the discolouration of the otherwise relatively white calcium carbonate.

In our British Patent Application No. 21638/78 Serial No. 1602358 there is described and claimed a method of processing a calcium carbonate-containing mineral which method comprises in sequence the steps of subjecting the calcium carbonate-containing mineral as an aqueous slurry including less than 40% by weight solids to a froth flotation; separating from the froth flotation an underflow product containing calcium carbonate-containing mineral from which discolouring impurities have been removed; dewatering the underflow product from said froth flotation to at least 60% solids by weight; and wet-milling the dewatered product to produce a material of which at least 80% by weight of the particles have an equivalent spherical diameter smaller than 2 microns.

The froth flotation conducted persuant to the method described and claimed in Application No. 21638/78 is carried out with the slurry having a solids content of less than 40% and preferably less than 30%. Useful collector agents for the froth flotation process are said to include xanthates, such as potassium ethyl xanthate (e.g. Dow C-2) as typical concentrations of 0.1 Ib/ton solids, various hydrocarbons, including kerosene, fuel oil, mineral oil or mineral oil fractions, aromatic hydrocarbons, such as dipentine, or other collectors known in the art. Similarly, frothers, such as pine oil, cresylic acid, polypropylene glycol ether or other well known agents of these types may be utilized in the froth floation.

According to the present invention there is provided a method of processing a calcium carbonate-containing mineral which process comprises in sequence the steps of subjecting the calcium carbonate-containing mineral as an aqueous slurry including less than 40% by weight solids to a froth flotation; separating from the froth flotation an underflow product containing the calcium carbonate-containing mineral from which discolouring impurities have been removed; dewatering the underflow product from said froth flotation to at least 60% solids by weight; and wet-milling the dewatered product to produce a material of which at least 80% by weight of the particles have an equivalent spherical diameter smaller than 2 microns, wherein the froth flotation is carried out in the presence of an imidazoline compound which is a 2-alkylimidazoline or a salt thereof.

The imidazoline compound is believed to act as a collector. Advantageously, the 2-alkyl substituent of the 2-alkyl-imidazoline or salt thereof contains from 6 to 20 carbon atoms.

Preferably, the imidazoline compound is a 1-hydroxyalkyl substituted compound, for example a 1-hydroxyethyl-2-alkylimidazoline. The imidazoline compound is advantageously used with a substantially non-polar or non-ionic compound such as an aliphatic hydrocarbon which latter compound is believed to function as a promoter or diluent.

Instead of a long chain aliphatic hydrocarbon such as a long chain alkane having a carbon chain of from 10 to 20 carbon atoms, there may be used a long chain aliphatic alcohol or ester in which the long chain contains from 10 to 20 carbon atoms. Most preferably, the 2-alkylimidazoline is a 1-hydroxyethyl-2-alkylimidazoline wherein the alkyl group has a carbon chain length of from 10 to 20 carbon atoms. The starting materials which we have found yield especially good reslts are alkylimidzolines in which the alkyl portion corresponds to the alkyl portion of oleic acid or tall oil; and these alkylimidazoline compounds are commercially available under the respective trade names Monazoline 0 and Monazoline T (Mona Industries Inc., Paterson, N.J.). The compounds are readily converted to salts by the addition of the appropriate acid in the necessary quantity.Thus the Monazoline O Acetate referred to in the subsequent Examples herein, is the acetate salt of 1-hydroxyethyl-2-oleylimidazoline.

We have discovered that the imidazoline compounds, such as the salts of the 2-alkylimidazoline compounds, especially when used in combination with a long chain alkane or a long chain aliphatic alcohol or ester having a carbon chain length of 10-20 carbon atoms, are effective in removing insoluble mineral impurities from natural calcitic ores.

The substantially non-polar or non-ionic organic compound may be a mixture of compounds of suitable chain length, the commonest and cheapest being kerosene or fuel oil. It is preferred to use a refined material which is similar to kerosene, but has had substantially all the aromatic or cyclic compounds removed by chemical means; and a material of this type is available under the name 2251 oil (Penreco Division of Pennzoil Co., Butler, PA). Such materials are advantageous because of their effectiveness and low toxicity. The process of the present invention does not necessarily require, however, that aliphatic paraffins (alkanes) be employed. Other substantially non-polar or non-ionic compounds of similar carbon chain length, such as alcohols or fatty acid esters can also be employed, examples being octadecane, cetyl alcohol, stearyl alcohol, oleyl alcohol or methyl stearate.

The product yielded by practice of the present invention is found to be especially well-suited to paper coating applications. In such environment the product has a significantly less detrimental effect on ink absorbency than does precipitated carbonates; and the product, further, has a less detrimental effect on gloss of coated papers than does conventional ground carbonates.

In other respects the method of the invention can be carried in a similar manner to the method disclosed in British Patent Application No. 21638/78 Serial no. 1602358. Thus, the calcium carbonate-containing mineral is preferably initially coarse milled to an extent such that it contains not more than 5% by weight of particles which are retained on a 325 mesh sieve and not more than 35% by weight of particles which are smaller than 2 microns equivalent spherical diameter. The coarse grinding operation may be effected by various techniques known in the art, such as, for example, by means of a ball mill or by use of autogeneous grinding or dry grinding. The coarse milled product is then subjected, as an aqueous slurry, including less than 40% by weight solids, to the froth flotation, which separates with the froth the relatively coarse colorbodies liberated in the initial coarse milling. The purified underflow is then dewatered to a solids content of at least 60%, and preferably at least 65%, by weight whereafter it is wet-milled, preferably in a sand mill, to yield a product of which at least 80% by weight of the particles have an equivalent spherical diameter of less than 2 microns. In this way it is possible to obtain a product characterised by a brightness of at least 94 on the G.E. scale, and an abrasion of less than 25 mg. as measured by the Valley Abrasion Test (carried out using Procedure 65 prescribed by the Institute of Paper Chemistry).

In the dewatering operation, which is carried out upon the underflow following the froth flotation, the product is dewatered to at least 60% solids by weight, and preferably to over 65% by weight solids. Dewatering can be accomplished by conventional devices down in the art, including rotary vacuum filters, pressure filters, or Bird or similar centrifuges.

The fine grinding step is preferably effected by sand grinding i.e. by grinding with a particulate grinding material consisting of particles which usually range in size from about 150 microns to 1/4" in diameter, and preferably from about 500 microns to about 2mm.

Details of the sand grinding operation, including citation of equivalent materials for use in sand grinding, are set forth in U.S. Patent Specification No. 3,604,634; and the conditions of grinding as set forth in that patent specification may be regarded as the preferred mode of operation with respect to the present invention. The fine-grinding step has as its objective a product of which at least 80% by weight of the particles have an equivalent spherical diameter of less than 2 microns.

The invention is illustrated by the following Examples, in which samples of various calcitic ores were used, which samples included as impurities orthoclase, quartz, tremolite, phlogopite mica and pyrite, the total amount of these impurities being between 11/2 and 5% by weight of the calcitic ore.

Example I Samples of the foregoing ore were dry ground and classified to yield feedstocks wherein 0.5% by weight of the particles were of a size such as to be retained on a 325 mesh sieve and 22% by weight were smaller than 2 microns e.s.d. These samples were slurried to 25% solids and floated utilizing various combinations of flotation reagents, including the previously discussed 1-hydroxyethyl-2-alkyl-imidazoline salts in combination with neutral aliphatic hydrocarbons.

In a typical procedure the collector (and, as appropriate, a frother) were added to the slurry at the start of the flotation process. Approximately one-third of the promoter was also added at the start of the float, and the remaining two-thirds were added incrementally, e.g. with a typical 45 minute flotation 2 lbs/ton of promoter were added at the start of flotation, with 1-2 lbs/ton being added in increments at 5-10 minute intervals.

The floated products were dewatered using 7 Ibs/ton CaC12 and then sand ground to 90% less than 2 microns at 70% solids using 9 lbs/ton of Dispex dispersing agent, after which brightnesses were determined. Floated brightnesses (prior to sand grinding) were also measured; and acid insolubles were determined for the samples both as feedstock and following flotation.Results yielded by these procedures are set out in Table I below: TABLE 1 Sample No. 1 2 3 4 5 6 Feed Brightness 90.7 90.5 90.6 93.2 93.3 93.3 Feed % Insoluble 3.2 2.26 2.24 2.6 2.03 1.36 Collector & Dose 2 2 2 1 1.75 2 (lbs/ton) Duomac T MTA* MOA* Duomac T MOA ** MOA** Frother & Dose 0.2 Igepal CO710 -- -- 0.2 Igepal CO710 -- - (lbs/ton) 0.1 Triton CF10 -- -- 0.1 Triton CF10 -- - Promoter & Dose 10 5 6 8 5 6 (lbs/ton) Kerosene Kerosene Kerosene Kerosene 2251 Oil Kerosene Floated Brightness 92.2 93.8 93.3 94.5 95.3 95.0 Floated % Insoluble 0.3 0.04 0.18 0.77 0.10 0.09 Flotation Recovery % 76 86 89 76 94 89 Sand Ground Brightness 95.2 95.4 96.3 95.8 96.3 97.0 * Monazoline T Acetate **Monazoline O Acetate Because the materials floated in this Example are of relatively fine particle size and contain such a variety of mineral impurities (which fortunately will all respond to cationic flotation) the selection of a suitable cationic collector is difficult. The mechanism of attachment of the collector to the mineral imurity is by electrostatic attraction of the cationic polar group of the collector to the negatively charged surface of the mineral. This is a comparatively weak mechanism compared to the adsorption or chemisorption mechanism which takes place in the flotation of, for example, sulphides with xanthates. It is therefore essential to use a collector having a strongly charged cationic polar group to ensure maximum attraction to the mineral. In this case, coating of the mineral by the collector would become almost impossible at reasonable collector concentrations because of the energy of repulsion between adjacent charged ionic polar groups of the collector.It is believed that the function of the neutral hydrocarbon is to lower this repulsion energy and allow the formation of an adequate coating of collector to allow bubble attachment and hence flotation to take place.

It will be noted from Table 1 that in the case of the carbonates considered, the lower the acid insoluble content of the material after flotation, the higher the sand ground brightness of the finshed slurry. Brightnesses of the finished products are seen in all instances to be well over 95; and it will be noted that where the feedstock is of relatively low contamination (as measured by acid insolubles) then extremely high brightnesses are obtained. Thus in the instances of Samples 5 and 6, which contained respectively 2.03% and 1.36% by weight of acid insolubles, final product brightnesses of 96.3 and 97.0 were yielded.

In Table 1, Samples 1 and 4 have been used as references to illustrate the superiority of the imidazoline/hydrocarbon combination over a Duomac T/frother/kerosene system. It can be seen that using either low or high brightness feed materials the 2-alkyl imidazoline system produces higher floated brightness, lower levels of acid insoluble residue, and higher sand ground brightness. In addition substantially higher recovery is achieved, no separate frothing compound is required, and dosages of kerosene or other neutral hydrocarbons are reduced.

Pursuant to the invention, the aforementioned 2-alkyl imidazoline salts are preferably added to the slurried ore in concentrations of from 1 to 5 lbs/ton of the calcitic ore in combination with the addition of the non-polar hydrocarbon in concentrations of from 3 to 15 lbs/ton of ore.

Example 2 In this Example a further Maryland calcitic ore similar to that used in Example 1 was treated. The ore was thus initially dry ground and classified to yield a feed material wherein 99% by weight of the particles passed through a 325 mesh sieve, 25% by weight were smaller than 2 microns E.S.D. (equivalent spherical diameter). The feed material had an initial brightness of 92.4 and included 3.0% of acid insolubles. When a portion of this feed material was slurried to 67% solids and sand ground to 90-92% less than 2 microns, the brightness dropped to 91.9.

The same dry ground material was diluted to 25% solids and floated utilizing various combinations of collector and promoters. -The collector and frother (if any) were added to the slurry in a single dose at the start of the flotation process. The promoter, when used, was added as roughly one-third of the total quantity at the start of the float and the remaining two-thirds in l/2 Ibs/ton increments at 5-10 minute intervals; the total time for flotation being for all samples approximately 45 minutes.

The floated products of the foregoing procedures, were dewatered and the sand ground (by the procedures described in Example IX). Floated brightness (prior to sand grinding) were measured, acid insolubles and flotation recoveries were determined; and the brightness of the floated samples after sand grinding (by the procedures of Example 1) were measured. Results yielded by these procedures are set forth in Table II below: TABLE II Flotation Chemicals Floated Floated Flotation Sand Ground & Dose Rates lbs/ton Brightness % Recovery Brightness G.E. Insolubles % G.E.

2.0 lb/ton Monazoline 0 93.1 2.0 < 60 92.0 2.0 lb/ton Monazoline 0 92.8 0.65 < 60 94.2 Acetate 2.0 lb/ton Monazoline 0 9.0 lb/ton Penreco 2251 Oil 94.9 0.4 86 95.0 2.0 lb/ton Monazoline 0 Acetate 94.8 0.16 83 96.6 6.0 lb/ton Penreco 2251 Oil It will be evident from Table II that the procedures of the present invention result in a product which in all instances displays a brightness of at least 95. The assembled data further illustrates the superior results yielded by use of the imidazoline salt derivatives (vis-a-vis the imidazoline); and more especially such data illustrate the brightness improvements yielded by combined use of such salt derivatives with the previously specified non-polar aliphatic hydrocarbons. Note should be taken, as well, of the reduction in acid insolubles achieved by practice of the present invention.

WHAT WE CLAIM IS: 1. A method of processing a calcium carbonate-containing mineral which process comprises in sequence the steps of subjecting the calcium carbonate-containing mineral as an aqueous slurry including less than 40% by weight solids to a froth flotation; separating from the froth flotation an underflow product containing the calcium carbonate-containing mineral from which discolouring impurities have been removed; dewatering the underflow product from said froth flotation to at least 60% solids by weight; and wet milling the dewatered product to produce a material of which at leash 80% by weight of the particles have an equivalent spherical diameter smaller than 2 microns, wherein the froth flotation is carried out in the presence of an imidazoline compound which is a 2-alkyl imidazoline or a salt thereof.

2. A method according to claim 1, wherein the 2-alkyl substituent of said imidazoline or salt thereof contains from 6 to 20 carbon atoms.

3. A method according to claim 1 or 2, wherein said imidazoline compound is a 1-hydroxyalkyl substituted 2-alkyl imidazoline or a salt thereof.

4. A method according to claim 3, wherein said imidazoline compound is a 1-hydroxyethyl-2-alkylimidazoline or a salt thereof.

5. A method according to claim 1, 2, 3 or 4, wherein the 2-alkyl substituent of said imidazoline or salt thereof corresponds to the alkyl portion of oleic acid or tall oil.

6. A method according to any one of claims 1 to 5, wherein said salt is an acetate salt.

7. A method according to any one of claims 1 to 6, wherein said imidazoline compound is used in an amount ranging from 1 to 5 Ibs per ton of calcium carbonate-containing mineral.

8. A method according to claim 1,2,3,4,5,6 or 7, wherein said imidazoline compound is used in admixture with a substantially non-polar or non-ionic organic compound.

9. A method according to claim 8, wherein said substantially non-polar or non-ionic compound is a long chain alkane or a long chain aliphatic alcohol or ester, in which the long chain contains from 10 to 20 carbon atoms.

10. A method according to claim 9, wherein said substantially non-polar or non-ionic compound is kerosene from which substantially all aromatic or cyclic compounds have been removed, octadecane, cetyl alcohol, stearyl alcohol, oleyl alcohol or methyl stearate.

11. A method according to any one of claims 8 to 10, wherein said substantially non-polar or non-ionic compound is used in an amount ranging from 3 to 15 lbs per ton of calcium carbonate-containing mineral.

12. A method according to any one of claims 1 to 11, wherein before said calcium carbonate-containing mineral is subjected to a froth flotation it is coarse-milled to an extent such that it contains not more than 5% by weight of particles which are retained on a 325 mesh sieve, and not more than 35% by weight of particles smaller than 2 microns equivalent spherical diameter.

13. A method according to claim 12, wherein said coarse-milling is effected by dry grinding.

14. A method according to any one or claims 1 to 13, wherein said wet milling is effected by sand grinding.

15. A method according to any one of claims 1 to 14, wherein said underflow product is dewatered to over 65% solids by weight.

16. A method of processing a calcium carbonate-containing mineral according to claim 1, substantially as described in either one of the foregoing Examples.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (17)

**WARNING** start of CLMS field may overlap end of DESC **. It will be evident from Table II that the procedures of the present invention result in a product which in all instances displays a brightness of at least 95. The assembled data further illustrates the superior results yielded by use of the imidazoline salt derivatives (vis-a-vis the imidazoline); and more especially such data illustrate the brightness improvements yielded by combined use of such salt derivatives with the previously specified non-polar aliphatic hydrocarbons. Note should be taken, as well, of the reduction in acid insolubles achieved by practice of the present invention. WHAT WE CLAIM IS:

1. A method of processing a calcium carbonate-containing mineral which process comprises in sequence the steps of subjecting the calcium carbonate-containing mineral as an aqueous slurry including less than 40% by weight solids to a froth flotation; separating from the froth flotation an underflow product containing the calcium carbonate-containing mineral from which discolouring impurities have been removed; dewatering the underflow product from said froth flotation to at least 60% solids by weight; and wet milling the dewatered product to produce a material of which at leash 80% by weight of the particles have an equivalent spherical diameter smaller than 2 microns, wherein the froth flotation is carried out in the presence of an imidazoline compound which is a 2-alkyl imidazoline or a salt thereof.

2. A method according to claim 1, wherein the 2-alkyl substituent of said imidazoline or salt thereof contains from 6 to 20 carbon atoms.

3. A method according to claim 1 or 2, wherein said imidazoline compound is a 1-hydroxyalkyl substituted 2-alkyl imidazoline or a salt thereof.

4. A method according to claim 3, wherein said imidazoline compound is a 1-hydroxyethyl-2-alkylimidazoline or a salt thereof.

5. A method according to claim 1, 2, 3 or 4, wherein the 2-alkyl substituent of said imidazoline or salt thereof corresponds to the alkyl portion of oleic acid or tall oil.

6. A method according to any one of claims 1 to 5, wherein said salt is an acetate salt.

7. A method according to any one of claims 1 to 6, wherein said imidazoline compound is used in an amount ranging from 1 to 5 Ibs per ton of calcium carbonate-containing mineral.

8. A method according to claim 1,2,3,4,5,6 or 7, wherein said imidazoline compound is used in admixture with a substantially non-polar or non-ionic organic compound.

9. A method according to claim 8, wherein said substantially non-polar or non-ionic compound is a long chain alkane or a long chain aliphatic alcohol or ester, in which the long chain contains from 10 to 20 carbon atoms.

10. A method according to claim 9, wherein said substantially non-polar or non-ionic compound is kerosene from which substantially all aromatic or cyclic compounds have been removed, octadecane, cetyl alcohol, stearyl alcohol, oleyl alcohol or methyl stearate.

11. A method according to any one of claims 8 to 10, wherein said substantially non-polar or non-ionic compound is used in an amount ranging from 3 to 15 lbs per ton of calcium carbonate-containing mineral.

12. A method according to any one of claims 1 to 11, wherein before said calcium carbonate-containing mineral is subjected to a froth flotation it is coarse-milled to an extent such that it contains not more than 5% by weight of particles which are retained on a 325 mesh sieve, and not more than 35% by weight of particles smaller than 2 microns equivalent spherical diameter.

13. A method according to claim 12, wherein said coarse-milling is effected by dry grinding.

14. A method according to any one or claims 1 to 13, wherein said wet milling is effected by sand grinding.

15. A method according to any one of claims 1 to 14, wherein said underflow product is dewatered to over 65% solids by weight.

16. A method of processing a calcium carbonate-containing mineral according to claim 1, substantially as described in either one of the foregoing Examples.

17. A calcium carbonate-containing mineral whenever processed by the method

claimed in any one of claims 1 to 16.