DE2900620C2 - - Google Patents

Description

The invention relates to a method for lightening a natural calcite-containing ore or minerals with production finely divided calcium carbonate particles with relatively very good whiteness properties, in which a first coarse grinding a photation treatment of the starting material aqueous slurry with subsequent drainage as well another fine grinding follows.

Calcium carbonate pigments are found in a wide variety of industrial and other fields an application. Such pigments are widely used as fillers, for example the production of paper, rubber and various plastics and used as an extender in paint formulations. Such pigments continue to be either alone or widely used in combination with other pigments for paper coating purposes used. Many of the above Applications, especially when the pigments are used as coatings or Coatings are used, it is desirable that the calcium carbonate has the highest possible degree of whiteness.

Calcium carbonate pigments with high whiteness have long been manufactured by chemical processes in which these carbonates as precipitates or precipitates. However, these processes are comparatively complex and they are not for large scale production or for a production at low cost is well suited. For this Basically, interest has long been focused on the possible use of naturally occurring calcium carbonate, especially since natural, calcite-containing materials are extremely common in practically all parts of the world and hence an easily accessible source of inexpensive raw material represent. In practice, however, it has been found that numerous of the natural, calcite-containing deposits so heavily contaminated with discolouring materials or fabrics are that when they are finely divided into their natural  State as pigments are simply unacceptable. So in typical cases deposits, mainly made of calcite exist, be contaminated with pyrites and with mica, which both different from the discoloration of the otherwise relative colorless calcium carbonates contribute.

Various suggestions have been made to improve whiteness the aforementioned naturally occurring calcium carbonates made. Many of these previous proposals will be Flotation process to remove contaminants from calcite-containing ores or minerals. The biggest However, part of this prior art focused on the removal of silica-like contaminants to achieve this to use cleaned product in cement production.

In some cases, flotation was also used to improve the whiteness properties of naturally occurring calcium carbonate recommended. Thus, according to that in US Pat. No. 3,512,722 described procedure a wet-ground, natural Calcium carbonate flotated, after which the as Underflow discharged material classified, partially drained, is dried and pulverized to form the agglomerates and crush larger particles.

A method of the type mentioned is known from US-PS 39 90 966 known. It is for cleaning pyrite impurities containing calcite ore using a flotation step of certain, cationic, surfactants intended. 1-Hydroxy- ethyl-2-heptadecenyl-glyoxalidine or 1-hydroxyethyl-2-alkyl- imidazolines or their salt derivatives used, wherein the alkyl part imidazoline is the alkyl portion of a fatty acid. The separated calcite is classified in the presence of a thickener let settle from a settling agent and dried.  

Another way of brightening natural, calcite-containing ores are disclosed in U.S. Patent 3,980,240. In this process, the ore is ground, an aqueous one Slurry made, the slurry coarsely ground and finely ground so that at least 70% of the particles are smaller than 2 µm, and then this finely ground, particulate material a separation step by using a magnetic field high intensity and / or by using flotation subject.

The known ways of working described above - with one exception the method of the last-mentioned US Pat. No. 3,980,240 - generally had limited performance in the production of calcium carbonate pigments with high Whiteness from highly contaminated, natural sources. Though the flotation mode of operation of U.S. Patent 3,990,966 may be a product with a whiteness of over 95, however achieved such results using a starting material, that initially had a whiteness of well over 94. Indeed, in most cases where pigments are on derived commercially from such natural sources, used an ore that is very high in purity at the beginning and is relatively free of discolouring contaminants. In this context, for example, the US-PS 3,661,610 and 3,674,529, in which the use of Calcium carbonate pigments is described, which from a raw, high-purity, natural lime chalk. This natural Chalk is subjected to a two-stage grinding process, whereby in this case the product is not required cleaning, d. i.e., to subject separation stages.

Although the operation of US-PS 39 80 240 in general very is powerful, it has nevertheless been found to have certain disadvantages occur when a finely ground carbonate, d. that is delivered material from the second fine grinding stage, refined shall be. Because such finishing stages usually at  relatively low solids, typically less than 50% by weight solids can be carried out in particular Problems with the subsequent stage of removal of water from the slurry may occur. In particular it was found that the dewatering of slurries of finely ground carbonates is very difficult, e.g. B. if the particulate material is such that 80% by weight or more of the particles have less than 2 µm to be one To achieve solids content at which such a slurry can be shipped commercially, d. H. one Solids content of preferably greater than 70%. As below is explained in more detail, it was found that at grinding the ore into very fine particles separating the colored grains so thoroughly and evenly be distributed in the material from which they are subsequently made should be removed that the performance of the flotation is inhibited to a large extent and the extraction of salable product from the flotation level greatly reduced becomes.

The object of the invention is therefore a method of the beginning mentioned type to create that the use of raw materials with relatively high levels of discolouring contaminants as well as obtaining a slurry, pumpable product with a high solids content and a whiteness of at least 94 enables. Furthermore, such a process is said to be finishing without negative effects on the subsequent drainage operations enable that as beneficial to Manufacturing a product in a commercial and technical advantageous form can be viewed.

To solve this problem, that specified in claim 1 Procedure proposed. The term G.E. scale refers rely on measurements of reflectance to determine the Whiteness as described in the TAPPI T-646-os-75  and T-452-os-77. The scale for the whiteness standard based on the reflection of magnesium oxide of 100.00; Reflection is measured at 457 nm.

Preferred embodiments are in the subclaims remove.

The delivery product in particular has less abrasion than 25 mg, measured according to the Valley Abrasion Test using the methods prescribed by the Institute of Paper Chemistry How it works 65.

Dewatering can be done in conventional, in the field known facilities are carried out, including using rotary vacuum filters or using a Bird centrifuge known per se or the like Centrifuges.

Preferred means for use as a collector in foam flotation include the salts of 1-hydroxyethyl-2-alkylimidazolines, such compounds mixed with non-polar or nonionic, aliphatic hydrocarbons, are used, the latter materials apparently act as a promoter or amplifier. Especially if this preferred agents or compositions in foam flotation used, resulted from the inventive Process Products with whitenesses of at least 95 measured on the aforementioned G.E. scale. The salts are preferred in a concentration of about 0.5 to 2.5 kg / t Calcite ore and the aliphatic hydrocarbons in one Concentration of about 1.5 to 7.5 kg / t calcite ore used.

Details of the flotation agents described above are in the US-PS 39 90 966 specified. Preferred starting materials  in the process according to the invention, 1-hydroxylethyl-2-alkyl imidazolines, wherein the alkyl portion is the alkyl portion of a fatty acid with a carbon chain length of between 10 and Is 20 carbon atoms. Starting materials used in the the method according to the invention gave particularly good results, are alkylimidazolines in which the alkyl portion is the alkyl portion of oleic acid or tall oil. These compounds are on the market available. These compounds are easily broken down into salts Add the appropriate acid converted in the required amount. Acetates are preferably used as salts. In the following examples, the acetate salt of 1-hydroxyethyl 2-oleylimidazoline used.  

It has been found that the salts and especially the acetate salts of the aforementioned compounds when used in Combination with aliphatic hydrocarbon compounds with a carbon chain length of 10-20 carbon atoms remarkably powerful at removal of insoluble, mineral impurities from natural, calcite-containing ores or Are minerals.

The hydrocarbon can be a mixture of compounds of the appropriate chain length, where the most accessible and cheapest materials Are kerosene or heating oil. A highly purified one is preferred Material used that is essentially kerosene is similar, from which, however, practically all aromatic or cyclic compounds removed by chemical means were. A composition of this kind is straightforward commercially available, and is referred to in the examples as 01 22 51. These materials are because of their performance and low Toxicity beneficial.

Other, less preferred collectors that use foam flotation of the method according to the invention are useful include xanthates such as potassium ethyl xanthate at typical concentrations of 0.05 kg / t solids, Amines and their salt derivatives are also available as usable, cationic collectors known. Different hydrocarbons including kerosene, heating oil, mineral oil or mineral oil fractions added as flotation promoters can also be used. In Foaming agents such as spruce oil, cresol, Polypropylene glycol ether or other well known means of this Type can be used.  

The obtained using the method according to the invention Product has proven to be particularly well suited for paper coating applications or paper coating purposes. In such an application, the product has one significantly less harmful influence on the color absorption capacity as precipitated carbonates, and the product owns continue to have a less harmful impact on the Gloss of coated or coated papers than conventional ground carbonates.

Preferred embodiments are explained in more detail below. to the performance of the invention To demonstrate the process using a number of examples.

Example 1

In this example, samples were taken from various calcite deposits used, the samples being high in calcium and as impurities - among other elements - fine quartz, sand, mica and lots of fine Contained pyrites.

In this example, a sample of natural calcite, which came from Phillipsburg, Quebec, and the one previously indicated Had a previous crushing in one Subjected to press, then it was further used crushed a cone crusher. The sample was then under Using a ball mill at 65% solids wet-ground, to provide a particulate material in which 28% by weight the particles were less than 2 µm in size and no more than 2% by weight of the particles were larger than 0.044 mm. During the ball milling a sodium polyacrylate composition as a dispersant at a concentration of 4.5 kg / t solids added to facilitate grinding.  

The mineral's whiteness at that time was on the G.E. scale determined to be 93.6. The details of the whiteness values were in all cases according to the standard of TAPPI Obtained T-646-m-54.

Example 2

The material from Example 1, which is in shape at this time a slurry with 65% solids was on Diluted 25% solids and became a foam flotation using a combination of kerosene, 0.075 kg / t, and a xanthate at a concentration of 0.05 kg / t as a collector. 0.05 kg / t Spruce oil and 0.08 kg / t of an agent in the form of straight-chain, higher alcohols were added as foaming agents. The pH during the flotation treatment was about 9.5. The purified product obtained showed a G.E. whiteness from 94.5.

Example 3

The one used as the material used for Example 1 is not processed material was wet-ground at 70% Solids in a sand mill using Ottawa sand finely ground as grinding medium. To facilitate grinding was added 4.5 kg / t of sodium polyacrylate agent used. This polyacrylate agent at the specified concentration was also used in all the following examples, if sand grinding was carried out. The grinding was up to one Point continued at which 96 wt .-% of the particles a Equivalent sphere diameter of less than 2 µm.

The whiteness of the material was that shown in Example 1 Value dropped from 93.6 to 93.2.  

Example 4

The floated carbonate material from Example 2 was included 3.5 kg / t calcium chloride flocculated and at 70% solids filtered, then it became fine grinding by wet grinding the previously coarsely ground product with ottawa sand, as in Example 3. This fine grinding was at 70% solids and for adequate Period of time to crush the particles in such a way that 95% of the particles have a sphere equivalent diameter of less than 2 µm. It was found, that the floated, sand-ground product G.E. whiteness of 95.8.

When comparing the whiteness achieved in Example 3 with the whiteness achieved in Example 4, i.e. H. 93.2 against 95.8, it can be seen that a comparatively enormous difference was achieved. Is of equal importance the fact given in Example 3 that the one found here Whiteness actually as a result of the fine grinding process had fallen off. The latter is believed to be the latter Result can be explained by the hypothesis that the relatively coarse, released in the initial grinding stage Color bodies have a limited effect on whiteness measurement possess when distributed discretely in the material are. After another grinding to a very However, the colored bodies are in a fine state of comminution distributed more evenly, which makes a disproportionate Effect on whiteness.

Using the procedure of Example 3 of US Patent 36 04 634 the particle size was that of interest according to the invention Reduced size; however, it was found that the whiteness of the original material (Example 1) from 93.6 to 93.2 as Result of the fine grinding had dropped.  

On the other hand, flotation of the material from Example 1 gives as in Example 2, only a minor improvement in whiteness of 0.9 units. According to the present invention however, the specific combination and sequence of Flotation and fine grinding unexpectedly a product with the desired size properties (as with the US PS 36 04 634) and with an increase in the degree of whiteness, which is due to the the operation of Example 2 and Example 3 achieved whiteness exceeds.

It can be seen from this that there is a synergistic effect in the process according to the invention. If the increase in the degree of whiteness achieved in the fine grinding is denoted by X units, where X can be positive or negative, the increase achieved in the flotation is denoted by Y units and the increase achieved in the process according to the invention is denoted by Z units, it is readily apparent that Z is greater than the sum of X and Y.

The initial coarse grinding process, as in the invention Procedure can be carried out according to various work in a manner known in the field, e.g. B. by wet grinding in a ball mill or by wet, autogenous grinding or by dry grinding. The fine grinding stage is preferably carried out, as in Example 4, by sand grinding, d. H. by grinding with a particulate grinding material, that consists of particles that are usually in the Size range from about 150 microns to 6.35 mm and preferably from about 500 µm to about 2 mm. Details of the sand grinding process including the naming of equivalents Materials for use in sand milling are available in the U.S. PS 36 04 634 indicated, as can those in this US-PS specified conditions of grinding as preferred embodiment with regard to the invention Procedure are considered. The fine grinding stage results in an output product in which at least 80% by weight of the obtained  Particles with a sphere equivalent diameter of less than 2 µm own, whereby the product continues to be a whiteness from at least 94 and preferably from at least 95 the G.E. scale.

Example 5

In this example, a sample of coarse calcite-containing Mineral with a grain size larger than 0.149 mm used from a deposit in Maryland. The sample was ball milled, 4.5 kg / t of sodium polyacrylate at 65% solids were used by 2% particles larger than 0.044 mm and 17% smaller than 2 µm Ball equivalent diameter, each in weight. At this point, the whiteness was 90.1. After the product had been sand-milled with the addition of 4.5 kg / t of Sodium polyacrylate agent, the whiteness was at 88.7 fallen off.

When using the coarsely ground material at 25% solids of 0.5 kg / t of a monoamine flotation, the whiteness was 94.4 increased. The floated product was then dewatered, flocculated (with 3.5 kg / t CaCl₂) and filtered and at 70% solids with 4.5 kg / t of the sodium polyacrylate agent sand milled. As a result, the whiteness had risen to 95.8.

In both cases, the sand-ground product contained 90% by weight Particles with a sphere equivalent diameter of less than 2 µm. The The difference in the whiteness values was 7.1 units.

Example 6

In this example, a sample of a mineral containing calcite used from an occurrence in Maryland, taking this sample was first dry ground and classified to a product obtained, in which 1 wt .-% of the particles larger than 0.044 mm and 15% by weight of the particles were smaller than 2 µm, the  Sample had an initial degree of 92.6. This sample was slurried to 67% solids and using of 4.5 kg / t of the sodium polyacrylate agent 90% sand milled to less than 2 µm. The whiteness as a result, fell to 90.5.

The same dry milled material was made up to 25% solids diluted and using 0.5 kg / t acetic acid salts of n-alkylamines and 4.5 kg / t of the sodium polyacrylate agent as a flotation agent floated at pH 9. The whiteness of the floated Materials was found to be 93.6.

The floated product from this process stage was under Use of 3.5 kg / t CaCl₂ dewatered and 90% less than 2 µm at 67% solids using 4.5 kg / t of the sodium polyacrylate agent sand-ground. The whiteness of the end product was 94.0. The difference in whiteness between the floated and non-floated, sand-ground products was 3.5 units.

Example 7

Another sample of an ore containing calcite ore in Maryland was dry ground and classified to to initially obtain a starting material in which 2% by weight of the particles larger than 0.044 mm and 18% by weight of the particles were smaller than 2 µm. The whiteness of this raw material was initially determined to be 90.7. The sample was used of 4.5 kg / t of the sodium polyacrylate agent 90% sand-milled to less than 2 µm, then was found that the whiteness had dropped to 90.3. In connection with this example and the previous example 6 It should be noted that certain advantages through the dry grinding mode of operation is given, in which the initial raw material is produced. In particular do not become dispersants at these early grinding stages used, which would otherwise give the possibility that  such dispersants through the later use of the Flocculants should be made harmless.

After diluting the used in this example Starting material on 25% solids and flotation using 6 kg / t kerosene and 1 kg / t N-tallow trimethylene diamine diacetate as Collector and 0.1 kg / t nonylphenoxypoly (ethyleneoxy) ethanol and 0.05 kg / t alkyl lauryl polyether as a foaming agent and implementation at a pH value from 8-9 the whiteness had risen to 92.2.

In this example, the flotation product was in one Büchner filter without using CaCl₂ as a flocculant dehydrated and then together with 4.5 kg / t of the sodium polyacrylate agent (Dispex) 90% to less than 2 µm ground. The final whiteness was determined to be 95.2.

From this it can be seen that the difference in whiteness between the floated and non-floated, sand-ground Products amounted to 4.9 units.

Example 8

The implementation of this example is similar to that of the Example 7 with the exception that the flotation, drainage and grinding stages on a larger scale of a technical Test facility were carried out. So it became Drainage in a Bird centrifuge instead of in a laboratory filter carried out. The source material was part of the general Type of material as it is in conjunction with the two previous examples were described and contained 15% by weight of particles with less than 2 µm. The flotation reagents used were the following:  

0.5 kg / tN-tallow trimethylene diamine diacetate 0.125 kg / t nonylphenoxy poly (ethyleneoxy) ethanol 0.075 kg / t alkyl lauryl polyether 6.0 kg / t kerosene

The whiteness determined for the original source material was 90.4. The whiteness of the sand-ground product was 90.5; The whiteness of the floated product was 93.5 and that of the floated, dewatered and sand-milled Product was 96.2. In all cases they corresponded Treatment levels to those of the previous examples. It is particularly noteworthy that the difference in the degree of whiteness between floated and non-floated, sand-ground Product was 5.7 units.

Example 9

In this example, a calcite mineral from Maryland, that is similar to that used in Examples 5 to 7 was treated. This mineral was determined to be contained the following impurities: orthoclase (potassium feldspar), Quartz, tremolite, phlogopite mica and pyrite, being the total amount of these impurities generally between 1.5 and 5 wt .-% of the calcite-containing mineral.

Samples of this mineral were dry ground and classified, to obtain starting materials in which 0.5% by weight of the particles larger than 0.044 mm and 22% by weight of the particles were smaller than 2 µm. These samples were at 25% solids slurried and using different Combinations of flotation reagents floated, including the aforementioned 1-hydroxyethyl-2-alkylimidazoline salts in combination with neutral, aliphatic hydrocarbons. In a typical way of working, the Collector (and if necessary the foaming agent) to the  Slurry added at the start of the flotation process. Approximately a third of the promoter was also the beginning of floating, and the remaining two thirds were added in portions, e.g. B. in a typical Flotation during 45 minutes can start with 1 kg / t amplifier added to the flotation and 0.5-1 kg / t in portions be added at 5-10 minute intervals.

The floated products were made using 3.5 kg / t CaCl₂ dewatered and then 90% less than 2 µm at 70% Solids using 4.5 kg / t sodium polyacrylate agent sand-ground, then the whiteness certainly. The whiteness of the floated product (before Sand grinding) was also measured, the in Acid-insoluble proportions in the samples both in the starting material as well as determined after the flotation. The Results obtained in these experiments are as follows Table I compiled:  

Table I

Because the materials floated in this example are relative have fine particle size and such a variety of mineral impurities - luckily all of them respond to cationic flotation - included is the Choosing a suitable cationic collector is difficult. The mechanism of adhesion of the collector to the mineral Contamination is due to electrostatic attraction cationic, polar group of the collector to the negative charged surface of the mineral. This is a comparative one weak mechanism compared to the adsorption or chemisorption mechanism used in the flotation of, for example Sulfides with xanthates takes place.

Therefore, the use of a collector is essential strongly charged, cationic, polar group to a ensure maximum attraction to the mineral. In this In case the mineral is coated by the collector reasonable collector concentration almost impossible because of the repulsive energy between neighboring, charged, ionic, polar groups of the collector. It is believed that the effect of the neutral hydrocarbon is to lower this recoil energy and the formation of a adequate coating of the collector to allow the Vesicle adhesion and thus allow the flotation to take place.

From Table I it can be seen that in the case of the considered Carbonate is the degree of whiteness of the sand-milled product finished slurry, the lower the content, the higher acidic components of the material the flotation is. The whiteness of the finished product is in all cases well over 95, and it can be seen, for example, that extremely high whiteness values are obtained when the starting material measured a relatively low level of contamination as components insoluble in acid. So lie  the whiteness values of the finished product in the case of the samples 5 and 6, which are 2.03 wt.% And 1.36 wt.%, Respectively, of insoluble in acid Materials included at 96.3 and 97.0, respectively.

In Table I, Samples 1 and 4 were used as comparative samples used to the superiority of the combination of Imidazoline / hydrocarbon versus a system of N-tallow show trimethylene diamine diacetate / foamer / kerosene. It can be seen that when using starting materials with both low and high whiteness Imidazoline system higher whiteness values of the floated product, lower levels of acid-insoluble residue and higher whiteness values of the sand-ground product results. In addition, a higher yield is achieved no separate foamer connection is required and the dose values of kerosene or other neutral hydrocarbons are reduced.

According to the invention, the aforementioned imidazoline salts to the slurried mineral in preferred concentrations from 0.5 to 2.5 kg / t of the calcite-containing mineral added in combination with the addition of the neutral hydrocarbon in concentrations of 1.5 to 7.5 kg / t of Minerals.

Example 10

In this example there was another mineral containing calcite from Maryland, which is similar to that of Examples 5, 6, 7 and 9 was treated. This mineral was initially dry milled and classified to get a raw material in which 99% by weight of the particles were smaller than 0.044 mm and 25% by weight of the particles less than 2 µm in sphere equivalent diameter exhibited. The starting material had an initial one Whiteness value of 92.4 and contained 3.0% of in Acid-insoluble components. If part of this raw material  slurried to 67% solids and 90-92% Whiteness was noticed to less than 2 µm 91.9 from.

The same dry milled material was made up to 25% solids diluted and using different combinations floated by collectors and amplifiers. The collector and the foamer (if any) became the Single dose slurry at the start of the flotation process added. When the amplifier was used, was about a third of the total at the start of flotation and the remaining two thirds in 0.25 kg / t aliquots added at 5-10 minute intervals, the total time flotation for all samples approximately 45 minutes amounted to.

The floated products of this way of working were dewatered and then sand-milled, in accordance with those in Example 9 described working methods. The whiteness of the floated product (before sand grinding) was measured, the insoluble in acid Shares and the amounts obtained in the flotation were determined and the whiteness of the floated samples after the Sand grinding (according to the procedure of example 9) was measured. The results achieved here are in the following Table II compiled.  

Table II

From Table II it can be seen that the invention Process results in a product that is whiteness in all cases of at least 95. Show the given values continue to use the superior results which of imidazoline salt derivatives compared to imidazoline, and in particular, these values show the excellent Improvements in whiteness, which through the combined Use of such salt derivatives with those previously specified aliphatic hydrocarbons were achieved. It should also be noted that the inventive Process an excellent reduction in acid insoluble shares is reached.

Claims (7)

1. A method for brightening a natural calcite-containing ore or mineral with the production of finely divided calcium carbonate particles with relatively very good whiteness properties, in which a first coarse grinding of the starting material is followed by a flotation treatment in an aqueous slurry with subsequent dewatering and a further fine grinding, characterized in that the coarse grinding takes place until the calcite-containing starting material is reduced in size, in which no more than 5% by weight of the particles have a grain size of more than 0.044 mm and no more than 35% a smaller sphere equivalent diameter than 2 μm, with this being a flotation stage foam flotation of the coarsely ground product in the form of an aqueous slurry containing less than 40% by weight solids with separation of the discolouring impurities with the foam, and dewatering of the product released as an underflow from the foam flotation followed by a solids content of at least 60% by weight and wet grinding of the dewatered product to form an output product in which at least 80% by weight of the particulate material obtained has a spherical equivalent diameter of less than 2 μm, the output product further being white is marked by at least 94 on the GE scale. 2. The method according to claim 1, characterized in that that the product of foam flotation to a solids content over 65% by weight is dewatered. 3. The method according to claim 1, characterized in that coarse grinding by dry grinding is carried out. 4. The method according to claim 1, characterized in that the output product by a whiteness of at least 95 is marked on the G.E. scale. 5. The method according to claim 1, characterized in that the coarsely ground product in the form of a less as an aqueous slurry containing 30% by weight solids is subjected to foam flotation. 6. The method according to claim 1, characterized in that that the flotation stage using a Flotation agent is carried out, this being a salt of a 1-hydroxymethyl-2-alkylimidazoline, in which the Alkyl part of imidazoline the alkyl part of a fatty acid with 10 to 20 carbon atoms in their carbon chain and that the flotation agent in conjunction with a  Amplifier is used, which is one or more aliphatic Hydrocarbons with a carbon chain length of 10 to 20 carbon atoms. 7. The method according to claim 1 or 6, characterized in that wet grinding by sand grinding is carried out.