ES2282015B2 - PROCEDURE FOR THE TREATMENT OF CAOLIN. - Google Patents

Abstract

Procedure for the treatment of kaolin. The object of the present invention is isostatic pressing with presence / absence of water as an essential variable during the industrial treatment of a kaolin, since it determines the degree of structural order of the kaolinite, as well as the morphology, particle size and surface specific. It also allows to optimize the modified properties, being of great importance in the paper, ceramics, paints, plastics and rubber industries.

Description

Procedure for the treatment of kaolin.

Technical sector

The present invention belongs to the area scientific of mineral resources, specifically minerals and industrial rocks and within this the technological applications of the kaolin.

Possible interested industries are the wastebasket, ceramics, plastics, adhesives and rubber, paints and pharmaceutical as well as the extraction and treatment industries of kaolin.

Object of the invention

The object of the present invention is to isostatic pressing with presence / absence of water as variable essential during the industrial treatment of a kaolin, since determines the degree of structural order of kaolinite, as well as the morphology, particle size and specific surface. It also allows to optimize the modified properties, being of great importance in the paper, ceramics, paints, Plastics and rubber

State of the art

Commercial kaolin is a rock that contains a certain proportion of minerals from the kaolin group, which can be economically extracted and concentrated. The minerals of the kaolin they are: kaolinite, nacrite and dickite, three polytypes of Si_ 4 O 10 Al 4 (OH) 8, and halloysite Si_ 4 O 10 Al 4 (OH) 8. 4H 2 O.

The current production of kaolin (including refractory clays) is about 40 million tonnes / year (Dickson T., Harben PW 2000. "Global Kaolin. Supply and industry structure". In: Industrial Clays (3 rd Ed. ) Industrial Minerals, London: 39-47.) Of which approximately 10 million come from the USA, especially from the deposits in Georgia; 2.3 million from the United Kingdom (St. Austell area) and 1.3 million from Brazil from the Amazon tertiary basin. This last value has increased to 1.7 million in 2000 (Industrial Minerals, July 2001. Mineral Spotlight "Kaolin", 21).

Annual production growth is 3%, although for paper kaolin it is only 2% because more and more it is replaced by other products (precipitated calcium carbonate, PCC; talcum powder). Other kaolin producers are France, Germany, Czech Republic, Ukraine, South Korea, China, India, Malaysia, Thailand, Iran, Mexico, Australia, Turkey, Egypt and Spain. In In the next few years Brazil will produce 10% of the production World and China will also be one of the largest producers.

The most important properties of a kaolin they are: chemical inertia before a wide range of pH, excellent dispersion in water, homogeneous particle size and the order of micron, low viscosity for high solids concentrations, high whiteness and brightness, opacity, good ink receptivity, good adherent and covering properties, low requirement of adhesives or glues, low abrasiveness, low electrical conductivity and thermal, low price, etc. At the same time it is also a subject Easy molding plastic, which regulates the rheological properties and the thickness of walls in the molds, with high mechanical resistance raw and cooked, refractory, which develops a porosity closed during vitrification, which cooks white, etc. The First properties are of great interest as cargo (paper, plastic, rubber, paints, fiberglass) and for coating or paper coating. The second are essential for ceramics Fine, glazed and refractory.

In the year 2000 the use of kaolin worldwide It was as follows (Industrial Minerals, July 2001):

- Paper industry: 45%

- Refractories: 16%

- Ceramics: 15%

- Fiberglass: 6%

- Cement: 6%

- Rubber and plastic: 5%

- Paint: 3%

- Catalysts: 2%

- Others: 2%

Physical properties and kaolin physicochemical depend heavily of the kaolinite properties, as well as the shape and size of its particles, granulometric distribution and structural order. All This conditions its possible application as an industrial rock.

The diffraction profiles of X-rays (DRX) for different kaolinites reveal the existence of a great variation in the structural order of this mineral. Bridley & Robinson (1946) studied by different DRX types of kaolinite and found a sequence of degree of order structural decrease from the kaolinite of perfect symmetry triclinic to halloysite, in its dehydrated form, which has a sequence of completely messy layers. They also deduce that the  structural disorder causes the weakening of some reflections and the appearance of bands. This structural variability of kaolinite is directly related to applications industrialists of the kaolin, since different authors have established significant correlations with certain technological properties such as: plasticity (Gomes C. (1988) Argilas. Or that s \ hat {a} or e to serve. Fundaçao Calouste Gulbeken, 458 pp .; Chavez, CL., Johns W. (1995) Mineralogical and ceramic properties pf refractory clays from central Missouri (USA). Applied Clay Science, 9: 407-424), whiteness (Velho J.A., Gomes C. (1991) Characterization of Portuguese kaolins for the paper industry. Beneficiation throght new delamination techniques. App. Clay Sci. 6, 155-170), viscosity (Murray H.H., Lyons S.C. (1956) Correlation of paper-coating quality with degree of crystal perfection of kaolinite. Proc. 41 th Nat. Conf. Clays Clay Miner., 4, 31-40; Velho & Gomes, 1991).

The effects of the degree of structural order of kaolin when used in the paper industry were studied by Murray & Lyons (1956) concluding that how much greater is the perfection of kaolinite crystals, the kaolin is more suitable for use as stucco, and more crystals Cluttered are more suitable for loading. These authors determined that the viscosity of a kaolin is lower the higher It is the degree of structural order of kaolinite. Velho & Gomes (1991), also in relation to the use of kaolin in industry of the paper, indicated that there is a relationship directly proportional between the degree of structural order of kaolinite and the whiteness, and inversely proportional to the viscosity.

The kaolin for ceramic use must produce white pieces of high mechanical resistance after high temperature cooking (Loughbrough R. (1993) Kaolin producers move upmarket. Industrial Minerals. October 1993, 51-69). The kaolinites of high degree of structural order present less plasticity than the disordered ones, probably because they have crystals of smaller thickness and dimensions (Gomes, 1988). Chàvez & Johns (1995) also found this relationship between plasticide / crystallinity of a series of highly plastic clay samples
illitic

In the plastics, adhesives and rubber industries, the usefulness of kaolin is because it replaces resins as a more economical load. The characteristics that must be met are: fine and uniform particle size, low oil and moisture adsorption and good dispersibility. According to Yvon et al . (1980) when a kaolin is used as a load in the manufacture of rubber, the kaolinite must have the highest degree of structural order possible. (Yvon J., Cases JM, Lietard O., Garin P., Lhote F. (1980) Influence des propriétes des charges kaoliniques sur les performances des caoutchoucs naturals charges. Clay Minerals 15: 351-368).

In the manufacture of paintings the kaolin is a competitive material with other products in terms of whiteness and hydrophilic capacity, although it fails to achieve on its own the hiding power of other white pigments. In this industry they must used kaolins that have high order kaolinite structural, since whiteness is directly proportional to same (Velho & Gomes, 1991).

In the pharmaceutical industry it is used as an inert in cosmetics and as an active element in stomach absorbers. The importance of controlling the degree of structural order of kaolinite in this industry was revealed by Delgado et al . (1994) (Delgado R., Delgado G., Ruiz A., Gallardo V., Gamiz E. The crystallinity of several Spanish kaolins: Correlation with sodium amylobarbitone release '' Clay Minerals, 29: 785-797), since controlling The particle size and mineralogical composition, together with the degree of structural order of the kaolinite, which acts as an excipient, can delay the release of the active substance.

From all this the importance of industrially control the degree of structural order of the kaolinite, evaluate the changes caused in kaolinite by effect of confinement pressure in the absence / presence of water, and relate the results obtained with properties of interest industrial of the kaolins.

Description of the figures

Figure 1.- Schematic of isostatic pressing.

It involves introducing the kaolin in a bag of rubber and this in turn in a container full of water on which Pressure is exerted by a pump. The pressure is exerted on the kaolin in all directions, so it is called from confinement. The time to get the final pressure has been 1 minute and has remained up to 1, the pressure range selected has been 1000, 1700, 2500 and 4000 kg / cm2.

Figure 2.- Percentage variation of the index of Hinckley of kaolins under pressure in absence (a) and presence (b) of water.

Figure 3.- Percentage variation of the index of Aparicio-Galán-Ferrell de kaolines under pressure in the absence (a) and presence (b) of water.

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Description of the invention

The object of the present invention is to isostatic pressing with presence / absence of water as variable essential during the industrial treatment of a kaolin, since determines the degree of structural order of kaolinite, as well as the morphology, particle size and specific surface. The introduction of an isostatic pressing phase in the treatment industrial kaolin, and the control of the presence / absence of water during this phase, allows modifying properties of interest Industrial in the kaolins.

Specifically the industrial treatment of kaolin It consists of the following stages:

to)

dispersion,

b)

fraction removal> 44 \ mum,

C)

separation of fractions by centrifugation

d)

delamination of thick fractions and centrifugation fractionation,

and)

impurity separation by flotation, flocculation or magnetic separator in fine kaolin

F)

chemical treatment

g)

filtration, with water removal and salts up to a concentration of 60% solids

h)

he drying, spraying or formation of high concentration slippers (70% solids)

i)

packing

For the realization of the proposed invention, an isostatic pressing phase (or of confinement) after the chemical treatment stage, establishing in said phase as an essential parameter the control of the  presence / absence of water mixed with the kaolin, varying the water ratio of 1: 1 to 10: 1 water: kaolin. The system selected must allow pressure to be exerted similar in all directions on the kaolin, for which this it is introduced (with or without water) in a rubber bag and this inside the  sinus of a container full of water, on which a pressure (1000, 1700, 2500 and 4000 kg / cm2). Temperature during the pressing phase it can range between temperature ambient and 300 ° C. The time to get the final pressure has been 1 minute and has remained at final pressure for 10 minutes The effect caused by the pressures exerted has been determined to the extent of the degree of structural order of the Kaolinite, BET specific surface and microscopy morphology scanning and transmission electronics.

It has been proven that the presence / absence of water controls the variations caused by the pressure of confinement reflecting this influence on variations structural aspects of kaolinite, and changes in morphology, size of particle and BET specific surface, which are properties High value techniques in the paper, ceramic, paints, plastics and rubber, so the results obtained can be used in the industries to improve these properties when interested according to product requirements wanted.

Specifically the absence of water during the Pressing process produces a decrease in the degree of order structural, an increase in specific surface area and a loss of pseudohexagonal morphology linked to a rounding of crystal edges and particle size decrease. By on the contrary the presence of water during the pressing process causes the degree of structural order of the kaolinite and in some cases it increases, a decrease in specific surface and that the size of the crystals is maintained and pseudohexagonal morphology.

The results obtained show that the introduction of an isostatic pressing phase in the process of industrial treatment of kaolin allows to modify properties of technological interest, by controlling the presence / absence of water, since the effect of pressure on the properties It depends on the presence of this fluid.

Physical properties and physical-chemical of the kaolin largely depend on  the properties of kaolinite, such as the shape and size of its particles, granulometric distribution and degree of order structural. All this determines the application of the kaolin as industrial rock

For example in the paper industry The greater the perfection of kaolinite crystals, the kaolin is more suitable for use as stucco, and crystals More messy are more suitable for loading. In relation to the application of ceramic kaolins, it has been proven that high-grade kaolinites of a structural order present less plasticity that disordered, probably because they have crystals of smaller thickness and dimensions, in addition to ceramics made with messy kaolinites present greater transparency than those made with orderly kaolinites. In the plastics, adhesives and rubber industries, the characteristics It must meet: fine and uniform particle size, low oil and moisture adsorption and good dispersibility; also when a kaolin is used as a load in the manufacture of rubber, kaolinite must present the highest degree of order structural possible.

In the manufacture of paints should be used kaolins that have high-grade kaolinite of structural order, since whiteness is directly proportional to it. Finally, in the pharmaceutical industry it is used as inert in cosmetics and as an active element in stomach absorbers, and by example controlling particle size and composition mineralogical, together with the degree of structural order of the Kaolinite, when it acts as an excipient, the delayed release of the active substance.

It has also been proven that there is a relationship directly proportional between the degree of structural order of the kaolinite and whiteness, and inversely proportional to the viscosity.

From all this the importance of industrially control the degree of structural order of the kaolinite, that is why this research work is based on evaluate the changes caused in kaolinite by the effect of confinement pressure in the absence / presence of water, and relate the results obtained with properties of interest industrial of the kaolins.

Specifically with the research carried out, verified that the absence of water during the pressing process produces a decrease in the degree of structural order, an increase of the BET specific surface and a loss of morphology pseudohexagonal attached to a rounding of the edges of the crystals and decrease in particle size. On the contrary the presence of water (in a 1: 1 ratio) during the process of pressing causes it to remain and even increase the degree of structural order of kaolinite, a decrease in surface area BET specific and that the size of the crystals and the pseudohexagonal morphology.

Embodiment of the invention

For the realization of the present invention, they have selected six kaolins of different degree of order structural, most of them used in ceramics, load in paper, plastic and paints and as coated in paper.

These kaolins once characterized from chemical, mineralogical, morphological point of view have undergone an isostatic pressing treatment, in which the effect of Pressure is similar in all directions. The kaolin (with or without water) has been placed in a plastic bag and inside the breast of a container full of water in which it has been subjected to pressure as indicated in figure 1. The time until the final pressure has been 1 minute and has remained at final pressure for ten minutes; the selected pressure range has been of 1000, 1700, 2500 and 4000 kg / cm2.

The effect caused by the pressures exerted has been determined to the extent of the degree of structural order of the Kaolinite, BET specific surface and microscopy morphology scanning and transmission electronics. The degree of structural order of kaolinite has been determined by diffraction of X-rays (Hinckley indices, 1963 and of Aparicio-Galán-Ferell, 2001; and by measure of the expert system of Plançon & Zacharie, 1990).

The pressure exerted in the absence of water produces a reduction in the degree of order of kaolinite, especially associated with interlaminar displacements of the type b / 3 (band 02 /, 20 ° -23 ° ° 2? Cu K ?), By the On the contrary, if the kaolin mixed with water is introduced (in a 1: 1 ratio) the degree of structural order is maintained and even increases, as evidenced by the results obtained from the measurement of the Hinckley and Aparicio-Galán-Ferrell indices (Figures 2 and 3). In these figures it can be seen that the percentage of variation of the Hickley and Aparicio-Galán-Ferrell indices, in the absence of water, indicates the transition from high-grade kaolinite of structural order to kaolinite of medium or low structural order, producing a decrease that ranges between 30% and 50%. On the contrary, the presence of water (1: 1 ratio) keeps the degree of structural order high in all cases, and a significant increase from 1000 kg / cm2 also occurs, especially in accordance with the Aparicio-Galán-Ferrell index that at 4000 kg / cm2 has increased between 20 and 50% in the kaolins studied (Figure 3b).

These results, especially those obtained with the index of Aparicio-Galán-Ferrell, they are agreement with those obtained through Plançon's expert system & Zacharie, since the percentage of phase well crystallized decreases during dry pressing and increases with pressing in damp.

Parallel to the BET specific surface of the kaolinite increases (in a range between 2% and 10%) in absence of water and remains or decreases slightly (in a range between 2% and 5%) in the presence of water. In relation to the morphology the pressure exerted in dry causes the crystals lose their pseudohexagonal morphology, that the edges are rounded and that the aggregates of vermicular kaolinite crystals or type Book fracture. On the contrary when introducing water into the morphology system apparently undergoes no change and the particle size does not decrease. These effects caused in the Morphology can be used to improve processes of delamination that are carried out in kaolins.

In conclusion, the results obtained demonstrate that the introduction of an isostatic pressing phase in the process of industrial treatment of kaolin allows modify properties of technological interest, by controlling the presence / absence of water, since the effect of pressure on The properties depend on the presence of this fluid.

Claims (10)

1. Procedure for the treatment of kaolin which includes the stages of:

to)

dispersion,

b)

fraction removal> 44 \ mum,

C)

separation of fractions by centrifugation

d)

delamination of thick fractions and centrifugation fractionation,

and)

impurity separation by flotation, flocculation or magnetic separator in fine kaolin

F)

chemical treatment

g)

filtration, with water removal and salts up to a concentration of 60% solids

h)

he drying, spraying or formation of high concentration slippers (70% solids)

i)

packing

and characterized in that it is subjected to isostatic pressing. 2. Procedure for the treatment of the kaolin according to claim 1 characterized in that the isostatic pressing takes place after the chemical treatment and before the filtration. 3. Procedure for the treatment of the kaolin according to claims 1 to 3 characterized in that the isostatic pressing step is carried out in the presence of water in water / kaolin ratios between 1: 1 and 10: 1. 4. Procedure for treating the kaolin according to claims 1 to 3, characterized in that the isostatic pressing stage is performed in the absence of water. 5. Procedure for the treatment of the kaolin according to claims 1 to 5 characterized in that the isostatic pressing step is carried out at a pressure between 1000 and 4000 kg / cm 2, the maximum pressure being maintained for 10 minutes. 6. Procedure for treating the kaolin according to claims 1 to 5, characterized in that the isostatic pressing step is carried out at a temperature between room temperature and 300 ° C. 7. Procedure for treating the kaolin according to claims 1 to 3, 5 and 6 characterized in that when the isostatic pressing is carried out in the presence of water,

to.

he degree of structural order of the kaolin is increased by a range between 20% and 50%

b.

the BET specific surface area decreases in a range between 2% and 5%

8. Procedure for the treatment of the kaolin according to claims 1, 2, 4 to 6 characterized in that when the isostatic pressing is performed in the absence of water,

to.

he degree of structural order of the kaolin decreases in a range between 30% and 50%

b.

the BET specific surface area increases in a range between 2% and 10%

C.

he particle size decreases

d.

be It produces a loss of the initial morphology of the kaolin.

9. Use of the kaolin obtained through a method according to claims 1 to 3, 5, 6 and 7 as stucco in the paper industry and in the manufacture of rubber and painting. 10. Use of kaolin obtained through a method according to claims 1, 2, 4 to 6 and 8 as a load in the paper industry and in the manufacture of ceramics.