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Mineralogy, chemistry and potential applications of a white bentonite in San Juan province, Argentina
Applied Clay Science 25 (2004) 237 – 243 www.elsevier.com/locate/clay
Technical Note
Mineralogy, chemistry and potential applications of a white bentonite in San Juan province, Argentina Wanda A. Allo *, Haydn H. Murray Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA Received 26 June 2003; received in revised form 2 October 2003; accepted 29 October 2003 Available online 22 January 2004
Abstract A white bentonite deposit of Pleistocene age located in San Juan Province, Argentina, has very promising commercial applications because of its mineralogy and physical and chemical properties. The bentonite occurs in the Lower Member of the Las Trancas Formation which is a hydrothermally altered rhyolitic to rhyodacitic pumice and breccia. Analysis shows the major minerals present are smectite and opal-CT along with minor amounts of quartz, clinoptilolite, feldspar and biotite. The majority of the quartz, clinoptilolite, and biotite occurs in the >325 mesh fraction. The smectite is mainly a sodium montmorillonite along with some calcium and magnesium in the exchange positions. The < 2 Am fraction consists of almost pure smectite and opal CT. Scanning electron micrographs show a typical ‘‘corn flakes’’ texture, which is characteristic of sodium montmorillonite. The physical and chemical properties including particle size, surface area, water and oil absorption, swelling index, cation exchange capacity, viscosity, and brightness indicate after wet beneficiation, that the processed white bentonite could be used in many industrial applications. These include paper coating and filling, paint, pharmaceuticals, cosmetics and filtering agents. Also the fine particle size fraction of < 2 Am could be used to make an excellent quality organoclay. D 2004 Elsevier B.V. All rights reserved. Keywords: White bentonite; Namontmorillonite; Industrial applications; Argentina
1. Introduction Bentonites are rocks that are composed dominantly of smectite. Many definitions conclude that these rocks were formed from the alteration of volcanic ash and tuff. As Elzea and Murray (1994) pointed out, it is difficult to apply a definition for an industrial mineral * Corresponding author. Tel.: +1-812-855-7899. E-mail addresses: [email protected], [email protected] (W.A. Allo). 0169-1317/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2003.10.003
that is based on origin and restricted to a specific parent material. Thus, the definition which states that bentonite is a clay consisting of smectite minerals regardless of origin or occurrence (Grim, 1973) seems to be a better one for an industrial mineral. Bentonites are important due to their physical properties, which make them valuable to a great variety of industries. Not only their rheological and absorbant properties are important, but also the cation exchange capacity, plasticity, high bonding strength, and swelling capacity.
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The major uses of bentonites in industry are as foundry sand bonds, drilling mud, pet litter and iron ore pelletizing. Many special and more refined uses are now in place such as filtering agents, water impedance, cosmetics, foods, pharmaceuticals, thickeners and extenders for paints, additives in ceramics, coating and filling of paper, organoclays and acidactivated bleaching earths. Each of these industrial applications requires specific properties and characteristics. Among the most valuable characteristics is the color, a function of the parent rock and its alteration. Isomorphous substitu-
tion of iron is responsible for the color in many bentonites. They are often green or gray and sometimes yellowish which precludes their use in many potential applications. White bentonites are rare and find use not only traditional applications, but especially in ceramics, paper, cosmetics, paint, wine clarification and pharmaceuticals. The price of white bentonite increases as much as 100– 1000% in comparison with regular bentonites (Murray, 2002). In Argentina, in San Juan province, a white bentonite deposit has been discovered (Fig. 1). This bentonite deposit of Pleistocene age occurs in the
Fig. 1. Location map.
W.A. Allo, H.H. Murray / Applied Clay Science 25 (2004) 237–243
Las Trancas Formation (De los Rios et al., 1995). The Lower Member of this geological unit is comprised of hydrothermaly altered rhyolitic to rhyodacitic pumices and breccias intruded by andesitic dikes. The thickness of the altered zones varies from centimeters up to 2 m. Minimum reserve estimates are at least 5 million tons. The aim of this study is to present the physical and chemical properties of the white bentonite in the Las Trancas formation and to discuss its potential industrial applications.
2. Methods of analysis The mineralogy of bulk, < 325 mesh and < 2 Am fractions were determined by X-ray diffraction using a Phillips XRG 3100 unit with CuKa radiation. Micrographs of the general texture and special fea-
239
tures were taken with a JEOL 5800 LV scanning electron microscope. The 325 and 200 mesh percentages were obtained by wet sieving and the < 2 Am by centrifugation at 750 rpm for 3V30U. The particle size distribution of the < 325 mesh material was determined using a Sedigraph 5100. Chemical analyses of the major oxides were obtained by ICP and the minor elements by ICP-MS after total digestion. The swelling percentage was obtain by adding 5 g of dry sample to deionized water in a 100-ml graduated cylinder and recording the volume before and after 24 h. A suspension of 22.5 g of bentonite in 335 ml of distilled water was prepared for viscosity measurements using a Fann viscometer. The yield point was calculated from dial readings at 300 and 600 rpm. The pH was measured in 5% and 10% solid slurries.
Fig. 2. X-ray diffraction patterns of the greater and less than 325 mesh fractions. Sm: smectite; M: mica; Cl: clinoptilolite; Op-CT: opal-CT; Qz: quartz; Fd: feldspar.
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W.A. Allo, H.H. Murray / Applied Clay Science 25 (2004) 237–243
The cation exchange capacity was determined by the Methylene Blue method and the surface area was obtained by the multiple Point BET method using a NOVA 1200 High speed gas sorption analyzer. Brightness was measured before and after wet magnetic separation and leaching on a Technibrite Model TB-1C Opacity Tester. The magnetic separation was performed at 1 minute retention time and 20 kilogauss capacity. Sodium dithionite (Na2S2O4) at 2– 3 pH was used for leaching. The slurries were settled with the reagent for one hour and then filtered and washed. Chemical analysis, swelling, viscosity, CEC, pH, surface area and brightness were determined for the < 325 mesh and < 2 Am fractions. Absorption analyses were performed on the raw material fraction which was crushed and retained between 4 and 20 mesh. The absorption value was
determined for oil and water by adding 75 ml of each of the substances to 50 g of clay in glass tubes with a metal mesh bottom with 60j and 30j inclination, respectively.
3. Results and discussion The Las Trancas bentonite consists of Na-montmorillonite and opal-CT with minor amounts of biotite, clinoptilolite, quartz and feldspar. The X-ray diagrams of the < 325 mesh fraction showed the presence of montmorillonite and opal-CT revealed ˚ (Fig. 2). The other minor by a reflection at 4.07 A components are larger in size and were removed by screening whereas traces of biotite that remains in this fraction are extracted magnetically. A small reflection ˚ that indicate the presence of halite was at 2.82 A
Fig. 3. X-ray diffraction patterns of oriented < 2 Am fraction sample air dry and glycolated.
W.A. Allo, H.H. Murray / Applied Clay Science 25 (2004) 237–243
241
Fig. 4. Scanning electron micrographs. (a and b) General Na-montmorillonite texture; (c) curled edges; (d) glass shard replacement feature.
randomly detected in the preparations. Because of the arid environment, halite was precipitated at the surface. In the < 2 Am fraction, the clay is almost pure montmorillonite. X-ray diffraction shows it to be a ˚ in the Na-montmorillonite with a reflection at 12.5 A oriented air-dry diagram that when glycolated shifts to ˚ (Fig. 3). 17 A The scanning electron microscope reveals a typical sodium bentonite texture with curled and lighter edges due to the presence of opal-CT. Replacement features of glass shards are also present (Fig. 4).
The raw bentonite samples analyzed contain an average of 15% grit (325 mesh) and a particle size distribution of the < 325 mesh fraction indicating that 80% of the material is finer than 10 Am and 72% is finer than 2 Am. Chemically, the SiO2 and Al2O3 contents are comparable with Wyoming bentonite, as are the CaO, Na2O, K2O and MgO contents. Also the Na2O as well as the MgO content increases in the finer fraction while the CaO decreases. Also the silica content decreases 10% in the finer fraction while the
Table 1 Chemical composition of the < 325 mesh and < 2 Am fractions Fraction
SiO2
Al2O3
Fe2O3
MgO
CaO
Na2O
K2 O
TiO2
P2O5
MnO
Cr2O3
LOI
SUM
< 2 Am < 325mesh
60.33 66.02
17.34 15.52
1.65 1.46
3.37 3.22
0.96 1.02
3.01 1.85
0.44 0.49
0.04 0.04
< 0.01 0.02
0.05 0.05
< 0.001 0.002
13.1 10.8
100.29 100.49
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Fig. 5. Some minor elements concentrations in the < 325 mesh and < 2 Am fractions.
alumina increases, confirming the minor amount of opal-CT and a proportional increase in the clay content consistent with the X-ray data. It is interesting to note that the Fe2O3 and TiO2 values are much lower than in general purpose bentonites, which is reflected by the white color of the bentonite. The LOI is on average two to three times the value of other Nabentonites due to the presence of Opal CT (Table 1). Total metallic elements such as Pb, Ni, As and Hg display low values; Cu and Zn are higher but show a decreasing trend in the 2Am fraction (Fig. 5). The swelling, viscosity, CEC, surface area, pH and absorption results are shown in Table 2. As noticed
earlier halite is present in a few samples which may cause a higher viscosity. However, halite was only detected in one small area of the deposit. Magnetic separation and leaching of the bentonite improves its brightness and decreases the yellowness in the two analyzed fractions as shown in Table 3. Due to the opal-CT content the less than 325 mesh fraction is as white as the < 2 Am fraction, contrary to what was expected. Nevertheless the yellowness of the < 2 Am fraction is lower indicating a whiter color.
Table 2 Physical properties results
The low iron and quartz contents, low As, Pb and Hg values, excellent whiteness and good absorption
Analysis
< 325 mesh
< 2 Am
Fraction percentage (%) Swelling (ml) C.E.C. Surface area (m2/g) pH Viscosity Effective viscosity (cP) Plastic viscosity (cP) Yield point (lb/100 ft2) Absorption (%)
90 – 80 17 74 36.96 7.5
50 – 72 28 90 37.55 7.5
9 4 5 Total sample Water: 56 Oil: 15
54 11 43
4. Potential applications
Table 3 Brightness test results Magnetic and leaching tests Raw material After magnetic separation After leaching
< 325 mesh
< 2 Am
Average
b value
Average
b value
78.60 80.93
3.77 4.64
78.69 80.03
4.37 4.23
85.44
2.19
84.71
2.04
The b value illustrates the yellowness of the color, the lower the value the whiter the material.
W.A. Allo, H.H. Murray / Applied Clay Science 25 (2004) 237–243
make this material potentially valuable for the paper, cosmetics, pharmacy and/or food industries. Because of improvement of the whiteness and decrease of the yellowness in the < 325 mesh and < 2 Am fractions, as well as the absence of quartz and low content of opal-CT in the finer fraction, it can be a serious contender as a coating and filler additive for the paper industry. These same characteristics are also very valuable for the cosmetics and pharmaceutical industries. In addition, due to its particle size, rheological attributes, and chemistry it would be an excellent prospective material for making an organoclay. The bentonite could also be a potential raw material as a filtering agent for the wine or juice industry due to its good absorption and surface area characteristics. Although Na-bentonites have good protein absorption properties as well as good clarifying effects, the high swelling capacity leads to voluminous sediment in the wine. New combinations of sodium and calcium bentonites have been successfully tested and employed. The Provinces around the mining area are the center of a very well developed wine industry, thus this bentonite should be considered for clarifying and filtering the Argentinean and Chilean wines.
5. Summary The physical and chemical properties of the Las Trancas Formation white bentonite are suitable for several industrial applications.
243
This Pleistocene bentonite is the product of hydrothermally altered rhyolitic and rhyodacitic pumices and its brightness in the natural state is unusually high. The clay fraction which averages 60% of the total sample, is comprised of Na-montmorillonite and a small amount of opal CT. The particle size, absorption, swelling and viscosity properties along with the brightness make this bentonite potentially useful in high value added markets. The wet-processed material could be used as coating and filler additives for paper; cosmetics, pharmaceuticals, and food industries, filtering agent for wine and juice and organoclays.
References De los Rios, J., Sosa, H., Lara, R., Attala, L., Quispe, O., 1995. Relevamiento geologico, evaluacion de reservas y aptitud tecnica del yacimiento ‘‘Don Juan’’. Dpto. Iglesias-San Juan. Report Instituto de Investigaciones Mineras, Universidad Nacional de San Juan, Argentina. Elzea, J., Murray, H.H., 1994. Bentonite. In: Carr, D.D. (Ed.), Industrial Minerals and Rocks, 6th ed. Society for Mining, Metallurgy, and Exploration, Littleton, CO, pp. 233 – 246. Grim, R.E., 1973. Technical properties and applications of clays and clay minerals. Proceedings, International Clay Conference 1972 (AIPEA), Madrid, pp. 719 – 721. Murray, H., 2002. Industrial clays case study. Report of the Mining, Minerals and Sustainable Development Project, vol. 64. International Institute for Environment and Development and World Business Council for Sustainable Development, UK.
Technical Note
Mineralogy, chemistry and potential applications of a white bentonite in San Juan province, Argentina Wanda A. Allo *, Haydn H. Murray Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA Received 26 June 2003; received in revised form 2 October 2003; accepted 29 October 2003 Available online 22 January 2004
Abstract A white bentonite deposit of Pleistocene age located in San Juan Province, Argentina, has very promising commercial applications because of its mineralogy and physical and chemical properties. The bentonite occurs in the Lower Member of the Las Trancas Formation which is a hydrothermally altered rhyolitic to rhyodacitic pumice and breccia. Analysis shows the major minerals present are smectite and opal-CT along with minor amounts of quartz, clinoptilolite, feldspar and biotite. The majority of the quartz, clinoptilolite, and biotite occurs in the >325 mesh fraction. The smectite is mainly a sodium montmorillonite along with some calcium and magnesium in the exchange positions. The < 2 Am fraction consists of almost pure smectite and opal CT. Scanning electron micrographs show a typical ‘‘corn flakes’’ texture, which is characteristic of sodium montmorillonite. The physical and chemical properties including particle size, surface area, water and oil absorption, swelling index, cation exchange capacity, viscosity, and brightness indicate after wet beneficiation, that the processed white bentonite could be used in many industrial applications. These include paper coating and filling, paint, pharmaceuticals, cosmetics and filtering agents. Also the fine particle size fraction of < 2 Am could be used to make an excellent quality organoclay. D 2004 Elsevier B.V. All rights reserved. Keywords: White bentonite; Namontmorillonite; Industrial applications; Argentina
1. Introduction Bentonites are rocks that are composed dominantly of smectite. Many definitions conclude that these rocks were formed from the alteration of volcanic ash and tuff. As Elzea and Murray (1994) pointed out, it is difficult to apply a definition for an industrial mineral * Corresponding author. Tel.: +1-812-855-7899. E-mail addresses: [email protected], [email protected] (W.A. Allo). 0169-1317/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2003.10.003
that is based on origin and restricted to a specific parent material. Thus, the definition which states that bentonite is a clay consisting of smectite minerals regardless of origin or occurrence (Grim, 1973) seems to be a better one for an industrial mineral. Bentonites are important due to their physical properties, which make them valuable to a great variety of industries. Not only their rheological and absorbant properties are important, but also the cation exchange capacity, plasticity, high bonding strength, and swelling capacity.
238
W.A. Allo, H.H. Murray / Applied Clay Science 25 (2004) 237–243
The major uses of bentonites in industry are as foundry sand bonds, drilling mud, pet litter and iron ore pelletizing. Many special and more refined uses are now in place such as filtering agents, water impedance, cosmetics, foods, pharmaceuticals, thickeners and extenders for paints, additives in ceramics, coating and filling of paper, organoclays and acidactivated bleaching earths. Each of these industrial applications requires specific properties and characteristics. Among the most valuable characteristics is the color, a function of the parent rock and its alteration. Isomorphous substitu-
tion of iron is responsible for the color in many bentonites. They are often green or gray and sometimes yellowish which precludes their use in many potential applications. White bentonites are rare and find use not only traditional applications, but especially in ceramics, paper, cosmetics, paint, wine clarification and pharmaceuticals. The price of white bentonite increases as much as 100– 1000% in comparison with regular bentonites (Murray, 2002). In Argentina, in San Juan province, a white bentonite deposit has been discovered (Fig. 1). This bentonite deposit of Pleistocene age occurs in the
Fig. 1. Location map.
W.A. Allo, H.H. Murray / Applied Clay Science 25 (2004) 237–243
Las Trancas Formation (De los Rios et al., 1995). The Lower Member of this geological unit is comprised of hydrothermaly altered rhyolitic to rhyodacitic pumices and breccias intruded by andesitic dikes. The thickness of the altered zones varies from centimeters up to 2 m. Minimum reserve estimates are at least 5 million tons. The aim of this study is to present the physical and chemical properties of the white bentonite in the Las Trancas formation and to discuss its potential industrial applications.
2. Methods of analysis The mineralogy of bulk, < 325 mesh and < 2 Am fractions were determined by X-ray diffraction using a Phillips XRG 3100 unit with CuKa radiation. Micrographs of the general texture and special fea-
239
tures were taken with a JEOL 5800 LV scanning electron microscope. The 325 and 200 mesh percentages were obtained by wet sieving and the < 2 Am by centrifugation at 750 rpm for 3V30U. The particle size distribution of the < 325 mesh material was determined using a Sedigraph 5100. Chemical analyses of the major oxides were obtained by ICP and the minor elements by ICP-MS after total digestion. The swelling percentage was obtain by adding 5 g of dry sample to deionized water in a 100-ml graduated cylinder and recording the volume before and after 24 h. A suspension of 22.5 g of bentonite in 335 ml of distilled water was prepared for viscosity measurements using a Fann viscometer. The yield point was calculated from dial readings at 300 and 600 rpm. The pH was measured in 5% and 10% solid slurries.
Fig. 2. X-ray diffraction patterns of the greater and less than 325 mesh fractions. Sm: smectite; M: mica; Cl: clinoptilolite; Op-CT: opal-CT; Qz: quartz; Fd: feldspar.
240
W.A. Allo, H.H. Murray / Applied Clay Science 25 (2004) 237–243
The cation exchange capacity was determined by the Methylene Blue method and the surface area was obtained by the multiple Point BET method using a NOVA 1200 High speed gas sorption analyzer. Brightness was measured before and after wet magnetic separation and leaching on a Technibrite Model TB-1C Opacity Tester. The magnetic separation was performed at 1 minute retention time and 20 kilogauss capacity. Sodium dithionite (Na2S2O4) at 2– 3 pH was used for leaching. The slurries were settled with the reagent for one hour and then filtered and washed. Chemical analysis, swelling, viscosity, CEC, pH, surface area and brightness were determined for the < 325 mesh and < 2 Am fractions. Absorption analyses were performed on the raw material fraction which was crushed and retained between 4 and 20 mesh. The absorption value was
determined for oil and water by adding 75 ml of each of the substances to 50 g of clay in glass tubes with a metal mesh bottom with 60j and 30j inclination, respectively.
3. Results and discussion The Las Trancas bentonite consists of Na-montmorillonite and opal-CT with minor amounts of biotite, clinoptilolite, quartz and feldspar. The X-ray diagrams of the < 325 mesh fraction showed the presence of montmorillonite and opal-CT revealed ˚ (Fig. 2). The other minor by a reflection at 4.07 A components are larger in size and were removed by screening whereas traces of biotite that remains in this fraction are extracted magnetically. A small reflection ˚ that indicate the presence of halite was at 2.82 A
Fig. 3. X-ray diffraction patterns of oriented < 2 Am fraction sample air dry and glycolated.
W.A. Allo, H.H. Murray / Applied Clay Science 25 (2004) 237–243
241
Fig. 4. Scanning electron micrographs. (a and b) General Na-montmorillonite texture; (c) curled edges; (d) glass shard replacement feature.
randomly detected in the preparations. Because of the arid environment, halite was precipitated at the surface. In the < 2 Am fraction, the clay is almost pure montmorillonite. X-ray diffraction shows it to be a ˚ in the Na-montmorillonite with a reflection at 12.5 A oriented air-dry diagram that when glycolated shifts to ˚ (Fig. 3). 17 A The scanning electron microscope reveals a typical sodium bentonite texture with curled and lighter edges due to the presence of opal-CT. Replacement features of glass shards are also present (Fig. 4).
The raw bentonite samples analyzed contain an average of 15% grit (325 mesh) and a particle size distribution of the < 325 mesh fraction indicating that 80% of the material is finer than 10 Am and 72% is finer than 2 Am. Chemically, the SiO2 and Al2O3 contents are comparable with Wyoming bentonite, as are the CaO, Na2O, K2O and MgO contents. Also the Na2O as well as the MgO content increases in the finer fraction while the CaO decreases. Also the silica content decreases 10% in the finer fraction while the
Table 1 Chemical composition of the < 325 mesh and < 2 Am fractions Fraction
SiO2
Al2O3
Fe2O3
MgO
CaO
Na2O
K2 O
TiO2
P2O5
MnO
Cr2O3
LOI
SUM
< 2 Am < 325mesh
60.33 66.02
17.34 15.52
1.65 1.46
3.37 3.22
0.96 1.02
3.01 1.85
0.44 0.49
0.04 0.04
< 0.01 0.02
0.05 0.05
< 0.001 0.002
13.1 10.8
100.29 100.49
242
W.A. Allo, H.H. Murray / Applied Clay Science 25 (2004) 237–243
Fig. 5. Some minor elements concentrations in the < 325 mesh and < 2 Am fractions.
alumina increases, confirming the minor amount of opal-CT and a proportional increase in the clay content consistent with the X-ray data. It is interesting to note that the Fe2O3 and TiO2 values are much lower than in general purpose bentonites, which is reflected by the white color of the bentonite. The LOI is on average two to three times the value of other Nabentonites due to the presence of Opal CT (Table 1). Total metallic elements such as Pb, Ni, As and Hg display low values; Cu and Zn are higher but show a decreasing trend in the 2Am fraction (Fig. 5). The swelling, viscosity, CEC, surface area, pH and absorption results are shown in Table 2. As noticed
earlier halite is present in a few samples which may cause a higher viscosity. However, halite was only detected in one small area of the deposit. Magnetic separation and leaching of the bentonite improves its brightness and decreases the yellowness in the two analyzed fractions as shown in Table 3. Due to the opal-CT content the less than 325 mesh fraction is as white as the < 2 Am fraction, contrary to what was expected. Nevertheless the yellowness of the < 2 Am fraction is lower indicating a whiter color.
Table 2 Physical properties results
The low iron and quartz contents, low As, Pb and Hg values, excellent whiteness and good absorption
Analysis
< 325 mesh
< 2 Am
Fraction percentage (%) Swelling (ml) C.E.C. Surface area (m2/g) pH Viscosity Effective viscosity (cP) Plastic viscosity (cP) Yield point (lb/100 ft2) Absorption (%)
90 – 80 17 74 36.96 7.5
50 – 72 28 90 37.55 7.5
9 4 5 Total sample Water: 56 Oil: 15
54 11 43
4. Potential applications
Table 3 Brightness test results Magnetic and leaching tests Raw material After magnetic separation After leaching
< 325 mesh
< 2 Am
Average
b value
Average
b value
78.60 80.93
3.77 4.64
78.69 80.03
4.37 4.23
85.44
2.19
84.71
2.04
The b value illustrates the yellowness of the color, the lower the value the whiter the material.
W.A. Allo, H.H. Murray / Applied Clay Science 25 (2004) 237–243
make this material potentially valuable for the paper, cosmetics, pharmacy and/or food industries. Because of improvement of the whiteness and decrease of the yellowness in the < 325 mesh and < 2 Am fractions, as well as the absence of quartz and low content of opal-CT in the finer fraction, it can be a serious contender as a coating and filler additive for the paper industry. These same characteristics are also very valuable for the cosmetics and pharmaceutical industries. In addition, due to its particle size, rheological attributes, and chemistry it would be an excellent prospective material for making an organoclay. The bentonite could also be a potential raw material as a filtering agent for the wine or juice industry due to its good absorption and surface area characteristics. Although Na-bentonites have good protein absorption properties as well as good clarifying effects, the high swelling capacity leads to voluminous sediment in the wine. New combinations of sodium and calcium bentonites have been successfully tested and employed. The Provinces around the mining area are the center of a very well developed wine industry, thus this bentonite should be considered for clarifying and filtering the Argentinean and Chilean wines.
5. Summary The physical and chemical properties of the Las Trancas Formation white bentonite are suitable for several industrial applications.
243
This Pleistocene bentonite is the product of hydrothermally altered rhyolitic and rhyodacitic pumices and its brightness in the natural state is unusually high. The clay fraction which averages 60% of the total sample, is comprised of Na-montmorillonite and a small amount of opal CT. The particle size, absorption, swelling and viscosity properties along with the brightness make this bentonite potentially useful in high value added markets. The wet-processed material could be used as coating and filler additives for paper; cosmetics, pharmaceuticals, and food industries, filtering agent for wine and juice and organoclays.
References De los Rios, J., Sosa, H., Lara, R., Attala, L., Quispe, O., 1995. Relevamiento geologico, evaluacion de reservas y aptitud tecnica del yacimiento ‘‘Don Juan’’. Dpto. Iglesias-San Juan. Report Instituto de Investigaciones Mineras, Universidad Nacional de San Juan, Argentina. Elzea, J., Murray, H.H., 1994. Bentonite. In: Carr, D.D. (Ed.), Industrial Minerals and Rocks, 6th ed. Society for Mining, Metallurgy, and Exploration, Littleton, CO, pp. 233 – 246. Grim, R.E., 1973. Technical properties and applications of clays and clay minerals. Proceedings, International Clay Conference 1972 (AIPEA), Madrid, pp. 719 – 721. Murray, H., 2002. Industrial clays case study. Report of the Mining, Minerals and Sustainable Development Project, vol. 64. International Institute for Environment and Development and World Business Council for Sustainable Development, UK.