292
methylene blue than the red mud. Raw materials show the sorption capacities
1.4 × 10
−5
(fly ash) and 7.8 × 10
−6
mol/g (red mud), respectively. Heat treatment of
fly ash and red mud results in adsorption capacity reduction for both sorbents,
whereas the acidic treatment using HNO 3 results in an increase (fly ash)
(2.4 × 10
−5
mol/g) or decrease (3.2 × 10
−6
mol/g) of adsorption capacity. The
Redlich–Peterson model proves to be the best for description of the equilibrium
data. The methylene blue retention is endothermic.
Gupta et al. (2004) also applied red mud for methylene blue sorption as well as
fast green and rhodamine B removal. The percentage removals of dyes on red mud
were 92.5 (rhodamine B), 94.0 (fast green), and 75.0 (methylene blue), respectively.
The column studies give 95–97% removals of dyes. The adsorption is exothermic
in nature.
Namasivayam and Arasi (1997) and Namasivayam et al. (2002) proposed red
mud for Congo red (red mud after purification by ultra-pure water, then dried at
60 °C for 5 h) and procin orange removal. They obtained nearly quantitative removal
of Congo red at pH 2.0. The adsorption capacity of Congo red was 4.05 mg/g, and
the adsorption mechanism is mostly ion exchange, whereas procin orange was
removed in 82% (pH = 2).
11.4.3 Natural Materials
Natural materials group include clays, siliceous materials, and zeolites. The oldest
and well-known natural ceramic material is natural clay minerals. The clays are
minerals possessing fine particles having an average diameter of about 2 mm (colloid fraction containing soils, rocks, sediments, and water suspended in aqueous
solutions) which may be mixtures of clay-sized crystals, fine-grained clay minerals,
and other minerals, e.g., quartz, metal oxides, carbonate, etc. Clays play a significant role as adsorbents due to its abundance in nature in most continents of the
world, low cost (e.g., market price of montmorillonite – 0.04–0.12 $ per kg and is
about 20 times cheaper than commercial activated carbons), as well as high sorption
ability (layered structure with high surface area, high porosity and open porous
structure, rapid kinetics, e.g., Fuller’s earth). Presence of exchangeable ions on clay
surface makes them strong candidate for ion-exchange results in sorption of cations
and/or anions through ion exchange mechanism, e.g., montmorillonites possesses
high ability for positively charged ions. Clay materials possess a layered structure
and included among others serpentine, sepiolite, vermiculite, mica, kaolinite, smectites, Fuller’s earth, etc. (Crini 2006; Shichi and Katsuhiko 2000; Yagub et al. 2014).
Clays show a strong affinity for dyes (cationic, anionic), e.g., bentonite (fine powder) is effective sorptive material for different class of dyes (combination of sorption and ultrafiltration gives more better efficiency of dyes removal), and dye clay
complexes can be formed. The main limitation of application of clays is the fact that
such sorbents are not efficient for pollutants of an acid character, their sorption
efficiency strongly depends on pH, and in many cases they required chemical
A. Wołowicz and M. Wawrzkiewicz
methylene blue than the red mud. Raw materials show the sorption capacities
1.4 × 10
−5
(fly ash) and 7.8 × 10
−6
mol/g (red mud), respectively. Heat treatment of
fly ash and red mud results in adsorption capacity reduction for both sorbents,
whereas the acidic treatment using HNO 3 results in an increase (fly ash)
(2.4 × 10
−5
mol/g) or decrease (3.2 × 10
−6
mol/g) of adsorption capacity. The
Redlich–Peterson model proves to be the best for description of the equilibrium
data. The methylene blue retention is endothermic.
Gupta et al. (2004) also applied red mud for methylene blue sorption as well as
fast green and rhodamine B removal. The percentage removals of dyes on red mud
were 92.5 (rhodamine B), 94.0 (fast green), and 75.0 (methylene blue), respectively.
The column studies give 95–97% removals of dyes. The adsorption is exothermic
in nature.
Namasivayam and Arasi (1997) and Namasivayam et al. (2002) proposed red
mud for Congo red (red mud after purification by ultra-pure water, then dried at
60 °C for 5 h) and procin orange removal. They obtained nearly quantitative removal
of Congo red at pH 2.0. The adsorption capacity of Congo red was 4.05 mg/g, and
the adsorption mechanism is mostly ion exchange, whereas procin orange was
removed in 82% (pH = 2).
11.4.3 Natural Materials
Natural materials group include clays, siliceous materials, and zeolites. The oldest
and well-known natural ceramic material is natural clay minerals. The clays are
minerals possessing fine particles having an average diameter of about 2 mm (colloid fraction containing soils, rocks, sediments, and water suspended in aqueous
solutions) which may be mixtures of clay-sized crystals, fine-grained clay minerals,
and other minerals, e.g., quartz, metal oxides, carbonate, etc. Clays play a significant role as adsorbents due to its abundance in nature in most continents of the
world, low cost (e.g., market price of montmorillonite – 0.04–0.12 $ per kg and is
about 20 times cheaper than commercial activated carbons), as well as high sorption
ability (layered structure with high surface area, high porosity and open porous
structure, rapid kinetics, e.g., Fuller’s earth). Presence of exchangeable ions on clay
surface makes them strong candidate for ion-exchange results in sorption of cations
and/or anions through ion exchange mechanism, e.g., montmorillonites possesses
high ability for positively charged ions. Clay materials possess a layered structure
and included among others serpentine, sepiolite, vermiculite, mica, kaolinite, smectites, Fuller’s earth, etc. (Crini 2006; Shichi and Katsuhiko 2000; Yagub et al. 2014).
Clays show a strong affinity for dyes (cationic, anionic), e.g., bentonite (fine powder) is effective sorptive material for different class of dyes (combination of sorption and ultrafiltration gives more better efficiency of dyes removal), and dye clay
complexes can be formed. The main limitation of application of clays is the fact that
such sorbents are not efficient for pollutants of an acid character, their sorption
efficiency strongly depends on pH, and in many cases they required chemical
A. Wołowicz and M. Wawrzkiewicz