1 1.1 Modified Bentonite Bentonite Bentonite classification structure and a montmorillonite clay minerals as the main rock, and the aqueous smectite layered aluminosilicate mineral, a silica tetrahedron layer two It is composed of an aluminum ( magnesium ) oxygen (hydrogen oxy) octahedral layer and belongs to the 2:1 type of three-layer clay mineral. In the process of clay mineral formation, isomorphous substitution often occurs, and there is excess negative charge between crystal structure layers. It can maintain electrical neutrality by electrostatic adsorption of cations. In addition, bentonite has a large surface area and a large surface area with a large surface energy, making it a huge adsorption capacity. Bentonite can be classified into sodium base, calcium base, magnesium base and aluminum base bentonite according to the proportional relationship of montmorillonite interlayer cations. Among them, calcium-based bentonite has the largest reserves, accounting for 70%-80% of the total reserves.
1.2 Modified bentonite In the natural bentonite, due to the strong hydrophilicity of the surface silicon oxide structure and the hydrolysis of a large number of exchangeable cations between the layers, a thin water film is usually present on the surface, and the hydrophobicity cannot be effectively adsorbed. Organic pollutants limit their use in water treatment. Therefore, the modification of natural bentonite has received extensive attention. The modification of bentonite by inorganic substances such as acid, oxidant and inorganic salt can significantly improve the adsorption and ion exchange performance of organic pollutants. At present, modified bentonites which are widely used in the field of water treatment include activated bentonite, organic bentonite, crosslinked bentonite and organic crosslinked bentonite.
1.3 Adsorption mechanism of modified bentonite 1.3.1 Exchange adsorption The adsorbate ions accumulate on the surface of bentonite due to electrostatic attraction, and the bentonite releases equivalent exchangeable cations between the layers to complete the adsorption process, and the adsorption binding force is ionic bond. For organic ion adsorbed matter, macromolecules are more easily adsorbed than small molecules, because not only cation exchange acts when organic large ions interact with montmorillonite, but van der Waals force also plays a considerable role. The larger the ion, the larger the van der Waals force is absorbed. more.
1.3.2 Physical adsorption Due to the molecular attraction between the adsorbate in the wastewater and the bentonite adsorbent, the pollutants to be treated in the wastewater are adsorbed. Physical adsorption can be carried out at low temperatures, but since the adsorption force and the adsorbent force are mainly van der Waals forces, the adsorption selectivity is not strong. In general, the actual wastewater adsorption treatment is often a combination of two adsorption mechanisms, and only some of them may be dominant in specific wastewater treatment.
2 Application of modified bentonite in water treatment 2.1 Treatment of organic wastewater Modified bentonite adsorbent can be used to treat various types of organic wastewater, and can adsorb non-polar organic substances, polar organic substances and various toxic and difficult biodegradable organic substances. Wu Pingqi and other organic cross-linked bentonite treatment of phenol wastewater, found that when the pH value is 10, after shaking at 120r / min for 30min at room temperature, the removal rate of phenol in water can be as high as 95% or more, corresponding to the corresponding organic bentonite and cross-linking The adsorption removal rate of bentonite has been significantly improved. Wu Pingqi et al. also studied the cyclic re-adsorption of organically cross-linked bentonite. The study showed that the organic crosslinked bentonite adsorbed with phenol can be regenerated by burning at 500 °C. Sun Jiashou and others used organic cross-linked bentonite to treat papermaking waste liquid. When the pH value is 4.5 and the dosage is 24g/L, the adsorption efficiency of COD is 61.5% and the adsorption capacity is 549.3mgCOD/g after 60min treatment at room temperature. Zhu Li used quaternary ammonium salt surfactant modified bentonite to treat simulated wastewater containing non-ionic organic compounds such as benzene, phenol, nitrobenzene, aniline and polycyclic aromatic hydrocarbons. It is considered as: (1) organic bentonite The interlayer spacing and the amount of adsorption to organic matter increase with the growth of the surfactant carbon chain used in the modification. (2) When the amount of surfactant added during modification is lower than the cation exchange capacity (CEC), the interlayer spacing of organic bentonite and the adsorption amount of organic pollutants increase with the addition amount; when the addition amount exceeds CEC, the layer The spacing and adsorption amount will generally not increase. (3) Adsorption depends mainly on the size of the organic cation and the CEC of the bentonite.
Smith et al. studied the adsorption and distribution properties of long and short quaternary ammonium salt modified bentonite to organic matter in water. The former is linear and the latter is nonlinear. Smith et al also studied monocationic and dianionic modified bentonite. Adsorption of organic pollutants. In addition, the United States ETVerture company uses amine-based polymers to improve the surface of bentonite ions from hydrophilic to lipophilic, to form clay minerals that are easily soluble in hydrocarbons, and then combined with activated carbon to treat the produced water of the Tensleep oil layer, which can be quickly and effectively Ground removal of hydrocarbon compounds in water.
2.2 removal of heavy metal ions of heavy metal ions in wastewater comes mainly from metal mining, smelting, electrolysis, plating industries. Heavy metal ions can be enriched in aquatic organisms and endanger human health through the food chain. Adsorption is a promising method for treating wastewater containing heavy metal ions. It not only reduces the concentration of heavy metal ions in water, but also facilitates the recovery of valuable heavy metals. Bentonite has a large specific surface area and ion exchange capacity, good adsorption performance, and has a special effect on the adsorption of heavy metal ions in wastewater. Related studies have shown that bentonite has a certain adsorption capacity for heavy metal ions, and its ability to remove heavy metal ions can be significantly improved by modification of bentonite. Jin Hui et al. discussed the possibility of adsorption of Hg 2+ in wastewater by sodium bentonite and its adsorption effect. The results show that: the use of sodium bentonite as adsorbent, adsorption of mercury-containing waste water treatment of Coagulation higher value. Bentonite adsorption flocculation
1.2 Modified bentonite In the natural bentonite, due to the strong hydrophilicity of the surface silicon oxide structure and the hydrolysis of a large number of exchangeable cations between the layers, a thin water film is usually present on the surface, and the hydrophobicity cannot be effectively adsorbed. Organic pollutants limit their use in water treatment. Therefore, the modification of natural bentonite has received extensive attention. The modification of bentonite by inorganic substances such as acid, oxidant and inorganic salt can significantly improve the adsorption and ion exchange performance of organic pollutants. At present, modified bentonites which are widely used in the field of water treatment include activated bentonite, organic bentonite, crosslinked bentonite and organic crosslinked bentonite.
1.3 Adsorption mechanism of modified bentonite 1.3.1 Exchange adsorption The adsorbate ions accumulate on the surface of bentonite due to electrostatic attraction, and the bentonite releases equivalent exchangeable cations between the layers to complete the adsorption process, and the adsorption binding force is ionic bond. For organic ion adsorbed matter, macromolecules are more easily adsorbed than small molecules, because not only cation exchange acts when organic large ions interact with montmorillonite, but van der Waals force also plays a considerable role. The larger the ion, the larger the van der Waals force is absorbed. more.
1.3.2 Physical adsorption Due to the molecular attraction between the adsorbate in the wastewater and the bentonite adsorbent, the pollutants to be treated in the wastewater are adsorbed. Physical adsorption can be carried out at low temperatures, but since the adsorption force and the adsorbent force are mainly van der Waals forces, the adsorption selectivity is not strong. In general, the actual wastewater adsorption treatment is often a combination of two adsorption mechanisms, and only some of them may be dominant in specific wastewater treatment.
2 Application of modified bentonite in water treatment 2.1 Treatment of organic wastewater Modified bentonite adsorbent can be used to treat various types of organic wastewater, and can adsorb non-polar organic substances, polar organic substances and various toxic and difficult biodegradable organic substances. Wu Pingqi and other organic cross-linked bentonite treatment of phenol wastewater, found that when the pH value is 10, after shaking at 120r / min for 30min at room temperature, the removal rate of phenol in water can be as high as 95% or more, corresponding to the corresponding organic bentonite and cross-linking The adsorption removal rate of bentonite has been significantly improved. Wu Pingqi et al. also studied the cyclic re-adsorption of organically cross-linked bentonite. The study showed that the organic crosslinked bentonite adsorbed with phenol can be regenerated by burning at 500 °C. Sun Jiashou and others used organic cross-linked bentonite to treat papermaking waste liquid. When the pH value is 4.5 and the dosage is 24g/L, the adsorption efficiency of COD is 61.5% and the adsorption capacity is 549.3mgCOD/g after 60min treatment at room temperature. Zhu Li used quaternary ammonium salt surfactant modified bentonite to treat simulated wastewater containing non-ionic organic compounds such as benzene, phenol, nitrobenzene, aniline and polycyclic aromatic hydrocarbons. It is considered as: (1) organic bentonite The interlayer spacing and the amount of adsorption to organic matter increase with the growth of the surfactant carbon chain used in the modification. (2) When the amount of surfactant added during modification is lower than the cation exchange capacity (CEC), the interlayer spacing of organic bentonite and the adsorption amount of organic pollutants increase with the addition amount; when the addition amount exceeds CEC, the layer The spacing and adsorption amount will generally not increase. (3) Adsorption depends mainly on the size of the organic cation and the CEC of the bentonite.
Smith et al. studied the adsorption and distribution properties of long and short quaternary ammonium salt modified bentonite to organic matter in water. The former is linear and the latter is nonlinear. Smith et al also studied monocationic and dianionic modified bentonite. Adsorption of organic pollutants. In addition, the United States ETVerture company uses amine-based polymers to improve the surface of bentonite ions from hydrophilic to lipophilic, to form clay minerals that are easily soluble in hydrocarbons, and then combined with activated carbon to treat the produced water of the Tensleep oil layer, which can be quickly and effectively Ground removal of hydrocarbon compounds in water.
2.2 removal of heavy metal ions of heavy metal ions in wastewater comes mainly from metal mining, smelting, electrolysis, plating industries. Heavy metal ions can be enriched in aquatic organisms and endanger human health through the food chain. Adsorption is a promising method for treating wastewater containing heavy metal ions. It not only reduces the concentration of heavy metal ions in water, but also facilitates the recovery of valuable heavy metals. Bentonite has a large specific surface area and ion exchange capacity, good adsorption performance, and has a special effect on the adsorption of heavy metal ions in wastewater. Related studies have shown that bentonite has a certain adsorption capacity for heavy metal ions, and its ability to remove heavy metal ions can be significantly improved by modification of bentonite. Jin Hui et al. discussed the possibility of adsorption of Hg 2+ in wastewater by sodium bentonite and its adsorption effect. The results show that: the use of sodium bentonite as adsorbent, adsorption of mercury-containing waste water treatment of Coagulation higher value. Bentonite adsorption flocculation
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