Treatment of wastewater. Large amounts of wastewater contain various dyes which are toxic and hazardous for the environment. This wastewater comes from the dye manufacturers and dyeing facilities of various industries.
Harmful substances get into the water reservoirs with wastewater, degrading their sanitary state and requiring special treatment of water before its use for domestic and industrial needs. The water goes through mechanical treatment where the contaminants and impurities are removed from the water, and neutralized with biological treatment, then extracted by such conventional purification techniques as settling, coagulation and flotation. At the end of this complex comprehensive water treatment process there is adsorption aftertreatment. As a rule, it is the final step of water purification.
The adsorption methods use non-carbon sorbents of natural and artificial origin for water purification. These sorbents have a sufficiently high adsorption capacity, selectivity, cation exchange properties, and are available at relatively low cost. The most widely used mineral natural sorbents are zeolites and clay materials. They are characterized by a variety of features and are constantly expanding the boundaries of application for water purification.
Treatment of wastewater. The theoretical ion exchange capacity of natural zeolites ranges from 2,6-5,8 mEq / g. That’s why natural zeolites are greatly used as ion exchangers and sorbents for purification of natural and wastewater, especially such materials as clinoptilolite and mordenite.
A well known chain structured mineral with sorption properties is palygorskite. Its adsorptive properties are defined by the zeolite channel structure (primary pores) with long and short fibers (secondary pores).
Bentonite is a clay mineral (consisting mainly from montmorillonite and beidellite) with varying degrees of absorption properties. Bentonite is not heat-resistant, it has low catalytic and adsorbent activity that requires acidic activation. Bentonite clay activity is determined by its cation exchange capacity, its crystalline structure of montmorillonitic type and bound water. When the bound water is removed at high temperature it leads to the destruction of the crystalline structure and loss of activity. Acid activates bentonite adsorption and catalytic properties, but generally degrades its physical strength. Therefore, the use of acid-activated bentonite is limited by clay contacting purification technology.
