The Research On Applying Modified Clay Minerals To Treat Heavy Metal Waste Water

Water is the vital factor of people's living. With the development of economic and rapid urbanization, many industries, including the electroplating, metal finishing, metallurgical, tannery, chemical manufacturing, mining, and battery manufacturing industries, produce aqueous effluents containing heavy metal contaminants, causing serious soil and water pollution. Various techniques have been used to remove the heavy metals from waste water, including chemical precipitation, ion exchange, electrolytic methods, chemical coagulation, membrane processes and adsorption. Today, numerous approaches have been studied for the development of cheaper metal sorbents, such as fly ash, peat, microbial biomass, clays and related minerals. This paper emphasizes the modification techniques of common clay minerals and their practical applications.First, this paper introduces the structure and some properties of clays, the application and research development of clay mineral materials to heavy metal waster water treatment are also summarized. Aiming at two different clays used in the study, different modification methods are put forward, and then modified clays are used to treat heavy metal waste water. The mechannism for their adsorption are also studied.After modified, the content of Mn in diatomite, the surface area and filtration rate have improved. The value of pHzpc decreased. Mn²⁺ hardly dissolved under different conditions. The properties and optimal condition for Mn-diaomite to adsorb heavy metal Pb²⁺, Zn²⁺ were investigated under static state in the laboratory and also the effects of modified diatomite dosage, pH value and ion strength of wastewater, adsorption time and temperature were discussed. Low ion strength of wastewater, room temperature, alkaline and neutrality condition were favorable, and the equilibrium time was 30min. After treated, the contents of Pb²⁺and Zn²⁺ in electroplating wastewater were prominently lower than discharge criterion of national industrial wastewater. The saturated adsorption amounts of Mn-diatomite for Pb²⁺and Zn²⁺ were 72.4 mg/g and 28.6 mg/g, respectively, which were compared with that of diatomite, organo-diaomite, and active carbon. Mn-diatomite saturated with Pb²⁺and Zn²⁺ can be regenerated by the solution of CaCl2.This paper also investigates the possibility of using raw bentonite clay as a precursor to produce HA-pillared clay (HA-PILC) for the removal of Pb²⁺ and Cd²⁺ from aqueous solutions. The adsorption of Pb²⁺ and Cd²⁺ onto HA-PILC has been dynamically and thermodynamically investigated. Batch experiments were carried out as a function of solution pH,contact time,initial concentration, adsorbent dose, ionic strength,and temperature. Adsorption of heavy metals onto HA-PILC decreases in the order: Pb²⁺ > Cd²⁺. The maximum adsorption capacity was observed in the pH range 5.0-6.0. The maximum adsorption of 92.8% and 63.7% took place at pH 6.0 from an initial concentration of 100 mg/L for Pb²⁺ and Cd²⁺, respectively. The temperature dependence indicates the endothermic nature of adsorption. The activation energy of sorption was also calculated. The percentage removal of Pb²⁺ and Cd²⁺ decreased with increasing ionic strength. After treated, the contents of Pb²⁺and Zn²⁺ in mine acidic wastewater were prominently lower than discharge criterion of national industrial wastewater. The equilibrium isotherm data were fitted to the Langmuir, Freundlich, and D-R isotherm equations to obtain the characteristic parameters of each model. The Freundlich isotherm was found to well represent the measured sorption data. The desorption data showed that the spent HA-PILC can be regenerated for further use by 2.5 M CaCl2.