Preparation Of Composite Adsorbents Based On Nano-metal Oxides For Removal Of Heavy Metals From Water

Wastewater containing heavy metals such as lead, cadmium, mercury, chromium, copper, etc., discharged from various industrial activities is becoming a serious global environmental problem facing man. Their presence in the aquatic ecosystem causes harmful effects to living organisms because these heavy metals are not biodegradable and can be accumulated through the food chain. Thus, the removal of heavy metals is very important for the protection of ecological environment and public health. In the last decade, adsorption has been considered as one of the most efficient and promising technologies for the removal of heavy metals from aqueous solutions due to its simplicity, ease in operation, relative low-cost, no sludge generation and low chemicals and energy consumption. In this study, a series of organic/inorganic composite adsorbents based on metal oxides were prepared and characterized by various techniques such as SEM, TEM, XRD, FT-IR and XPS. In batch sorption experiments, effect parameters were studied including solution pH, contact time, adsorbent dose, initial concentration of metal ions and ionic strength. To understand the adsorption mechanisms, adsorption models such as kinetic, thermodynamic, equilibrium models were used to fit the experiment data.1. MnO2 nanorods encapsulated in PVA gels for Hg(Ⅱ)adsorptionPoly(vinyl alcohol) (PVA) is a water-soluble material containing large amounts of hydroxide groups that has been developed for biomedical applications since it is biocompatible and nontoxic, and exhibits minimal cell adhesion. In this study, MnO2 nanorods were encapsulated in PVA macroporous gel beads. The adsorption performance of Hg2+ by PVA/MnO2 was investigated in batch mode. From kinetic studies, it is found that the adsorption of Hg2+ is fast in the initial time and it reaches equilibrium around approximately240min. The kinetics of adsorption of Hg2+was found to follow pseudo-second-order model indicating the applicability of this kinetic equation for this system and the process controlling the rate may be a chemical sorption. The equilibrium adsorption data are tested with various isotherm models among which Freundlich model fits the experimental data well.2. MnO2 nanorods modified fly ash for Hg(Ⅱ) and Pb(Ⅱ) removalFly ash, as a coal combustion byproduct from thermal power plants, is abundantly available and thus cheap in Chinese market. The superior properties of high porosity, large surface area, ultralight weight and chemically inert nature make it a strong candidate as nonconventional and low-cost adsorbents. The primary objective of this study was to adsorbHg2+ and Pb2+ from water by fly ash modified with nanostructured MnO2 by evaluating adsorption properties as a function of initial concentrations, pH, contact time and ionic strength. The sorption mechanisms of Hg2+ and Pb2+onto FA@nM were investigated from points of thermodynamics and kinetics. The impacts of solution chemistry conditions on adsorption were evaluated and the equilibrium adsorption data were applied to Langmuir, Freundlich, Temkin and Dubinin- Radushkevich (D-R) isotherm models.3. Biopolymer tannic acid (TA) modified fly ash for Pb(Ⅱ) removal from waterFly ash (FA) contains various metal oxides, i.e. SiO2, A12O3, Fe2O3, CaO, etc. among which several oxides have been reported to possess a strong binding with heavy metals in water. And abundant natural materials may be potential low-cost adsorbent modifier for heavy metal removal. TA (hydrolysable tannins) contains several o-dihydroxy and trihydroxy aromatic rings (polyhydroxy polypHenols) and thus is capable of forming chelates with metal ions. Moreover, metal-binding properties, antimicrobial and anticorrosive activities of tannic acid in aqueous solutions are of great interest. The composite adsorbents based on FA, TA and BaP were synthesized and their removal efficiency for Pb2+ adsorption was carried out in batch mode. The maximum adsorption capacity of FA/TA/BaP was 221.1 mg/g. The kineticswas found to follow pseudo-second-order model and the Freundlich equilibrium model fits the experimental data well.