Preparation Of Materials For The Asorption Of Heavy Metal Ions And Dyes

With the rapid development of economy, the modern industry has made greatdevelopment, and the resulting environmental problems have become increasinglyserious. Especially the contamination of heavy metals and organic dye caused theattention of people because the heavy metal ions can’t decompose and introduce thepotential danger of bioaccumulation, which may eventually affect man through thefood chain. Dyes can cause hazards to the environment due to the presence of a largenumber of contaminants like toxic organic residues, acids, bases and inorganiccontaminants. Some of the dyes are carcinogenic and mutagenic because they wereformerly made by hazardous chemicals such as benzidine, metals, etc.. The dischargeof colored wastes into the receiving water bodies not only affects their aestheticnature but also interferes with the transmission of sunlight and therefore reduces thephotosynthetic activity. Therefore, it is very necessary to remove effectively heavymetal ions and dyes from waterbodies.Oil shale, called kerogen, is a kind of sedimentary rock containing varying amountsof a solid, waxy mixture of hydrocarbon compounds and disseminates throughout the rock. The oil shale is considered one of the largest energy resources in the world. Inrecent years, oil shale has been widely used as an alternative source of energy with theincrease of oil price. However,(the) large quantities of oil shale ash (OSA)(which isa by-product ash) are generated due to the direct combustion process of oil shale. Thiskind of ash is considered a serious environmental problem. Therefore, it is necessaryto make a proper strategy for ash handling, disposal and utilization. At present, someresearchers are focusing on using oil shale ash as a low cost, promising and efficientadsorbent material for the removal of heavy metals and dyes from wastewater.In the paper, Na-A zeolite was successfully synthesized based on the oil shale ashas raw materials and used as an adsorbent to remove heavy metal ions and dyes fromaqueous solution. Hydrophobic alumina aerogel was also prepared using oil shale ashas aluminum source. This work provided a new direction for the comprehensiveutilization of oil shale ash and had great theoretical and practical significance. Thedetailed novelties of this thesis can be categorized as following:1. The Na-A zeolite was successfully synthesized by the alkaline fusion methodusing oil shale ash as raw materials. The effect of weight ratio of NaOH/OSA onthe preparation of zeolite was studied. The optimum weight ratio of NaOH/OSAfor synthesizing zeolite is1.6. The synthesized zeolite was characterized by analysis techniques. SEM image shows that the as-synthesized zeolite is cube andits average diameter is about2μm. Pore size distributions reveal that zeolitebelongs to the mesoporous material. The surface area of the synthesized zeolite iscomparatively twice higher than that of the oil shale ash, indicating that the zeolitehas great potential as an efficient adsorption material.2. The synthesized Na-A zeolite and oil shale ash were used to remove Cu2+ionsfrom aqueous solution. Effects of initial concentration and pH value on theadsorption have been discussed. The adsorption isotherm, kinetics andthermodynamics have also been investigated. The results showed that the optimalpH value for removing Cu2+was about5-6. The adsorption data were fitted withLangmuir model. The maximum adsorption capacities of the obtained zeolite andoil shale ash from Langmuir adsorption isotherm were found to be156.7mg/g and38.9mg/g for Cu2+, respectively. The batch kinetic data fitted with thepseudo-second order equation better. The negative ΔG and positive Δ Hatdifferent temperatures confirmed that the adsorption processes were spontaneousand endothermic. 3. The prepared Na-A zeolite was used to remove methylene blue and congo redfrom aqueous solution. The effects of various factors on adsorption have beenstudied. The experimental data were correlated with the Langmuir model. Themaximum adsorption capacities of methylene blue and congo red were18.73mg/gand31.05mg/g, respectively. Adsorption kinetics data were correlated to thepseudo-first-order and pseudo-second-order equation. The batch kinetic data fittedwith the pseudo-second order equation better.4. Hydrophobic alumina aerogels were successfully prepared using oil shale ash asalumina source. The effects of methyltrimethoxysilane (MTMS) andtetraethylorthosilicate (TEOS) used as surface modifying agents on thephysicochemical properties of the alumina aerogels were investigated. Comparedwith the unmodified aerogels, the water contact angles of alumina aerogelsfunctionalized with TEOS and MTMS were54°and110°, respectively. Thesurface area of the modified aerogels was higher than that of unmodified aerogels,which has great potential as efficient adsorption material. The maximumadsorption capacities of the modified aerogels and modified with MTMS andTEOS from Langmuir adsorption isotherm were found to be22.36mg/g and24.31mg/g for methylene blue. 5. Magnetic–chitosan composites were synthesized, characterized and were used forthe adsorption Pb2+and Cu2+ions from aqueous solution. The optimum pH value is5.0for Cu2+and6.0for Pb2+.The maximum adsorption capacities of Pb2+and Cu2+ions based on the Langmuir isotherm model were224.21mg/g and64.35mg/g,respectively. Adsorption kinetics data fitted with the pseudo-second orderequation better. The thermodynamic results demonstrated that the adsorptionprocess was exothermic under natural conditions.