Adsorption Behaviors Of Heavy Mentals On Modified Bagasse

With the development of industry, the disposal of wastewatercontaining heavy metals brings out serious environmental pollution, andthe problem of heavy metal pollution in water has become one of themost serious environmental problems in the world. This problem isextremely urgent. Nowadays, some methods including chemicalprecipitation, oxidation-reduction, ion exchange, solvent extraction,electrolysis and membrane separation, are used to remove heavy metalions from wastewater. However, these methods have some disadvantages,such as high running cost, cumbersome operation, and easy to causesecondary pollution. The bio-adsorption method attracts manyresearchers’ concern owing to its high efficiency andenvironmental-friendly. However, the adsorption capacity of unmodifiedadsorbents for heavy metals is low, and the modification of adsorbentshas been the research focus.In the thesis, the bagasse which was modified with pyromelliticdianhydride （PMDA） and ethylenediaminetetraacetic dianhydride（EDTAD） were used to adsorb Cu²⁺, Zn²⁺, Pb²⁺, and Cd²⁺through asimple and mild method. The bagasses before and after modification werecharacterized by infrared spectrophotometric （FTIR） and scanningelectron microscope （SEM）. Effects of time, metallic ion concentration,adsorbents amount and pH value were investigated. The adsorptionproperties of the unmodified and two kinds of modified adsorbents forheavy metal ions of Cu²⁺, Zn²⁺, Pb²⁺and Cd²⁺were studied. The effects offour interference ions including Na+, K+, Ca²⁺, Mg²⁺on adsorption andthe concentration of eluants （HCl, HNO3and EDTA） on desorptioncapability were examined as well. The obtained results are as follows.1. The adsorption capacities of the two modified adsorbents for theheavy metal ions of Cu²⁺, Zn²⁺, Pb²⁺, Cd²⁺with PMDA or EDATD wereimproved significantly. FTIR demonstrated that a large number of carboxyl and epoxy groups were introduced on the surface of biosorbents.The adsorption rates were both very high at20min when the twoadsorbents were used to adsorb the four heavy mental ions of Cu²⁺, Zn²⁺,Pb²⁺and Cd²⁺. The adsorption capacity is more than90%of the amountof equilibrium adsorption. Both of the adsorption processes of the twomodified bagasse to the four heavy mental ions fit thepseudo-second-order model. It indicated that the adsorption rates of twoadsorbents were mainly controlled by the concentration of heavy mentalions and the active sites on the surface of the adsorbents. The isothermaladsorption behaviors of these processes can be described by Langmuirmodel. It shows that surfaces of modified and unmodified bagasse arewell-proportioned. The adsorption of the two adsorbents to heavy mentalions obeys the formation of monolayer molecule adsorption with thephysical and chemical adsorption simultaneously.2. Thermodynamic parameters showed that all the adsorptionprocesses were spontaneous in the study. The adsorption process ofPMDA modified adsorbent for Cu²⁺and Pb²⁺were endothermic physicaladsorption process, and for Zn²⁺and Cd²⁺were exothermic physicaladsorption process.3. There is no obvious influence on the adsorption of bagassemodified by EDTAD with the scope of pH （2.0-7.0） widely. Coexistenceion interference experiments showed that it had comparatively only alittle of effects on the adsorption capability of the modified bagasse whenthe combination of Na⁺, K⁺, Mg²⁺, Ca²⁺with different concentration.Bagasse modified by EDTAD as an adsorbent to adsorb the heavy mentalions possesses a vast range of application prospect owing to its rich acidresistance and strong anti-interference.4. Three adsorption and desorption experiments for the adsorbedheavy metal ions on the modified adsorbents were carried out with theeluent of EDTA successively. The results show that the loss of theadsorption capacity was less than10%. It indicated that the two adsorbents possessed good regeneration capacity which can be used totreat practical wastewater containing heavy mental ions.5. Adsorption experiment showed that carboxyl and hydroxyl groupson the surface of the modified sorbent involved in the adsorption process,and the main mechanism was ion exchange. Additionally, surfaceprecipitation was happened for Pb²⁺. Sorption affinity order for the fourmetal ions was: Pb²⁺>Cu²⁺>Cd²⁺>>Zn²⁺. It would be possible to selectiveadsorption of Pb²⁺and Cu²⁺by controlling the experiment conditions.