Preparation Of Fly Ash/rare Earth Composite Material And，Its Adsorptive Properties For Cd²⁺ From Aqueous Solution

According to the present situation of the frequent occurrence of China’sheavy metal pollution event and for the full development and utilization ofInner Mongolia region’s solid waste fly ash and rare earth resources, in thispaper, fly ash/alkali melting/doped rare earth composite materials wereprepared by high-temperature calcining method and characterized. Preparingconditions of the composite materials, their adsorption properties for Cd²⁺from aqueous solution and some importent influencing factors wereresearched respectively. The adsorption kinetics, adsorption equlibrium andthermodynamics, economic and technical analysis, environmental impactassessment, the mechanism of adsorption for adsorbents revoming Cd²⁺industrial applications and other related issues were further investigated. Thedetailed results are as follows:（1） The effects of preparation conditions of the fly ash/alkali melting/dopedrare earth composite materials，such as the flux Na₂CO₃amount, Ce（SO₄）₂doping level, calcination temperature and time, on removing Cd²⁺werestudied. The obtained optimal preparation conditions were that the mass ratioof FA and Na₂CO₃is1:2, Ce（SO₄）₂doping amount is9%, the calcinationtemperature and time are800°C and2h respectively, the obtainedCe-Na₂CO₃-FA adsorbents have large adsorption capacity for Cd²⁺revomalfrom aqueous solution and the removal rate almost reached100%withsolution pH value of6.0and initial Cd²⁺concentration of500mg·L^-1.（2） The adsorption properties and influence factors of Ce-Na₂CO₃-FAadsorbents for Cd²⁺revomal were discussed. The results showed that: thesolution pH value is an important impact factor on the adsorption ofCe-Na₂CO₃-FA adsorbents for Cd²⁺. The adsorption amount increased withthe increase of adsorbent dosage and decreased with increasing initial Cd²⁺concentration. The adsorption capacity and the removal rate of Cd²⁺were48.88mg·g^-1and97.76%when the amount of the adsorbent was0.5g, initialCd²⁺concentration in50mL solution was500mg·L^-1with pH6.0. （3） The adsorption kinetics study showed that: the adsorption rate andadsorption capacity increased with the extension of time within90min andthen become slow, and the basic adsorption equilibrium reached at120min.Kinetic curves have same change trend at different temperatures. Theadsorption kinetics of Ce-Na₂CO₃-FA adsorbents for Cd²⁺better followed thepseudo-second-order model （R²>0.996）. The adsorption process was mainlycontrolled by the intra-particle diffusion. The apparent activation energy Eaobtained by experiments and calculation was67.616kJ·mol^-1.（4） Adsorption equilibrium and thermodynamics study showed that:isotherm adsorption data of Ce-Na₂CO₃-FA adsorbent for Cd²⁺can welldescribed by Freundlich model at various temperatures （25℃,35℃and45℃） and also obeyed Langmuir model, from which the maximumadsorption capacities were66.67mg·g^-1,71.94mg·g^-1and83.33mg·g^-1respectively at different temperatures. The negetive value of change inadsorption free energy（△G°） and the positive value of change in adsorptionstandard enthalpy （△H°） indicated that the adsorption of Ce-Na₂CO₃-FAadsorbent for Cd²⁺was of spontaneous and endothermic nature. The rise ofthe temperature was favorable to sorption.（5） Heavy metal leaching experiments showed that: the leaching values ofseven kinds of ions of Cd²⁺、 Cu²⁺、 Zn²⁺and so on in Ce-Na₂CO₃-FAadsorbents were lower than the national surface water environmental qualitystandards （GB3838-2002） at different pH values. The results showed that theCe-Na₂CO₃-FA adsorbent should be safety and feasible for its application inthe treatment of general Cd²⁺wastewater and Cd²⁺wastewater of even suddenhigh concentration and would not cause secondary pollution. Otherwisemixed-ion interference experiments indicated that: the coexistence ofcommon Cu²⁺、 Zn²⁺、 Pb²⁺with a certain concentration and Cd²⁺had littleeffect on the adsorption property of Ce-Na₂CO₃-FA adsorbents for Cd²⁺revomal.（6） The adsorption mechanism of Cd²⁺by Ce-Na₂CO₃-FA adsorbents werecharacterized and analyzed by XRD, SEM, the FT-IR and surface charge ditermination. The adsorption mechanism of adsorbents for Cd²⁺was exploredand thought that adsorption was a progress of interaction of physicaladsorption and flocculation sedimentation.（7） The preparation and performance of Ce-Na₂CO₃-FA adsorbent is simpleand economically feasible though economic analysis and environmentalimpact assessment. If Ce-Na₂CO₃-FA adsorbent is used to treat Cd²⁺wastewater, it can get certain economic benefits at the same time of obtaininga certain environmental and social benefits.