| The hexavalent chromium is recognized toxic heavy metal ions for environment and itwill produce thousands tons of industrial wastewater contained chromium ever year with thedevelopment of industry and chromium application broadly. The methods which have beenused to remove heavy metal ions, such as chemical precipitation, ion-exchange, and solventextraction have been found to be limited, since they often involve amount of discharge sludgeor secondary wastes which present treatment problems. The use of adsorption is becomingresearch hot spot and important subject in recent years due to its low cost and convenientoperation. Therein the use of magnetic particle as adsorbents for heavy metal offers apotential alternative to existing methods for purification and recovery of these componentsfrom industrial wastewaters.The preparation and application of Fe-Me complex oxide magnetic particle in theremoval of hexavalent chromium from simulative wastewater were studied in the work.Firstly, Series of spinel MFe2O4(M=Co,Ni,Cu,Zn,Mg,Mn)magnetic material were synthesizedby sol-gel method, Cr(Ⅵ) adsorption tests also studied and the results show Fe-Ni oxide hasthe best Cr(Ⅵ) removal capacity. Fe-Ni oxide was synthesized by sol-gel method,coprecipitation method and hydrothermal method, reseperately. Then the adsorption capacityof hexavalent chromium was compared in the same conditions by the batch system. Theresults show that the Fe-Ni oxide particle obtained by the coprecipitation methods wasselected as the adsorbents due to it has the best Cr(Ⅵ) removal capacity and low costpreparation. In addition, the effect on the chromium uptake from the adsorbent Crystal form,which obtained by sinter temperature in synthesized, was tested, the results indicated that thepoorer crystalline, i.e obtained at 160℃sinter temperature, has the better Cr(Ⅵ) removalcapacity. Also, the molecular formula was determined as NiFe2O4.2H2O by chemistryelements analysis combined TG technology, it is a form of hydrous iron nickel complexoxide.Secondly, the effects on Cr(Ⅵ) adsorption of pH, time, temperature, Cr(Ⅵ) initialconcentration, ionic strength, dosage were investigated by Fe-Ni hydrous oxide., The resultsshow that pH=4 is the optimal condition for Cr(Ⅵ) adsorption, the Cr(Ⅵ) removal efficiencyis 97.56%, strong acidic and alkaline solution are both unfavourably for adsorption. Theadsorption process happened very quick and finished within 20min, adsorption capacitydecreased with ionic strength incresing and sorbent dosage increased, adsorption capacity increased with initial concentration and solution temperature; common coexisting cation andanion have no effect on Cr(Ⅵ) adsorption, unless HPO42-, which illustrated selectivity isgood. Experiments data were analyzed by Langmuir model and Freundlich model, it notedLangmuir isotherm was better described the adsorption process.In addition, the process of desorption, sorbent regeneration and recycle tests were alsostudied using 0.1M NaOH solution as regeneration agent, the results illustrated the desorptionprocess complete quickly and efficiency, Fe-Ni oxide can be reused many times in recoveryof Cr(Ⅵ).Finally, the adsorption mechanism of hexavalent chromium onto the Fe-Ni hydrousoxide magnetic particle was investigated by XRD, SEM combined binding energy, TEM,FT-IR, EPMA technologies and analyzed according the performance of adsorption isotherm,it suggested that the main action role is outer-sphere complex with ligand exchange and somephysical adsorption.
|
PDF Full Text Request