Studies On The Reduction Of Fixed Pyrrhotite Rhenium And Its Influencing Factors

The objectives of this research were to study the feasibility of pyrrhotite as amedia for pertechnetate removal from wastewater. To ease the experimentalwork, perrhenate is used as a analogue of pertechnetate. The batch experimentswere carried out to determine the kinetic and reductive regulations. The effectsof various parameters such as reductive time, the initial pH value, temperatureand coexisting ions were investigated. Under saturated and unsaturatedconditions, we studied the effect of the reduction-immobilization rhenium bypyrrhotine by the column experiments. The scanning electron microscope(SEM), the energy dispersive spectrometer (EDS), the X-ray diffraction (XRD),the X-ray photoelectron spectroscopy (XPS) were used to observe surfacemorphologies and determine composition of natural pyrrhotite.The batch experimental results showed that pyrrhotite (100g/L) were able toreductively remove97%of perrhenate （5×10-5mol/L） from water within80days. Experimental facts also tell us that the Re(Ⅶ) removal rate tends toincrease with the increase of the dosage of pyrrhotite and the reaction time. Atthe same time, the observed experimental results imply that adding0.1mol/LNaCl could improve ionic strength of the system and have positive effects onreduction of Re(Ⅶ).A pseudo-first-order kinetic model was able to interpret thekinetic data (R2=0.9675), which gave a pseudo first order rate constant (kobs)value of0.0463d-1at room temperature(25°C) and pH=5.2. The pH has anobvious influence on the removal of perrhenate, perrhenate was absolutelyremoved within24hours at pH=1, but at pH3-8.5the reaction rate almost hadno change, while the pH is greater than12, the reaction does not occur. Withincreasing of temperature, treatment effect of perrhenate was increased, theoptimal temperature was80℃, and perrhenate was absolutely removed within7days (pH=5.2), The reaction process meets Arrhenius formula with the apparentactivation energy of40.606kJ/mol.The column experimental results showed: under the saturation condition, theeffect was not remarkably that only10.23%of rhenium has been immobilized inthe mix column. But under the unsaturation condition,67.85%of rhenium has been immobilized in the mix column. The effect was much better than saturatedclumn.This finding indicates that natural pyrrhotite can be used to remove ReO-4insoil and groundwater, and was of great value in the remediation of pertechnetatecontaminated groundwater. Finally, the resoults is meaningful for safetyassessment and engineering barriers design of high level radioactive wastedisposal repository site.