Study On The Removal Of Cesium From Simulated Liquid Waste By A Countercurrent Two-stage Adsorption-microfiltration Process

The leakage of radioactive materials from Fukushima Daiichi Nuclear PowerPlant due to the earthquake in Japan caused the people’s extensive concern. Amongthe radioactive nuclides, cesium has high heat fission and a long half-life. Theexistence of cesium becomes a long-term threat to the environment. In this paper,countercurrent two-stage adsorption-microfiltration process was developed for thecesium removal from simulated liquid waste. Copper ferrocyanide and microfiltrationmembrane were used for adsorption and solid-liquid separation, respectively. Thepurpose of this research was to acquire higher decontamination factor andconcentration factor, and to provide technical support in response to the nuclearincident.Copper ferrocyanide with the molecular formula of Cu₂Fe（CN）₆·7H₂O wasprepared in this study. The adsorption behavior of cesium on copper ferrocyanidecould be best described by the Freundlich isotherm model and a pseudo-second orderkinetic model. Ion exchange was the main mechanism during the adsorption process.The distribution coefficient was more than2.94×10⁶mL/g when the pH of solutionwas between2.6-10.9, and the initial cesium concentration was approximately100μg/L. The existence of K⁺and Na⁺with the concentration below20mg/L and1000mg/L in the solution did not affect the removal of cesium. Desorption could beignored after the adsorption of cesium on copper ferrocyanide. The highertemperature of solution could help the adsorption process.Lab-scale tests with a conventional adsorption-microfiltration process were usedfor the removal of cesium from simulated liquid waste, the concentration of cesium inthe effluent decreased gradually with the operation time, and the meandecontamination factor was between287-1349with the copper ferrocyanide dosagebetween20-80mg/L. Because the ion exchange, the concentration of copper in theeffluent was higher than that in the influent, however, both the concentration ofcopper and the cyanide, which could be introduced into the effluent, met the ChineseStandards for Drinking Water Quality （GB5749-2006）.Based on the adsorption of cesium on copper ferrocyanide, a countercurrenttwo-stage adsorption-microfiltration process was developed and the corresponding mathematical model was established. The concentration of cesium in the effluentcould be predicted more accurately by the model. A series of jar tests and lab-scaletests were achieved to verify this model. In the jar tests, the decontamination factorsobtained were615and1123when the initial cesium concentration was approximately100μg/L, the dosage of copper ferrocyanide was40mg/L, and the dilution factorswere0.7and0.4, respectively. The experimental values fitted quite well with thevalues calculated by the model.The results of lab-scale tests with the countercurrent two-stageadsorption-microfiltration process showed that the effluent cesium concentrationremained stable with operation time, and the decontamination factors obtained were593and964when the dilution factors were0.7and0.4, respectively. Compared withthe conventional adsorption-microfiltration process, the decontamination factorobtained could increase1-2times with the same dosage of adsorbent by using thecountercurrent two-stage adsorption-microfiltration process. The experimental valuesof suspended solid in the membrane separator were close to those of calculated ones.Membrane fouling rate was slower and a higher concentration factor could beacquired in the countercurrent two-stage adsorption-microfiltration process.