Research On Removal Of Iodide From Simulated Radioactive Wastewater Using Hybrid Process Combining Precipitation-microfiltration

The radioactive iodine was detected in the several major nuclear accidents in history,especially in Japan after the Fukushima nuclear accident.Radioactive iodine is one of the main components of early nuclear pollution,which brings great damage to human life.The removal of radioactive iodine is one of the main issues in the field of radioactive control concerned in recent years.In this paper,the adsorption of powdered activated carbon?PAC?on iodine ions was discussed.The thermodynamics and kinetics of PAC adsorption were also studied.The removal efficiency of the iodide from deionized water was about 60%,and the removal effect of iodide ion was greatly influenced by the coexisting ions and pH values.The level of removal efficiencyneed to be further improved.In this paper,precipitation and membrane separation technology were combined to treat the simulated wastewater containing radioactive iodide on a laboratory scale.When the initial iodide concentration was approximately 5 mg/L,the dosage of Na₂SO₃ was 40 mg/L,which was used for removing oxygen from the influent and the dosage of CuCl was 260 mg/L,which was used as a precipitant.This study investigated I^-removal efficiency and other water quality parameters under different temperatures conditions and the effects on membrane fouling when the two membrane flux were 4.17×10^-6 m/s and 8.33×10^-6 m/s,respectively.The operation time was 168h and the volumes of treated wastewater were 1540 L.In the two tests,the average I^-removal efficiency was 94.8%and the effluent qualities were stable.Under the conditions that the membrane fluxes were 4.17×10^-6 m/s and 8.33×10^-6 m/s,the final membrane specific flux decreased to 65%and 55%of the initial one,respectively.The membrane specific flux values of the membrane modules were respectively recovered to 90.0%and 79.0%of the initial one after physical and chemical cleaning.Furthermore,the average concentration factor value was 2.02×10³,the volume of the sludge produced in the experiment was small,and the cost of radioactive waste for final disposal could be reduced.Due to the high concentration of Cu²⁺in the membrane effluent,the Na₂CO₃could not reach the requirement of the water on the basis of the guarantee of the removal effciency of iodide ions in the membrane separation reactor.In combination with the research for the removal of strontium by using granulation method in the previous work,Na₂CO₃ was used as a precipitant to treat the wastewater containing copper and strontium.Experimental results showed that the existence of a large number of Cu²⁺inhibited the formation of SrCO₃ crystals,and with the increase of the precipitant dosage,the removal effciency of Sr²⁺was obviously improved,but when the dosage of Na₂CO₃ increased to 400 mg/L,the removal effciency of Sr²⁺was increasefinitely.When the dosage is 1 g/L,the removal effciency of Sr²⁺was 94.5%.However,with the increase of the Na₂CO₃ dosage,the pH values was increased,a large number of blue Cu?OH?₂ fine flocculent precipitate produced,which increased the difficulty in solid-liquid separation.