Non-contact Membrane Distillation Method For The Treatment Of Radioactive Wastewater

China has formed a complete nuclear industry system,and uranium mining and hydrometallurgy purification,nuclear fuel component processing,and spent fuel reprocessing.Managing radioactive wastewater generated by the operation and decommissioning of nuclear facilities is an essential issue for developing atomic energy worldwide.The different nature of radioactive wastewater brings difficulties to the treatment and disposal of waste liquid.The lack of purification technology suitable for waste liquid of different nature restricts the development of the nuclear industry.Therefore,it is urgent to study the efficient,stable,and universal new technology of waste liquid treatment.Membrane distillation technology is a hydrophobic microporous membrane on both sides of the vapor pressure difference as the driving force of a wastewater purification technology,has low operation pressure,the inorganic ions.Other non-volatile components intercept effect is good to wait for an advantage and can effectively utilize solar energy,industrial waste heat,such as low-grade heat source,is considered to be meet the demand of radioactive waste liquid capacity reduction purification technology of excellence.However,the traditional contact membrane distillation has some problems,such as membrane fouling and wetting,resulting in short membrane life,low permeate flux,and instability,which limit its industrial application.In this study,a non-contact membrane distillation method was established.Based on the self-made non-contact membrane distillation device,the influences of process parameters such as hot side inlet temperature,hot side inlet flow rate,cold side sweeping gas temperature,cold side sweeping gas flow rate,the effective area of membrane module,and several sweeping gas chamber on permeate flux were studied.The purification ability of this method for strontium ion in simulated radioactive wastewater and actual radioactive wastewater from uranium-containing hydrometallurgical purification plant was investigated.Experimental results show that;The membrane flux of non-contact membrane distillation is mainly affected by the hot side inlet airflow,cold side scavenging air flow,inlet air temperature,and other operating parameters,but the cold side gas temperature has little influence on the membrane flux.The membrane flux can be effectively increased by increasing the inlet flow rate on the hot side and scavenging the airflow rate on the cold side.The increase in inlet temperature is the most significant.When the inlet temperature increased from 44.9℃to77.7℃,the membrane flux increased from 5.21kg/（m²·h）to24.87kg/（m²·h）.Increasing the contact area between the membrane and the hot side gas can increase the effective water yield.Under the optimized conditions,the rejection rate of Sr²⁺in 0.25g/L simulated radioactive wastewater is more than 99.99%,and the decontamination factor can reach more than 4.5×10⁶.The totalαactivity concentration of the distillate treated by the unit is 0.205Bq/L,and the totalβactivity concentration is 0.877Bq/L,the totalαactivity concentration of21279.7Bq/L and the totalβactivity concentration of 17811.9Bq/L,which proves that the unit has the deep purification function.In addition,three classical mass transfer models,namely Knudsen diffusion,molecular diffusion,and transition diffusion,were used to investigate the mass transfer process of non-contact membrane distillation.Non-contact membrane distillation technology uses the design of the membrane on both sides of hot and cold all contact with the gas,reducing the ions in the membrane and membrane pore surface deposition probability,effectively reducing the membrane fouling and membrane wetting phenomenon,prolonging the service life of the hydrophobic membrane,can be developed into highly radioactive wastewater to reduce the capacity of industrial application and deep purification technology.