In the formula, J is the membrane flux, V is the volume of distillate within a certain period of time, A is the effective evaporation membrane area, and t is the time required to collect V distillate. Membrane flux refers to the volume of distillate passing through a unit membrane area per unit time. This evaporation-mass transfer-condensation process is called membrane distillation. When the partial pressure is higher than the cold side, the water vapor will pass through the membrane pores from the hot side (high vapor pressure) and enter the cold side (low vapor pressure) to condense. Due to the hydrophobicity of the membrane, the aqueous solutions on both sides cannot pass through the membrane pores and enter the other side, while the water vapor at the interface between the aqueous solution on the hot side and the membrane cannot enter the other side. Membrane distillation is a new type of membrane separation process using a microporous hydrophobic membrane with the vapor pressure difference on both sides of the membrane as the driving force for mass transfer.Īs shown in Figure 1, the aqueous solutions on the cold and hot sides are separated by a hydrophobic microporous membrane. The effect of system operating temperature, flow rate and concentration on membrane flux and rejection rate was verified, and the purification effect of the system on real high-salt low-level waste liquid was verified.ġ.1 Key performance evaluation parameters of membrane distillation
In this study, the high-salt and low-level discharge wastewater produced by a nuclear facility was treated as the object, and the main chemical compositions Ca(NO3)2 and Al(NO3)3 were used as the simulated source items to prepare the feed liquid, and the air-gap membrane distillation module was studied. Compared with traditional low-level wastewater treatment methods, such as evaporation, chemical precipitation, filtration, ion exchange or a combination of these processes, membrane distillation The technology has many advantages such as simple process flow, low application cost and high efficiency, especially for the concentration and crystallization treatment of high-salinity wastewater, which has irreplaceable advantages. Membrane distillation has gradually attracted widespread attention as a new membrane separation technology.
At present, although this kind of wastewater has been effectively treated and disposed, there are still problems such as complex treatment process, high cost and low efficiency. To protect the environment and human health, these wastewaters must be disposed of in a safe, economical and efficient manner. Complex low-level wastewater, high-salt low-level wastewater generated from spent fuel reprocessing, etc. Each process test link of the nuclear fuel cycle will produce low-level radioactive wastewater (referred to as “low-level wastewater”), such as uranium-containing fluorine-containing low-level wastewater from uranium conversion and purification, boric acid-containing low-level wastewater from nuclear power plants, and various types of nuclear fuel reprocessing.