Removal of silver colloids from radioactive wastewater by means of ultrafiltration

110mAg is the most common colloidal nuclide found in the radioactive liquid of nuclear power plants (NPPs). This paper investigates the morphology of silver colloids through a simulation experiment. The results show that the radionuclide 110mAg in the process water is reduced to Ag0 to form colloidal silver existing in regular shape with a size around 100 nm and a negative zeta potential. This zero-valent silver colloid can not be removed by the existing treatment process of ion exchange in NPPs effectively. One potential method for removal is ultrafiltration. The results demonstrate an effective removal of more than 98% of the silver colloids, accompanied by a flux increase of 146.9%. This is different from the traditional trade-off between membrane permeability and selectivity. Scanning electron microscopy (SEM) was utilized to study the membrane morphology, revealing a filtration mechanism that combines adsorption and sieving. The xDLVO theory was used to reveal the interfacial interaction between silver colloids and membrane materials. The results indicate that silver colloids can adsorb on the membrane surface spontaneously. The silver adsorbed by the membrane may form loose and hydrophilic silver colloids (an "aquifer") and improve membrane hydrophilic and permeability properties simultaneously. The advantages of ultrafiltration on adsorption of silver colloids and improvement of water permeability provide a new method for the treatment of radioactive waste liquid containing colloidal silver.