Utilization of reverse osmosis and nanofiltration for the separation of SiO2 from boric acid solutions at nuclear power plants
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Even though the problem with an increasing SiO2 concentration in the reactor cooling system (RCS) emerges at most nuclear power plants, no publications yet have focused on the separation of SiO2 from solutions simulating RCS composition regarding boric acid (16 g/L) and silica concentrations (0–12 mg/L). Therefore, we examined the utilization of reverse osmosis and nanofiltration to separate SiO2 from H3BO3 solutions simulating RCS composition to meet the operation limits of SiO2 and to minimize additional costs for H3BO3 refill. The rejection of both H3BO3 and SiO2 by reverse osmosis was generally high (>90%). The maximal separation efficiency of SiO2 from H3BO3 was achieved at low pH and high temperature and was 1.30. The rejection of H3BO3 by nanofiltration was around 20% and of SiO2 around 80%. The highest separation efficiency was achieved at low pH and intermediate SiO2 concentrations and was 2.23. To achieve the operation limits for SiO2, a multi-stage nanofiltration system must be used for the solutions with intermediate and high SiO2 concentrations. Nanofiltration is for the separation of SiO2 from H3BO3 solutions more favorable than reverse osmosis, because of the higher separation efficiency of SiO2 from H3BO3, and thus, lower H3BO3 loss.
Abstract
Even though the problem with an increasing SiO2 concentration in the reactor cooling system (RCS) emerges at most nuclear power plants, no publications yet have focused on the separation of SiO2 from solutions simulating RCS composition regarding boric acid (16 g/L) and silica concentrations (0–12 mg/L). Therefore, we examined the utilization of reverse osmosis and nanofiltration to separate SiO2 from H3BO3 solutions simulating RCS composition to meet the operation limits of SiO2 and to minimize additional costs for H3BO3 refill. The rejection of both H3BO3 and SiO2 by reverse osmosis was generally high (>90%). The maximal separation efficiency of SiO2 from H3BO3 was achieved at low pH and high temperature and was 1.30. The rejection of H3BO3 by nanofiltration was around 20% and of SiO2 around 80%. The highest separation efficiency was achieved at low pH and intermediate SiO2 concentrations and was 2.23. To achieve the operation limits for SiO2, a multi-stage nanofiltration system must be used for the solutions with intermediate and high SiO2 concentrations. Nanofiltration is for the separation of SiO2 from H3BO3 solutions more favorable than reverse osmosis, because of the higher separation efficiency of SiO2 from H3BO3, and thus, lower H3BO3 loss.