Treatment Of Radioactive Wastewater Containing Strontium By Hydraulic Mixing/Carrying Precipitation-Microfiltration Process

Hydraulic mixing/precipitation-microfiltration combined process has been approved to reach a good comprehensive index with high decontamination factor and concentration factor. The effect of sodium cabonate dosage and crystal seed on simulated non-radioactive strontium(88Sr) removal, precipitate thickening and membrane fouling were studied by the lab-scale test. Meanwhile,it was applied in low-level radioactive strontium(90Sr)removal by the jar test.Strontium was removed by hydraulic reactor when crystal seed and Na2CO3 were used as carrier and precipitating agent, respectively. Strontium and calcium co-precipitated rapidly in the form of hybrid crystal which was removed by solid-liquid separation. FeCl3 was added as flocculant in the membrane separator to relieving membrane fouling. The average strontium concentration in the effluent was 7.84 ?g/L and 33.48 ?g/L,the average decontamination factor(DF)was 842 and 201,concentration factor(CF)was 2790 and 4433 when the Na2CO3 dosage was 1.0 g/L and 0.5 g/L,respectively. The pH of effluent was 10.18 when the Na2CO3 dosage decreased to 0.5 g/L,which reduced the volume of chlorhydric acid used for adjusting pH. The final effluent reached ?Drinking Water Sanitary Standards?(GB 5749-2006) with chloride concentration was 162.9 mg/L. Precipitations in the hydraulic reactor were spherical glossy granules noticeably increasing constract to the crystal seed.The crystal seed has played an important role on co-precipitation. The average strontium concentration in the effluent was 11.83 ?g/L,11.77 ?g/L and 11.27 ?g/L,the average DF was 337,520 and 473 when the crystal seed was 1.0 g/L CaCO3 prilled 30 cycles,1 g/L SrCO3 and 1 g/L SrCO3 prilled 10 cycles,respectively. The results showed that strontium removal of the process was influenced by crystal seed in the initial period for operation. CaCO3 was prior to form on the surface of seed and became aragonite,which contributed to the incorporatin of strontium.Box-Behnken Design of Response Surface Methodology was applied on the treatment of low-level radioactive strontium-containing wastewater to approve the feasibility of practical application. A quadratic model for assessing the influences of Sr2+ concentration,Ca2+ concentration and Na2CO3 dosage on decontamination factor had been established. According to the model established,decontamination factor could be calculated by the given data within the limits of concentration. The order of these three influencing factors was:Na2CO3 dosage>[Sr2+]>[Ca2+]. It indicated that Na2CO3 dosage was the most key factors in the whole process.