Treatment Of Wastewater Containing Strontium And Cesium By Combined Microfiltration Process And Pelleting Process

The development of nuclear industry provides energy resources for human, but it also brings some problems such as producing a lot of liquid and gas radioactive waste. Liquid radioactive waste has larger proportion of all radioactive waste and many researches on treatment of radioactive wastewater have been carried out by other contries. In order to enhance purification effect, this paper developed an adsorption-microfiltration process and a coagulating coprecipitation-microfiltration process to treat radioactive wastewater which containing cesium and strontium respectively. This process is traditional treatment of radioactive waste combined with membrane technology.Three stages of researches were carried out. The first stage adopted continuous operation mode adsorption-microfiltration process to treat the cesium containing wastewater with the potassium zinc hexacyanoferrate as the adsorbent. Two tests were conducted and the experiment result showed that this process was effective to treat wastewater containing cesium. When the cesium concentration of the raw water was about 100μg/L, the removal of the cesium was higher than 97% and the decontamination factor was 53.43, 86.41 and concentration factor was 1869, 2385 respectively. The effluent turbidity was lower than 0.1 NTU. The calcium and the magnesium were not rejected while iron was rejected completely and the concentration Zn²⁺ was low if the asorbent being washed well, the effluent quality met Integrated Wastewater Discharge Standard (GB8978-1996).The second stage test was a full-scale test and used coagulating coprecipitation-microfiltration process in the batch operation mode to treat wastewater containing strontium. Two tests were developed according to whether pretreat membrane and different times of aeration. The process took Na₂CO₃ as the precipitant and FeCl₃ as the coagulant, the Na₂CO₃ dose was 1000 mg/L. The FeCl₃ dose was 20 mg/L and 10 mg/L in the sendimentator and membrane reactor respectively in order to enhance effect of strontium removal and slow membrane fouling. The capacity of system was 500 L/h, design water treatment quality is 100 m3. The operation effect of the full-scale cold test was good, when the strontium concentration of the raw water was about 5.1 mg/L and 3.9 mg/L and that of the effluent was 51.8μg/L and 59.5μg/L respectively, the average decontamination factor was 158 and 72 respectively. During the operation, the strontium didn't dissolve again. The effluent quality was good and the turbidity was lower than 0.1 NTU, the average turbidity was 0.06 NTU and 0.07 NTU respectively. The average removal of calcium reached 95.8% and 93.8% respectively and that of magnesium reached 56.6% and 61.8% respectively.The third stage was pelleting with jar-test. The sludge concentration of full-scale test was high and it was to difficult discharge due to clogging by cake. The purpose of pelleting research was to solve this problem and made the sludge discharge easily. The research was jar-test and took tap water as raw water, Na₂CO₃ as the precipitant, Na₂CO₃ dose was 1000 mg/L same as that used in the full-scale test. CaCO₃ was taken as crystal seed in order to make granular sediment. Based on many times tests, the optimum condition was 30 minutes to mix, 10 minutes to settle, and rotation speed was 120 rpm. The test result showed that practical size of CaCO₃ became bigger and centralized distribution with the operation. In addition, pelleting water softening was feasible to low effluent turbidity and remain hardness, this way was effective for slowing down the membrane fouling.