| A prilling method was investigated through hydraulic stirring in order to solve theincreasing management difficults of mechanical equipment and radiation protection inmechanical mixing prilling-microfiltration combination process which has a goodeffect on strontium removal. The strontium element was removed by formingcompacted crystal particles when Na2CO3and CaCO3were used as precipitating agentand crystal seed, respectively. In order to improve the settling effect and reducemembrane fouling, flocculant FeCl3was dosed in the membrane separator withconcentration of10mg/L.The sedimentation performance of the particles formed byprilling was improved and the effluent turbidity was reduced so that the load offollowing microfiltration process was alleviated.The hydraulic mixing prilling-microfiltration combination process for strontiumremoval is divided into the seed crystal-preparation stage and the strontium-removalstage. In the seed crystal-preparation stage, the results showed that the formed crystalparticles were compacted after30prilling cycles. The mean removal rate of hardnesswas55%and the turbidity was under0.50NTU in the precipitated effluent. Practicalsize became bigger and centralized in distribution with the operation, the average sizeof crystal particles that obtained was49.10μm. The crystal seed particle size waslarge enough with good settleability to meet the requirements of the laterstrontium-removal stage. The later study found that lower prilling efficiency became abottleneck of experiments of high crystal seed dosing quantity in strontium-removalstage. So the research changed CaCO3dosing quantity, mixing speed and the numberof prilling respectively to improve the prilling efficiency. On the basis of meeting therequirements of crystal seed preparation, determined the mixing speed was320rpm,CaCO3dosing quantity was2g/L with30times prilling cycles. The study resultshowed that prilling efficiency improved in new prilling conditions.On the basis of above tests, the strontium-containing wastewater treatment effectwas investigated by the hydraulic mixing prilling-microfiltration combination processwith different hydraulic retention time, the concentration of seed crystal, membrane fouling and tempreture in the the strontium-removal stage. The treatment effect andthe stability of the effluent were monitored. The theory of strontium-containingwastewater treatment by hydraulic mixing prilling process was analyzed in crystaltype aspect. During the operation, the strontium didn’t dissolve again. The effluentquality was stable and the turbidity was lower than0.10NTU. The results showed thatreducing hydraulic retention time could improve the decontamination factor (DF),increase the sludge concentration factor (CF). The increase of seed crystal dosingquantity rose DF and reduced CF. The formation of mud cake layer played animportant role in further strontium removal, helped to maintain a stable treatmenteffect. When600L wastewater was treated, DF became stabe. Temperature affectedsignificantly the efficiency of strontium removal, DF at room temperature and lowtemperature during the runtime were617and9, respectively. In the period ofstrontium removal process by hydraulic prilling method, CaCO3in the structure ofcalcite crystal was gradually transfered into a mixed crystal stucture, mainly of whichwas aragonite stucture. Through the comprehensive analysis, the result showed thatthe hydraulic mixing prilling-microfiltration combination process had potential forwider application in the removal of strontium from radioactive wastewater. |
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