Treatment Of Wastewater Containning Tin By Precipitation-Coagulation- Microfiltration Process And Design Of Pilot Test Device For Strontium Removal

With the rapid development of electrolytic tin plate,printed circuit board,mirror and other industries,wastewater containing tin caused the attention of people in recent years.Excessive intake of inorganic tin would cause diseases,and high concentration of tin would cause harm to aquatic organisms.Inorganic tin could be converted into organic tin by alkylation under certain conditions if discharged directly without treatment,which would result in more serious harm.Precipitation-coagulation process and precipitation-coagulation-microfiltration process were developed for the treatment of the wastewater containing tin.Effects of precipitant type,precipitant dosage,reaction time and stirring intensity on chemical precipitation process and effects of coagulant type,coagulant dosage,stirring rate and settling time on the coagulation process were studied in the jar tests,and the optimum values of each factor were determined.The results showed that,when pH value was about 3.0 and tin concentration was about 17.7 mg/L in the raw water,sodium carbonate was used as precipitant agent,with the optimum dosage 90 mg/L;ferric chloride was used as coagulant,with the optimum dosage 14 mg/L;the reaction time was 15 mins;and the optimum G value was 120 s^-1.Precipitation-coagulation process could meet the ralated standard when settling time was 60 minutes.However,precipitation-coagulation-microfiltration process could greatly improve the quality of the effluent,with the optimum settling time 15 minutes.The operation mode of the precipitation-coagulation-microfiltration process was investigated in the lab-scale tests.The results showed that both intermittent operation and continuous operation were advantageous to remove tin.The parameters determined by jar test,removal rates for tin were both 99.97%,when temperature was25?,the tin concentration in the raw water?pH value was 3.0?was 17.5 mg/L,respectively.The membrane fouling rate of the two operation modes were slow,and the recovery rate of membrane flux after physical cleaning were 86.5%and 92.4%for intermittent operation and continuous operation,respectively.In solid phase analysises,X ray photoelectron spectroscopy analysis?XPS?proved that Sn²⁺formed Sn?OH?₂,Fe³⁺formed Fe?OH?₃,so that the tin and iron ions were transferred from the liquid phase to the precipitation.The results of scanning electron microscope?SEM-EDS?showed that the precipitate was of the shape of aggregates with a regular pattern,and the element analysis results confirmed the results of XPS analysis.The previous research showed that carrier precipitation-microfiltration combination process for the removal of strontium achieved good results.In order to achieve large-scale applications,the design and calculation of pilot-scale test device were carried out,including the optimal design of process,calculation of equipment and supporting structures and the design of PLC control program.This work laid a solid foundation for the pilot test research.