| Phosphogypsum is an industrial waste residue produced by wet-process phosphoric acid in the phosphorus chemical industry,with an annual increase of up to 50 million tons of emissions.Phosphogypsum contains more impurities and is difficult to be comprehensively treated,with a utilization rate of only 30% to 40%.At present,electrochemical treatment of phosphogypsum mostly uses bipolar membrane electrodialysis technology to directly process phosphogypsum to obtain sulfuric acid and calcium hydroxide,or electrolytically process phosphogypsum decomposition liquid to obtain sulfuric acid and alkali.However,the current cost of bipolar membranes is high,and the amount of ion penetration is large.Compared with the ion exchange membranes in diaphragm electrolysis,the bipolar membranes have poor adaptability to changes in p H.In this paper,diaphragm electrolysis tec hnology is used to form a complete set of phosphogypsum recycling process,which is mainly divided into the following three parts:(1)Sodium hydroxide alkaline washing phosphogypsum,analysis of the effect of experimental conditions on the recovery rate o f sulfuric acid in phosphogypsum decomposition liquid.The experimental results show that under the best conditions(the mass ratio of phosphogypsum to sodium hydroxide is 1.6,the p H of the sodium hydroxide solution is 13.50,the reaction temperature is room temperature and the reaction time is 60 min),the sulfuric acid recovery rate can reach 83.21%;The residue was filtered under this condition for characterization,and the product was found to be a pure and excellent calcium hydroxide precipitate.(2)Electrolytic treatment of phosphogypsum decomposition liquid by diaphragm to obtain recyclable sulfuric acid and sodium hydroxide.Experiments in the existing dual-membrane three-chamber electrolyzers with a membrane spacing of 10 mm and 2 mm respectively found that reducing the membrane spacing greatly improved the performance of the device.The optimal conditions for the reaction can be achieved at a lower voltage.In the improved device with a diaphragm spacing of 2 mm,the OH-recovery rate of the alkali chamber is increased by approximately 25% and the electrolysis efficiency is increased by 12%.(3)Based on the experimental results of the previous two chapters,the calculated processing cost is 478.4 yuan / ton,which is about 700 yuan / ton less than the bipolar membrane electrodialysis technology.Using Chem CAD to simulate the process flow to explore its stability and define the reaction parameters based on the experimental optimization results of the first two chapters,analyze the material balance results of the two process processes of alkali-washed phosphogypsum and electrolytic sodium sulfate,and analyze the economic feasibility.The results show that the total treatment cost for the daily treatment of 2000 kg / d phosphogypsum is only RMB 31.05 / ton.Diaphragm electrolytic phosphogypsum is based on the assumption of bipolar membrane electrodialysis treatment of phosphogypsum in the existing research.It is based on electrochemistry and does not add any additional agents to achieve efficient treatment.Convert the phosphogypsum into raw materials such as sodium hydroxide and sulfuric acid at a lower treatment cost to solve the current treatment problems of phosphogypsum. |
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