| The production of phosphogypsum is the largest industrial by-product, the yield almost equivalent to the annual output of natural gypsum in China. And it is also one of the largest emissions of solid waste in the chemical industry. Phosphorus gypsum is the main solid waste of phosphorus chemical industry. When producing about 1 ton of wet process phosphoric acid(in P2O5), there would be about 4~5t of phosphorgypsum(CaSO4·2H2O) produced. According to statistics, the by-product phosphogypsum were about 50 million tons in China in 2011, and the accumulation of phosphogypsum was more than 300 million tons. Although people have done a lot of research on the comprehensive application of phosphorus gypsum, the utilization ratio of the phosphorus gypsum is still very low. Due to the complex process of traditional gypsum sulfuric acid, the investment is very big, the energy consumption is very high,the craft process produces and the serious secondary pollution has been difficult to promote. How to make full use of domestic resources to produce low energy consumption, low cost, low investment, no environmental pollution and high quality sulfuric acid has become the focus of attention of the industry. The technology of bipolar membrane electrodialysis(BMED) is combined bipolar membrane with anion cation exchange membrane and used the chemical properties of hydrolysis generating H+ and OH- which reacted in bipolar interface layer under the effect of DC field,which convert the salt in aqueous solution into corresponding acid and base. This method is called bipolar membrane electrodialysis and has been widely used in the field of cleaner production of acid and alkali and treatment of chemical waste water inother fields.In order to use the phosphogypsum resource effectively, this paper aims to seek new ways to solve the problem. On the basis of BMED, we study the influence factors and rules of producing sulfuric acid of phosphogypsum, which will build a foundation for realizing sulfur cycling utilization in the process of wet phosphoric acid production. However, BMED technology has many advantages, for example, simple operation, low energy consumption, less pollution, and low cost, which is a beneficial method to use phosphogypsum efficiently and promote the sustainable development of phosphorus chemical industry.In this paper, bipolar membrane electrodialysis method is applied in phosphogypsum sulfate. The operating voltage, the material quality concentration,and electrodialysis time of each evaluation index in the single factor experiment was investigated. The factor affecting the concentration of sulfuric acid was also examined,and its mechanism was studied. The main research work and achievements are as follow:(1) Operation voltage, concentration of material quality, and the time of electrodialysis were studied on the influences of each evaluation index respectively.The results showed that: when change the operating voltage, within a certain range,sulfuric acid concentration and the energy consumption increases with the operating voltage. When we change the mass concentration of materials, current efficiency decreases with increasing mass concentration of the material, and energy consumption increases with increasing mass concentration of the materials. When we change the electrodialysis time, current efficiency decreases with longer time, energy consumption increases with the extension of electrodialysis, sulfuric acid concentration increases and then decreases with longer time.(2) We also studied the three factors, four levels orthogonal experiment, to choose the optimal conditions, in which the three factors were operating voltage, mass concentration and electrodialysis time. The concentration of sulfuric acid was seen as evaluation index, and the experimental results show that: concentration of material affects the results of experiments largely, and then the electrodialysis time, operatingvoltage. So combined with the index of sulfuric acid concentration, energy consumption, and current efficiency, we preferred liquid concentration of 13g/L,electrodialysis time of 150 minutes, operating voltage of 15 V as the process conditions. Finally, sulfuric acid concentration was 0.075mol/L, and energy consumption was 0.165 kW·h/mol.(3) This paper also studied the causes of sulfuric acid concentration by intermittent electrodialysis and continuou electrodialysis experiment. The results show that: sulfuric acid concentration was related to solubility.(4) Researched on attempting to add EDTA-2 sodium into phosphogypsum so that the complexing agent complexed with calcium ions, and the phosphorus gypsum were changed into hemihydrate gypsum to increase the solubility of gypsum,hemihydrate gypsum were treated by filtration to reduce the impact on experimental results of solid.The results showed that we would obtain mixed acid by adding EDTA-2 sodium in material; sulfuric acid concentration would be improved by changing phosphorus gypsum into hemihydrate gypsum; reduced separation performance since the film stack were prolonged use. |
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