| As the development of industry, the demand for rare element material increases, but amounts of water would be polluted by wet extraction method or treatment of waste gas with water by smelt. In the process of Selenium extraction, Selenium in the waste water could be400～3000mg/L, at the same time it contained a amount of sulfate ion and chloride ion. Selenium easily permeates the common fixed column ion exchange system (CFCS) because of the high salinity of the solutions. It results in the low resin usage rate, the concentration of product decreased, and the expended energy increased. The running cost is high in the process of selenium recovery by chemical reduction method (RMB200～400per ton water), which would create giant economical load. Considering selenium is a rare element with high market value, the method to recover selenium from waste water with low running cost and to prevent environmental pollutant at the same time is significant for enterprise and society.The goal of this work was to select the commercial resins capable of extracting selenate ion or selenite ion with high selectivity. Batch adsorption experiments were performed. It proves that resin of C100(Fe3+) has good selectivity for selenite ion and resin of S108has good selectivity for selenate ion, and the combined process to recover selenium using resin of C100(Fe3+) and resin of S108is chosen. The absorption quantity of C100(Fe3+) for selenite solution with concentration of853mg/L is92.198mg/g-R and the adsorption quantity of S108for selenate with concentration of856mg/L is102.464mg/g-R. When waste water contains amounts of sulfate ion or chloride ion, the adsorption capacity of C100(Fe3+) for selenite is not reduced, but the adsorption capacity of S108for selenate is reduced to44%.Through the study on the velocity of adsorbing selenite ion and selenate ion by different resins, it is found that the major control factor (particle diffusion, liquid film diffusion and chemical reaction) changes during different adsorption phrase, which makes it impossible to calculate rapidly the adsorption process by the single model.The thermodynamic experimental of selenite ion and selenate ion adsorption by chosen resins shows that the value of ΔG0(-3.174KJ/mol) of C100(Fe3+) absorbing selenite ion is much less than the value of ΔG0(-0.314KJ/mol and-0.0650KJ/mol) of C100(Fe3+) absorbing selenate ion and sulfate ion, which further proves that C100(Fe3+) has better selectivity for selenite ion. The value of ΔG0(-8.809KJ/mol) of S108for selenate ion is much less than the value of ΔG0(-6.157KJ/mol and-4.243KJ/mol) of S108absorbing selenite ion and sulfate ion, which proves that S108has better selectivity for selenate ion.The dynamic experiment by counter-current decantation column and conventional column experiments investigate the effluent concentration and pH value,and resin usage rate by changing the height of column, flow speed and inflow concentration.The results show that the resin usage rate of conventional column is affected by all the above parameters.. When changed from column system to counter-current decantation system, and when the inflow water concentration is856mg/L, the height of column is80mm and flow rate is0.6mL/min, the utilization rate of C100(Fe3+) absorbing selenite ion, S108absorbing selenite ion and selenate ion are improved24.1%,22.83%,30.2%.The desorbing experiment of saturated resin from different exits of the U shaped column, the concentration of liquid in the resin grows and then reduces, and forms secondary adsorption during the late stages. The concentration of desorbed concentrated solution is improved365%by split and counter-current desorption system(CCDS) comparing with CFCS and the usage of desorption liquid is reduced46.15%.Base on electrical network model to simulate and compute the CCDS by the particle diffusion, liquid film diffusion and chemical reaction of the ion exchange process to series circuits and each unit is changed to a series of resistance, inductance, capacitance, current, voltage etc. and it is verified that the simulation reached stable through25cycles and the error of outlet concentration between it and experiment result is1.89%, which improves the computing speed and the accuracy of the simulation result. By simulating and optimizing the process of CCDS by simulating and computing the concentration of inflow water, it is found that the best treatment concentration of selenium ion could reach around300mg/L by using the CFCS and it could improve the best treatment concentration of selenium ion to300～2000mg/L by using CCDS. Then it shows that selenium products with recovery ratio of92%,88%and91%and concentration of24.2g/L,21.6g/L,27.4g/L would be produced by simulating and computing the process of C100(Fe3+) recovering selenium(Ⅳ), S108recovering selenium(Ⅳ) or selenium (Ⅵ) by using the process of CCDS method and confirming the best inflow water speed, the best resin transfer quantity per cycle, operation cycle, and the split current ratio and inflow water speed of concentrated solution, which improves the processing efficiency significantly, and comparing with experiment, the treatment capacity per unit resin is improved12%,11%and17%, and the usage of desorption solvent is reduced32%,28%and41%respectively. |
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