Study On Treatment Of Ammonia Nitrogen Wastewater From Vanadium Shale Extraction By Stripping-ion Exchange Process

The process of vanadium was precipitated by ammonium salt of vanadium shale is widely used because of its high vanadium precipitation rate and good selectivity.In order to achieve better vanadium precipitation effect,excessive ammonium salts are often added in the process of vanadium precipitation,resulting in a large amount of residual ammonia nitrogen in the liquor of vanadium precipitation.The concentration of ammonia nitrogen is far higher than the discharge standard.At the same time,the national requirements for pollutant discharge are increasingly stringent.Therefore,nitrogen must be removed before discharge.In this study,the combined process of stripping and ion exchange was used to treat and recover ammonia nitrogen from the liquor of vanadium precipitation.The optimum conditions for removing high concentration of vanadium precipitation liquor by stripping were studied.And when the concentration of vanadium precipitation liquor was reduced to about 2000 mg/L,the stripping efficiency was reduced,so the vanadium precipitation wastewater after stripping was removed by ion exchange resin.The choosen of ion exchange resin,the best static adsorption conditions and the best dynamic adsorption and desorption conditions,as well as the mechanism of adsorption of ammonia nitrogen by ion exchange resin were studied.The cyclic stability of the resin was also studied.Using resin desorption solution that containing high ammonia nitrogen and high acid as ammonia absorption solution after stripping off and ammonium sulfate was precipitated.According to the research contents,the following conclusions are as follows:?1?The liquor of vanadium precipitation with ammonia nitrogen concentration up to 27500 mg/L was pretreated by stripping method.The concentration of ammonia nitrogen was reduced to 1999.56 mg/L under the optimum condition of 40?C,2 h,gas-liquid ratio 3200 and pH value 10.5,and the pH value of vanadium precipitation wastewater after stripping was 8.?2?The vanadium precipitation wastewater after stripping was further treated with ion exchange resin.Comparing the adsorption effects of four different ion exchange resins on ammonia nitrogen in vanadium precipitation wastewater,it was found that T-42 resin had a better removal rate of ammonia nitrogen and the optimum pH value value was 8.In dynamic test,under the optimum adsorption conditions of flow rate 9mL/min and column height-diameter ratio 21.0,the permeability point adsorption capacity is 21.91 mg/g and the end point adsorption capacity is 34.31 mg/g.The ammonia nitrogen concentration of 1999.56 mg/L with volume of 413 mL wastewater after two-stage series adsorption reduce to 0.15 mg/L,which meets ammonia nitrogen emission standard for new vanadium industry?GB26452-2011?.The desorption experiment of ion exchange resin showed that the desorption rate of ammonia nitrogen on resin saturated by adsorption was more than 99%under the desorption condition:the volume concentration of desorbent sulfuric acid solution was 18%,the flow rate was 3 mL/min,and the volume of desorbent solution was 2.67 beds.Ammonium sulfate was prepared from ammonia gas absorbed by desorbed sulfuric acid solution.After 10cycles of adsorption and desorption,the adsorption performance of resin was stable,thus,T-42 resin has good performance.?3?The adsorption of ammonia nitrogen by resin conforms to Langmuir isothermal adsorption model.The adsorption equilibrium time was 9 min,the pseudo-second-order kinetic model can better to describe the adsorption process.Particle diffusion as a velocity control step.The enthalpy change of the adsorption process is3.38 kJ/mol,and the entropy changes is 18.90 J/?mol K?.The Gibbs free energy is negative at different temperatures,which indicates that the reaction of T-42 resin adsorbing ammonia nitrogen is a spontaneous endothermic process.Infrared analysis showed that the adsorption process of ammonia nitrogen by resin was ion exchange between H⁺and NH₄⁺from sulfonic acid group of resin functional group.?4?The combined process of stripping and ion exchange was used to treat the liquor of vanadium precipitation with ammonia nitrogen concentration of 27500 mg/L in a vanadium plant in Jiangxi Province.The cost of comprehensive wastewater was2.43 yuan/m³.