Vacuum Membrane Distillation Treatment Of Wastewater Produced In Vanadium Extraction From Stone Coal

Stone coal is an important vanadium resource in China. With the rapid development of steel industry, sophisticated technique in national defence, chemical industry, the demand of vanadium increases sharply and the vanadium extraction from stone coal interserting people more and more. In the roasting process of extracting vanadium from stone coal, large amouts of industrial salts are needs to promote the roasting effect and a lot of ammonium salts also are needed to precipitate vanadium from leaching solution. Hence, the wastewater containing high salinity and ammonium is produced in vanadium extraction from stone coal.The wastewater containing many heavy metals, ultra-high salinity, high SS content and turbidity was desalinated by vacuum membrane distillation (VMD) after pretreatment. The results showed that, the flux of the dilute can reach11.359kg/m2·h when the temperature was70℃, flow rate was60L/h and vacuum of osmosis side was0.095MPa during desalinating the wastewater containing high salinity after pretreatment. When the wastewater was concentrated by5times, the membrane flux deduced to7.219kg/m2·h, when the wastewater was concentrated by10times, the membrane flux also can arrived in3.185kg/m2·h. During the desalination processing, the conductivity of the dilute was less than10μS·cm-1and the salt rejection rate was up to99.98%. The produced fresh water can be reused to the vanadium extraction process, and the concentrated brine can be used to produce salts which also can be reused in vanadium extraction process by solar evaporation.The ammonia-nitrogen wastewater was treated by the vacuum membrane under the conditions of65℃,40L/h,0.09MPa at the initial pH value of11.0. The ammonia removal efficiency can reach95.52%after3.5h, and the ammonia-nitrogen in wastewater can be reduced from8950mg/L to403.2mg/L. The average water flux in this process was8.71kg·m-2·h-1. The treated ammonia-nitrogen wastewater then was adjusted to the pH value of11.0again, and continue to deammonia for2h, the ammonia-nitrogen in wastewater can be reduced to12.6mg/L, reaching the first class discharging standard of wastewater in China (GB-8978-1996). The treated ammonia wastewater can be reused as regeneration solution for ion exchange in the process of vanadium extraction from stone coal.A theoretical mass transfer model had been established for treating high salinity wastewater in this study, and the model predictions were very well in agreement with the experimental data. Economic analysis results showed that the running cost of treating the high salinity wastewater by vacuum membrane is1.97yuan/m3, and the running cost of treating ammonia-nitrogen wastewater is13.92yuan/m. The results showed that VMD is appropriate to treat the high salinity wastewater and high ammonia-nitrogen wastewater produced in vanadium extraction from stone coal.