Application of RSM to optimize the recovery of ammonia nitrogen from high chromium effluent produced in vanadium industry using struvite precipitation

Abstract

It is difficult to achieve resource separation and recovery from hazardous vanadium-extracted effluent containing high ammonia nitrogen and hexavalent chromium. Multi-objective optimization by response surface methodology (RSM) based on the Box-Behnken design (BBD) was applied to maximize ammonia nitrogen recovery percent (R(N), %) and minimize the Cr loadings (L(Cr), %) during struvite precipitation to realize Cr(VI) separation and resources recovery from vanadium-extracted effluent. The response variables were correctly predicted by two second-order polynomial models, and R(N) of 98.87% and L(Cr) of 0.118% were achieved under optimal conditions (pH of 9.16, Mg/N of 1.3, and P/N of 1.165). Besides, the morphology of the precipitation sample under the optimal condition was confirmed as struvite crystals by XRD and SEM, and the Cr content of the recovered struvite meets the requirements of fertilizer. This paper demonstrated the reliability and validity of direct recover ammonia nitrogen by struvite precipitation from the vanadium-extracted effluent. Moreover, it provided practical support for an effective way on Cr(VI) separation and resources recovery from high hexavalent chromium and ammonia nitrogen complicated effluent like hazardous vanadium-extracted effluent.