Study On Treatment Of Vanadium,Chromium And Ammonia Nitrogen In The Vanadium Extraction Wastewater

In this paper,the vanadium extraction wastewater from Jianlong steel plant is taken as the research object,and the semi-dry flue gas desulfurization ash is used as a reductant for vanadium and chromium removal in the wastewater by chemical reduction precipitation,the byproduct gypsum and chromium sludge are obtained.Besides,MgCl2·6H2O and Na3PO4 are used as reagents for ammonia nitrogen removal in the wastewater by chemical precipitation,and the magnesium ammonium phosphate(MAP)is obtained.The details are as follows:(1)Removal of vanadium and chromium from vanadium extraction wastewater by chemical reduction precipitation.The effects of main operational parameters(reaction pH,desulfurization ash dosage,reaction time and reaction temperature)on the heavy metal removal are investigated,and the main reaction mechanism for this treatment technology is also proposed,and the optimum experimental conditions are determined.The optimum reduction conditions of Cr(VI)and V(V)are as follows:reduction pH is 2.5 desulfurization ash dosage is 5.9 g(29.5 g/L),reaction time is 15 min and reaction temperature is 25?.The optimum removal conditions of total Cr and V are as follows:reaction pH is 7.5,reaction time is 15 min.Under the optimal conditions,the residual concentrations of Cr(VI),total Cr and V are 0.17 mg/L,0.40 mg/L and 0.16 mg/L,respectively;(2)Removal of ammonia nitrogen from vanadium extraction wastewater by chemical precipitation.The effects of main operational parameters(combination of reagents,reaction pH,Mg2+:NH4+:PO43-molar ratio,reaction time and reaction temperature)on ammonia nitrogen removal are investigated,and the main reaction mechanism for this treatment technology is also proposed,and the optimum experimental conditions are determined.The optimum removal conditions of ammonium nitrogen are as follows:reagents are MgCl2·6H2O and Na3PO4,reaction pH is 9.5,Mg2+:NH4+:PO43-molar ratio is 1.1:1:1,reaction time is 15 min and reaction temperature is 25?.Under the optimal conditions,the removal efficiency of ammonia nitrogen is 95.54%and the residual concentration of ammonia nitrogen and phosphorus are 133.60 mg/L and 5.00 mg/L,respectively;(3)The precipitations produced in the experiment are characterized using X-ray diffraction(XRD),fourier transform infrared spectroscopy(FT-IR),scanning electron microscope-energy dispersive spectrometer(SEM-EDS)and thermogravimetric analysis(TGA),respectively,and these precipitations are gypsum(CaSO4·2H2O),chromium sludge and magnesium ammonium phosphate(MgNH4PO4·6H2O),respectively.Finally,the resource utilization methods of the byproduct gypsum,chromium sludge and magnesium ammonium phosphate from this technology are also proposed.The byproduct gypsum can be utilized to sinter or make cement.The chromium sludge could be used as a chromium resource to produce primary Cr2O3(the content of Cr2O3 is about 83.79%)by calcination at 1000 ?.The magnesium ammonium phosphate can be used as slow release fertilizer.In general,this study not only provides a novel resource utilization method of semi-dry flue gas desulfurization ash,but provides a low cost and efficient treatment technology for the vanadium extraction wastewater.