ABSTRACT
A new comprehensive utilization of vanadium slag (VS) method focusing on inhibiting leaching of iron (Fe) during the leaching of vanadium (V) using sulfuric acid (SA) was proposed. In this process, Cr2O3 was added to VS to conjugate with Fe in the VS to form (Fex,Cr1-x)2O3 which is insoluble in SA, resulting in the decrease of leaching ratio (LR) of Fe to avoid the subsequent separation difficulty of V in leachate. The phase evolutions of VS during the roasting and SA leaching process, and the influences of roasting temperature, roasting time, and addition of Cr2O3 on the LR of V, Fe and chromium (Cr) from VS were studied. When the addition of Cr2O3 is 12 wt.%, the mass concentration of V in the leachate is 1 order magnitude higher than Fe and the mass ratio of V to Fe reaches 18.34. The LR of V, Fe and Cr are 91% 1.39% and 0.28%, respectively. The leaching residue can be reused as ironmaking raw material. More importantly, the (Fex,Cr1-x)2O3 and Fe2TiO5 can be separated from the leaching residue and recycled as raw materials for black ceramic pigments and titanium dioxide production by mineral processing technology, respectively.
ABSTRACT
A novel resource utilization of the calcium-based semi-dry flue gas desulfurization ash is investigated. In the present study, the semi-dry desulfurization ash is used as a reductant for chromium and vanadium removal by chemical reduction precipitation, the byproduct gypsum and chromium-contained sludge are obtained. Besides, the effects of main operational parameters (reaction pH, desulfurization ash dosage and reaction time) on the heavy metal removal are investigated, and the main reaction mechanism for this treatment technology is also proposed. Under the optimal conditions, the residual concentrations of Cr(VI), total Cr and V are 0.163mg/L, 0.395mg/L and 0.155mg/L, respectively. Additionally, byproduct gypsum and chromium-contained sludge are characterized using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscope-energy dispersive spectrometer (SEM-EDS) and thermogravimetry differential scanning calorimetry (TG-DSC), respectively. Finally, the resource utilization methods of the byproduct gypsum and chromium-contained sludge from this technology are also submitted. The byproduct gypsum can be utilized to produce hemihydrate calcium sulfate whisker, and the roasted heavy metal precipitation can be used as a primary chromium raw material (Cr2O3 content is about 83%).
ABSTRACT
In the present study, a novel resource utilization method using wet magnesia flue gas desulfurization (FGD) residue for the simultaneous removal of ammonium nitrogen (NH4-N) and heavy metal pollutants from vanadium (V) industrial wastewater was proven to be viable and effective. In this process, the wet magnesia FGD residue could not only act as a reductant of hexavalent chromium [Cr(vi)] and pentavalent vanadium [V(v)], but also offered plenty of low cost magnesium ions to remove NH4-N using struvite crystallization. The optimum experimental conditions for Cr(vi) and V(v) reduction are as follows: the reduction pH = 2.5, the wet magnesia FGD residue dose is 42.5 g L-1, t = 15.0 min. The optimum experimental conditions for NH4-N and heavy metal pollutants removal are as follows: the precipitate pH = 9.5, the n(Mg2+) : n(NH4 +) : n(PO4 3-) = 0.3 : 1.0 : 1.0, t = 20.0 min. Finally the NH4-N, V and Cr were separated from the vanadium containing industrial wastewater by forming the difficult to obtain, soluble coprecipitate containing struvite and heavy metal hydroxides. The residual pollutant concentrations in the wastewater were as follows: Cr(vi) was 0.047 mg L-1, total Cr was 0.1 mg L-1, V was 0.14 mg L-1, NH4-N was 176.2 mg L-1 (removal efficiency was about 94.5%) and phosphorus was 14.7 mg L-1.
ABSTRACT
A novel treatment for chromium, vanadium and ammonium from vanadium industrial wastewater using a byproduct of magnesium-based wet flue gas desulfurization is investigated. In the present study, the byproduct is used as a reductant for chromium and vanadium removal by chemical precipitation, and the residual magnesium ion can also be used to remove ammonium in the present of phosphate by struvite crystallization. Besides, the effects of main operational parameters (reaction pH, byproduct dosage and reaction time) on the heavy metal removal and ammonium removal (reaction pH, Mg2+:NH4+:PO43- molar ratio and reaction time) are investigated, and the reaction mechanism for this treatment technology is also proposed. Under the optimal conditions, the residual concentrations of chromium(IV), total chromium and vanadium are 0.046mg/L, 0.468mg/L and 0.06mg/L, respectively. The removal efficiency of ammonium is 95.72% and the residual concentrations of ammonium and phosphorus are 137.12mg/L and 5.49mg/L, respectively. Additionally, the precipitations are characterized using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscope-energy dispersive spectrometer (SEM-EDS) and thermogravimetry differential scanning calorimetry (TG-DSC), respectively. Finally, a resource utilization method of the precipitation sludge from this technology is also presented.
