ABSTRACT
This paper proposed a novel roasting process of extracting vanadium from high chromium vanadium slag. In this process, the high chromium vanadium slag was treated by NaOH-NaNO3 binary sodium salts, roasted in microwave heating furnace, and leached by water. During the roasting process, the temperature and time took a significant role in the conversion of vanadium and chromium. This novel microwave roasting was able to improve heating speed, accelerate the oxidization and decomposition of slag, and shorten the roasting time, compared with conventional muffle roasting. Under the optimum microwave roasting conditions (1 NaOH/NaNO3 mass ratio, 450â¯â roasting temperature, and 10â¯min roasting time), the leaching rates of vanadium and chromium were 94.11% and 90.81%, respectively. In the leaching process, the reaction mechanism for the water leaching process was proposed. The process showed that leaching time and sample size played a significant role, while leaching temperature and liquid-to-solid ratio showed no obvious effect. The leaching residue analysis showed the major mineralogical phases were Fe2O3, Na2TiO3, NaFeSiO4, and a small amount of polymeric substance ((Mn,Ca)x(Fe0.6,Cr0.4)yOz·nSiO2).
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%).
