Office Online
Journal Online
The sodium roasted-acid leaching tailing (SRALT) of vanadium slag with a certain amount of vanadium exhibits potential environmental risk. To investigate the leaching behavior of vanadium from the SRALT, neutral batch leaching tests were performed. The evolution of vanadium concentration, pH, redox potential (Eh), dissolved oxygen, and conductivity as a function of time was measured. Pourbaix diagrams of V–H2O system with different vanadium concentrations were obtained to identify the ionic speciation of vanadium in leachate. X-ray diffraction, X-ray photoelectron spectroscopy, field emission-scanning electron microscopy, and thermogravimetry–differential scanning calorimetry analysis were conducted to investigate the mineralogical evolution of the SRALT during the leaching process. It was found that the major minerals of the original SRALT are titanomagnetite, spinel, olivine, and augite. The valence states of V existing in the original SRALT are V3+ and V5+. The pH and Eh values of the obtained leachates are 10.00–10.58 and (-43)–(+67) mV, respectively. In this pH and Eh region, the released vanadium is mainly present as HVO42-. The FeOOH and CaCO3 would form during the leaching process. The HVO42- would be mainly adsorbed by the FeOOH and slightly incorporated into the CaCO3, resulting in the decline in the vanadium concentration. The vanadium concentration above 27 mg L-1 and the dissolved oxygen value below 5.0 mg L-1 can be obtained after a short leaching period. As a V(V)-releasing and oxygendepleting substance, the leaching toxicity of the SRALT should not be ignored.
To solve the problem of difficult utilization of steel slag, the liquid steel slag was modified and the air-quenching granulation process was carried out to make steel slag into a value-added end product: air-quenching granulated steel slag. The granulated slag was tested to analyze the variation rule of slag properties under different modification conditions. Based on the phase diagram of CaO–Si2O–FeO–MgO–Al2O3 slag system, the feasibility of blast furnace (BF) slag as modifier was determined. When the addition of BF slag was increased from 0% to 35%, following results were obtained. The slag fluidity was improved, and the air-quenching temperature range was expanded. Then, the yield of air-quenched steel slag increased, while the granulation rate, the degree of sphericity, the compactness were decreased. Furthermore, the air-quenching granulation process could substantially improve the stability and the amorphous content of steel slag. The maximum removal rate of free CaO was above 80% and the amorphous content was up to 95%. Taking the factors of yield and properties of granulated steel slag into full consideration, the optimum proportion of BF slag is around 15%.
Microstructural classification is typically done manually by human experts, which gives rise to uncertainties due to subjectivity and reduces the overall efficiency. A high-throughput characterization is proposed based on deep learning, rapid acquisition technology, and mathematical statistics for the recognition, segmentation, and quantification of microstructure in weathering steel. The segmentation results showed that this method was accurate and efficient, and the segmentation of inclusions and pearlite phase achieved accuracy of 89.95% and 90.86%, respectively. The time required for batch processing by MIPAR software involving thresholding segmentation, morphological processing, and small area deletion was 1.05 s for a single image. By comparison, our system required only 0.102 s, which is ten times faster than the commercial software. The quantification results were extracted from large volumes of sequential image data (150 mm2, 62,216 images, 1024 × 1024 pixels), which ensure comprehensive statistics. Microstructure information, such as three-dimensional density distribution and the frequency of the minimum spatial distance of inclusions on the sample surface of 150 mm2, were quantified by extracting the coordinates and sizes of individual features. A refined characterization method for two-dimensional structures and spatial information that is unattainable when performing manually or with software is provided. That will be useful for understanding properties or behaviors of weathering steel, and reducing the resort to physical testing.
News
Author Center
Links