Guangshi Li

Oxygen permeability and CO2-tolerance of Ce0.8Gd0.2O2-δ-LnBaCo2O5＋δ dual-phase membranes

Abstract A series of oxygen permeable dual-phase composite oxides 60 wt% Ce0.8Gd0.2O2–δ-40 wt% LnBaCo2O5+δ (CGO-LBCO, Ln = La, Pr, Nd, Sm, Gd and Y) were synthesized through a sol-gel route and effects of the Ln3+ cations on their phase structure, oxygen permeability and chemical stability against CO2 were investigated systemically by XRD, SEM, TG-DSC and oxygen permeation experiments. XRD patterns reveal that the larger Ln3+ cations (La3+, Pr3+ and Nd3+) successfully stabilized the double-layered perovskite structure of sintered LBCO, while the smaller ones (Sm3+, Gd3+, and Y3+) resulted in the partial decomposition of LBCO with some impurities formed. CGO-PBCO yields the highest oxygen permeation flux, reaching 2.8×10−7 mol·s−1·cm−2 at 925 °C with 1 mm thickness under air/He gradient. The TG-DSC profiles in 20 mol% CO2/N2 and oxygen permeability experiments with CO2 as sweep gas show that CGO-YBCO demonstrates the best chemical stability against CO2, possibly due to its minimum basicity. The stable oxygen permeation flux of CGO-YBCO under CO2 atmosphere reveals its potential application in the oxy-fuel combustion route for CO2 capture.

Extraction of metals from complex sulfide nickel concentrates by low-temperature chlorination roasting and water leaching

The recovery of valuable metals from complex sulfide concentrates was investigated via chlorination roasting followed by water leaching. A reaction process is proposed on the basis of previous studies and the results of our preliminary experiments. During the process, various process parameters were studied, including the roasting temperature, the addition of NH4Cl, the roasting time, the leaching time, and the liquid-to-solid ratio. The roasted products and leach residues were characterized by X-ray diffraction and vibrational spectroscopy. Under the optimum condition, 95% of Ni, 98% of Cu, and 88% of Co were recovered. In addition, the removal of iron was studied in the water leaching stage. The results demonstrate that this process provides an effective approach for extracting multiple metals from complex concentrates or ores.

In–situ XRD and EDS method study on the oxidation behaviour of Ni–Cu sulphide ore

The oxidation mechanism of sulfides is the key issue during the sulphide–metallurgy process. In this study, the phase transformation and element migration were clearly demonstrated by in–situ laboratory–based X–ray diffraction (XRD) and energy–dispersive X–ray spectroscopy (EDS), respectively. The reaction sequence and a four–step oxidation mechanism were proposed and identified. The elemental distribution demonstrated that at a low temperature, the Fe atoms diffused outward and the Ni/Cu atoms migrated toward the inner core, whereas the opposite diffusion processes were observed at a higher temperature. Importantly, the unique visual presentation of the oxidation behaviour provided by the combination of in–situ XRD and EDS might be useful for optimising the process parameters to improve the Ni/Cu extraction efficiency during Ni–Cu sulphide metallurgy.

In-situ high temperature X-ray diffraction study on the phase transition process of polymetallic sulfide ore

The phase transformation of the polymetallic sulfide ore is quite complicated, especially the variety and diversity of the roasted intermediate. The mineralogy properties of the ore particles were characterized by XRF, ICP and SEM-EDS. The thermal stability of the complex ore was investigated using TG-DSC under different atmosphere (pure N2 and 1% O2–N2). The phase changes and intermediates were revealed by the in-situ XRD in pure N2 and 1% O2-N2 atmospheres with the temperature range from 25 to 800°C. These results indicated that the crystal transformation of the pyrrhotite from monoclinic to hexagonal at 320°C, and the pentlandite and chalcopyrite were decomposed into monosulfide solid solution in pure N2. While the pentlandite and chalcopyrite were completely oxidized into M*xFe3-xO4 (M*=Fe, Ni, Cu) and Fe2O3, which is also the final product of the ore sample oxidized under 1% O2–N2 atmosphere.

Recovery of Nickel and Copper from Polymetallic Sulfide Concentrate through Salt Roasting Using NH 4 Cl

The roasting of nickel-bearing sulfides is a complex but important process which has not been adequately characterized. Combination of X-ray diffraction and scanning electron microscopy has been proved to be useful for such experiments. The leaching results of nickel, copper, iron and cobalt was analyzed by ICP methods. Process possibility of polymetallic sulfide concentrates through a three-step procedure (oxidation roasting — chlorination — water leaching) was suggested. Ammonium chloride could react with nickel/copper oxides to produce intermediate complexes. At the temperature range of 280~340 oC, these complexes further decomposed to the corresponding simple chlorides. Roasting sulfide concentrate using NH4Cl is effective for complex ores.

Mineralogical Analysis of Nickel/Copper Polymetallic Sulfide Ore by X-Ray Diffraction Using Rietveld Method

The analysis of mineralogical characteristics has important significance in comprehensive utilization of polymetallic sulfide mineral resources. The wavelength dispersive X-ray fluorescence (WDXRF) and X-ray diffraction were performed for the standardless quantitative analysis of Ni/Cu polymetallic sulfide ore. On the basis of fundamental parameter approach and Rietveld refinement Method, the validity of mineralogical identification and quantification was confirmed for analyzing this complex sulfide ore. The quantification results were in good agreement with elemental concentrations determined by XRF and ICP, which has explained the subtle differences among four samples in the range of different granularity (>10mm; 6–10mm; 1–6mm; <1mm;). In addition, the thermogravimetric curves and magnetic hysteresis curves, as well as element distribution map characterized by SEM-EDS, shown tiny differences among four samples. These results indicate that quantitative phase analysis using the Rietveld method represents a new powerful and fast tool in studies of the complex sulfide deposit.

Phase Transformation and Element Migration in the Oxidation Process of Nickel-Copper Sulfide Ore

The preoxidation of the ore has a profound significance to the concentration, separation and purification of nickel and copper from the lean complex ore. In this paper, the natural Ni-Cu sulfide mineral samples under the elevated temperature condition in air were investigated, as well as under isothermal condition at 600 °C in air. The mineralogical characterization was studied using XRF, ICP and the Rietveld method. The oxidation behavior and the element migration of the Ni-Cu sulfide ore were studied by XRD, SEM-EDS and TG. The XRD Rietveld method was successfully developed in the phase identification and quantification of this complex ore powder sample. The oxidative intermediates (Cu/Ni-ferrite) were detected by XRD, and the process of the element migration was obviously revealed by the line scans using SEM-EDS. It is the preoxidation of this mineral that provides guidance for the extraction of valuable metals from low-grade Ni-Cu sulfide ores in the future.

Corrosion Mechanism of MgO‐C Ladle Refractory in Contact with MgO‐CaO‐Al2O3‐SiO2 SLAG

The corrosion resistance and corroded microstructure of MgO-C refractory in molten slag are investigated by immersion test in muffle furnace at 1600 °C. The microstructure and chemical compositions of the specimens after erosion experiment are characterized by scanning electron microscope (SEM) and energy dispersive X-ray (EDX). The results confirm that the oxidation of graphite is the most important degradation mode of MgO-C refractory. The structure of the refractory material is damaged due to the decrease of graphite, as a result, the periclase substrate reacts with the molten slag directly. The corrosion process is controlled by the dissolution of the refractory materials into slag, low melting point oxides are therefore generated which lead to the damage of MgO-C refractory finally.