Recovery of Rare Earth Elements from Phosphate Rock by Hydrometallurgical Processes - A Critical Review

Generally, phosphate rock contains about 0.05wt% rare earth elements (REEs) on average. And the world commercial phosphate rock production is estimated to be 250 million tons per year, which makes phosphate rock a potential new REEs resource. However, low content of REEs in phosphate rock leads to the technical challenges and cost overages that hindered the commercial recovery of REEs. In this paper, an overview of achievements aiming at solving the challenges is given. Based on the decomposition processes of phosphate rock by H2SO4, HNO3, HCl, H3PO4, various REEs recovery processes via crystallization, precipitation, solvent extraction and ion exchange methods are systematically reviewed. In H2SO4 processes, REEs are recovered based on the removal of impurities from phosphoric acid and phosphogypsum since the main challenge is the diluted content of REEs in these products. In the case of HCl, HNO3 and H3PO4 processes, REEs entirely transfers into leaching solution and the recovery research are mainly focused on REEs extraction from leaching solutions. For REE extraction from high phosphorus content leaching solutions, crystallization, precipitation, and ion exchange methods are currently inconsiderable due to the high energy consumption, impurity involvement and low efficiency, respectively. Solvent extraction seems to be the potential promising method in terms of its good overall performance. Finally, recommendations to promote the development of REEs recovery technologies from phosphate rock are provided.

Bearing capacity and seismic performance of Y-shaped reinforced concrete bridge piers in a freeze-thaw environment

A quantitative study is performed to determine the performance degradation of Y-shaped reinforced concrete bridge piers owing to long-term freeze-thaw damage. The piers are discretized into spatial solid elements using the ANSYS Workbench finite element analysis software, and a spatial model is established. The analysis addresses the mechanical performance of the piers under monotonic loading, and their seismic performance under low-cycle repeated loading. The influence of the number of freeze-thaw cycles, axial compression ratio, and loading direction on the pier bearing capacity index and seismic performance index is investigated. The results show that freeze-thaw damage has an adverse effect on the ultimate bearing capacity and seismic performance of Y-shaped bridge piers in the transverse and longitudinal directions. The pier peak load and displacement ductility coefficient decrease with increasing number of freeze-thaw cycles. The axial compression ratio is an important factor that affects the pier ultimate bearing capacity and seismic performance. Upon increasing the axial compression ratio, the pier peak load increases and the displacement ductility coefficient decreases, the effects of which are more significant in the longitudinal direction

Altered N-glycan composition impacts flagella-mediated adhesion in Chlamydomonas reinhardtii

For the unicellular alga Chlamydomonas reinhardtii, the presence of N-glycosylated proteins on the surface of two flagella is crucial for both cell-cell interaction during mating and flagellar surface adhesion. However, it is not known whether only the presence or also the composition of N-glycans attached to respective proteins is important for these processes. To this end, we tested several C. reinhardtii insertional mutants and a CRISPR/Cas9 knockout mutant of xylosyltransferase 1A, all possessing altered N-glycan compositions. Taking advantage of atomic force microscopy and micropipette force measurements, our data revealed that reduction in N-glycan complexity impedes the adhesion force required for binding the flagella to surfaces. This results in impaired polystyrene bead binding and transport but not gliding of cells on solid surfaces. Notably, assembly, intraflagellar transport, and protein import into flagella are not affected by altered N-glycosylation. Thus, we conclude that proper N-glycosylation of flagellar proteins is crucial for adhering C. reinhardtii cells onto surfaces, indicating that N-glycans mediate surface adhesion via direct surface contact

Improved Dark Channel Defogging Algorithm for Defect Detection in Underwater Structures

Underwater structures are crucial for national economic and social development. However, because of their complex environment, they are susceptible to damage during service. This damage should be prevented to minimize casualties and economic loss. Therefore, this study investigates the problems of disease identification and area statistics of underwater structures. To this end, the Dark-Retinex (DR) algorithm that can enhance the image of underwater structure defects is proposed. The algorithm consists of a combination of a dark channel algorithm and the Retinex algorithm. This study analyzes the current research status of underwater image processing technology, designs the overall framework of the DR algorithm, and uses the underwater structure disease image to verify the algorithm. Comparing the effect of the image with only the dark channel defogging and DR algorithm processing, the DR algorithm is observed to achieve “defogging” processing of underwater structural disease images to achieve better enhancement effects. Moreover, for accurate disease area statistics, the binary morphology and optimal threshold segmentation theories are combined to perform disease edge screening and remove interference information. Finally, accurate statistics of the proportion of diseased pixels are achieved, as well as the quantitative detection of surface diseases of underwater structures. After actual operational verification, the improved image dehazing and parallel boundary screening algorithms can achieve better application results to detect underwater structure defects and disease statistics. The objective evaluation shows that the DR algorithm facilitates image processing, can obtain relatively high-quality target images, and can solve the problems of time-consuming and labor-intensive detection of underwater structures, with significant risks and limitations. This helps pave the way for (1) the actual engineering of surface structure detection of underwater structures, (2) future storage in the database and assessment of hazard levels, and (3) a guide for engineering technicians to take corresponding maintenance measures

Numerical Simulation of the Effect of Heat Conductivity on Proton Exchange Membrane Fuel Cell Performance in Different Axis Directions

In this paper, the effect of changes in the thermal conductivity of porous electrodes in three coordinate directions on the capability of proton exchange membrane fuel cells is investigated on the basis of current density versus voltammetry curves, and the temperature distribution and water-carrying capacity distribution of the membrane. The results show that when the cell discharge voltage of the PEMFC is 0.3 V, the thermal conductivity in the Z-direction of the porous electrode has a greater effect on the performance of the PEMFC than in the other directions, with the thermal conductivity in the X- and Y-directions of the porous electrode having less than a 5% effect on the performance of the PEMFC, which can therefore be neglected. When the thermal conductivity of the porous electrode in the Z-direction of the PEMFC is 500 W/(m·K) and 1000 W/(m·K), the performance of the PEMFC is improved by 5.78% and 5.87%, respectively, and when the thermal conductivity of the porous electrode in the X-direction of the PEMFC is 500 W/(m·K) and 1000 W/(m·K), the performance of the PEMFC is improved by 2.09% and 2.89%, and the PEMFC performance is improved by 1.51% and 2.00% when the Y-direction thermal conductivity of the porous electrode of the PEMFC is 500 W/(m·K) and 1000 W/(m·K), respectively. The improvement in performance decreases with increasing thermal conductivity, because the thickness of the porous electrode is too thin. Since the side of the model is set to adiabatic heat exchange conditions, while the top and bottom surfaces are set to natural convection heat exchange conditions, the Z-direction thermal conductivity of the porous electrode plays the most important role in the temperature distribution of the PEMFC. The Z-direction thermal conductivity of the porous electrode causes the temperature distribution of the PEMFC assembly to be more uniform, and the Z-direction thermal conductivity of the porous electrode also causes the area of the high-water-content region on the proton exchange membrane to significantly increase

Behaviors of vanadium and chromium in coal-based direct reduction of high-chromium vanadium-bearing titanomagnetite concentrates followed by magnetic separation

The reduction behaviors of FeO·V_2O_3 and FeO·Cr_2O_3 during coal-based direct reduction have a decisive impact on the efficient utilization of high-chromium vanadium-bearing titanomagnetite concentrates. The effects of molar ratio of C to Fe n(C)/n(Fe) and temperature on the behaviors of vanadium and chromium during direct reduction and magnetic separation were investigated. The reduced samples were characterized by X-ray diffraction (XRD), scanning election microscopy (SEM) and energy dispersive spectrometry (EDS) techniques. Experimental results indicate that the recoveries of vanadium and chromium rapidly increase from 10.0% and 9.6% to 45.3% and 74.3%, respectively, as the n(C)/n(Fe) increases from 0.8 to 1.4. At n(C)/n(Fe) of 0.8, the recoveries of vanadium and chromium are always lower than 10.0% in the whole temperature range of 1100–1250 °C. However, at n(C)/n(Fe) of 1.2, the recoveries of vanadium and chromium considerably increase from 17.8% and 33.8% to 42.4% and 76.0%, respectively, as the temperature increases from 1100 °C to 1250 °C. At n(C)/n(Fe) lower than 0.8, most of the FeO·V_2O_3 and FeO·Cr_2O_3 are not reduced to carbides because of the lack of carbonaceous reductants, and the temperature has little effect on the reduction behaviors of FeO·V_2O_3 and FeO·Cr_2O_3, resulting in very low recoveries of vanadium and chromium during magnetic separation. However, at higher n(C)/n(Fe), the reduction rates of FeO·V_2O_3 and FeO·Cr_2O_3 increase significatly because of the excess amount of carbonaceous reductants. Moreover, higher temperatures largely induce the reduction of FeO·V_2O_3 and FeO·Cr_2O_3 to carbides. The newly formed carbides are then dissolved in the γ(FCC) phase, and recovered accompanied with the metallic iron during magnetic separation

Sep. Purif. Technol.

Low-grade, highly reactive V-Ti concentrate was obtained from V-bearing titanomagnetite via selective reduction-magnetic separation. The main phases of the concentrate are anosovite and pyroxene. Two-stage acid leaching was employed to remove the impurities in the concentrate. The leaching behavior of impurities Ca/Mg/Al/Si under different acid leaching conditions in the first stage was investigated in detail. The optimal leaching conditions of the first-stage were as follows: 383 K leaching temperature, 1.40 mol/L HCl concentration, 1/10 solid-liquid mass ratio, and 120 min leaching time, under which the residue obtained contained 79.54% of TiO2 and 2.50% of V2O5. The result of molecular structure simulation indicate that the Ti-O and Mg-O bonds in the anosovite phase are broken under oxygen pressure conditions in the second stage by reacted with HCl solution. The content of TiO2 in the Ti-enriched slag prepared by two-stage acid leaching can reach 92.5% with further removal of residual carbon. (C) 2014 Elsevier B.V. All rights reserved.Low-grade, highly reactive V-Ti concentrate was obtained from V-bearing titanomagnetite via selective reduction-magnetic separation. The main phases of the concentrate are anosovite and pyroxene. Two-stage acid leaching was employed to remove the impurities in the concentrate. The leaching behavior of impurities Ca/Mg/Al/Si under different acid leaching conditions in the first stage was investigated in detail. The optimal leaching conditions of the first-stage were as follows: 383 K leaching temperature, 1.40 mol/L HCl concentration, 1/10 solid-liquid mass ratio, and 120 min leaching time, under which the residue obtained contained 79.54% of TiO2 and 2.50% of V2O5. The result of molecular structure simulation indicate that the Ti-O and Mg-O bonds in the anosovite phase are broken under oxygen pressure conditions in the second stage by reacted with HCl solution. The content of TiO2 in the Ti-enriched slag prepared by two-stage acid leaching can reach 92.5% with further removal of residual carbon. (C) 2014 Elsevier B.V. All rights reserved

Hydrometallurgy

A novel process for the extraction of iron, titanium, vanadium, and chromium from high-chromium vanadium-bearing titanomagnetite concentrates is proposed. This process involves several steps: partial reduction of the concentrates, magnetic separation, hydrochloric acid leaching of the titanium-bearing tailing, and alkaline desilication of the HCl leach residue. The partial reduction ensures that the vanadium and chromium are predominantly concentrated in the titanium-bearing tailing. Subsequently, magnetic separation is used to recover an iron concentrate with a total iron content of 94.57%. During add treatment, 90.8% vanadium leaching and 93.4% chromium leaching were obtained, with titanium losses of less than 0.3%, 96.3% of the silicon was removed by alkaline desilication, and titanium-rich slag with a purity of 93.39% was produced. The total recoveries of iron, titanium, vanadium, and chromium under the experimental conditions were 88.3%, 93.7%, 81.7%, and 84.4%, respectively. (C) 2014 Elsevier B.V. All rights reserved.A novel process for the extraction of iron, titanium, vanadium, and chromium from high-chromium vanadium-bearing titanomagnetite concentrates is proposed. This process involves several steps: partial reduction of the concentrates, magnetic separation, hydrochloric acid leaching of the titanium-bearing tailing, and alkaline desilication of the HCl leach residue. The partial reduction ensures that the vanadium and chromium are predominantly concentrated in the titanium-bearing tailing. Subsequently, magnetic separation is used to recover an iron concentrate with a total iron content of 94.57%. During add treatment, 90.8% vanadium leaching and 93.4% chromium leaching were obtained, with titanium losses of less than 0.3%, 96.3% of the silicon was removed by alkaline desilication, and titanium-rich slag with a purity of 93.39% was produced. The total recoveries of iron, titanium, vanadium, and chromium under the experimental conditions were 88.3%, 93.7%, 81.7%, and 84.4%, respectively. (C) 2014 Elsevier B.V. All rights reserved