The influence of temperature on rare earth flotation with naphthyl hydroxamic acid

The influence of temperature on the complex process of Bayan Obo rare earth (RE) ore flotation with a collector of naphthyl hydroxamic acid (LF8#) was investigated. Industrial test data shows that the grade and recovery of RE increase with the temperature. However, the proportion of bastnaesite in the bulk concentrate increases as the RE grade improves. Adsorption mechanism of LF8# on the surfaces of bastnaesite and monazite were confirmed via zeta potential, UV/Vis Spectrophotometer (UV/Vis), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy analyses (XPS). Although the results indicate that the total amount of the LF8# adsorption on the surface of bastnaesite and monazite decreases with increasing the temperature, the amount of stable adsorbed predominance of characteristic bonds (C(O)N) from LF8# uptake on bastnaesite surfaces increases significantly at high temperatures. This conclusion indicates that the adsorption stability increases with increasing the temperature. For monazite, the amount of characteristic elements C and N in LF8# does not increase as the temperature increases on the mineral surface, but the proportion of characteristic bonds increases, which shows that the adsorption stability of LF8# on the surface of monazite also increases, but it is not as significant as bastnaesite, which may be one of the reasons that the floatability of bastnaesite is better than those of monazite. Pulp dispersion results show that the temperature improve the dispersions of both the gangue and RE minerals. This improved the flotation selectivity so that it favored RE minerals. The calculated bubble size distribution confirms that higher temperatures generate smaller bubbles, thereby increasing the bubble-particle collision probability and the recovery of RE minerals.     

Reaction mechanism of fluoride conversion into BF_4~- during sulphuric acid leaching of roasted bastnaesite

The bastnaesite used in hydrometallurgy usually contains 7%-11% fluorine,and the conversion of fluorine into high-value products is the key to achieving green production of rare earths and improving the comprehensive utilization of bastnaesite.In order to recover fluorine from bastnaesite in the form of KBF4,the mechanism of F^-conversion to BF^4-in sulphuric acid leaching solution of roasted bastnaesite was studied by using Eh-pH diagram and simulation experiment.It shows that the formation of BF^4-is affected by pH in the absence of rare earths.BF^4-is hydrolyzed to BF3 OH-and F-when the pH is greater than 3.9,and part of F-exists as HF^2-when pH is lower than 2.In the presence of La³⁺,the formation of BF^4-is mainly affected by LaF₃ when pH is greater than 0,and in the case that the pH is lower than 2,it is mainly affected by HF^2-.When Ce4+is present in solution,CeF₂²⁺ can exist stably in sulphuric acid solution.Bringing down the pH can reduce the stability of CeF₂²⁺ and increase the BF^4-conversion rate.Based on these results,KBF4 was prepared in the alkaline solution of bastnaesite,and the conversion of BF^4-is 84.31%.This provides a theoretical basis for the recovery of fluorine from bastnaesite in the form of KBF₄.     

Compositional Variations and Its Implications of a Bastnaesite Crystal,Mianning County,Sichuan Province

ＣｏｍｐｏｓｉｔｉｏｎａｌＶａｒｉａｔｉｏｎｓａｎｄＩｔｓＩｍｐｌｉｃａｔｉｏｎｓｏｆａＢａｓｔｎａｅｓｉｔｅＣｒｙｓｔａｌ，ＭｉａｎｎｉｎｇＣｏｕｎｔｙ，ＳｉｃｈｕａｎＰｒｏｖｉｎｃｅＷｕＣｈｅｎｇｙｕ（吴澄宇），ＹｕａｎＺｈｏｎｇｘｉｎ（袁忠信...     

Enhancing mineral liberation of a Canadian rare earth ore with microwave pretreatment

Liberation, as an attribute of mineralogy characteristic, whose impacts on finely disseminated Canadian rare earth ore was studied with microwave pretreatment. Samples of a light rare earth ore along with mostly ankerite and biotite as dominant gangue minerals as well as bastnaesite, strontianite and goethite as dominated minerals were exposed to further comminution by ball mill and microwave pretreatment fragmentation. Mineralogical characteristics were analyzed by using a mineral liberation analyzer (MLA). The results indicated that tight association mutually penetrates among dominated minerals in the range size of ?300 + 212 μm and ?212 + 150 μm and gangue minerals in the form of adjacent type, fine vein type, shell type and packing type. Temperature in the ore samples pre-treated by microwave can rapidly rise to 250 °C with microwave power of 0–1.5 kW and microwave time of 0–2 min. Applying the microwave pretreatment merely reduces the hardness of the ore causing the fracture of rare earth ore, but this does not transform or change the original mineralogy characteristics of the ore samples. On the basis of above study, the liberation value of bastnaesite, strontianite and goethite with microwave pretreatment is greater than with conventional comminution when the liberation class is above 75%. The distribution of particle size of rare earth ore samples is better with microwave pretreatment than with conventional comminution for particle size of 7.4 × 10^?5 m. With microwave pretreatment, the theoretical grade–recovery of bastnaesite, strontianite and goethite in the rare earth ore attains better results than with conventional comminution at a given grade.     

Promoting effect of tantalum and antimony additives on deNOx performance of Ce3Ta3SbOx for NH3-SCR reaction and DRIFT studies

A superior Ce-Ta-Sb composite oxide catalyst prepared using homogeneous precipitation method exhibited excellent deNOx efficiency and nearly 100% N_2 selectivity with broad operation temperature window and better resistance to higher space velocity, meanwhile strong resistance to H_2 O and SO_2. This catalyst was systematically characterized using XRD, N_2 adsorption, SEM, TEM, XPS, ESR, Raman, H_2-TPR,NH3-TPD and in situ DRIFTS. There exists a synergistic effect between Ce, Ta and Sb species. It is further indicated that the prominent deNOx performance of the Ce3 Ta3 SbOx catalyst is attributed to the elevated Ce3+ concentrations, abundant active surface oxygen species, as well as surface acidity and reducibility,which is closely linked with the synergistic effect between Ce, Sb and Ta species. Results from DRIFTS reveal that the reaction mechanism of surface-adsorbed NH3 and NO_x species is linked to temperature,the L-H mechanism mainly occurs at low temperature(300 ℃),while the E-R mechanism occurs at high temperature(300 ℃). Overall,these findings indicate that Ce3 Ta3 SbOx is promising for NO_x practical abatement.     

Thermal decomposition and oxidation of bastnaesite concentrate in inert and oxidative atmosphere

To clearly elucidate the oxidative roasting behaviors of the bastnaesite, the thermal decomposition and oxidation of the bastnaesite concentrate in inert and oxidative atmosphere have been investigated in detail. Experimental data indicated that the initial decomposition temperature of the concentrate under N_2 atmosphere is 150 ℃ higher than that under O_2 atmosphere,most likely because the oxidation of the cerium induces the decomposition of the concentrate. For the roasted samples under N_2 atmosphere at500 ℃ and above,the oxidation efficiency of the cerium is 19.8%-26.8% because of the fact that rareearth fluorocarbonate is first decomposed to form rare-earth oxyfluoride and CO_2, and the cerium oxyfluoride is then partially oxidized by the CO_2 gas. The rest cerium in these samples can be further oxidized in air at room temperature, with the oxidation efficiency of the cerium gradually increasing to above 80% in 7 d. This can be attributed to the obvious changes in the inner morphology of the roasted samples under N_2 atmosphere at high temperatures, which largely induce the diffusion of the air and improves the oxidation activity of CeOF, and further induces the oxidation of CeOF by the air. XRD and XPS techniques were used to further verify the significant differences in the thermal decomposition behaviors of the bastnaesite concentrate under N_2 and O_2 atmosphere. Moreover, no oxidation of Pr~(3+) to Pr~(4+) in the roasted samples under both N_2 and O_2 atmosphere is observed. This gives an overall understanding of the oxidative roasting of the bastnaesite concentrate without additives.     

Preparation and characterization of sodium silicate/epoxy resin composite bonded Nd-Fe-B magnets with high performance

As an organic binder for bonded Nd-Fe-B magnets, epoxy resin(EP) has poor heat resistance but good moisture resistance, while sodium silicate(SS) has poor moisture absorption but better heat resistance and corrosion resistance. In order to improve high temperature stability and decrease moisture absorption of bonded Nd-Fe-B magnets, EP/SS composites were applied as the binder to prepare bonded Nd-Fe-B magnets. The magnetic properties, moisture absorption, corrosion resistance, compressive strength and microstructure of composite bonded magnets were investigated. The results show that EP/SS bonded magnets can obtain excellent magnetic properties at room temperature, and even useable magnetic properties a thigh temperature environments at 200°C. EP/SS composite binder effectively improves heat resistance and corrosion resistance of bonded Nd-Fe-B magnets, and reduces the hygroscopic properties. The molecule of sodium silicateis rigid and keeps it original shape at high temperature environments. In addition, SS in composite binder improves the mobility of the magnetic powders during the pre-pressing process, which makes the magnetic powders attain a more regular structure. These two factors will increase the mechanical properties. Moreover, sodium silicate in the composite binder can also cover the surfaces protecting the magnetic powders from oxidation and corrosion. EP in composite binder can cover SS surface to reduce the water absorption of SS as epoxy is a hydrophobic material. The EDX analysis shows that the composite binder has accumulated in the gaps of the magnet powders, which not only improves heat resistance and corrosion resistance, but also increases the mechanical properties. Therefore, EP/SS composite binder endows bonded Nd-Fe-B magnets excellent comprehensive properties.     

Synergistic catalytic removals of NO,CO and HC over CeO2 modified Mn-Mo-W-Ox/TiO2-SiO2 catalyst

A series of Mn-Mo-W-O_x/TiO_2-SiO_2 catalysts was modified with CeO_2 using an extrusion molding method. The catalytic activities of the obtained catalysts were tested for the synergistic catalytic removals of CO, NO and C_3H_8. The ratio of catalyst composition on catalytic activities for NH_3-SCR was optimized, which reveals that the molar ratio of Ti/Si was 9:1 and the catalyst containing 1.5 wt% CeO_2 and 12 wt% Mn-Mo-W-O_x exhibits the best catalytic performances. These samples were characterized by XRD, N_2-BET, Py-IR, NH_3-TPD, SEM/element mapping, H_2-TPR and XPS, respectively. Results show that the optimal catalyst exhibits more than 99% NO conversion, 86% CO conversion and 100% C_3H_8 conversion under GHSV of 5000 h~(-1). In addition, the GHSV has little influence on removal of NO when it is less than 15,000 h~(-1). Furthermore, the addition of CeO_2 will enhance the surface acidity, increase Mn~(4+)concentration and inhibit the grain growth, which are favorable for the excellent catalytic performance.Anyway,the 1.5 wt% CeO_2-12 wt% Mn-Mo-W-O_x/TiO_2-SiO_2 possesses outstanding redox properties,abundant acid sites and high Mn~(4+) concentration, which provide a guarantee for synergistic catalytic removal of CO, NO and HC.     

Study of Physicochemical Properties and Active Oxygen in Structures of Layered Mixed La_4BaCu_5-_xM_xO_(13 λ)(M=Mn,Co)

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Ce(Ⅲ)-modulation over non-enzymatic Pt/CeO2/GO biosensor with outstanding sensitivity and stability for lactic acid detection

A series of non-enzymatic graphene functionalized biosensors was developed via deposition precipitation method for lactic acid(LA) detection,which we re characterized by transmission electron micro scopy(TEM),Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),gas chromatography-mass spectrometry,liquid chromatography-mass spectro metry,and proton nuclear magnetic re sonance(¹H NMR).The electrochemical performances of the non-enzymatic biosensors were measured by means of the ele...     

Cerium(Ⅳ)oxide nanocomposites:Catalytic properties and industrial application

This review article provides a new insight on the application of cerium oxide(CeO₂)-metal oxide nanocomposites as catalyst with enhanced reducibility and improved oxygen(O₂)storage capacity,especially in the varying chemical reaction processes including combustion,oxidation,epoxidation and redox.The CeO₂-metal oxide interaction plays an important role in controlling particle size,O₂ availability and coke resistance properties of the catalyst.Strong metal oxide-CeO₂ interaction also assists in generating small and highly dispersed particles,resists sintering of catalyst particles during the catalysis process,and consequently improves the O₂ availability of the catalyst.Indeed,CeO₂ not only provides an active support to heterogeneous catalyst,but also creates a new active site at the metal-support interface to produce stronger nanoparticle bonding through the surface O₂ vacancy.This consequently produces a heterogeneous catalytic system with promising reaction rate and catalytic stability in many industrial applications such as CO₂ hydrogenation,CO oxidatio n,biodiesel productio n,gas reduction,photocatalytic and methane steam reforming.