Extraction of valuable metals from low nickel matte by calcified roasting-acid leaching process

A calcified roasting-acid leaching process was developed as a highly effective method for the extraction of valuable metals from low nickel matte in the presence of CaO additive. The influences of process parameters on the metal extraction were studied, including the roasting temperature, roasting time, addition of CaO, H2SO4 concentration and liquid-solid ratio. Under the optimum condition, 94.2% of Ni, 98.1% of Cu, 92.2% of Co and 89.3% of Fe were recovered. Additionally, 99.6% of Fe was removed from the leachate as goethite by a subsequent goethite iron precipitation process. The behavior and mechanism of CaO additive in the roasting process was clarified. The role of CaO is to prevent the formation of nonferrous metal ferrite phases by a preferential reaction with Fe2O3 during the roasting process. The metal oxides(Cu O and NixCu1-xO) remained stable during high-temperature roasting and were subsequently efficiently leached using a sulfuric acid solution.

Interfacial reactions of chalcopyrite in ammonia–ammonium chloride solution

The interfacial reactions of chalcopyrite in ammonia–ammonium chloride solution were investigated.The chalcopyrite surface was examined by scanning electron microscopy and X-ray photoelectron spectroscopy(XPS)techniques.It was found that interfacial passivation layers of chalcopyrite were formed from an iron oxide layer on top of a copper sulfide layer overlaying the bulk chalcopyrite,whereas CuFe1-xS2 or copper sulfides were formed via the preferential dissolution of Fe.The copper sulfide layer formed a new passivation layer,whereas the iron oxide layer peeled off spontaneously and partially from the chalcopyrite surface.The state of the copper sulfide layer was discussed after being deduced from the appearance of S2-,S22-,Sn2-,S0 and SO42-.A mechanism for the oxidation and passivation of chalcopyrite under different pH values and redox potentials was proposed.Accordingly,a model of the interfacial reaction on the chalcopyrite surface was constructed using a three-step reaction pathway,which demonstrated the formation and transformation of passivation layers under the present experimental conditions.

Molten salt electrosynthesis of silicon carbide nanoparticles and their photoluminescence property

A one-step molten salt electrochemical strategy was proposed to synthesize SiC nanoparticles from ultra-fine silicon dioxide/carbon(SiO_(2)/C)mixtures.The electrosynthesis process and physicochemical properties of the synthesized products were systematically analyzed via X-ray diffraction,electron microscopy,Raman spectroscopy and photoluminescence spectroscopy,etc.A combined chemical/electrochemical reaction,electrochemical deoxidation,and in-situ carbonization reaction mechanism was proposed to reveal the electrochemical synthesis process of SiC nanoparticles from SiO_(2)/C in molten CaCl_(2).The as-prepared SiC with particle size ranging from 8 to 14 nm possesses a polycrystalline structure.In addition,the SiC nanoparticles demonstrate obvious photoluminescence property due to the synergetic size effect and microstructural characteristics.

Direct oxygen removal from titanium aluminide scraps by yttrium reduction

Titanium aluminum(TiAl)scraps with a high oxygen content were treated with yttrium(Y)in a liquid chemical deoxidization process for recycling.The Gibbs free energy and the equilibrium constant of the deoxidization reaction were calculated,and the effects of the yttrium content and the system pressure on the oxygen content in the product were determined.The results showed that the oxygen in TiAl scraps could be removed by yttrium,and the oxygen content of the deoxidized TiAl scraps had only 10%of the original content after deoxidization.Furthermore,the oxygen content of the deoxidized TiAl scraps was decreased with the increase of yttrium addition.The higher the chamber pressure,the greater the oxygen content in the final TiAl alloys.These results were consistent with calculated values.The microstructure of the deoxidized alloys was akin to that of the original material;however,Y_(2)O_(3) particles were observed in the deoxidized alloys.

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. © 2017, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.

Phase transformation and reduction kinetics during the hydrogen reduction of ilmenite concentrate

The reduction of ilmenite concentrate by hydrogen gas was investigated in the temperature range of 500 to 1200℃. The microstructure and phase transition of the reduction products were studied by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and optical microscopy （OM）. It was found that the weight loss and iron metallization rate increased with the increase of reduction temperature and reaction time. The iron metallization rate could reach 87.5% when the sample was reduced at 1150℃ for 80 min. The final phase constituents mainly consist of Fe, M305 solid solution phase （M=Mg, Ti, and Fe）, and few titanium oxide. Microstructure analysis shows that the surfaces of the reduction products have many holes and cracks and the reactions take place from the exterior of the grain to its interior. The kinetics of reduction indicates that the rate-controlling step is diffusion process control with the activation energy of 89 kJ.mo1-1.

Reductive kinetics of Panzhihua ilmenite with hydrogen

The hydrogen reduction of Panzhihua ilmenite concentrate in the temperature range of 900?1050 °C was systematicallyinvestigated by thermogravimetric analysis (TG), X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. It wasshown that the products of the Panzhihua ilmenite reduced at 900 °C were metallic iron and rutile. Above 1000 °C, ferrouspseudobrookite solid solution was generated. During the reduction process, element Mg gradually concentrated to form Mg-rich zonewhich can influence the metallization process. The reduction reaction proceeded topochemically and its related reduction kineticswere also discussed. The kinetics of the reduction indicated that the rate-controlling step was the diffusion process. The apparentactivation energy of the hydrogen reduction of Panzhihua ilmenite was calculated to be 117.56 kJ/mol, which was larger than that ofsynthetic ilmenite under the same reduction condition.

Electrolytic production of Ti-Ge intermetallics from oxides in molten CaCl_2-NaCl

Titanium germanium intermetallics （TixGey）were directly prepared from titanium oxide （TiO2） and germanium oxide（GeO2） powders mixture by using an electrodeoxidation process. The electrochemical experiment was carried out in a molten fluxCaCl2-NaCl at 800℃ with a potential of 3.0 V. The results show that monolithic germanide Ti5Ge3 intermetallic can be directlyproduced from TiO2-GeO2 or CaTiO3-GeO2 precursors （both molar ratios are 5：3）, and the obtained Ti5Ge3 powders exhibithomogenous particle structure. In addition, the phase composition of the final product can be dramatically affected by the initialmolar ratio of TiO2 to GeO2. The reaction mechanism of the electrodeoxidation process was discussed based on the experimentalresults. It is suggested that the electrodeoxidation process is an environmentally friendly method for the preparation of Ti-Geintermetallics.

Progress in Ti_(3)O_(5):Synthesis,properties and applications

The crystal structure,physical,chemical and phase transition properties of trititanium pentoxide(Ti_(3)O_5)have aroused a broad range of research effort since the 1950s.Different crystalline forms(α,β,γ,δandλ)of Ti_(3)O_5 exhibit various properties.Particularly,reversible phase transitions betweenλ-andβ-Ti_(3)O_5 have been attracting increasing research interest,which brings new potential applications of Ti_(3)O_5 materials in the field of energy and data storage.More recently,Ti_(3)O_5 materials have shown excellent performance in trace detection,microwave absorption and virus adsorption,which has expanded its application fields.Here,the essential properties of different crystal forms of Ti_(3)O_5 are described in detail.An intensive overview of Ti_(3)O_5 preparation methods and applications is comprehensively summarized.

Thermodynamic modeling of ZrO_(2)−CaO−TiO_(2)system

The phase diagram of ZrO_(2)−CaO−TiO_(2)system was essential for the development of photocatalytic materials and refractory materials.In this work,the ZrO_(2)−CaO−TiO_(2)system was accessed by using the CALPHAD method.The substitutional solution models were used to describe liquid and solid solution phases,the sub-lattice models were used to describe ternary compounds,and then the thermodynamic parameters were obtained by the least square method combined with literature experiment results.The acquired thermodynamic parameters were used to calculate the isothermal sections of the ZrO_(2)−CaO−TiO_(2)system at 1473 and 1673 K.There existed a good agreement between experimental and predicted phase relationships,the experimental points which were inconsistent with calculated results may be attributed to experimental errors and the sluggish kinetics of cations for ZrO_(2)-based materials.In order to further verify the validity of the database,the thermodynamic parameters were also used to simulate the thermodynamic properties(specific heat capacity,enthalpy,and entropy)of CaZrTi_(2)O_(7) within 5%errors.Good consistency demonstrated that the present thermodynamic database was self-consistent and credible.

Interaction mechanism between BaZrO_(3)/Y_(2)O_(3) refractory and Ti_(2)Ni alloy melts

The titanium alloys with highly chemical activity require stable crucible refractories that can withstand the erosion of alloy melts.The phase composition and microstructure are crucial factors that affect the stability of the refractory crucible.The effect of Y_(2)O_(3) on the composition and microstructure of BaZrO_(3) crucible was systematically investigated,and the improved mechanism of the stability of BaZrO_(3)/Y_(2)O_(3) crucible was clarified in comparison with the BaZrO_(3) crucible.The results showed that the erosion layer thickness of the BaZrO_(3)/Y_(2)O_(3) crucible was only 63μm,which was far less than that in the BaZrO_(3) crucible(485μm),and the erosion layer in the BaZrO_(3)/Y_(2)O_(3) crucible also exhibited a higher density than that in the BaZrO_(3) crucible.During the sintering,Y_(2)O_(3) could improve the densification of the BaZrO_(3) crucible due to the solid solution effect between Y_(2)O_(3) and ZrO_(2),which also caused the evaporation of BaO,resulting in the generation of a Y_(2)O_(3)(ZrO_(2))film on the surface of the crucible.Furthermore,the Y_(2)O_(3)(ZrO_(2))had higher thermodynamic stability than Y_(2)O_(3),confirming that the BaZrO_(3)/Y_(2)O_(3) crucible with high density exhibited a superior erosion resistance to titanium alloys.This dual-phase structure provides a strategy to design a long-life and stable refractory for melting titanium alloys.

Recovery of rare earth elements from permanent magnet scraps by pyrometallurgical process

In order to recover valuable rare earth elements from Nd-Fe-B permanent magnet scraps, a high-temperature pyrometallurgical process was developed in this work. The magnet scraps were first pulverized and oxidized at 1000℃ in normal atmosphere. The oxidized mixtures were then selectively reduced by carbon in the temperature range of 1400-1550℃. In this way, the rare earth elements were extracted to the form of oxides, whereas Fe and B were separated to metal phase. For improving the purity of rare earth oxides, the effects of temperature and reaction time on the reduction of B_(2)O_(3) in oxide phase were investigated. It is found that increasing reaction temperature and extending reaction time will help the reduction of B_(2)O_(3) contents in rare earth oxide phase. Almost all rare earth elements can be enriched in the oxide phase with the highest purity of 95 %.

Effect of controlled rolling/controlled cooling parameters on microstructure and mechanical properties of the novel pipeline steel

The study of controlled rolling/controlled cooling process parameters which affect the microstructure and mechanical properties of a novel pipeline steel has been optimized by the orthogonal experiment with four factors and three levels in this paper. However, the parameters of thermo-mechanical control process （TMCP） optimized by the Gleeble-3500 hot simulator could not satisfy performance requirements of the X100 pipeline steel. In order to improve the performance of this steel, the influence of finish cooling temperature （FCT） on the microstructure and property is studied in detail. It is found that, as this steel is thermo-mechanically treated by this set of parameters （the start heating temperature, finish rolling temperature （FRT）, FCT and cooling rate of 1,180 ℃, 810 ℃, 350 ℃ and 35 ℃/s, respectively）, the micro- structures are mainly composed of granular bainite （GB） and acicular ferrite （AF）. The effective grain sizes are below 20 μm; the steel reaches the optimal balance between the strength and the toughness; the yield strength is 695 MPa; the tensile strength is 768 MPa; the elongation is 16.6 %; the impact energy is 262 J at room temperature. All indexes could meet the requirements of X100 pipeline steel.

Multiple gaseous reduction of ilmenite: thermodynamic and experimental study

In this paper, the thermodynamics of the reduction of ilmenite using multiple gases (H2/CO) was calculated. It is found that the metallization rate of 20.1%–98.8%, H2 consumption rate of 43.0%–99.1%, and carbon deposition amount of 5.7×10?7?0.49mol can be obtained based on the conditions of hydrogen volume fraction of 10%–90% and temperature of 450–1200°C. Experimental study was also carried out using synthetic ilmenite as initial materials and reduced in a static bed reactor at 1100°C. The metallization rate reaches 97% when the multiple gas (70% H2/10% CO/20% Ar) flow rate is 120ml·min?1. A thermogravimetric analyzer was used to measure the variation of sample weight caused by the deposition of solid carbon. The amount of carbon deposited during experiments reaches its maximum while the original hydrogen volume content is 20%. The experimental results are well consistent with the thermodynamic analysis.

Calculation of phase equilibria in Al-Fe-Mn ternary system involving three new ternary intermetallic compounds

In this study, the Al-Fe-Mn ternary system is reassessed by the CALPHAD method. Three new ternary intermetallic compounds are initially described and a rea- sonable and self-consistent set of thermodynamic parameters are established to describe this system. The 973 K, 1 073K, 1 173K, 1 273K, 1 373K, and 1 473K isothermal sections and the 1 073 K, 1 013 K, 968 K and 913 K isothermal sections at the AI corner as well as the liquidus projection at the Al corner are calculated. It is shown that the calculated results are in good agreement with almost all of the experimental results previously reported.

Performance of Sm_(0.7)Sr_(0.3)CoO_(3-δ) dmembrane under CO_2-containing atmosphere

The permeability and stability of Sm_（0.7）Sr_（0.3）CoO_（3-δ）（SSCO） regarding the special requirements for carbon capture and storage（CCS） application were investigated.Pure CO_ was used as the sweep gas at 900 °C,leading to that the oxygen permeation flux decreases by about 34 %.Several cycles of changing the sweep gas between helium and CO_2 indicate the good reversibility of this degradation.Both carbonate formation and adsorption of CO_2 on the membrane surface are responsible for the degradation of the membrane performance.The better CO_2 resistance results from the substitution of Sm for Sr due to the higher acidity of Sm_2O_3（1.278） than that of Sr O（0.978） and a discontinuous layer of carbonate.