Co-recovery of iron,chromium, and vanadium from vanadium tailings by semi-molten reduction–magnetic separation process

A co-recovery process used to extract iron, chromium, and vanadium in the form of chromium–vanadium-bearing metallic iron from vanadium tailings via a semi-molten reduction-magnetic separation method was investigated. The effects of the reductant (carbon) dosage, temperature, and time on the recovery rates of iron, chromium, and vanadium were studied. The phase compositions, microstructures, and micro-constitutions of the reduced samples, products, and byproducts were analysed using X-ray powder diffraction, SEM and EDS. As the reduction temperature increased, the recovery of iron, chromium, and vanadium improved. When the carbon dosage was increased from 8 to 11%, the recovery enhanced; however, the recovery deteriorated with carbon dosage of over 11%. Under optimum conditions, two products were obtained, namely a primary product consisting of chromium–vanadium-bearing metallic iron, where the recovery rates of iron, chromium, and vanadium were over 98, 82, and 65%, respectively, and a byproduct consisting of titanium-bearing slag, where the titanium yield was approximately 68%. The co-recovery process exerts a significant influence on the recovery of valuable metals and the minimisation of hazardous materials for clean utilisation of vanadium tailings.     

Effect of alumina on slag–metal separation during iron nugget formation from high alumina Indian iron ore fines

Abstract

Iron nuggets can be obtained from ore–coal composite pellets by high temperature reduction. Alumina in the ore plays a vital role in slag–metal separation during nugget formation, as it increases the liquidus temperature of the slag. In this study, the effect of carbon content, reduction temperature and lime addition on slag–metal separation and nugget formation of varying alumina iron ore fines were studied by means of thermodynamic modelling. The results were validated by conducting experiments using iron ore fines with alumina levels ranging from 1·85 to 6·15%. Results showed that increase in reduction temperature enhances slag metal separation, whereas increasing alumina and carbon content beyond the optimum level adversely affects separation. Carbon below the required amount decreases the metal recovery, and carbon above the required amount reduces the silica and alters the slag chemistry. Optimum conditions were established to produce iron nuggets with complete slag–metal separation using iron ore–coal composite pellets made from high alumina iron ore fines. These were reduction temperature of 1400°C, reduction time minimum of 15 min, carbon input of 80% of theoretical requirement and CaO input of 2·3, 3·0 and 4·2 wt-% for 1·85, 4·0 and 6·15 wt-% alumina ores respectively.     

Selective and Efficient Extraction of Zinc from Mixed Sulfide–oxide Zinc and Lead Ore

Mixed sulfide–oxide lead and zinc ores are generally composed of both sulfides and oxides. The dissolution of sulfides is more difficult than oxides thus the addition of oxidant is necessary. In this paper, oxidative leaching of mixed ore in NH₃-(NH₄)₂SO₄ solution using ammonium persulfate as oxidant under atmospheric pressure and relatively low temperature was investigated for the first time. The effects of factors on the leaching of pure ZnS were studied and the optimal conditions with zinc 98.7% were determined. Selective and efficient extractions of 93.9% and 94.9% zinc from zinc sulfide ore and mixed ore were also achieved, respectively.     

Palladium–lead alloys for the purification of hydrogen-containing gas mixtures and the separation of hydrogen from them

Ingots of palladium alloys with 5, 8, 12, 16, and 20 wt % Pb, which correspond to the Pd-based solid solution region, are prepared by arc melting in a protective atmosphere. Foils 50 μm thick are prepared from the ingots subjected to cold rolling and intermediate vacuum annealing. The membrane characteristics of the foils, which include the strength, the hydrogen permeability, the corrosion resistance, the α ? β hydride transition temperature, and the crystal lattice parameters, have been studied. The Pd–8 wt % Pb alloy is shown to exhibit the maximum specific hydrogen permeability (2.6 N m³ mm/(m² h MPa^0.5)) at 500°C, an adequate plasticity (δ = 12%), a high strength (\({\sigma _{{u_{hard}}}}\) = 550 MPa, \({\sigma _{{u_{ann}}}}\) = 230 MPa), and corrosion resistance against one of the hydrocarbon-conversion products (CO₂), which allow us to recommend this alloy for application as the membranes in filtration membrane elements.     

Co-extraction of tungsten and molybdenum from refractory scheelite–powellite blend concentrates by roasting with Na2CO3 and SiO2 and leaching with water

Studies on the recovery of tungsten and molybdenum from refractory scheelite–powellite blend concentrates – mainly composed of scheelite, powellite, and fluorite – were performed using soda-silicon roasting and water leaching processes. However, significant amounts of scheelite and powellite ore are present in an intergrowth state and the application of mineral dressing is not suitable for the separation and extraction of tungsten and molybdenum from this refractory ore. The effects of roasting parameters including sodium carbonate addition, roasting temperature, roasting time, and mass ratio of SiO₂/concentrate (w_SiO2/w_conc.) and the effects of leaching parameters including leaching temperature, leaching time, and liquid-to-solid ratio on the leaching efficiency of tungsten and molybdenum were investigated. The results demonstrated the efficiency of this process for the extraction of tungsten and molybdenum from the ore. Under the optimum experimental conditions where soda-silicon roasting is performed for 2?h at 850°C with three times, the stoichiometric ratio of Na₂CO₃ (Na₂CO₃:WO₃ and Na₂CO₃:MoO₃) and w_SiO2/w_conc of 12%, and water leaching is subsequently performed for 1?h at 70°C with a liquid-to-solid ratio of 3:1, the leaching ratios of W and Mo are 98.89% and 99.41%, respectively.     

Isothermal enriching and separation of perovskite phase from CaO–TiO2–SiO2–Al2O3–MgO melt by centrifugal force

Abstract

A new approach to isothermal enriching combined with separating perovskite phase from CaO–TiO₂–SiO₂–Al₂O₃–MgO melt by centrifugal force was investigated. Using a two-stage centrifugal separation process, the recovery ratio of Ti in the second concentrate was 99·34% and the tailings were 0·66%, thus demonstrating excellent Ti separation. These materials can be considered as suitable raw materials for titanium white and cement respectively.