Iron recovery and rare earths enrichment from Bayan Obo tailings using Coal-Ca(OH)2-NaOH roasting followed by magnetic separation

The recovery of iron and enrichment of rare earths from Bayan Obo railings were investigated using Coal Ca（OH） 2 NaOH roasting followed by magnetic separation. The influences of roasting temperature, roasting time, coal content, milling time, Ca（OH）2 dosage and NaOH dosage on the iron and rare earths recovery were explored. The results showed that the magnetic concentrate containing 70.01 wt. % Fe with the iron recovery of 94.34G and the tailings of magnetic separation containing 11.46 wt. % rare earth oxides （REO） with the REO recovery of 98. 19% were obtained under the optimum conditions （i. e. , roasting temperature of 650℃, roasting time of 60 min, coal content of 2.0%, milling time of 5 min, and NaOH dosage of 2.0%）. The Ca（OH）2 dosage had no effect on the separation of iron and rare earths. According to the mineralogical and morphologic analysis, the iron and rare earths of Bayan Obo tailings could be utilized in subsequent ironmaking process and hydrometallurgy process.

Novel method for improving iron recovery from electric arc furnace slag: on-site hot modification

The iron element in electric arc furnace(EAF)slag is extremely difficult to recycle due to the low specific magnetic susceptibility of the RO phase(a solid solution of FeO,MgO,CaO,and MnO).Landfilling EAF slag is strictly forbidden for environmental consideration because of poisonous Cr^(6+) leaching.The original RO phase could be transformed to a spinel structure,whose specific magnetic susceptibility is much higher than that of other minerals,through hot modification,resulting in significantly increased iron recovery by magnetic separation.Precipitation of spinel crystals encloses chromium,such that iron and chromium could be recovered simultaneously.The chromium in obtained iron concentrates is considerably useful for stainless steel making rather than polluting the environment.As a result,recovering iron and chromium is truly beneficial for cleaner production.Hot modification of EAF slag should be conducted at 1500-1600ºC for at least 60 min to guarantee homogeneous liquid slag.The liquid slag was poured onto an iron mold to obtain modified slag(MS)through air quenching.MS was characterized by thermodynamic analysis,X-ray diffraction,and scanning electron microscopy combined with energy-dispersive spectroscopy to correlate the relationship between mineral structures and iron recovery.The iron recovery rate of MS first increased and then decreased with increasing modifier.It was less than 10%when the modifier addition amount was below 12 wt.%,but it increased rapidly as the modifier addition amount increased from 16 to 24 wt.%,mainly due to spinel formation.The highest iron recovery rate was 81.9%when the modifier amount reached 20 wt.%.Meanwhile,Cr^(6+) was enriched in the spinel phase but was not observed in other minerals.Industrial tests were performed on-site with the modifier ranging from 12 to 18 wt.%because additional heat was not provided during the tests.Results showed that MS with 18 wt.%modifier addition exhibited an iron recovery rate of 61.0%,much higher than that(34.6%)of the original slag.

Optimization of magnetic separation process for iron recovery from steel slag

To improve the efficiency of iron recovery from steel slag and reduce the wear-and-tear on facilities, a new method was proposed by adding a secondary screen sizer to the magnetic separation process according to grain size distribution of magnetic iron （M-Fe） in the slag. The final recycling efficiency was evaluated by calculating the percentage of recycled M-Fe to the maximum amount of M-Fe that could be recovered. Three types of slags, namely basic oxygen furnace slag, desul- furization slag, and iron ladle slag, were studied, and the results showed that the optimized re- covery efficieneies were 93.20%, 92. 48%, and 85.82% respectively, and the recycling efficien eies were improved by 9.58%, 7.11%, and 6.24% respectively. Furthermore, the abrasion between the mill equipment and the remaining slags was significantly reduced owing to the efficient recovery of larger M-Fe particles. In addition, the using amount of grinding balls was reduced by 0. 46 kg when every 1 t steel slag was processed.

Iron and copper recovery from copper slags through smelting with waste cathode carbon from aluminium electrolysis

To recover metal from copper slags,a new process involving two steps of oxidative desulfurization followed by smelting reduction was proposed in which one hazardous waste(waste cathode carbon)was used to treat another(copper slags).The waste cathode carbon is used not only as a reducing agent but also as a fluxing agent to decrease slag melting point.Upon holding for 60 min in air atmosphere first and then smelting with 14.4 wt%waste cathode carbon and 25 wt%CaO for 180 min in high purity Ar atmosphere at 1450℃,the recovery rates of Cu and Fe reach 95.89%and 94.64%,respectively,and meanwhile greater than 90%of the fluoride from waste cathode carbon is transferred into the final slag as CaF_(2) and Ca_(2)Si_(2)F_(2)O_(7),which makes the content of soluble F in the slag meet the national emission standard.Besides,the sulphur content in the obtained Fe-Cu alloy is low to 0.03 wt%.

Mixture of ilmenite and high phosphorus iron ore smelted by oxygen-enriched top-blown smelting reduction

In order to reasonably utilize the abundant resources of high-phosphorus iron ore and ilmenite in China, the technology of top-blown smelting reduction with oxygen enrichment was used to smelt the mixed ore of high-phosphorus iron and ilmenite. The effect, which is related to basicity, reduction temperature, carbon-oxygen ratio and time of ventilated oxygen to iron recovery, dephosphorization rate, content of iron, phosphorus, sulfur and titanium in pig iron, was investigated in the experiment. The results show that an ideal outcome can be gained in condition of 6：4 ration on Mengqiao concentrate and Huimin iron ore, temperature of 1 500℃, basicity of 1.3, 1.0 on molar ration of carbon to oxygen, time of 10 min on blowing-oxygen. The outcome is that there is no foamy slag in generation, a good separation of slag and iron, iron recovery with 91.41%, content of phosphorus with 0.27% and tilanium content less than 0.001%, The atmosphere of strong oxidizing in the upper of reduction container and high potential of oxygen in the composition of slag in this technique bring phosphorus, titanium and silicon into slag, which ensures less content of impurity in pig iron.

Magnetizing roast and magnetic separation of iron in rare-earth tailings

Magnetic separation of iron in rare-earth tailings was achieved by magnetizing roast process with coal as reductant. Effects of the temperature, carbon to oxygen ratio, and cooling type on magnetic susceptibility and composition of rare-earth tailings were investigated. The results show that roast conditions with the temperature of 650℃, carbon to oxygen ratio of 3.85, and holding time of 2.5 h are in favor of reduction of Fe_2O_3 to Fe_3O_4 when the roasted rare-earth tailings is cooled along with furnace. Under these roast conditions, magnetic susceptibility of rare-earth tailings is 2.36 that is very close to theoretical value（2.33）. However, magnetic separation results of iron in rare-earth tailings cooled along with furnace are not satisfactory. Through comparing magnetic separation results of iron in rare-earth tailings cooled by different ways, it is found that water cooling is more favored of magnetic separation of iron in the roasted rare-earth tailings than furnace cooling and air cooling. Grade and recovery of iron in concentrate from rare-earth tailings cooled by water are 45.00%-49.00% and 65.00%-77.50%, respectively.

Review on coal-based reduction and magnetic separation for refractory iron-bearing resources

The application of coal-based reduction in the efficient recovery of iron from refractory iron-bearing resources is comprehensively reviewed.Currently,the development and beneficiation of refractory iron-bearing resources have attracted increasing attention.However,the effect of iron recovery by traditional beneficiation methods is unacceptable.Coal-based reduction followed by magnetic separation is proposed,which adopts coal as the reductant to reduce iron oxides to metallic iron below the melting temperature.The metallic iron particles aggregate and grow,and the particle size continuously increases to be suitable for magnetic separation.The optimization and application of coal-based reduction have been abundantly researched.A detailed literature study on coal-based reduction is performed from the perspectives of thermodynamics,reduction kinetics,growth of metallic iron particles,additives,and application.The coal-based reduction industrial equipment can be developed based on the existing pyrometallurgical equipments,rotary hearth furnace and rotary kiln,which are introduced briefly.However,coal-based reduction currently mainly adopts coal as a reductant and fuel,which may result in high levels of carbon dioxide emissions,energy consumption,and pollution.Technological innovation aiming at decreasing carbon dioxide emissions is a new trend of green and sustainable development of the steel industry.Therefore,the substitution of coal with clean energy(hydrogen,biomass,etc.)for iron oxide reduction shows promise in the future.

Recovery of Iron From High-Iron Red Mud by Reduction Roasting With Adding Sodium Salt

Red mud is the waste generated during aluminum production from bauxite, containing lots of iron and other valuable metals. In order to recover iron from red mud, the technology of adding sodium carbonate—reduction roasting—magnetic separation to treat high-iron red mud was developed. The effects of sodium carbonate dosage, reduction temperature and reduction time on the qualities of final product and the phase transformations in reduction process were discussed in detail. The results showed that the final product (mass percent), assaying Fe of 90.87% and Al2O3 of 0.95% and metallization degree of 94.28% was obtained at an overall iron recovery of 95.76% under the following conditions of adding 8% sodium carbonate, reduction roasting at 1 050 ℃ for 80 min and finally magnetic separation of the reduced pellets by grinding up to 90% passing 0.074 mm at magnetic field intensity of 0.08 T. The XRD (X-ray diffraction) results indicated that the iron oxides were transformed into metallic iron. Most of aluminum mineral and silica mineral reacted with sodium carbonate during the reduction roasting and formed nonmagnetic materials.

Fe extraction from high-silicon and aluminum cyanide tailings by pretreatment of water leaching before magnetic separation

Pretreatment of high content of Si- and Al-containing cyanide tailings by water leaching to remove some impurities, such as the major impurities minerals of Si and A1, as well as its effect on Fe extraction in the water leaching process was investigated. The effects of different parameters on iron recovery were studied, and the reaction parameters were proposed as follows： sodium carbonate content of 30%, water leaching at 60 ~C for 5 min, liquid/solid ratio of 15：1, and exciting current of 2 A. Under these optimal conditions, magnetic concentrate containing 59.11% total iron and a total iron recovery rate of 76.12% was obtained. In addition, the microstructure and phase transformation of the process of water leaching were studied by X-ray powder diffraction technique （XRD）, Electronic image of backscattering （BEI）, X-ray fluorescence （XRF）, and energy dispersive spectrometry （EDS）. The results indicate that the soluble compound impurities generated in the roasting process are washed out, and the dissoluble substances enter into nonmagnetic materials by water leaching, realizing the effective separation of impurities and Fe.

Recovery of iron from copper slag via modified roasting in CO-CO2 mixed gas and magnetic separation

A novel technology,modified roasting in CO-CO2 mixed gas and magnetic separation,was presented to recover iron from copper slag.The effects of various parameters such as dosage of flux(CaO),gas flowrate of CO and CO2,roasting temperature,roasting time,particle size of modified slag and magnetic flux density on the oxidized modification and magnetic separation were investigated by comparison of the X-ray diffraction patterns and iron recovery ratio.The optimum conditions for recovering iron by oxidizing roasting and magnetic separation are as follows:calcium oxide content of 25 wt.%,mixed gas flow rates of CO2 and CO of 180 and 20 mL/min,oxidizing roasting at 1323 K for 2 h,grinding the modified slag to 38.5-25.0μm and magnetic separation at 170 mT.The mineralogical and microstructural characteristics of modified slag revealed that the iron-bearing minerals in the copper slag were oxidized,the generated magnetite grew into large particles,and the silicate in copper slag was combined with calcium oxide to form calcium silicate.Finally,the iron-bearing concentrate with an iron grade of 54.79%and iron recovery ratio of 80.14%was effectively obtained.

Slag/metal Separation Process of Gas-reduced Oolitic High-phosphorus Iron Ore Fines

Slag/metal separation process of the highly reduced oolitic high-phosphorus iron ore fines was investigated. Samples were prepared using the reduced ore fines （metallization rate： 88%） and powder additives of CaO and Na2CO3. Slag/metal separation behavior tests were conducted using a quenching method and the obtained metal parts were subjected to direct observation as well as microstructure examination with SEM and EDS; iron recovery and phosphorus distribution tests were conducted using a Si-Mo high temperature furnace and the obtained metal parts were examined by ICP-AES analysis and mass measurement. Thermodynamic calculation using coexistence theory of slag structure was also performed. Results show that temperature for slag/metal separation must be higher than 1823 K and a satisfying slag/metal separation of the highly reduced ore fines needs at least 4 min; phosphorus con- tent of hot metal is mainly determined by thermodynamics; temperature of 1823-1873 K and Na2CO3 mixing ratio of about 3 % are adequate for controlling phosphorus content to be less than 0.3 mass% in hot metal; temperature, time and Na2CO3 mixing ratio do not have significant effect on iron recovery, and iron recovery rate could be higher than 80% as long as a good slag/metal separation result is obtained.

Modeling assessment of recovering iron from red mud by direct reduction： magnetic separation based on response surface methodology

Red mud, the waste generated during alumina production, contains iron and other valuable metals. To recover the iron efficiently from red mud, a three-factor five-level central composite design in response surface methodology was used to study the effects of process parameters, such as FC/O （the molar ratio of fixed carbon in coal to reducible oxygen of iron oxide in red mud）, reduction temperature, reduction time, and their interaction on the iron recovery rate and total iron content in magnetic product obtained from the process of direct reduction-magnetic separation. The relevant assessment model was established. The model could predict the changing rules of iron recovery rate and total iron content in the magnetic product affected by the process parameters. The results show that the iron recovery rate is significantly influenced by three factors and reduction temperature plays the most important role. The iron recovery rate and total iron content in magnetic product could be up to 98.37 and 82.52%, respectively, under the numerically optimal process parameters condition of reduction temperature of 1400 ℃, FC/O of 0.80 and reduction time of 100 min obtained by the assessment model. The predicted values are in good agreement with the experimental values.

Influence of Mechanical Activation on Acid Leaching Dephosphorization of High-phosphorus Iron Ore Concentrates

High pressure roll grinding（HPRG）and ball milling were compared to investigate the influence of mechanical activation on the acid leaching dephosphorization of a high-phosphorus iron ore concentrate,which was manufactured through magnetizing roasting-magnetic separation of high-phosphorus oolitic iron ores.The results indicated that when high-phosphorus iron ore concentrates containing 54.92 mass% iron and 0.76 mass% phosphorus were directly processed through acid leaching,iron ore concentrates containing 55.74mass%iron and 0.33mass%phosphorus with an iron recovery of 84.64%and dephosphorization of 63.79% were obtained.When high-phosphorus iron ore concentrates activated by ball milling were processed by acid leaching,iron ore concentrates containing56.03mass%iron and 0.21mass% phosphorus with an iron recovery of 85.65% and dephosphorization of 77.49%were obtained.Meanwhile,when high-phosphorus iron ore concentrates activated by HPRG were processed by acid leaching,iron ore concentrates containing 58.02mass%iron and 0.10mass% phosphorus were obtained,with the iron recovery reaching 88.42% and the dephosphorization rate reaching 88.99%.Mechanistic studies demonstrated that ball milling can reduce the particle size,demonstrating aprominent reunion phenomenon.In contrast,HPRG pretreatment contributes to the formation of more cracks within the particles and selective dissociation of iron and P bearing minerals,which can provide the favorable kinetic conditions to accelerate the solid-liquid reaction rate.As such,the crystal structure is destroyed and the surface energy of mineral particles is strengthened by mechanical activation,further strengthening the dephosphorization.

Ilmenite Smelted by Oxygen-Enriched Top-Blown Smelting Reduction

Total ilmenite from Yunnan, China, difficult to smelt in blast furnace, was smelted by oxygen-enriched top-blown smelting reduction ironmaking technology. Much more details on smelting were discussed. Specifically, the influence of reduction temperature, slag basicity and molar ratio of carbon to oxygen on the reduction quality level including iron recovery and titanium and sulfur contents in the pig iron produced in the experiment was investigated. Iron recovery rate could reach 95 % with titanium content below 0.05 % in pig iron produced, under the conditions of holding time of 30 min at 1 823 K, basicity of 1.1, carbon to oxygen molar ratio of 1.0 and oxygen enriched flow rate of 250 L/h. Oxidization potential of top-space of smelting reduction vessel and slag combination could create the driv ing force to partition phosphorous, titanium and silicon into the slag, which ensured low contents of the impurities involved above and carbon in pig iron. In addition, it avoided the generation of Ti（C,N） that could reduce interracial tension of slag, which induced the formation of foaming slag seriously. Furthermore, jam of chargings and bubble flooding would be triggered, resulting in deterioration of BF state, increase of iron loss and decline of desulfurization rate.

Niobium and phosphorus behavior during melting-separation process of pre-reduced niobium ore concentrate

The pre-reduced Bayan Obo ferroniobium（FeNb）ore concentrate block was taken as raw materials for studying the physical properties of niobium-enriched slag and changes in niobium recovery rate.In addition,the dephosphorization rate of the slag under different melting-separation conditions was investigated using the melting-separation test.The research results demonstrate that（i）the niobium recovery rate and dephosphorization rate of the slag decrease with the increase in melting-separation temperature;（ii）the niobium recovery rate of the slag initially increases and then decreases with increase in basicity and time;and（iii）the dephosphorization rate of the slag increases with the increase in basicity and time.When the test was performed under the conditions of basicity of 0.6-0.7,time of 7-10min,and temperature of 1400-1450°C,the niobium recovery rate and dephosphorization rate are over 96%and 95%,respectively.By scanning electron microscopy,it is observed that niobium mainly exists in the form of calcium and titanium silicate within the slag phase,with uneven distribution.