Reaction behavior and non-isothermal kinetics of suspension magnetization roasting of limonite and siderite

In order to develop limonite and decrease CO_(2) emissions,siderite is proposed as a clean reductant for suspension magnetization roasting(SMR) of limonite.An iron concentrate(iron grade:65.92wt%,iron recovery:98.54wt%) was obtained by magnetic separation under the optimum SMR conditions:siderite dosage 40wt%,roasting temperature 700℃,roasting time 10 min.According to the magnetic analysis,SMR achieved the conversion of weak magnetic minerals to strong magnetic minerals,thus enabling the recovery of iron via magnetic separation.Based on the phase transformation analysis,during the SMR process,limonite was first dehydrated and converted to hematite,and then siderite decomposed to generate magnetite and CO,where CO reduced the freshly formed hematite to magnetite.The microstructure evolution analysis indicated that the magnetite particles were loose and porous with a destroyed structure,making them easier to be ground.The non-isothermal kinetic results show that the main reaction between limonite and siderite conformed to the two-dimension diffusion mechanism,suggesting that the diffusion of CO controlled the reaction.These results encourage the application of siderite as a reductant in SMR.

Basic characteristics of Australian iron ore concentrate and its effects on sinter properties during the high-limonite sintering process

The basic characteristics of Australian iron ore concentrate (Ore-A) and its effects on sinter properties during a high-limonite sintering process were studied using micro-sinter and sinter pot methods. The results show that the Ore-A exhibits good granulation properties, strong liquid flow capability, high bonding phase strength and crystal strength, but poor assimilability. With increasing Ore-A ratio, the tumbler index and the reduction index (RI) of the sinter first increase and then decrease, whereas the softening interval (Delta T) and the softening start temperature (T (10%)) of the sinter exhibit the opposite behavior; the reduction degradation index (RDI+3.15) of the sinter increases linearly, but the sinter yield exhibits no obvious effects. With increasing Ore-A ratio, the distribution and crystallization of the minerals are improved, the main bonding phase first changes from silico-ferrite of calcium and aluminum (SFCA) to kirschsteinite, silicate, and SFCA and then transforms to 2CaO center dot SiO2 and SFCA. Given the utilization of Ore-A and the improvement of the sinter properties, the Ore-A ratio in the high-limonite sintering process is suggested to be controlled at approximately 6wt%.

Recovering limonite from Australia iron ores by flocculation-high intensity magnetic separation

Successful recovery of limonite from iron fines was achieved by using flocculation-high intensity magnetic separation （FIMS） and adding hydrolyzed and causticized flocculants according to the characteristic of iron fines. The separation results of the three iron samples are as follows： iron grade 66.77%- 67.98% and the recovery of iron 69.26%-70.70% by the FIMS process with flocculants. The comparative results show that under the same separation conditions the F1MS process can effectively increase the recovery of iron by 10. 97%- 15.73%. The flowsheet results confirm the reliability of the process in a SHP high intensity magnetic separator. The concentrate product can he used as raw materials for direct reduction iron-smelting. The hydrolyzed and causticized flocculants can selectively flocculate fine feebly-magnetic iron mineral particles to increase their apparent separation sizes. The larger the separation size, the stronger the magnetic force. By comparing the separation results of the three samples it is found that among the three samples the higher the limonite content, the better the separation result. This means that the separation result relates closely to the flocculation process and the adding pattern of the flocculant.

Effects of reduction on the catalytic performance of limonite ore

The catalytic performance of Ni-containing limonite ore in the dry reforming reaction of methane （CH_4＋CO_2→2H_2＋2CO） was determined before and after hydrogen reduction, and under a flow of hydrogen. After hydrogen reduction, the limonite ore exhibited higher catalytic performance, because of the formation of Fe-Ni. However, the Fe in Fe-Ni was readily oxidized by the input CO_2 gas. resulting in a rapid decrease in the catalytic performance of limonite ore. The performance de- crease was due to a decrease in the Ni surface area; Ni could not dissolve in iron oxides and this caused segregation in the iron oxides. When the reaction was conducted under a hydrogen flow, the Fe-Ni was formed and maintained. Ni was highly dispersed in the Fe-Ni phase, resulting in greater surface area of Ni and higher conversion rate of CH_4 and CO_2. The catalytic performance of the limonite ore was inferior to the Ni/Al_2O_3 catalyst because the effect of catalyst support was small, however, the limonite ore was more stable during catalytic use and much cheaper than the Ni/Al_2O_3.

Optimization of iron ore blending based on replacing Australian low alumina limonite

Mauritanian iron ore powder(OM)has advantages of high iron grade,low aluminum content,and low loss on ignition,which can be used as a new mineral to replace low alumina limonite that has been exhausted in Australia.However,it will have a certain negative impact on sintering because of its high SiO_(2) content.The mechanism of SiO_(2) content affecting the sintering behavior was first studied through FactSage 7.2.Then,the liquid fluidity,penetration,and high-temperature performance of different iron ore powders were compared.Finally,the optimization of ore blending structure was studied by the micro-sintering method and the sinter pot test.The results show that the increase in SiO_(2) content can reduce the assimilation temperature.The low penetration of OM can lead to an increase in the amount of liquid,and the high SiO_(2) content of OM increases the viscosity of the liquid phase.What is more,the increase in SiO_(2) also increases the formation of silicate and fayalite phase and inhibits the formation of silico-ferrite of calcium and aluminum(SFCA).To optimize ore blending structure,OM and the low SiO_(2) powder OD from Australia were used together,which improves the content of SFCA by 2.04%and decreases the contents of calcium silicate and fayalite by 0.63%and 4.99%,respectively.The results of the sinter pot test indicated that the properties of sinter have been improved.

Leaching behavior of metals from limonitic laterite ore by high pressure acid leaching

The leaching behavior of metals from a nickeliferous limonitic laterite ore was investigated by high pressure acid leaching process for the extraction of nickel and cobalt.The effects of sulfuric acid added,leaching temperature,leaching time and liquid/solid（L/S） ratio on metals extraction were examined.More than 97% Ni,96% Co,93% Mn,95% Mg and less than 1% Fe are extracted under optimum conditions.Analysis of the high pressure acid leaching residue by chemical and XRD analysis indicates that the residual iron and sulfur are mainly present in phases of hematite and alunite,respectively.The high pressure leaching process provides a simple and efficient way for the high recovery of nickel and cobalt from laterite ore,leaving residue as a suitable iron resource.

Thermodynamics of the Reduction Roasting of Nickeliferous Laterite Ores

The global nickel sulphide resources are becoming more difficult to mine and, as a result, there is increasing interest in the current and future development of the oxidic nickel laterite deposits. In comparison to the sulphide ores, the nickel laterites cannot be readily upgraded by conventional means and growing attention is being focused on the development of new methods for processing these ores. In this paper, firstly, brief overviews of laterite ore mineralogy and the conventional techniques used to extract the nickel from both the limonitic and the saprolitic nickeliferous laterites are provided. Secondly, previous research on the thermodynamic modelling of the reduction of the laterites is discussed. Thirdly, an improved thermodynamic model is used to predict the equilibrium products arising from the solid state reduction of both the limonitic and the saprolitic ores. Based on these thermodynamic predictions, the reduction behaviors of the two ore types are compared in terms of nickel recovery and grade in the ferronickel product. The effects of reduction temperature, ore composition and carbon additions were studied. Finally, the results from the simulations are compared to the experimental data available in the literature.

Microwave pretreatment for enhanced selective nitric acid pressure leaching of limonitic laterite

As clean energy,the microwave is commonly used to pretreat various ores.In this work,the microwave dielectric properties of limonitic laterite ore were measured by resonant cavity perturbation technique and the effects from microwave were systematically investigated.Results indicated that limonitic laterite had high microwave absorbance.After microwave pretreatment,the microstructure of the laterite became less aggregated and more porous and the main phase transformed from goethite to hematite that improved leaching in nitric acid(1.2 kg HNO3/kg ore);Ni,Co,Fe,and Mg extraction ratios were 95.2%,98.1%,1.8%and 15%,respectively,after leaching for 60 min at 200°C and 500 r/min.Furthermore,in the process of goethite to hematite by microwave pretreatment,the nickel-containing mineral is activated,which makes nickel be leached easily.The leaching process has high Ni extraction ratio compared to that without microwave(82%)and conventional pretreatment(90.4%).Therefore,microwave pretreatment of limonitic laterite before nitric acid pressure leaching is an effective way to improve the selectivity and extraction of the leach.

Nitric acid pressure leaching of limonitic laterite ores:Regeneration of HNO3 and simultaneous synthesis of fibrous CaSO4·2H2O by-products

An innovative technology,nitric acid pressure leaching of limonitic laterite ores,was proposed by our research team.The HNO3 regeneration is considerable significance for the improvement of the proposed technology and its commercial application,but it has not been systematically investigated.Herein,regenerating HNO3 from Ca(NO3)2 solution with low-cost H2SO4,and simultaneous synthesis of fibrous CaSO4·2H2O by-products were studied.As a theoretical basis,the solubility of CaSO4·2H2O in HNO3 medium is studied.It is concluded that the solubility of CaSO4·2H2O increases with increasing temperature or increasing HNO3 concentration,which has considerable guiding significance for the subsequent experimental research and analysis.Then,the effects of various factors on the residual Ca^2+ concentration of filtrate,the regenerated HNO3 concentration and the morphology of synthesized products are investigated using ICP-AES and SEM.And the effect mechanism is also analyzed.The results indicate the regenerated HNO3 concentration reaches 116 g/L with the residual Ca^2+ concentration being 9.7 g/L at the optimum conditions.Moreover,fibrous CaSO4·2H2O by-products with high aspect ratios(length,406.32μm;diameter,14.71μm;aspect ratio,27.62)can be simultaneously synthesized.

Difference of sintering performance of different types of limonitic nickel laterite

To achieve the more extensive utilization of limonitic nickel laterite,the difference of sintering performance of different types of limonitic nickel laterite including high-gangue and low-gangue nickel ores was investigated by sinter pot tests and relevant mechanism analyses such as thermodynamic analysis and the chemistry and mineralogy of product sinter.With the type of limonitic nickel laterite transformed from high-gangue to low-gangue nickel ore,tumble index and productivity are improved from 45.87%and 0.97 t m^(-2) h^(-1) to 50.16%and 1.05 t m^(-2) h^(-1),respectively,and solid fuel rate is reduced from 140.52 to 131.13 kg/t,indicating that the low-gangue nickel ore possesses relatively better sintering performance.This is mainly due to the fact that the much lower contents of MgO and Al2O3 improve the formation ability and fluidity of liquid phase,which eventually contributes to the formation of relatively tighter sinter microstructure with the lower sinter porosity,more silico-ferrite of calcium and alumina amount and better bonding of hercynite by liquid phases.In addition,the metallurgical performance and nickel content of product sinter would not be reduced as different types of limonitic nickel laterite are blended for sintering.On this basis,it is entirely feasible to more widely utilize limonitic nickel laterite and simultaneously obtain much better-quality Ni-containing product sinter via effective sintering strengthening technologies.

Large deformations in deep tunnels excavated in weak rocks:Study on Y-Basque high-speed railway tunnels in northern Spain

Designing the support system for a deep tunnel in weak rock is always challenging,because a misjudgment of real rock behavior can lead to failures.During the construction of the Legutiano tunnel,which belongs to the high-speed railway network named Y-Basque in Spain,the measured convergences exhibited large deformations,which were significantly higher than those in the detailed design.At first glance,these deformations were associated with squeezing,as the tunnel was excavated in flysch-shales and limonite with a maximum cover of approximately 360 m.The aim of this study is to perform a retrofit analysis to compare the most popular empirical and analytical approaches for evaluating the squeezing effect,using geotechnical data pertaining to other tunnels excavated in the same area and in the same geological formations.Finally,a non-linear finite element analysis,focusing on time-dependent rock behavior,is conducted to reproduce the convergences measured.

Pressure nitric acid leaching of alkali-pretreated low-grade limonitic laterite

The pressure nitric acid leaching of alkali-pre- treated low-grade limonitic laterite, as well as removing impurity AI（III） and preparing intermediate product of nickel/cobalt sulphide from leaching liquor were investi- gated. After pretreatment, iron exists in the form of amorphous iron oxides, while nickel is adsorbed on the surface of iron oxides in the form of nickel oxide. The preferable pressure leaching conditions are determined as follows： leaching temperature of 458 K, leaching duration of 60 min, initial acidity of nitric acid of 1.90 mol.L-~ and liquid to solid ratio of 3：1 （volume to mass ratio）. Under these conditions, the leaching efficiencies of Ni, Co and A1 are 95 %, 88 % and 55 %, respectively, and that of Fe is less than 1%. The loss rates of Ni and Co are 1.8 % and 1.5 %, respectively, during the step of removing impurity AI（III）. The sulphide precipitation process produces the interim production of nickel/cobalt sulphides, recovering greater than 99 % of Ni and Co in the purified solution. The iron-rich （〉60 %） pressure leaching residue with low Cr, S can be further reclaimed as the raw materials for iron making.

Achieving efficient utilization of limonitic nickel laterite and CO_(2) emission reduction through multi-force field sintering process

Strengthening limonitic nickel laterite sintering and reducing CO_(2) emission were performed by the application of multiforce fields including external thermodynamic and pressure fields.Sinter pot tests of limonitic nickel laterite were carried out,and the relevant industrial production was briefed.The chemistry and mineralogy of product sinter and the thermodynamic and kinetic conditions during sintering were analyzed to reveal the relevant mechanism.The results indicate that sintering performance of limonitic nickel laterite in the new sintering process with multi-force fields is significantly improved with tumble index and productivity increased by 24.11%and 18.56%,respectively,and solid fuel rate reduced by 23.21%,compared with those in traditional sintering process.In this case,greenhouse and pollutant gas emissions are greatly reduced,and metallurgical performances of product sinter are excellent.The industrial production has been successfully conducted,indicating a bright application prospect.Mechanism analysis shows that the great improvement of thermodynamic and kinetic conditions during sintering and the densification of loose sinter can be achieved via the application of multi-force fields.Sinter microstructure is transformed from large thin-wall pores to small thin-wall pores or medium thick-wall pores with the dramatic reduction of sinter porosity and more formation of silico-ferrite of calcium and alumina(SFCA).Meanwhile,the homogenization of mineral compositions is achieved,and much denser interlocking texture between hercynite and SFCA is formed.The application of multi-force fields contributes to the substantial improvement of sintering performance of limonitic nickel laterite and CO_(2) emission reduction.

Significant influence of self-possessed moisture of limonitic nickel laterite on sintering performance and its action mechanism

In consideration of the abundant moisture of limonitic nickel laterite mined,it is essential to determine whether the selfpossessed moisture of limonitic nickel laterite after pre-dried is appropriate for sintering.Thus,based on the characterization of limonitic nickel laterite,the influence of its self-possessed moisture on sintering performance was expounded by sinter pot tests and the relevant mechanism was revealed by the systematical analyses of the granulation properties of sinter mixture,thermodynamic conditions during sintering and mineralogy of product sinter.The results indicate that the selfpossessed moisture of limonitic nickel laterite indeed has significant infuence on its sintering performance.At the optimum self-possessed moisture of 21 mass%,sinter indices are relatively better with tumble index,productivity and solid fuel rate of 48.87%,1.04 t m^(-2) h^(-1)and 136.52 kg t^(-1),respectively,due to the superior granulation properties of sinter mixture and thermodynamic conditions during sintering,relatively large amount of silico-ferrite of calcium and alumina and tighter sinter microstructure.However,sintering performance of limonitic nickel laterite is still much poorer than that of ordinary iron ores.It is feasible to strengthen limonitic nickel laterite sintering by inhibiting the over-fast sintering speed and improving the thermodynamic conditions during sintering.