Preparation and Microwave Absorbing Properties of Double-layer Fine Iron Tailings Cementitious Materials

To develop the microwave absorbing(MA)properties of cementitious material mixed with mine solid waste,the iron tailings cementitious microwave absorbing materials were prepared.The iron tailings was treated into different particle sizes by planetary ball mill,and the physicochemical properties of iron tailings were tested by laser particle size analyzer and scanning electron microscope(SEM).The electromagnetic parameters of iron tailings cementitious materials were characterized by a vector network analyzer and simulated MA properties,and the MA properties of iron tailings-cement composite system with steel fiber as absorber was studied.Based on the design of the single-layer structure,optimum mix ratio and thickness configuration method of double-layer structure were further studied,meanwhile,the mechanical properties and engineering application were analyzed and discussed.The results show that the particle size of iron tailings can afiect its electromagnetic behavior in cementitious materials,and the smaller particles lead the increase of demagnetisation efiect induced by domain wall motion and achieve better microwave absorbing properties in cementitious materials.When the thickness of matching layer and absorbing layer is 5 mm,the optimized microwave absorbing properties of C1/C3 double-layer cementitious material can obtain optimal RL value of-27.61 dB and efiective absorbing bandwidth of 0.97 GHz,which attributes to the synergistic efiect of impedance matching and attenuation characteristics.The double-layer microwave absorbing materials obtain excellent absorbing properties and show great design flexibility and diversity,which can be used as a suitable candidate for the preparation of favorable microwave absorbing cementitious materials.

Determination of critical state line(CSL)for silty-sandy iron ore tailings subjected to low-high confining pressures

The disposal of filtered tailings in high dry stacks can induce particle breakage,changing the material's behaviour during the structure's lifetime.The grading changes influence material properties at the critical state,and this is not mature for intermediate artificial soils(tailings)in a broad range of confining pressures.In this paper,it aims to describe the behaviour of iron ore tailings in a spectrum of confining pressures broader than the reported in previous studies.A series of consolidated drained(CD)triaxial tests was carried out with confining pressures ranging from 0.075 MPa to 120 MPa.These results show that the amount of breakage plays an essential role in the response of iron ore tailings.The existence of curved critical state line(CSL)in both specific volume(ν)-logarithm of mean effective stress(p′)and deviatoric stress(q)-mean effective stress(p′)planes,and different responses in the deviatoric stress-axial strain-volumetric strain curves were verified.An inverse S-shaped equation was proposed to represent the silty-sandy tailings'behaviour up to high pressures onν-lnp′plane.The proposed equation provides a basis for enhancing constitutive models and considers the evolution of the grading up to severe loading conditions.The adjustment considered three regions with different responses associated with particle breakage at different pressure levels.

Mechanical behavior of iron ore tailings under standard compression and extension triaxial stress paths

The disposal of mining tailings has increasingly focused on the use of dry stacks.These structures offer more security since they use filtered and compacted material.Because of the construction method and the heights achieved,the material that compounds the structure can be subjected to different stress paths along the failure plane.The theoretical framework considered in the design of these structures generally is the critical state soil mechanics(CSSM).However,the data in the literature concerning the uniqueness of critical state line(CSL)is still controversial as the soil is subjected to different stress paths.With respect to tailings,this question is even more restricted.This paper studies two tailings with different gradings due to the beneficial processes over extension and compression paths.A series of drained and undrained triaxial tests was conducted over a range of initial densities and stress levels.In the q-p'plane,different critical stress ratio(M)values were obtained for compression and extension stress paths.However,the critical state friction angle is very similar with a slightly higher critical state friction angle for extension tests.Curved stress path dependent CSLs were obtained in the n-lnp0 plane with the extension tests below the CSL defined in compression.Regarding the fines content,the studied tailings presented very similar M and critical state friction angle values.However,the fines content af-fects the volumetric behavior of the studied tailings and the CSLs on the n-lnp0 plane shift downwards with the increasing fines content for compression and extension tests.In relation to dilatancy analysis,the fines content did not present an evident influence on the dilatancy of the materials.However,different values of mean stress ratio N were obtained between compression and extension tests and can corroborate the existence of non-unique CSLs for these materials.

AEROCRETE MADE WITH LOW SILICON TAILINGS OF CHENGCHAO IRON ORE MINE

The experimental study on the tailings from Chengchao Iron Ore Mine has been introduced briefly. By analyzing the chemical and mineral compositions of Chenchao Iron Ore, the technological process has been constituted. According to the comparison experiments, the optimal proportion of cement and lime, dosage of the additional silicon - materials, calcium-silicon proportion, dosage of aluminum powder and other parameters have been decided. Aerocrete has been trial-produced successfully with the low-silicon iron ore tailings. It has opened up a new way for the exploitation of the low-silicon iron ore tailings.

Iron ore tailings used for the preparation of cementitious material by compound thermal activation

In the background of little reuse and large stockpile for iron ore tailings, iron ore tailing from Chinese Tonghua were used as raw material to prepare cementitious materials. Cementitious properties of the iron ore tailings activated by compound thermal activation were studied. Testing methods, such as XRD, TG-DTA, and IR were used for researching the phase and structure variety of the iron ore railings in the process of compound thermal activation. The results reveal that a new cementitious material that contains 30wt% of the iron ore tailings can be obtained by compounded thermal activation, whose mortar strength can come up to the standard of 42.5 cement of China.

Different Effects of Wet and Dry Grinding on the Activation of Iron Ore Tailings

Improving the activity of Iron Ore Tailings(IOTs)to utilize them as a mineral admixture in cement-based minerals is still challenging.In this paper,the wet grinding technology was employed to stimulate the activity of IOTs,and the traditional dry grinding method was used as a reference.The effect of wet grinding on the activation of IOTs was evaluated through ion leaching from an alkaline solution and the reactivity index.Additionally,a detailed comparison between Dry-grinding Iron Ore Tailings(DIOTs)and Wet-grinding Iron Ore Tailings(WIOTs)was made.This comparison was based on particle characteristics,crystal structures,chemical structure,and surface properties.The results showed that the particle size of IOTs reduced rapidly during wet grinding.In addition,WIOTs had a higher activity index compared to DIOTs.The storage of lattice distortions in the quartz crystal structure was also more significant during the wet grinding process than during the dry grinding process.Moreover,both prolonged dry and wet grinding could destabilize the Si-O bond and decrease the surface binding energy.

Relationship between polymerization degree and cementitious activity of iron ore tailings

The aim of this study is to understand the relationship between the polymerization degree and cememitious activity of iron ore tailings. In light of the poor usage of iron ore tailings, stockpile samples from Tangshan were studied in terms of their ability to become cementitious materials. Compound thermal activation was used to improve the cementitious properties of the tailings, while analyzing methods, such as X-ray diffraction （XRD）, infrared spectroscopy （IR）, nuclear magnetic resonance （NMR）, and X-ray photoelectron spectrometer （XPS）, were employed to study the changes in phase and structure under different activation conditions. The results reveal clear relationships between the binding energies of Si2p and O 1 s, polymerization degree, and cementitious activity of iron ore tailings.

Preparation of Micro-Iron Ore Tailings by Wet-Grinding and Its Application in Sulphoaluminate Cement

Herein,micro iron ore tailings(micro-IOTs)were prepared by wet-grinding and applied to improve sulphoaluminate cement(SAC)performance.The physicochemical properties of micro-IOTs were investigated by particle size analysis,XRD,and XPS.The hydrates trait and the hydration mechanism of micro-IOTs-SAC composite were studied by XRD,TGA,MIP,and SEM.The results demonstrated that micro-IOTs with an average grain diameter of 517 nm could be obtained by wet-grinding.The setting time of SAC gradually decreased with increasing micro-IOTs content.By adding 2%micro-IOTs,the compressive strengths of SAC pastes were enhanced about 22%and 10%at 4 h and 28 d,respectively.Moreover,the addition of micro-IOTs accelerated ettringite precipitation and changed its morphology,resulting in early strength improvement of the binary system.And increased later strength by micro-IOTs was closely related to the high content of AH_(3),fine pore structure,and high hydration degree of SAC.The findings suggested one new approach to utilize iron ore tailings in cementbased materials.

Pavement Performance Research Progress and Evaluation of Asphalt Mixture Incorporating Iron Ore Tailings

In order to solve the problems caused by the storage of iron ore tailings (IOTs), many researchers conducted a series of experimental studies on the reuse of IOTs. The results of many studies showed that it was feasible to use IOTs for road engineering. This paper summarized the composition, gradation and particle characteristics of IOTs from chemical and physical aspects, and proved the feasibility of IOTs replacing traditional aggregate for asphalt concrete. Then, the research on the road performance of asphalt concrete incorporating IOTs were summarized and reviewed, including the evaluation of high-temperature stability, low-temperature crack resistance, fatigue resistance and water stability. The water stability and the improvement of adhesion between asphalt and IOTs aggregate were discussed in detail. Finally, the performance of IOTs as asphalt concrete aggregate and the existing defects were evaluated, and future research directions were proposed.

Hydrometallurgical Processing of Brazilian Iron Ore Tailings for the Synthesis of Pigments

The aim of this study was to investigate the synthesis of iron oxide pigments from IOT. The sample of IOT was obtained through mining activity of the Quadrilátero Ferrífero in the state of Minas Gerais, Brazil. The procedure was carried out by hot acid leaching with hydrochloric acid (HCl) which allowed the recovery of about 95% of the iron in a liquor. The iron-based pigments—red (IBP_R), black (IBP_B), and yellow (IBP_Y)—were synthetised from the liquor by selective precipitation, crystallisation, and thermal procedures. The pigments were characterised by particle size distribution, mineral and chemical compositions, as well as colourimetric properties. The process of synthesis was successful and the procedure was shown to maximise the utilisation of mineral resources and minimise the environmental, social, and economic impacts associated with IOT disposal.

Effect of bastnaesite as reductant on hematite reduction during in-situ suspension magnetization roasting of refractory iron ore under neutral atmosphere

The iron tailings of Bayan Obo mines are solid waste,which occupies land area and also causes environmental pollution;however,this waste can be recycled.In this study,based on the characteristics of iron minerals and fluorocarbonate contained in Bayan Obo iron tailings,clean magnetization roasting of iron minerals by bastnaesite from iron tailings during in-situ suspension magnetization roasting in a neutral atmosphere was explored.The results show that for iron tailings with a mass of 12 g,a N_(2) gas flow rate of 600 mL/min,and roasting for 5 min at 800℃,iron concentrate with a 60.44%iron grade at an iron recovery of 76.04%could be obtained.X-ray diffraction analysis showed that the weak magnetic hematite was reduced to strong magnetic magnetite in the neutral atmosphere,without additional reductant.The kinetics of the magnetization roasting of mineral mixtures(bastnaesite and hematite)in a neutral atmosphere showed that the optimal reaction mechanism function was the three-dimensional diffusion model with activation energy of 161.8838 kJ·mol^(-1);this indicates that the reaction was a heterogeneous,diffusion-controlled solid-state reaction.

Volcanic Activity and Thermal Excitation of Rich-silicon Iron Ore Tailing in Concrete

In order to distinguish the filling effect and volcanic activity and explore the ways motivating the activity of rich-silicon iron ore tailing（IOT）, inert quartz was brought in as the correction standard, the influences of fineness, calcination, thermal curing system and some other factors were investigated by IR, XRD, MIP, and so on microscopic methods. The experimental results show grinding and calcination can only change the amorphous state of SiO2, and IOT do not have volcanic activity in concrete cured under room temperature condition. Thermal curing systems can stimulate the activity of IOT, especially mortar cured by autoclave curing system can consume a large amount of Ca（OH）2 and hard calcium silicate and has a closer structure. When the specific surface area of IOT powder is 800 m^2/kg, and 30% cement is replaced by IOT powder, the mortar strength with IOT powder is even higher than that with cementonly.

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.