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Iron ores always contain several forms of alumina, which may have different effect on sintering performance. In this paper, sinter pot tests were systematically conducted with various alumina types and contents by means of alumina additives substituting for the corresponding types of alumina, and the relevant action mechanism on sintering performance was clarified by the mineralogy of product sinter. The results show that kaolinite is beneficial to the granulation process rather than other three alumina types. In addition, it contributes to relatively better sintering performance while aluminous goethite ranks the only next, followed by gibbsite and free alumina. Mechanism analysis indicates that kaolinite and aluminous goethite are preferable to achieve relatively lower sinter porosity and higher amount of silico-ferrite of calcium and alumina (SFCA) compared with gibbsite and free alumina. Besides, the former two alumina types are apt to promote the formation of higher strength SFCA such as dendritic and acicular SFCA. Furthermore, much tighter interlocking texture in product sinter is formed as alumina occurs in kaolinite or aluminous goethite. Kaolinite and aluminous goethite are the preferably desirable alumina types for sintering rather than free alumina and gibbsite.

This study is aimed to obtain better-quality Ni–Cr composite sinter for the production of 300 series stainless steel via the sintering-blast furnace process at lower cost. Based on the complementary advantages of limonitic nickel laterite and chromite, co-sintering pot tests of the two ores were conducted in various chromite proportions and then strengthened by multi-force fields. Mechanistic analysis was performed, including the chemistry and mineralogy of product sinter and the thermodynamic and kinetic conditions of the co-sintering process. The results indicate that the addition of chromite effectively improves tumble index and productivity, especially at a chromite ratio of 15%, due to the improvement of sinter microstructure and the thermodynamic and kinetic conditions during sintering. However, solid fuel rate is increased gradually because of the greater amount of high smelting minerals. With the application of multi-force fields, higher tumble index is obtained owing to the further densification of sinter bed and the formation of tighter interlocking texture. Solid fuel rate is greatly decreased due to the efficient supply of extra physical heat. Productivity is weakened to some extent as the flame fronts speed is reduced. In addition, excellent metallurgical performance is achieved. The co-sintering process of limonitic nickel laterite and chromite is significantly improved via multi-force fields.

Zinc-bearing dusts from steel plants were classified as hazardous solid waste, but are important secondary resources to extract iron and zinc through direct reduction technology. In this study, three kinds of Zinc-bearing dusts from a steel plant were made into carbon-containing pellets and reduced at 1323 K–1473 K. The results showed that the efficiency of zinc removal was controlled by the Jander three-dimensional diffusion. The mechanism of zinc removal from the pellets was analyzed by optical microscope, scanning electron microscope, energy dispersive spectrometer, X-ray diffraction and thermodynamic calculation. It was found that the zinc element in the zinc-bearing dust pellets presented in the form of zinc ferrite, hardystonite and zinc chloride. The process of the zinc removal from the pellets in direct reduction could be divided into four stages according to the efficiency of zinc removal and the microstructure of the reduced pellets.

The alumina content of iron ores for sintering is gradually increasing with the growing depletion of high-grade iron ores, which is harmful to the sintering process. Therefore, it is essential to reveal the action mechanism of alumina on sinter quality. In this paper, the aluminum occurrence of various iron ores was determined by applying X-ray diffraction (XRD), optical microscopy, scanning electron microscopy and energy dispersive spectrum analysis (SEM-EDS). Then, the effects of iron ore type, aluminum occurrence (free alumina, gibbsite, diaspore, alumogoethite and kaolinite) and alumina content on formation characteristics of SFCA bonding phases as well as sinter matrix strength were investigated based on laboratory compact sintering tests. The results show that the discrepancy of aluminum occurrence contributes to different SFCA formation characteristics and then sinter matrix strength, due to different reactivity of various aluminum-containing minerals with iron oxides and fluxes. Increasing alumina content generally results in an increase in the porosity of sinters and deterioration of sinter matrix strength for all aluminum occurrence. Aluminum in the form of kaolinite is more conducive to form dendritic or acicular SFCA with superior sinter matrix strength compared with other aluminum occurrences. In contrast, aluminum occurring in free alumina presents greatest adverse impacts on sinter matrix strength due to its poor reactivity and high porosity of resultant sinters.

The poor sintering performance of limonitic laterite hinders its utilization. Hot exhaust-gas recirculation sintering was conducted to improve its sintering performance and intensification mechanism was revealed. Evaluating sinter indices in systematical sinter pot tests were substantially improved with tumble index and productivity increased by 18.01% and 7.22% respectively and solid fuel rate lowered by 13.71%, further proved by extensive industrial application. Effective CO2 emissions reduction and huge economic benefits were realized. The improvement of thermodynamic conditions converted sinter microstructure from large thin-wall pores into small thin-wall or large thick-wall pores. The amount of silico-ferrite of calcium and alumina in sinter pot tests and industrial application was increased from 8.78% to 18.61% and 21.25% respectively. Grains aggregation and growth of hercynite and close adhesion between solid phases and liquid bonding phases were achieved. Hot exhaust-gas recirculation sintering of limonitic laterite contributed to dramatically improving sinter performance and reducing CO2 emission.

As is well known, the process of direct reduction and magnetic separation is effective route to deal with low-grade saprolite laterite, but generally limited by the reduction of nickel (iron)-bearing minerals and growth of Fe-Ni alloy particles in the reduction process, causing the low recovery of nickel and iron. To improve beneficiation of nickel and iron from low-grade saprolite laterite with 1.29 wt.%Ni and 16.31 wt.%Fe, co-reduction with limonitic laterite ore and basicity optimization were adopted as strengthening measures in this paper with better economic efficiency than before. The enhancing mechanism was investigated via the thermodynamics analysis and mineralogical study. The phase transformation and growth behaviors of metallic alloy particles during reduction process were revealed as well. The results indicated that co-reduction with limonitic laterite ore is capable of promoting phase transformation from Ni2SiO4 in saprolite laterite to NiFe2O4. CaCO3 can not only destroy the structure of magnesium silicate to release nickel(iron)-bearing phase, but also enhance the reduction of Fe2SiO4 to form efficiently iron-based eutectoid with nickel and liquid phases to accelerate the growth of Fe-Ni fine particles larger than 40 μm. A superior crude alloy was obtained with 5.11 wt.%Ni and 82.15 wt.%Fe with corresponding recovery rates of 91.89% and 85.15% respectively. Keywords: Nickel laterite ore, Co-reduction, Basicity, Phase transformation, Particle growth, Fe-Ni alloy

An innovative one-step process for activated carbon production from low-rank coal is proposed in this research by applying oxidized pellets as activator. The new process can realize synchronous production of the activated carbon and direct reduction iron through combination of carbonization and activation of low-rank coal in one step while no solid wastes were discharged. The desulfurization and denitrification performance of the obtained activated carbon was also evaluated on the simulative sintering flue gas in comparison with one type of commercial activated carbon. The results indicated that a superior activated carbon with high specific surface area of 370.42 m

Aiming at the effective utilization of the abundant high-alumina iron ores with low iron grade, the influence of alumina concentration and type on high-temperature characteristics was clarified based on the analyses of eight typical iron ores. The results indicate that high-temperature characteristics of iron ores in various alumina types are different. Higher Al2O3 concentration is deleterious to assimilability and liquid phase fluidity, but the influence extent of each alumina type is substantially different. Kaolinite (Al2O3&middot, 2SiO2&middot, 2H2O) contributes to correspondingly better assimilability, followed by hercynite (Fe(Fe, Al)2O4), gibbsite (Al(OH)3), diaspore (AlO(OH)), and free state alumina (Al2O3) in turn. Diaspore promotes relatively higher liquid phase fluidity, followed by kaolinite, free state alumina, and hercynite, while gibbsite possesses the maximum adverse impact. Kaolinite and hercynite are more beneficial to form dendritic or acicular silico-ferrite of calcium and alumina (SFCA) with high strength due to the better reactivity, and gibbsite and diaspore lead to more formation of relatively lower strength lamellar or tabular SFCA, while free state alumina is preferable to form disseminated SCFA with rather poorer strength. Kaolinite and hercynite are the most desirable alumina types for sintering rather than free state alumina.

Limonitic laterite contains low iron and nickel grades and much high smelting minerals and loss on ignition (LOI), identified as refractory iron ore for sintering. Thus, sinter pot tests of limonitic laterite via pressurized densification sintering and its intensification mechanism were conducted, and the industrial application prospect was explored. The results indicate that the sintering performance of the limonitic laterite of the new process is significantly improved with the tumble index and productivity increased by 19.2% and 18.6%, respectively, and solid fuel rate lowered by 10.3%. The external pressure field promotes the synchronization of heat front velocity and combustion front velocity for better sintering heat and mass transfer conditions, which also greatly improves the mineral compositions and microstructure of the product sinter. The microstructure is converted from large thin-wall pores into small thin-wall or large thick-wall pores with the sinter porosity decreased by 42.4%. Much close interlocking texture between hercynite and silico-ferrite of calcium and alumina (SFCA) is formed with hercynite grains aggregation and growth, and SFCA amount substantially increased. The better sintering performance will bring about a remarkable economic benefit of 282.78 million RMB/a if the industrial application is implemented. The pressurized densification sintering process is considered as one of the effective technologies for improving limonitic laterite sintering.

Ferronickel tailings, by-products from nickel laterite direct reduction-magnetic separation process, are now stored up in large quantities with low utilization because of the high MgO content. In this paper, ferronickel tailing with 5.82% Fe, 0.51% Ni, 44.08% SiO2, and 31.98% MgO was adopted to replace the traditional Mg-bearing flux, i.e. serpentine. The laboratory pot sintering tests show that, this new technique increases sinter productivity and tumble index by 4.12% and 10.63%, respectively, and reduces solid fuel rate by 6.35%. The mineralogical study of product sinter shows that the addition of ferronickel tailing contributes to the increase of the amount of SFCA by 4.03%. Mg and Al elements were found to migrate into magnetite grains to form three types of spinel solid solutions, i.e. (Fe, Mg)Fe2O4, Fe (Fe, Al)2O4, and (Fe, Mg)·(Fe, Al)2O4. Meanwhile, eutectic compound melts were obtained by the co-melting of kirschsteinite (CaO·FeO·SiO2), monticellite (CaO·MgO·SiO2), and fayalite (2FeO·SiO2).

Thermodynamic analysis of chlorination of zinc-bearing phases in pyrite cinder was conducted by FactSage thermochemical software. The effects of temperature and main components of pyrite cinder on the chlorination of ZnO and ZnFe2O4 were studied. The results show that the presence of CaO and MgO has no effect on the chlorination of ZnO while the starting chlorination temperatures of ZnO decrease from 1525 °C to 1200, 950, 850 °C with the presence of Fe2O3, SiO2, and Al2O3, respectively. In contrast, the presence of Fe2O3 and MgO has no effect on the chlorination of ZnFe2O4 while the starting chlorination temperatures of ZnFe2O4 change from 1350 °C to 825, 1075, 1525 °C with the presence of SiO2, Al2O3, and CaO, respectively. The thermodynamic analysis is consistent with the experimental results available in the literature.

With a growing demand for high-grade pellet feeds as well as a considerable increase in ore price, using cost-effective and high-grade sinter feeds for oxidized pellets production becomes more attractive. In this paper, one hematite concentrate from the wet grinding of a typical coarse sinter feed (GSF#) was used as raw material for manufacturing oxidized pellets. The effect of GSF# proportion in ore mixture, up to 40 wt% on roasting and metallurgical properties of oxidized pellets was investigated. Moreover, the effects of binary basicity and MgO content were also studied. The results show that in the case of natural basicity and MgO content, increasing the proportion of GSF# improves high-temperature softening–melting properties of oxidizing pellets, whereas imposes negative impacts on pellet strength as well as reduction swelling performance. The adverse effects can be eliminated by increasing binary basicity and MgO content to produce Mg-bearing fluxed pellets, which indicates the feasibility of using high proportion of ground sinter feed to manufacture high-quality oxidized pellets at low production cost.

The research proposed an innovative, efficient, and clean process which used low-rank coals and oxidized pellets as carbon-based feedstocks and activators for one-step preparation of activated carbon with direct reduction iron as co-production. The co-effect between low-rank coals and oxidized pellets was disclosed. The properties characterization of activated carbon was comprehensively analyzed as well. The results indicated that semi-coke can be produced via the pyrolysis and carbonization of low-rank coal, which is the raw material of activated carbon and the reductant of oxidized pellets. Meanwhile, CO2, generated circularly via the reduction of iron oxides, acts as the activating agent of semi-coke to produce activated carbon. Furthermore, CO, generated via gasification reaction of carbon, can act as the main reductant for the reduction of iron oxides. Under the optimum conditions of SF coal as carbon-based feedstock, activated temperature of 850 °C for 140 min with C/Fe of 2.0, one-step prepared activated carbon, characterised by specific surface area of 370.42 m2 g−1, iodine sorption value of 685.67 mg g−1, compressive strength of 234.67 N·per−1, can be obtained with direct reduction iron as co-production processing metallization ratio of 86.96%. Compared with commercial activated carbon, the new SF activated carbon possesses a more superior microstructure, higher graphitization degree, preferable composition, and content of functional groups for its better adsorption property and compressive strength.

Copper slag, generated mainly during copper smelting, and classified as a potentially harmful waste, is an important secondary resource containing not only valuable metals, such as Cu, Fe, Zn, Co and Ni, in abundant quantities, but also hazardous elements, such as Pb and As. Hence, in response of its potential economic performances and environmental benefits, copper slag needs to be subjected to further metallurgical recycling and cleaning instead of being dumped or abandoned without treatment. Here, a critical review of the generation mechanism, and chemical and physical characteristics of copper slag is provided. Details of the mainstream and recently developed routes for metallurgical recycling and further cleaning of copper slag are also summarised, such as flotation, leaching, and reduction roasting followed by magnetic separation, smelting reduction, and molten modification followed by physical separation. The technical challenges and developmental bottlenecks of the metallurgical processes are pointed out, which indicate that the improved processes characterised by high recycling efficiency, low energy consumption, and low secondary environmental pollution continue to be the focus of research and development in sustainable waste utilization of copper slag.

COREX smelting reduction process which is freed of metallurgical coke provides a sustainable developing way for ironmaking industry. However, the shortage and high cost of pellets limit its development in China. Meanwhile, iron ore sinter has a great output in China. This work studied the reduction behaviors of sinter made from magnetite concentrates during the reducing process of COREX shaft furnace and compared the RI and RDI of sinter with BF process. The results showed that the reduction degree of sinter increased obviously during the temperature zone from 600 to 850 °C, while the reduction degradation presented rapidly aggravate in the temperature zone from 425 to 550 °C in COREX shaft furnace, and the increase of metallic iron content leads to the degradation of sinter got decreased slightly during the stage of temperature above 650 °C. Sinter got higher RI than BF process but also got higher RDI in low reduction temperature of 550 °C, which means sinter would have heavier disintegration in COREX shaft furnace.