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REE-Nb-Fe ore is a typical refractory resource rich in valuable elements. In this article, coal-based reductive roasting followed by magnetic separation is proposed to recover rare earth element (REE), niobium (Nb), and powdered metallic iron (Fe) concentrate from a REE-Nb-Fe raw concentrate containing 31.9% total iron grade (TFe), 3.2% rare earth oxides (REO), and 2.9% Nb2O5. Sodium sulfate is employed to enhance the reduction of iron oxide and to facilitate the growth of metallic iron grains. A magnetic fraction with TFe of 89.3%, iron metallization of 95.8% and iron recovery of 91.5% is obtained by magnetic separation after the raw concentrate is reduced to 1100°C for 120 min in the presence of 15 wt.% sodium sulfate. The contents of rare earth and niobium in the nonmagnetic fraction are enriched to 5.4% (REO) and 4.6% (Nb2O5) with recoveries of 96.1% and 95.8%, respectively. The TFe in the nonmagnetic fraction obtained after the separation is decreased to 4.8% accordingly. The reactions between sodium sulfate and SiO2/Al2O3 enhance the reduction by destroying the mineral structure. The separation of iron from rare earth and niobium is highly improved as metallic iron grains grow markedly when roasted in the presence of sodium sulfate.

Reduction roasting-acid leaching process was utilized to process high-iron-content manganese oxide ore using black charcoal as reductant. The results indicate that, compared with the traditional reductant of anthracite, higher manganese extraction efficiency is achieved at lower roasting temperature and shorter residence time. The effects of roasting parameters on the leaching efficiency of Mn and Fe were studied, and the optimal parameters are determined as follows: roasting temperature is 650 °C, residence time is 40 min, and black charcoal dosage is 10% (mass fraction). Under these conditions, the leaching efficiency of Mn reaches 82.37% while that of Fe is controlled below 7%. XRD results show that a majority of MnO2 and Fe2O3 in the raw ore are reduced to MnO and Fe3O4, respectively.

Manganese oxide ore is one of the most important resources. Owing to the depletion of high-grade ores, attention has turned to low-grade ones containing multiple elements such as iron, silicon, and aluminum. Conventional processes for extracting manganese are characterized by high production costs, intensive energy consumption, heavy environmental issues, or high co-leaching of impurities. In this study, selective sulfation roasting–water leaching is proposed for recovering manganese from iron rich low-grade manganese oxide ores using SO2 as reductant. Thermodynamic analysis indicated that manganese dioxide is readily transformed to sulfate. However, the sulfation of ferric oxide only occurs in the presence of both SO2 and O2. The thermodynamic stability region for MnSO4 and Fe2O3 demonstrated selective sulfation of manganese dioxide is feasible. The experimental validation for sulfation roasting and water leaching revealed that 90.6% of manganese and only 3.5% of iron were extracted when sulfation roasting was conducted at 500 °C for 60 min with SO2 partial pressure (SO2 / (SO2 + N2)) of 0.5%–1.0% (Vol.), and the leaching process was performed at 50 °C for 15 min with liquid-to-solid ratio of 5. This process is able to recover manganese from various low-grade manganese oxide ores.

Sodium stannate is widely used in the electroplating and tin alloy industries. The traditional sodium stannate production processes suffer a variety of disadvantages including long flowsheet, high production cost and strict requirements for the equipment. In this study, a novel process for preparing sodium stannate is developed by roasting tin dioxide and sodium carbonate in CO/CO 2 mixed gas followed by leaching the intermediate products in a diluted sodium hydroxide solution. The effects of roasting and leaching parameters on the leaching efficiency of Sn were investigated. The Sn leaching efficiency reaches 85.6% under the optimal experimental conditions: roasting temperature of 875 °C, CO content of 15%, roasting time of 15 min, Na 2 CO 3 /SnO 2 mole ratio of 1.5, liquid-to-solid ratio of 4 cm 3 /g, leaching temperature of 40 °C, leaching time of 60 min, and stirring speed of 300 rpm. Sodium stannate trihydrate (Na 2 SnO 3 · 3H 2 O) having a purity of 95.8% is successfully produced from cassiterite concentrates with a SnO 2 content of 76.4% through the new process, which is superior to the traditional approach for producing the industrial first-grade stannate.

Sn-, Zn-, and As-bearing iron ores are typical complex ores and are abundantly reserved in China. This kind of ore is difficult to use effectively due to the complicated relationships between iron and the other valuable metal minerals. Excessive Sn, Zn, and As contents would adversely affect ferrous metallurgy operation as well as the quality of the products. In this study, thermodynamic calculations revealed that it was feasible to synchronously volatilize Sn, Zn, and As via CO reduction. Experimental results showed that preoxidation was necessary for the subsequent reductive volatilization of Zn from the pellets, and the proper preoxidation temperature was 700–725°C under air atmosphere. Synchronous volatilization of Sn, Zn, and As was realized by roasting under weak reductive atmosphere after the pellets were preoxidized. The volatilization ratios of 75.88% Sn, 78.88% Zn, and 84.43% As were obtained, respectively, under the conditions by reduction at 1000°C for 100 min with mixed gas of 50% CO + 50% CO2 (in vol.). A metallic pellet (direct reduction iron) with total iron grade of 87.36%, Fe metallization ratio of 89.27%, and residual Sn, Zn, and As contents of 0.071%, 0.009%, and 0.047%, respectively, was prepared. Sn and As were mainly volatilized during weak reductive atmosphere roasting, and those volatilized in the metallization reduction process were negligible. Most of Zn (78.88%) was volatilized during weak reductive atmosphere roasting, while the metallization reduction process only contributed to 16.10% of total Zn volatilization.

Lead-rich molybdenite is a typical rhenium-bearing molybdenum resource in China, which has not been efficiently utilized due to its high contents of lead and gangue minerals. In this study, hydrochloric acid was used for preliminarily removing lead and calcite from a lead-rich molybdenite concentrate. Oxidative roasting-ammonia leaching was then carried out for separation of rhenium and extraction of molybdenum. The hydrochloric acid leaching experiments revealed that 93.6% Pb and 97.4% Ca were removed when the leaching was performed at 95 °C for 10 min with HCl concentration of 8 wt. % and liquid-solid ratio of 5 (mL/g). The results of direct oxidative roasting indicated that 89.3% rhenium was volatilized from the raw concentrate after roasting at 600 °C for 120 min in air. In contrast, the rhenium volatilization was enhanced distinctly to 98.0% after the acid-leached concentrate (leaching residue) was roasted at 550 °C for 100 min. By the subsequent ammonia leaching, 91.5% molybdenum was leached out from the calcine produced from oxidative roasting of the acid-leached concentrate, while only 79.3% Mo was leached from the calcine produced by roasting molybdenite concentrate without pretreatment.

In recent years, the comprehensive utilization of low-grade manganese oxide ores has received much attention due to the shortage of high-grade manganese ore resources. In this study, low-grade manganese oxide ores were treated by reduction roasting using chemically pure sulfur as a reductant. Then, the roasted samples were subjected to sulfuric acid leaching to extract manganese (Mn). The effects of roasting temperature, roasting time, S/Mn mole ratio, sulfuric acid concentration, leaching temperature, stirring rate, leaching time and liquid-to-solid ratio on the Mn and Fe leaching were discussed. The leaching efficiencies of 95.6% for Mn and 14.5% for Fe were obtained under the following optimized conditions: 550 °C of roasting temperature, 10 min of roasting time, 0.50 of S/Mn, 1.0 mol/L of sulfuric acid concentration, 25 °C of leaching temperature, 200 r/min of stirring rate, 5 min of leaching time and 5:1 of liquid-to-solid ratio.

Low-grade manganese oxide ore is generally characterized by high iron content. In this work, sulfidation roasting of an iron-rich manganese oxide ore with elemental sulfur was characterized. The experimental results indicated that manganese dioxide can be selectively reduced over iron oxide by using elemental sulfur. The manganese phases in roasted product included low-valence manganese oxide, manganese sulfide and manganese sulfate, while those of iron mainly depended on the sulfur addition. Iron oxide would only be reduced or sulfidized at larger sulfur additions. The effect of roasting temperature and S/Mn mole ratio on the phase transformations was also investigated; extractions of Mn/Fe by sulfuric acid were evaluated. An extraction of Mn greater than 95% was obtained while that of Fe was controlled less than 10% under the optimal conditions.

Sn-bearing iron ore containing small amount of Zn, Pb and As is one of the typical complex polymetallic ores in China. This kind of ore is not extensively utilized due to the complicated relationships between iron and other associated nonferrous metal minerals. Excessive contents of these elements would adversely affect the metallurgical operation as well as the quality of steel products. In this study, reduction behavior of Sn was detailedly investigated using H2 or mixed H2/CO as reductant. The results revealed Sn volatilization was improved in the presence of H2 than individual CO/CO2 atmosphere. Simultaneous volatilization of these elements was realized by roasting under weak H2/CO reducing potential, and metallization reduction was advantageous for further Zn volitilization. A metallic pellet (DRI) with Fe metallization greater than 90%, residual Sn, Zn, Pb and As content of 0.054%, 0.012%, 0.0045% and 0.09% was prepared via a simulated reducing gas of coal gasification.