Zhucheng Huang

Leaching kinetics of pyrolusite from manganese–silver ores in the presence of hydrogen peroxide

Abstract The leaching kinetics of pyrolusite from manganese–silver ores in sulfuric acid solution in the presence of hydrogen peroxide has been investigated. It is found that the H 2 SO 4 concentration has the most important influence on the leaching rate. A reaction order of 0.95 for hydrogen ions is obtained at 0.55–1.6 mol/L H 2 SO 4 concentration. The leaching rate is clearly improved with increasing H 2 O 2 concentration although the effect is eroded by the decomposition of H 2 O 2 , which is catalyzed by MnO 2 . The leaching rate strongly depends on the stirring speed below 950 r/min. The particle size also distinctly affects the leaching process; the leaching rate is directly proportional to the inverse of the square of the average initial particle diameter. The effect of temperature is not apparent and the manganese can be extracted at room temperature in the presence of H 2 O 2 . The leaching process follows the kinetic model 1−(2/3 x )−(1− x ) 2/3 = kt and the apparent activation energy is determined to be 4.45±0.3 kJ/mol at 30–60 °C. It is concluded that the leaching process of pyrolusite from Mn–Ag ores in acidic sulfuric solution in the presence of H 2 O 2 is controlled by diffusion through an insoluble layer composed of the associated minerals.

Simultaneous leaching of manganese and silver from manganese–silver ores at room temperature

Abstract Manganese–silver ores are typical refractory ores and are not amenable to conventional silver extraction methods. A simultaneous leaching process to extract manganese and silver by one-step leaching in sulfuric acid solution in the presence of hydrogen peroxide is proposed in this paper. Thermodynamic investigations of the Mn–H 2 O and Ag–H 2 O systems show that there is a predominance area in the Eh–pH diagram where Mn 2+ and Ag + coexist in solution. Hydrogen peroxide was used in the leaching process in order to simultaneously extract manganese and silver. A recovery of 98% for manganese and 85% for silver was attained for an ore analyzing 12.2% Mn and 1850 g/t Ag under the conditions of 0.8 mol/L H 2 O 2 , 0.8 mol/L H 2 SO 4 , 25 °C, 2 h of leaching time. Investigations show that hydrogen peroxide is critical to the simultaneous leaching of manganese and silver at room temperature, and it plays a dual role as an oxidizing agent for native silver and a reducing agent for manganese dioxide.

Preheating and roasting characteristics of hematite–magnetite (H–M) concentrate pellets

Abstract Regressive orthogonal design experiments have been carried out based on the analysis of the oxidation and induration behaviours of individual magnetite and hematite pellets. The research shows that the optimal pellet preheating time and temperature, and roasting time and temperature change with hematite/magnetite (H/M) ratio. Under the conditions of preheating temperature 900°C, preheating time 10 min, roasting temperature 1275°C and roasting time 15 min, the compression strength of preheated and roasted pellets is found to be respectively more than 444 N/pellet (N/P) and 3993 N/P when the magnetite content in the pellets exceeds 20%. The pellet strengths meet the requirements of rotary kilns and blast furnaces respectively.

Tin and zinc separation from tin, zinc bearing complex iron ores by selective reduction process

Abstract Tin, zinc bearing complex iron ores are typically intractable and have not been efficiently utilised in China. In this investigation, the process mineralogy of the tin, zinc bearing iron ores and reduction behaviours of iron, tin and zinc oxides by CO were investigated. A selective reduction roasting process was initially developed to separate tin and zinc from the complex iron ores. Under optimum conditions, most of the tin and zinc were effectively removed from the iron ore pellets, and the roasted pellets could be used as high quality ironmaking burdens for large scale blast furnaces.

Reduction Enhancement Mechanisms of a Low-Grade Iron Ore–Coal Composite by NaCl

The reduction behavior of a low iron grade with high SiO2 content ore–coal composite was investigated in the temperature range of 1143 K to 1263 K (870 °C to 990 °C). Sodium chloride was chosen as an additive to promote this reduction process. The effect of the sodium chloride addition and its mechanism was also investigated. Results showed that the added sodium chloride could enhance the reduction of wustite to iron due to the decrease of fayalite, and a higher metallization ratio of reduced sample was obtained. Thermogravimetric–differential scanning calorimeter analysis showed that sodium chloride could greatly facilitate the gasification process of coal and, thus, provide sufficient carbon monoxide to the reduction process of iron oxides. Meanwhile, sodium chloride promoted the reduction process of iron ore pellets directly as the coal gasification effect was excluded. Microstructures of reduced sample revealed that sodium chloride broke the structure of ore and enhanced the growth of newly formed iron particles. As the ore–coal composite with mol (C/Fexa0=xa01.4) and 3xa0mass pct sodium chloride addition was roasted at 1233 K (960 °C) for 55 minutes, a reduced sample with metallization ration of 74.45 pct could be obtained.

Mechanisms of Strengthening the Reduction of Fine Hematite in High Silicon Coal-Containing Mini-Pellets by Sodium Additives

The reduction roasting-magnetic separation and its strengthening of high silicon coal-containing mini-pellets by sodium additives were researched. The results show that the carbon gasification reaction and reduction of fine hematite in high silicon coal-containing mini-pellets with 3% sodium additives were enhanced. Comparing with no sodium additives, the gasification rate of carbon with 3% sodium additives reacting with CO2 for 40 minutes at 950 °C and the metallization rate of reduced pellets with 3% sodium additives after roasting for 35 minutes at 960°C increased from 35.15% and 58.72% to 86.98% and 86.15%, respectively. The analysis of SEM equipped with EDS demonstrates that the inner pore of reduced pellets with 3% sodium additives was more developed and the iron grains size significantly enlarged, meanwhile, the iron grade of concentrate increased from 60.45% to 80.23% and the iron recovery rate decreased from 84.67% to 80.78% after grinding-magnetic separation.

Effect of Temperature on Reduction Roasting of Low-Grade Iron Ore after Granulating with Coal

The method of red uction roasting a nd magnetic separatio n of low- grade, micro- fine disseminated refractory iron ore following granulation with coal produced unexpected success. Pellets of iron ore with diameter between 3 and 8mm were granulated with coal, bentonite and water. The raw pellets a nd reduction products were analyzed by scanning electron microscopy and x-ray diffraction. Results show uniformly distributed coal powders inside the pellets improved the kinetics of the reduction process and accelerated the reduction rate. Reduction time was higher at temperatures below 890°C, which resulted in the formation of substantial amounts of fayalite. When temperature was increased, micro-fine hematite was then quickly reduced to iron metal a nd the amount of fayalite decreased sharply. When pellets were reduced at 950°C for 25min, reduc tion products with 56.73% metallization rate were obtained. After grinding and magnetic separation, a concentrate with 72.18% Fetot was obtained.

Study on Direct Reduction of Low-Grade Iron Ore-Coal Mini-pellets in Coal-Based Rotary Kiln

In this work, research of reduction process was studied by means of rotary kiln (φ1.5 m × 15 m) process anatomy in order to provide fine guidance to large-scale operation. It was shown that the average reduction degree of 89.96% and metallization ratio of 85.15% were obtained at the highest temperature of 977 °C and total residence time of 90 min. The generation amount of metallic iron in section of temperature higher than 900 °C and lower than 900 °C was 34.15 and 56.38%, respectively. The section of lower temperature of 830–900 °C played an important role in formation of metallic iron, making it possible for mini-pellet to reduce quickly at lower temperature. Two main tasks were completed for mini-pellets in rotary kiln: the reduction of iron oxides in the range of 15.0–4.5 m as well as migration and beneficiation of metallic iron, facilitating the subsequent separation of iron and gangue minerals.