International Journal of Minerals, Metallurgy and Materials

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Effect of pH values on the extracellular polysaccharide secreted by Acidithiobacillus ferrooxidans during chalcopyrite bioleaching

Run-lan Yu, Jing Liu, Jian-xi Tan, Wei-min Zeng, Li-juan Shi, Guo-hua Gu, Wen-qing Qin, Guan-zhou Qiu

2014, 21(4): 311-316. doi: 10.1007/s12613-014-0910-0

中文摘要(283) PDF(10) SpringerLink

摘要:
The pH value plays an important role in the bioleaching of sulphide minerals. The effect of pH values on the extracellular polysaccharide secreted by Acidithiobacillus ferrooxidans was investigated in different phases of bacterial growth during chalcopyrite bioleaching. It is found that extracellular polysaccharide secretion from the cells attached to chalcopyrite is more efficiently than that of the free cells in the bioleaching solution. Three factors, pH values, the concentration of soluble metal ions, and the bacterial growth and metabolism, affect extracellular polysaccharide secretion in the free cells, and are related to the bacterial growth phase. Extracellular polysaccharide secretion from the attached cells is mainly dependent on the pH value of the bacterial culture.

Influence of acid leaching and calcination on iron removal of coal kaolin

Pei-wang Zhu, Wei-qiang Zeng, Xiu-lin Xu, Le-ming Cheng, Xiao Jiang, Zheng-lun Shi

2014, 21(4): 317-325. doi: 10.1007/s12613-014-0911-z

中文摘要(264) PDF(15) SpringerLink

摘要:
Calcination and acid leaching of coal kaolin were studied to determine an effective and economical preparation method of calcined kaolin. Thermogravimetric-differential thermal analysis (TG-DTA) and X-ray diffraction (XRD) demonstrated that 900℃ was the suitable temperature for the calcination. Leaching tests showed that hydrochloric acid was more effective for iron dissolution from raw coal kaolin (RCK), whereas oxalic acid was more effective on iron dissolution from calcined coal kaolin (CCK). The iron dissolution from CCK was 28.78wt%, which is far less effective than the 54.86wt% of RCK under their respective optimal conditions. Through analysis by using Mössbauer spectroscopy, it is detected that nearly all of the structural ferrous ions in RCK were removed by hydrochloric acid. However, iron sites in CCK changed slightly by oxalic acid leaching because nearly all ferrous ions were transformed into ferric species after firing at 900℃. It can be concluded that it is difficult to remove the structural ferric ions and ferric oxides evolved from the structural ferrous ions. Thus, iron removal by acids should be conducted prior to calcination.

Effect of reduction roasting by using bio-char derived from empty fruit bunch on the magnetic properties of Malaysian iron ore

Nurul A. Yunus, Mohd H. Ani, Hamzah M. Salleh, Rusila Z. A. Rashid, Tomohiro Akiyama, Hadi Purwanto, Nur E. F. Othman

2014, 21(4): 326-330. doi: 10.1007/s12613-014-0912-y

中文摘要(285) PDF(14) SpringerLink

摘要:
Beneficiation of Malaysian iron ore is becoming necessary as iron resources are depleting. However, the upgrading process is challenging because of the weak magnetic properties of Malaysian iron ore. In this study, bio-char derived from oil palm empty fruit bunch (EFB) was utilized as an energy source for reduction roasting. Mixtures of Malaysian iron ore and the bio-char were pressed into briquettes and subjected to reduction roasting processes at 873–1173 K. The extent of reduction was estimated on the basis of mass loss, and the magnetization of samples was measured using a vibrating sample magnetometer (VSM). When reduced at 873 K, the original goethite-rich ore was converted into hematite. An increase in temperature to 1073 K caused a significant conversion of hematite into magnetite and enhanced the magnetic susceptibility and saturation magnetization of samples. The magnetic properties diminished at 1173 K as the iron ore was partially reduced to wustite. This reduction roasting by using the bio-char can assist in upgrading the iron ore by improving its magnetic properties.

Distribution behavior of phosphorus in the coal-based reduction of high-phosphorus-content oolitic iron ore

Yong-sheng Sun, Yue-xin Han, Peng Gao, Duo-zhen Ren

2014, 21(4): 331-338. doi: 10.1007/s12613-014-0913-x

中文摘要(330) PDF(11) SpringerLink

摘要:
This study focuses on the reduction of phosphorus from high-phosphorus-content oolitic iron ore via coal-based reduction. The distribution behavior of phosphorus (i.e., the phosphorus content and the phosphorus distribution ratio in the metal, slag, and gas phases) during reduction was investigated in detail. Experimental results showed that the distribution behavior of phosphorus was strongly influenced by the reduction temperature, the reduction time, and the C/O molar ratio. A higher temperature and a longer reaction time were more favorable for phosphorus reduction and enrichment in the metal phase. An increase in the C/O ratio improved phosphorus reduction but also hindered the mass transfer of the reduced phosphorus when the C/O ratio exceeded 2.0. According to scanning electron microscopy analysis, the iron ore was transformed from an integral structure to metal and slag fractions during the reduction process. Apatite in the ore was reduced to P, and the reduced P was mainly enriched in the metal phase. These results suggest that the proposed method may enable utilization of high-phosphorus-content oolitic iron ore resources.

Effect of aluminum oxide on the compressive strength of pellets

Jian-liang Zhang, Zhen-yang Wang, Xiang-dong Xing, Zheng-jian Liu

2014, 21(4): 339-344. doi: 10.1007/s12613-014-0914-9

中文摘要(296) PDF(18) SpringerLink

摘要:
Analytical-reagent-grade Al₂O₃ was added to magnetite ore during the process of pelletizing, and the methods of mercury intrusion, scanning electron microscopy, and image processing were used to investigate the effect of Al₂O₃ on the compressive strength of the pellets. The results showed that, as the Al₂O₃ content increased, the compressive strength of the pellets increased slightly and then decreased gradually. When a small amount of Al₂O₃ was added to the pellets, the Al₂O₃ combined with fayalite (2FeO·SiO₂) and the aluminosilicate (2FeO·2Al₂O₃·5SiO₂) was generated, which releases some iron oxide and reduces the inhibition of fayalite to the solid phase of consolidation. When Al₂O₃ increased sequentially, high melting point of Al₂O₃ particles hinder the oxidation of Fe₃O₄ and the recrystallization of Fe2O3, making the internal porosity of the pellets increase, which leads to the decrease in compressive strength of the pellets.

Dissolution and diffusion of TiO₂ in the CaO-Al₂O₃-SiO₂ slag

Zhong-shan Ren, Xiao-jun Hu, Xin-mei Hou, Xiang-xin Xue, Kuo-chih Chou

2014, 21(4): 345-352. doi: 10.1007/s12613-014-0915-8

中文摘要(317) PDF(11) SpringerLink

摘要:
The dissolution of TiO₂ in the CaO-Al₂O₃-SiO₂ slag under static conditions was studied in the temperature range from 1643 K to 1703 K. After TiO₂ dissolved, the microstructure of the interface between TiO₂ and the slag was observed by scanning electron microscopy, and the concentration profiles of Ti⁴⁺ and other ions across the TiO₂/slag interfaces were analyzed by energy-dispersive X-ray spectroscopy. On the basis of these results, the dissolution behavior of TiO₂ was evaluated, and the diffusivity of Ti⁴⁺ in the bulk slag was estimated. According to the Stokes-Einstein relation, the viscosity calculated by a previously reported model gave a diffusivity of Ti⁴⁺ ions greater than that estimated by the concentration profiles of Ti⁴⁺ ions. The mechanism of TiO₂ dissolution in the CaO-Al₂O₃-SiO₂ slag is discussed in detail.

Effects of basicity and MgO content on the viscosity of the SiO₂-CaO-MgO-9wt%Al₂O₃ slag system

Yun-ming Gao, Shao-bo Wang, Chuan Hong, Xiu-juan Ma, Fu Yang

2014, 21(4): 353-362. doi: 10.1007/s12613-014-0916-7

中文摘要(386) PDF(33) SpringerLink

摘要:
The effects of basicity and MgO content on the viscosity of SiO₂-CaO-MgO-9wt%Al₂O₃ slags with basicity from 0.4 to 1.0 and MgO content from 13wt% to 19wt% were investigated using the rotating cylinder method. A correlation between the viscosity and the slag structure was determined by Fourier transform infrared (FTIR) spectroscopy. It is indicated that the complex network structure of the slag melt is depolymerized into simpler network units with increasing basicity or MgO content, resulting in a continuous decrease in viscosity of the slag. The viscosity is strongly dependent on the combined action of basic oxide components in the slag. Under the present experimental conditions, increasing the basicity is found to be more effective than increasing the MgO content in decreasing the viscosity of the slag. At higher temperatures, the increase of basicity or MgO content does not appreciably decrease the viscosity of the slag, as it does at lower temperatures. The calculated activation energy of viscous flow is between 154 and 200 kJ·mol⁻¹, which decreases with an increase in basicity from 0.4 to 1.0 at a fixed MgO content in the range of 13wt% to 19wt%.

Effect of scanning speed during PTA remelting treatment on the microstructure and wear resistance of nodular cast iron

Hua-tang Cao, Xuan-pu Dong, Qi-wen Huang, Zhang Pan, Jian-jun Li, Zi-tian Fan

2014, 21(4): 363-370. doi: 10.1007/s12613-014-0917-6

中文摘要(362) PDF(9) SpringerLink

摘要:
The surface of nodular cast iron (NCI) with a ferrite substrate was rapidly remelted and solidified by plasma transferred arc (PTA) to induce a chilled structure with high hardness and favorable wear resistance. The effect of scanning speed on the microstructure, microhardness distribution, and wear properties of PTA-remelted specimens was systematically investigated. Microstructural characterization indicated that the PTA remelting treatment could dissolve most graphite nodules and that the crystallized primary austenite dendrites were transformed into cementite, martensite, an interdendritic network of ledeburite eutectic, and certain residual austenite during rapid solidification. The dimensions of the remelted zone and its dendrites increase with decreased scanning speed. The microhardness of the remelted zone varied in the range of 650 HV_0.2 to 820 HV_0.2, which is approximately 2.3–3.1 times higher than the hardness of the substrate. The wear resistance of NCI was also significantly improved after the PTA remelting treatment.

In situ measured growth rates of bainite plates in an Fe-C-Mn-Si superbainitic steel

Zhang-wei Hu, Guang Xu, Hai-jiang Hu, Li Wang, Zheng-liang Xue

2014, 21(4): 371-378. doi: 10.1007/s12613-014-0918-5

中文摘要(261) PDF(24) SpringerLink

摘要:
The growth rates of bainite plates in an Fe-C-Mn-Si superbainitic steel were investigated by in situ observation. The lengthening rates of ferrite bainite during both cooling and isothermal holding processes were observed and the growth rates of bainite plates nucleating at grain boundaries, within grains and on preformed bainite were measured. It is indicated that the lengthening rates of bainite plates during the cooling and isothermal processes were different, and that the growth rates of bainite plates nucleating at different types of sites also demonstrated diversity. The bainite plates initiating at grain boundaries during cooling grew the fastest, while the plates nucleating on preformed bainite did the slowest. However, the growth rate of the bainite plates nucleating at grain boundaries during isothermal transformation decreased the most, whereas the bainite plates initiating within grains grew the fastest. In addition, the growth rate of ferrite bainite in the study supported the diffusion transformation mechanism of bainite from the viewpoint of growth rate.

Study on precipitation and transition mechanisms from the magnetic properties of silicon steel during annealing

Yong-fei Fan, Hao Yu, Jing Sun, Pan Tao, Cheng-hao Song, Xun Zeng

2014, 21(4): 379-387. doi: 10.1007/s12613-014-0919-4

中文摘要(228) PDF(10) SpringerLink

摘要:
Precipitates play an important role in determining the mechanical and magnetic properties of silicon steel. This paper aims to investigate the growth kinetics of precipitates in commercial silicon steel by analyzing its magnetic properties during isothermal annealing at 200℃. The growth of precipitates was studied by optical microscopy, scanning electron microscopy, transmission electron microscopy, and magnetic measurements. In combination with the coercive field and initial susceptibility, this technique offers the advantage of being non-destructive and providing quantitative information about the number, mean radius of precipitates, and fraction of transformation. An observed decrease in the number of precipitated particles indicates that the transformation starts from particles of appreciable initial size.

Effect of H₂S concentration on the corrosion behavior of pipeline steel under the coexistence of H₂S and CO₂

Da-peng Li, Lei Zhang, Jian-wei Yang, Min-xu Lu, Jin-hui Ding, Ming-liang Liu

2014, 21(4): 388-394. doi: 10.1007/s12613-014-0920-y

中文摘要(298) PDF(16) SpringerLink

摘要:
The effect of H₂S concentration on H₂S/CO₂ corrosion of API-X60 steel was studied by scanning electron microscopy, a weight-loss method, potentiodynamic polarization tests, and the electrochemical impedance spectroscopy technique. It is found that the corrosion process of the steel in an environment where H₂S and CO₂ coexist at different H₂S concentrations is related to the morphological structure and stability of the corrosion product film. With the addition of a small amount of H₂S, the size of the anode reaction region is decreased due to constant adsorption and separation of more FeS sediment or more FeHS⁺ ions on the surface of the steel. Meanwhile, the double-layer capacitance is diminished with increasing anion adsorption capacity. Therefore, the corrosion process is inhibited. The general corrosion rate of the steel rapidly decreases after the addition of a small amount of H₂S under the coexistence of H₂S and CO₂. With a further increase in H₂S concentration, certain parts of the corrosion product film become loose and even fall off. Thus, the protection provided by the corrosion product film worsens, and the corrosion rate tends to increase.

Microstructure and properties of hydrophobic films derived from Fe-W amorphous alloy

Song Wang, Yun-han Ling, Jun Zhang, Jian-jun Wang, Gui-ying Xu

2014, 21(4): 395-400. doi: 10.1007/s12613-014-0921-x

中文摘要(212) PDF(7) SpringerLink

摘要:
Amorphous metals are totally different from crystalline metals in regard to atom arrangement. Amorphous metals do not have grain boundaries and weak spots that crystalline materials contain, making them more resistant to wear and corrosion. In this study, amorphous Fe-W alloy films were first prepared by an electroplating method and were then made hydrophobic by modification with a water repellent (heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane. Hierarchical micro-nano structures can be obtained by slightly oxidizing the as-deposited alloy, accompanied by phase transformation from amorphous to crystalline during heat treatment. The micro-nano structures can trap air to form an extremely thin cushion of air between the water and the film, which is critical to producing hydrophobicity in the film. Results show that the average values of capacitance, roughness factor, and impedance for specific surface areas of a 600℃ heat-treated sample are greater than those of a sample treated at 500℃. Importantly, the coating can be fabricated on various metal substrates to act as a corrosion retardant.

Fabrication, microstructure, and optical properties of nanocrystalline transparent LAST glass ceramics containing CeO₂

Mohammad Sadegh Shakeri

2014, 21(4): 401-407. doi: 10.1007/s12613-014-0922-9

中文摘要(199) PDF(8) SpringerLink

摘要:
In the present research, the effect of CeO₂ dopant on the fabrication of transparent lithium aluminosilicate titanate (LAST) glass ceramics was investigated. Nanocrystalline β-quartz solid solution (s.s.) was observed to be the main phase crystallized in this system. Comparable refractive indices of the glassy matrix and β-quartz s.s., as well as the incorporation of very fine grains size were determined as the main reasons for retaining the transparency of the glass ceramics. CeO₂ was introduced as a suitable optical agent, playing a role as a network modifier in the glass ceramics, because it does not accelerate the growth process and retards the extended growth of crystals. Optical investigations indicate that the Fermi energy level, direct and indirect band gaps, and Urbach energy decrease with increasing nanocrystal content in the glassy matrix of specimens, which can be related to the expansion of conduction band, the enhancement of ionic bonds in the crystal lattice, and the enhancement of structural arrangement degree, respectively.

Influence of particle size and temperature on the dielectric properties of CoFe₂O₄ nanoparticles

Deepshikha Rathore, Rajnish Kurchania, R. K. Pandey

2014, 21(4): 408-414. doi: 10.1007/s12613-014-0923-8

中文摘要(434) PDF(22) SpringerLink

摘要:
The objective of this study was to establish the dielectric properties of CoFe₂O₄ nanoparticles with particle sizes that varied from 28.6 to 5.8 nm. CoFe₂O₄ nanoparticles were synthesized using a chemical coprecipitation method. The particle sizes were calculated according to the Scherrer formula using X-ray diffraction (XRD) peaks, and the particle size distribution curves were constructed by using field-emission scanning electron microscopy (FESEM) images. The dielectric permittivity and loss tangents of the samples were determined in the frequency range of 1 kHz to 1 MHz and in the temperature range of 300 to 10 K. Both the dielectric permittivity and the loss tangent were found to decrease with increasing frequency and decreasing temperature. For the smallest CoFe₂O₄ nanoparticle size, the dielectric permittivity and loss tangent exhibited their highest and lowest values, respectively. This behavior is very useful for materials used in devices that operate in the microwave or radio frequency ranges.

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2014年第21卷第4期

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2014年第21卷第4期