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31.
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The dissolution rate coefficients of Cr‐substituted (0‐20 at.% Cr) iron oxides viz. hematite and magnetite were determined by using an inverse cubic rate (ICR) law applicable for spherical particles as well as by a general kinetic equation (GKE) applicable for polydispersed particles. An attempt is made to compare both the treatments for different kinds of dissolution profiles obtained by employing oxides with narrow particle size distribution in V(II)‐EDTA and citric acid‐EDTA‐ascorbic acid formulations at 353±5K. The dissolution profiles could be classified into three types based on the nature of oxide and formulations. It is observed that both ICR and GKE treat the dissolution course as a function of decrease in fraction of undissolved mass, m/m0. The dissolution rate coefficients determined by ICR and GKE have shown the similar trend of decrease with increasing Cr content of the oxides and was ascribed to lattice stabilization. 相似文献
33.
《分离科学与技术》2012,47(13):2028-2035
A composite magnetic sorbent with a relatively high content of humic substances (above 35% of organic carbon) was prepared by co-precipitation of Fe2+/Fe3+ salts with commercially available alkaline humate concentrate. Magnetite (Fe3O4) was identified as the main crystalline phase bearing the magnetic properties of the sorbent. Scanning electron microscope (SEM) images revealed the presence of uniform sub-micron structures on the surface of the sorbent grains. Due to the presence of humic substances, the sorbent exhibited good sorption ability towards low-polarity organic pollutants, namely chlorophenols. The sorption efficiency increased in the order of 4-mono- < 2,4-di- < 2,4,5-trichlorophenol in accordance with growing hydrophobicity of these compounds, confirming a hydrophobic nature of the interactions involved in the sorption process. Similar trends were found in the desorption study utilizing water and methanol as leachants. Some polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, fluoranthene, pyrene) were also retained on the sorbent. The chemical composition as well as the main physical characteristics (surface area, phase composition) of the sorbent remained virtually unchanged during the sorption process. The sorbent retained its magnetic properties during the sorption of organic substances from aqueous solutions, which provides an opportunity for its regeneration. 相似文献
34.
ABSTRACT Separation of ilmenite from titanaugite was investigated by magnetic coating. By enlarging magnetic difference between ilmenite and titanaugite, ilmenite was efficiently recovered. Scanning electron microscope and vibrating sample magnetometer results indicated that magnetite selectively coated onto ilmenite surface and increased its magnetism, which resulted in different magnetic separation behavior between ilmenite and titanaugite. FTIR and contact angle measurements confirmed that the adsorption difference of sodium oleate resulted in a stronger hydrophobicity on magnetite and ilmenite than titanaugite. Interaction energy analysis illustrated that hydrophobic association interaction on ilmenite was stronger than that on titanaugite, and which led to the selective coating of magnetite onto ilmenite. 相似文献
35.
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In the present investigation, the effect of the most important process variables, which are teeter water velocity (TW) and pressure set point (SP), on the classification and beneficiation performance of a laboratory-scale teetered bed separator (TBS) was evaluated and discussed. Pure silica sand, magnetite concentrate and their artificial mixture were used to observe the effect of mineral density. Classification test results revealed that separation cut size linearly increases with increasing TW and SP. From the beneficiation studies and the size-by-size chemical analysis of artificial mixture, it can be concluded that significant removal of silica is possible by employing TBS. 相似文献
37.
In this study, 2,4-DNPH coated magnetite was used for removal of As(V) and V(V) ions from aqueous solution. The synthesized nanoparticles were characterized by XRD analysis, FT-IR, SEM, and SEM-EDXS measurement. The size of the nanoparticles according to SEM was obtained as around 20–35 nm. Equilibrium isotherm data showed that the Langmuir–Freundlich model was in a good agreement with the experimental data according to high correlation coefficient. The maximum adsorption capacities of As(V) and V(V) on adsorbent were 338.4 and 266.8 mg g?1, respectively. Kinetic study showed that the fractal like-PSO model was appropriate to describe the adsorption process. The optimum pH was obtained to be 7 and 5 for As(V) and V(V) ions, respectively. 相似文献
38.
《Ceramics International》2017,43(7):5794-5804
Effects of hydrothermal temperature and time on physical, magnetic and thermal properties of Zn-substituted magnetite nanoparticles (Zn0.3Fe2.7O4) were assessed. The magnetic nanoparticles were synthesized via citric acid-assisted hydrothermal reduction route at temperatures of 150, 175 and 200 °C for duration of 10, 15 and 20 h. The nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and specific loss power (SLP) measurements. The results showed that temperature and time of the hydrothermal process both had significant effects on nanoparticles composition and properties. It was observed that at 150 °C, heat generation was insufficient to produce activation energy required for nucleation of Zn0.3Fe2.7O4 spinel nanoparticles, even after a long time. At 175 °C, although temperature was low, but the suitable condition for nucleation of nanoparticles was made and spinel nanoparticles with the size of about 13 nm were formed after 15 h. Nonetheless, since crystallinity and SLP of the nanoparticles was low, they showed weak performance for magnetic hyperthermia. At 200 °C, the required activation energy was provided for nanoparticles nucleation; however, the spinel was oxidized to hematite, resulting in a decrease in thermal and magnetic properties. In overall, the nanoparticles synthesized at 200 °C for 15 h possessed the best characteristics of reasonable purity, saturation magnetization of about 35.9 emu/g and SLP of 18.7 W/g. 相似文献
39.
40.
从资源紧缺、环境污染、产品低端等方面,总结了我国钒、钛、镍、钴、锂稀有金属资源在战略性新兴产业迅猛发展时代所面临的国家重大需求,回顾了领域近年来通过升级和变革传统稀有金属资源利用技术取得的主要进展和成就。其中煤基钠化冶炼、高温碳化?低温氯化、亚熔盐氧化等非常规介质强化手段是实现钒钛磁铁矿中钒、钛绿色高值高效利用的核心;盐酸常压浸出?低温选择性水解?共沉淀新技术是一种低成本、短流程高效高值利用红土镍矿全组分的先进技术代表;双功能协同复合萃取原理是实现高镁盐湖卤水的锂资源绿色利用的关键基础。基于固废资源化和源头减废两个思路,现阶段战略性金属资源的利用技术初步解决了环境污染和资源利用率低的问题,但仍存在资源绿色利用基础原理匮乏、产品科技含量低等普遍问题。以战略性产业关键材料为导向的绿色高值利用技术的应用基础研究是稀有金属相关绿色产业战略性发展的重要科技保障,是未来重要的前沿研究方向。 相似文献