Synthetic fayalite Fe2SiO4 by kinetically controlled reaction between hematite and silicon carbide

The present work explores the preparation of fayalite α-Fe₂SiO₄, the iron-rich end-member of the olivine solid-solution series, as a tar removal catalyst for biomass gasification. The synthetic procedure was developed starting from the stoichiometric mixture of hematite and micrometer size silicon carbide and employing thermal treatments in controlled atmospheres at 1000-1100°C supported by thermodynamic modeling to assess the required redox conditions. The treatments in dry and humidified inert gas yielded phase mixtures containing metallic Fe as one of the main phases, thus emphasizing a shortage of oxygen supply. XRD and TGA studies of precursor mixtures on heating in dry CO₂ demonstrated a multistep mechanism of the overall reaction including (a) fast reactivity between silicon carbide and hematite at ~920°C with formation of metallic Fe and amorphous silica followed by (b) formation of fayalite involving oxygen supplied in the form of CO₂ and competing with (c) over-oxidation to thermodynamically favorable Fe₃O₄+SiO₂ mixture. Comparative studies of reactivity in powdered and pelletized samples emphasized the importance of the kinetic factor in the formation of Fe₂SiO₄ while preventing further oxidation. The preferential formation of fayalite in the CO₂ atmosphere is shown to be favored by shorter treatments of compacted samples at higher temperatures. The procedure was designed (2-step heating to 1100°C in CO₂ followed by fast cooling) for the preparation of pelletized fayalite α-Fe₂SiO₄ catalyst with only minor traces of surface over-oxidation which can be suppressed by adding 10 vol.% of forming gas to CO₂ flow.     

开江—梁平海槽西侧飞仙关组不同类型鲕滩储层特征及其控制因素研究

针对开江—梁平海槽西侧飞仙关组鲕滩储层特征及主控因素存在较大差异的问题,基于鲕滩沉积演化规律，结合物性与地球化学分析，对开江—梁平海槽西侧飞仙关组鲕滩储层进行了研究。结果表明:伴随区内飞仙关期高能坡折带不断迁移，对应形成三期鲕滩，发育鲕粒云岩和鲕粒灰岩2类储层，物性及孔隙结构以鲕粒云岩型储层最优，次为鲕粒灰岩型储层。在鲕滩沉积的物质基础上，轻度蒸发海水诱发的回流渗透叠加深部热液白云石化作用共同控制鲕粒云岩型储层的形成，而有机酸主导的埋藏期保孔-扩孔作用既进一步改善先期形成的鲕粒云岩型储层，又影响了鲕粒灰岩型储层的形成。该研究对鲕滩储层的差异性成储机理相关研究有很好的借鉴意义。     

Separation of hematite from banded hematite jasper (BHJ) by magnetic coating

The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions.     

油酸钠作捕收剂时变性淀粉对赤铁矿、石英可浮性的影响

以油酸钠为捕收剂,以木薯原淀粉、取代度为0.026和0.21的羧甲基淀粉、取代度为0.0065和0.055的磷酸酯淀粉作为抑制剂,考察了赤铁矿和石英的可浮性。重点研究了变性淀粉基团取代度对其抑制性能的影响。浮选试验结果表明,原淀粉与变性淀粉对赤铁矿的抑制作用规律一致,提高变性淀粉的取代度可增强其对赤铁矿的抑制能力;对于Ca~(2+)活化的石英,在较低的Ca~(2+)用量时,原淀粉和变性淀粉均没有明显的抑制作用,但是随着Ca~(2+)用量的增加,变性淀粉表现出一定的抑制作用、且取代度越高越显著。这种抑制作用与油酸钠、Ca~(2+)及变性淀粉三者的用量有关。Ca~(2+)以Ca(OH)+的形式吸附于石英表面,油酸钠或变性淀粉再与Ca(OH)+作用,如果油酸钠用量较大,全部Ca(OH)+优先与油酸钠作用,则石英被捕收;如果油酸钠用量相对较小,变性淀粉与剩余的Ca(OH)+作用,则对石英产生抑制作用。控制Ca~(2+)和油酸钠的用量在最佳范围,增加变性淀粉的取代度可提高其在赤铁矿脱硅反浮选中的抑制性能。     

Significance of interface barrier at electrode of hematite hydroelectric cell for generating ecopower by water splitting

Recent increase in energy demand and associated environmental degradation concern has triggered more research towards alternative green energy sources. Eco‐friendly energy in facile way has been generated from abundantly available iron oxides using only few microliters of water without any external energy source. Hydroelectric cell (HEC) compatible to environment benign, low cost oxygen‐deficient mesoporous hematite nanoparticles has been used for splitting water molecules spontaneously to generate green electricity. Hematite nanoparticles have been synthesized by coprecipitation method. Chemidissociated hydroxyl group presence on hematite surface has been confirmed by infrared spectroscopy (IR) and X‐ray photoelectron spectroscopy (XPS). Surface oxygen vacancies in nanostructured hematite have been identified by transmission electron microscopy (TEM), XPS, and photoluminescence (PL) measurement. Hematite‐based HEC delivers 30 mA current with 0.92 V emf using approximately 500 μL water. Maximum off‐load output power 27.6 mW delivered by 4.84 cm² area hematite‐based HEC is 3.52 times higher than reported 7.84 mW power generated by Li‐magnesium ferrite HEC. Electrochemistry of HEC in different irreversible polarization loss regions has been estimated by applying empirical modeling on V‐I polarization curve revealing the reaction and charge transport mechanism of cell. Tafel slope 22.7 mV has been calculated by modeling of activation polarization overvoltage region of 0.11 V. Low activation polarization indicated easy charge/ion diffusion and faster reaction kinetics of Ag/Zn electrode owing to lesser energy barrier at interface. Dissociated H₃O⁺ ions diffuse through surface via proton hopping, while OH^? ions migrate through interconnected defective crystallite boundaries resulting into high output cell current.     

河南某鲕状赤铁矿石工艺矿物学研究

河南某鲕状赤铁矿石铁品位为52.50%,铁主要以赤铁矿形式存在,分布率为75.37%。矿石中主要矿物为赤铁矿、伊利石及菱磷铝锶矾。为给矿石合理开发利用提供参考,对其进行了工艺矿物学研究。结果表明:赤铁矿常呈椭圆形鲕粒,细粒或隐晶状赤铁矿集合体与脉石矿物呈椭圆状的包复颗粒由核心和同心状外壳聚集而成,鲕粒中各成分相互混杂,局部赤铁矿聚集;部分赤铁矿呈他形粒状单体或集合体不均匀分布;偶见赤铁矿呈隐晶状胶结物分布于砂屑粒间;赤铁矿嵌布粒度微细,0.037~0.003 mm粒级占87.17%。采用传统选矿方法处理该矿石难以取得理想的指标。推荐采用深度(直接)还原工艺将微细粒弱磁性铁矿物转变为可通过弱磁选分离的磁铁矿或金属铁,再通过磁选分离。     

东鞍山某鲕状赤铁矿石悬浮焙烧试验

东鞍山某鲕状赤铁矿石铁品位为44.53%、P2O5含量为2.25%。矿石中赤铁矿主要以鲕状集合体形式存在,嵌布粒度微细,属难选矿石,采用传统选矿工艺难以获得理想的选别指标。为给该矿石合理开发利用提供依据,进行了悬浮焙烧—磁选试验。结果表明:在给矿细度为-0.074 mm占75%、总气流量为8 m~3/h、H2浓度为40%、焙烧温度为650℃、焙烧时间为75 s条件下进行悬浮焙烧,焙烧产品磨细至-0.074 mm占95%,在磁场强度为85.1k A/m条件下磁选,获得了铁品位为56.73%、回收率为83.96%、磷含量为0.78%的铁精矿,该精矿磷含量较高,还需进一步进行降磷研究。试验结果为我国鲕状赤铁矿石的开发利用提供了参考。     

铁矿石浮选过程中矿物的交互影响及机理研究

复杂矿石浮选体系中矿物间会产生交互影响,研究了在油酸钠浮选体系中,不同粒级的磁铁矿、赤铁矿和石英的交互影响,并讨论了其机理。结果表明:-45+18μm粒级磁铁矿会显著降低赤铁矿的回收率,主要是因为微细粒级矿物消耗了大量捕收剂;-18μm粒级磁铁矿能够大幅度降低石英的回收率,其原因是-18μm粒级磁铁矿在石英粗颗粒表面发生了罩盖;不同粒级磁铁矿,对赤铁矿和石英混合矿浮选会有不同的影响,由于-106+18μm粒级磁铁矿被抑制进入浮选精矿,使浮选精矿铁品位略有提高,-18μm粒级磁铁矿降低浮选精矿铁品位与矿物罩盖有关。     

高磷鲕状赤铁矿金属化还原焙烧-磁选-熔分新工艺研究

针对高磷鲕状赤铁矿中有价组元铁与杂质元素磷、硅、铝的分离难题,提出了低温选择性金属化还原—磁选—熔分处理新工艺,添加复合促进剂强化还原并促进金属铁微粒迁移、聚集、长大。研究了焙烧温度、促进剂用量、煤量、焙烧时间等条件对焙砂磨矿磁选后精矿铁品位、铁回收率及脱杂效果的影响。结果表明,添加剂对铁的富集及脱杂影响显著。优化的焙烧工艺条件下,原矿加入6%促进剂、25%的煤,975℃下恒温焙烧150 min,焙砂中铁主要以单质铁呈棒条状、蠕虫状产出,利于磨矿解离;磷仍主要以磷灰石存在;焙砂经磨矿—磁选,可获得含Fe 86.77%、P0.20%、Al_2O_3 1.81%、SiO_2 3.86%的精矿类海绵铁粉,Fe回收率88%;类海绵铁粉在1 550℃下熔分,可以得到含磷小于0.01%、含铁大于99%的优质铁水,全流程Fe回收率85%,杂质磷、硅、铝脱除率99%,实现了铁的高效回收和铁与磷、硅、铝组元的深度分离。     

油酸钠体系下细粒赤铁矿精矿过滤影响因素研究

油酸钠浮选的细粒赤铁矿精矿存在过滤困难问题，为找到解决问题的办法，以巴西某细粒赤铁矿精矿（-75 μm占96.90%）为研究对象，考察了油酸钠用量、矿浆pH、矿浆温度以及淀粉用量等对赤铁矿精矿过滤效果的影响。结果表明：①油酸钠用量对细粒赤铁矿精矿的过滤有显著影响，随着油酸钠用量的增加，赤铁矿精矿滤饼比阻增大。②矿浆pH对赤铁矿精矿滤饼比阻的影响较大，强酸性条件能减弱甚至消除油酸钠对赤铁矿精矿过滤的阻碍作用，近中性环境下赤铁矿精矿滤饼比阻变化不大，强碱性条件下赤铁矿精矿的过滤效果变差。③矿浆温度对赤铁矿精矿滤饼比阻的影响较小，随着温度的升高滤饼比阻减小。④添加少量的淀粉可促进赤铁矿精矿的过滤，过量的淀粉会增大赤铁矿精矿滤饼比阻。