Rare Earths, Niobium and Tantalum Minerals in Bayan Obo Ore Deposit and Discussion on Their Genesis

Bayan Obo ore deposit is endowed with and lie hidden in the Proterozoic strata. The localities and occurrences of the minerals in the ore deposit were described. It is obviously that some minerals are strata minerals and some are post strata minerals. The rare earths, niobium and tantalum minerals are exactly the post strata minerals. In these minerals the hydrothermal metasomatic phenomena distinctly reveal their metallogenic characteristics. According to tectonic movement, magma activity, mineral paragenesis, hydrothermal metasomatism, geological age and lasting time scale of metallogenesis, and some other factors, it is supposed that genesis of rare earths, niobium and tantalum minerals in Bayan Obo ore deposit are closely related with hydrothermal metallogenic solution which is differentiated from silica acid and carbonic acid magma and derived from deep seated source, and then intruded into Proterozoic strata and metasomatized. It is recognized that the metallogenesis of Bayan Obo ore deposit is undergoing a long geological period and many episodes.

Trace and Rare Earth Element Geochemistry of Micrite Mound Carbonates and Other Related REE Mineralized Carbonates from Bayan Obo Area in Inner Mongolia

Geochemical study on trace and rare earth element geochemistry was carried out for different carbonates including the very REE-rich ones in the main ore bodies, a carbonatite dyke and two micrite mounds from Heilaobao far away from the Bayan Obo ore deposit, and Xishan in west Beijing. The results show that both carbonatite dyke and REE mineralized carbonates (dolomite and marble) in the main ore bodies and outside ore bodies have similarities to each other, with very extreme positive anomaly of Ba, Th, Nb, La, Ce, Nd, Sm, Pb, medium positive anomaly of Y, Ho, Tb, Er, Yb and negative anomaly of Sc, Ti and Cu. The REE concentration in the mineralized carbonates changes greatly, the total REE content changes from 262×10^(-6) in both east and west ore deposits to 104562 ×10^(-6) (10.46%), which is relatively lower than those samples of carbonatite dyke, whose REE contents vary greatly, from 1% up to 20 % of mass fraction. Light REE in the carbonatites are enriched and highly fractionated relative to heavy REE and there is no Eu anomaly. The REE distribution patterns of both mineralized carbonate and carbonatite dyke are of some similarities. However, the sedimentary carbonate micrite of Salinhudong Group in Heilaobao far outside the ore bodies and the pure carbonates from Xishan in Beijing, central part of North China plate, have the similarities in REE distributions with much lower REE contents, which are significantly different from those of carbonatite dyke and REE mineralized carbonate. In Bayan Obo district, both carbonates in the ore deposit and micrite mound outside the ore deposit underwent widespread metasomatism by fluids that resulted in formation of the superlager Fe-Nb-REE mineralization. It appears that the carbonates represent the evolution products of different geological stages.

The occurrences and geochemical characteristics of thorium in iron ore in the Bayan Obo deposit, Northern China

The Bayan Obo deposit in northern China is an ultra-large Fe–REE–Nb deposit.The occurrences,and geochemical characteristics of thorium in iron ores from the Bayan Obo Main Ore Body were examined using chemical analysis,field emission scanning electron microscopy,energy dispersive spectrometer,and automatic mineral analysis software.Results identified that 91.69%of ThO2 in the combined samples was mainly distributed in rare earth minerals(bastnaesite,huanghoite,monazite;56.43%abundance in the samples),iron minerals(magnetite,hematite,pyrite;20.97%),niobium minerals(aeschynite;14.29%),and gangue minerals(aegirine,riebeckite,mica,dolomite,apatite,fluorite;4.22%).An unidentified portion(4.09%)of ThO2 may occur in other niobium minerals(niobite,ilmenorutile,pyrochlore).Only a few independent minerals of thorium occur in the iron ore samples.Thorium mainly occurs in rare earth minerals in the form of isomorphic substitution.Analyses of the geochemical characteristics of the major elements indicate that thorium mineralization in the Main Ore Body was related to alkali metasomatism,which provided source material and favorable porosity for hydrothermal mineralization.Trace elements such as Sc,Nb,Zr,and Ta have higher correlation coefficients with thorium,which resulted from being related to the relevant minerals formed during thorium mineralization.In addition,correlation analysis of ThO2 and TFe,and REO and TFe in the six types of iron ore samples showed that ThO2 did not always account for the highest distribution rate in rare earth minerals,and the main occurrence minerals of ThO2 were closely related to iron ore types.

Geochemical Characteristics of a Carbonatite Dyke Rich in Rare Earths from Bayan Obo, China

The whole-rock geochemistry of a rare earths rich carbonatite dykes that locates at Dulahala and lies 3 km north-east to the East Ore body of the giant Bayan Obo RE-Nb-Fe deposit was analysed. The dyke cuts cross H1 coarse quartz sandstone and H2 fine quartzite of the Proterozoic Bayan Obo group. RE content in the dyke varies greatly up to 20% (mass fraction), which comprises rich RE ores. Light RE in carbonatites are extremely enriched and strongly fractionated relative to heavy RE, but no Eu anomaly. The carbonatite may be produced by mechanisms as follows: the carbonatite mana is directly formed by very low degree (F <1%) partial melting of enriched lithospheric mantle, leaving residual minerals characterized by abundant garnet; then the magma arises into a chamber within the crust where they will undergo fractional crystallization, which makes RE further concentrated in carbonatite. The RE patterns and spider diagrams of the carbonatite are identical to those fine-grained dolomite marble that is the ore-host rock for the Bayan Obo deposit. However, the carbonatite is calcic, which is different from the fine-grained dolomite marble in major element geochemistry. The difference is suggested to be resulted from that the carbonatite dyke is not affected by a large scale dolomitization, while the fine-grained dolomite marble might be the product of dolomitized carbonatite intrusive body that might set up a hydrothermal system in the region, which transported Mg from the Bayan Obo sediments, especially form the shales to the carbonatite intrusion.

Decomposition of monazite in Bayan Obo rare earth ore by roasting of Na_(2)CO_(3)pellets

To resolve the issue of rotary kiln agglomeration during the sodium carbonate roasting of dolomite rare earth ore,this study introduces an oxidation-sodization pellet roasting method for decomposing mixed rare earth concentrates.The focus of this paper lies in understanding the bonding and roasting mechanism of sodium polyacrylate as a binder to dolomite ore and examining the process index of Na_(2)CO_(3)pellets roasting-acid leaching using X-ray diffraction(XRD),scanning ele ctron microscopy with energy dispersive spectroscopy(SEM-EDS),and zeta potential analysis,The results indicate that sodium polyacrylate facilitates the bonding of sodium carbonate to monazite via adsorption of positive and negative charges,and upon roasting at 750℃for 1.5 h to obtain rare earth oxides.Under conditions of a hydrochloric acid(HCl)concentration of 9 mol/L,a reaction for 60 min,a solid-to-liquid ratio(g:mL)of 1:5,and reaction temperature of 90℃,the leaching rates of rare earth elements and thorium(Th)reached maxima of 85.14%and 95.53%,respectively.The process results in a yield of 47.61%for fluorine(F)and89.25%for phosphorus(P).This research forms a foundation for the sodium carbonate roasting decomposition of mixed rare earth concentrates.

Geology and mineralization of the Bayan Obo supergiant carbonatite-type REE-Nb-Fe deposit in Inner Mongolia, China: A review

The Bayan Obo supergiant carbonatite-related rare-earth-element-niobium-iron(REE-Nb-Fe) endogenetic deposit(thereafter as the Bayan Obo deposit), located at 150 km north of Baotou City in the Inner Mongolia Autonomous Region, is the largest rare-earth element(REE) resource in the world. Tectonically,this deposit is situated on the northern margin of the North China Craton and adjacent to the Xing’anMongolian orogenic belt to the south. The main strata within the mining area include the Neoarchean Se’ertengshan Group and the Mesoproterozoic Bayan Obo Group. Generally, the rare earth, niobium, and iron mineralization within the deposit are intrinsically related to the dolomite carbonatites and the extensive alteration of the country rocks caused by the carbonatite magma intrusion. The alteration of country rocks can be categorized into three types: contact metasomatism(anti-skarn and skarn alteration), fenitization,and hornfelsic alternation. As indicated by previous studies and summarized in this review, the multielement mineralization at Bayan Obo is closely associated with the metasomatic replacement of siliceous country rocks by carbonatite magmatic-hydrothermal fluids. The metasomatic process is comparable to the conventional skarnification that formed due to the intrusion of intermediate-acid magmatic rocks into limestone strata. However, the migration pattern of Si O2, Ca O, and Mg O in this novel metasomatic process is opposite to the skarn alteration. Accordingly, this review delineates, for the first time, an antiskarn metallogenic model for the Bayan Obo deposit, revealing the enigmatic relationship between the carbonatite magmatic-hydrothermal processes and the related iron and rare earth mineralization.Moreover, this study also contributes to a better understanding of the REE-Nd-Fe metallogenetic processes and the related fluorite mineralization at the Bayan Obo deposit.

A Geochemical Study of an REE-rich Carbonatite Dyke at Bayan Obo,Inner Mongolia,Northern China

An REE-rich carbonatite dyke was found in Dulahala, close to the Bayan Obo superlarge REE-Nb-Fe mineral deposit in Inner Mongolia, northern China. The REE content in the dyke varies greatly, from 1% up to 20% (wt), which might constitute rich REE ores. Light REEs in the carbonatite are enriched and highly fractionated relative to heavy REEs and there is no Eu anomaly. The REE and trace element distribution patterns of the carbonatite are identical to those of fine-grained dolomite marble which is the host rock of the Bayan Obo REE-Nb-Fe superlarge mineral deposit. This indicates a petrogenetic linkage between the REE-rich carbonatite and the mineralizations in this region.

The Chemistry of Niobium Mineralisation at Bayan Obo,Inner Mongolia,China:Constraints on the Hydrothermal Precipitation and Alteration of Nb-Minerals

As well as world class Fe and REE resources the Bayan Obo mineral deposits also hosts significant niobium resources(estimated as 2.2 Mt Nb with an average grade of 0.13 wt% Nb).Niobium in this study is primarily hosted in aeschynite-(Ce) and(Nd),but with subsidiary amounts of pyrochlore,fergusonite-(Ce),fersmite and columbite.Here we report on the paragenetic and textural setting of aeschynite,pyrochlore and fergusonite in the main ore bodies and in a carbonatite dyke.Niobium in a carbonatite sample is hosted in a phase tentatively(due to significant Ca,Mn and Ti contents) identified as fergusonite-(Ce).Aeschynite occurs overgrowing foliation in banded ores,in fractures and vugs in aegirine-rich rocks and in calcite veins.The composition in all settings is similar,but some examples in banded ores develop significant zonation in Y,Th and the REE,inferred to relate to buffering of halogen acid species to low levels by dissolution and fluoritisation of calcite,and the preferential precipitation of LREE from solution due to lower mineral solubility products compared to the HREE.Although lower in total concentration the ratios of REE in pyrochlore are similar to those of aeschynite and suggest the same metal source.The crystallisation of pyrochlore probably relates to growth in paragenetic settings where carbonates had already been eliminated and hence the buffering of F-species activities in the hydrothermal fluid was reduced.Both aeschynite and pyrochlore show evidence of alteration.Primary alteration of aeschynite resulted in leaching of A-site cations(Ca,REE,Th) and Nb,addition of Fe,and ultimately replacement by Ba-Ti phases(baotite and bafertisite).Secondary,metamictisation enhanced,possibly supergene alteration of pyrochlore resulted in hydration,leaching of A-site cations leading to the development of lattice vacancies and increases in Si.The presence of hydrothermal Nb resources at Bayan Obo suggests there may be potential for further Nb discoveries in the area,whilst the trends in element mobility during alteration have significant implications for the utility of A-B oxides as components of materials for immobilisation of radionuclides.

内蒙古白云鄂博铁-铌-稀土矿床矿化蚀变矿物组合及流体组成

针对内蒙古白云鄂博铁-铌-稀土矿床是否多期成矿及底板白云岩的成因争论,本文通过光薄片岩矿鉴定和扫描电子显微镜研究,获得如下信息:(1)碳酸岩脉、磁铁矿石、蚀变岩及矿化白云岩中矿化蚀变的矿物组成类似,均以磁铁矿(碳酸岩脉中除外)、独居石、氟碳酸稀土矿物(氟碳铈矿等)、方解石、萤石、磷灰石、富钡矿物(重晶石或毒重石)、黑云母、富钠矿物(钠闪石、霓石)等为主,常见硫化物,显示为同一种富含Fe、REE、Ca、Ba、K、Na、Si及挥发分CO_(2)、P_(2)O_(5)、F、S的流体,岩(矿)石的结构构造也显示出明显的一期成矿特点,支持白云鄂博矿床主体是一期成矿事件的产物。(2)稀土矿化与底板白云岩不是同一流体的产物,稀土矿化与方解石为主的碳酸岩脉有关,有可能为火成碳酸岩或浆液过渡态流体;底板白云岩是稀土矿化的围岩,有更多的沉积成因信息,可能为热水沉积岩,或者为热液改造的沉积碳酸盐岩。(3)磁铁矿化与稀土矿化是同一成矿事件的产物,但碳酸岩中缺乏磁铁矿表明,铁质来源与稀土来源是否相同仍需要进一步研究。

Reaction characteristics of carbon-bearing pellets of Bayan Obo lean iron ores in a static magnetic field

The use of low-grade,refractory and composite paragenetic mineral resources is necessary for overcoming the shortage of iron ore resources in China.As a solution to the treatment of such iron ores,the direct reduction of carbon-bearing pellets can ensure complete iron removal and the effective enrichment of other high-value elements.Thus,this technology enjoys a broad application prospect.However,there are several problems with low-temperature reduction,such as low iron ore reaction efficiency,long reaction time,and high energy consumption.To improve the low-temperature carbothermic reduction efficiency of iron ores,a static magnetic field with magnetic induction intensity of 1.0 T was introduced.An isothermal reduction experiment was conducted at 1223 K to study the low-temperature self-reduction characteristics of carbon-bearing pellets of Bayan Obo lean iron ores in the static magnetic field.Also,the acting mechanism of the magnetic field was explored from the perspective of the reduction process,reaction efficiency,phase composition,microstructure changes,and dynamic behavior of iron ores.The results showed that the magnetic field can increase the low-temperature reduction rate of carbon-bearing pellets of Bayan Obo lean iron ores.Under the conditions of reduction temperature of 1223 K,magnetic induction intensity of 1.0 T,and reduction time of 60 min,the reduction degree was 92.42%,1.65 times that without a magnetic field.The magnetic field promoted the replacement of Ca^(2+)and Fe^(2+),so that the hard-to-reduce iron-bearing silicates were reduced in the order of Fe2SiO_(4)→(Ca,Na)FeSiO_(4)→FeO→Fe.The magnetic field enabled loose minerals,more pores and cracks,and changes in the growth morphology and distribution position of metallic iron.Compared with the case under the non-magnetic condition,the metallic iron precipitated from the slag phase in a foliated shape,separated from the matrix iron oxides,and grew up at the junction of the slag phase and coke.The magnetic field significantly increased the interfacial chemical reaction rate of the carbothermic reduction of iron ores and reduced the internal diffusion resistance of gas in the product layer.Specifically,the interfacial chemical reaction rate increased by 138%and the internal diffusion coefficient increased by 309%.Therefore,the effect of the magnetic field on the internal diffusion resistance was the main cause for strengthening the low-temperature reduction of iron ores.

Iron recovery and rare earths enrichment from Bayan Obo tailings using Coal-Ca(OH)2-NaOH roasting followed by magnetic separation

The recovery of iron and enrichment of rare earths from Bayan Obo railings were investigated using Coal Ca（OH） 2 NaOH roasting followed by magnetic separation. The influences of roasting temperature, roasting time, coal content, milling time, Ca（OH）2 dosage and NaOH dosage on the iron and rare earths recovery were explored. The results showed that the magnetic concentrate containing 70.01 wt. % Fe with the iron recovery of 94.34G and the tailings of magnetic separation containing 11.46 wt. % rare earth oxides （REO） with the REO recovery of 98. 19% were obtained under the optimum conditions （i. e. , roasting temperature of 650℃, roasting time of 60 min, coal content of 2.0%, milling time of 5 min, and NaOH dosage of 2.0%）. The Ca（OH）2 dosage had no effect on the separation of iron and rare earths. According to the mineralogical and morphologic analysis, the iron and rare earths of Bayan Obo tailings could be utilized in subsequent ironmaking process and hydrometallurgy process.

白云鄂博稀土混合精矿工艺矿物学研究

目前白云鄂博稀土元素的提取主要采用重污染和高能耗的高温浓硫酸焙烧法,“三废”问题至今没有得到合理的解决,且钍元素作为一种伴生组分难以得到再回收利用。采用自动矿物分析仪、X射线衍射分析、扫描电镜分析、配分分析、光学显微镜等分析方法对白云鄂博稀土混合精矿的化学成分、矿物组成、粒度及嵌布特征等进行了工艺矿物学研究,结果表明,该稀土混合精矿REO品位为59.25%,主要稀土矿物由氟碳铈矿、独居石和氟碳钙铈矿组成,主要脉石矿物为磷灰石、萤石、黄铁矿和磁/赤铁矿。在矿物中主要分布的稀土元素为La、Ce、Pr、Nd、Sm、Gd。矿样中矿石-38μm粒级含量占95.92%,氟碳铈矿和独居石单体解离度均在55%以上,矿石整体嵌布特征较为复杂,稀土矿物与萤石和磷灰石的连生关系最为密切。为简化冶金工艺,高效提取稀土元素,提出了采用矿相转化后“浮少抑多”的方法分离氟碳铈矿和独居石的展望,为白云鄂博稀土混合精矿的合理开发应用提供新思路。

CaO-SiO_(2)-La_(2)O_(3)体系中最佳稀土富集相的在线分离与表征

内蒙古白云鄂博矿是世界上最大的铁-铌-稀土多金属共伴生矿床,稀土远景储量位居世界第一。在该矿床开采过程中,稀土等有价元素未能得到有效的提取而进入渣中,形成重要的稀土二次资源。为了回收其中的稀土资源,基于白云鄂博冶金矿渣主组元,以CaO-SiO_(2)-La_(2)O_(3)三元基础体系为研究对象,首先明确了该体系的最佳稀土富集相为Ca_(x)La_(4.67-x)(SiO_(4))3O_(1-0.5 x)相。随后引入超重力场,在G=1000、时间10 min、温度1350℃的条件下对Ca_(x)La_(4.67-x)(SiO_(4))3O_(1-0.5 x)稀土相与渣相进行在线分离,得到了高纯稀土相晶体。最后对得到的稀土晶体进行结构表征和Rietveld精修,明确了其具体化学式为Ca_(1.11)La_(3.56)Si_(3)O_(12.36),并获得了该稀土相的晶体结构、晶体数据等信息,进一步完善了稀土相的基础物理化学数据,为稀土资源的回收利用提供了理论依据。

白云鄂博某难选铁矿石氢基矿相转化——磁选尾矿浮选稀土试验

堆置多年的白云鄂博中贫氧化矿含有铁、稀土等成分,常规工艺难以高效分选,但氢基矿相转化—磁选工艺可高效回收其中的铁。为了解氢基矿相转化过程是否影响富稀土铁尾矿中稀土矿物的可浮性,进行了系统的选矿试验。结果表明,在506E用量4200 g/t、水玻璃用量1800 g/t、矿浆温度65℃条件下,采用2粗3精、中矿顺序返回闭路浮选流程处理矿样,能够获得REO品位59.00%、REO回收率67.91%的稀土精矿。化学成分分析及X射线衍射分析结果表明,浮选精矿中主要成分为稀土氧化物(Ce_(7)O_(12))、独居石及少量萤石,稀土组分有效富集在精矿中;氢基矿相转化过程未对稀土组分的浮选回收造成不利影响。

内蒙古白云鄂博矿床年代学特征及其地质意义

内蒙古白云鄂博矿床是世界罕见的特大型REE-Nb-Fe多金属共生矿床,由于经历了复杂的区域地质演化历史,至今仍对稀土成矿时代认识不一。基于前人的同位素年代学研究成果,结合矿床地质特征对稀土成矿时代进行讨论。研究表明,白云鄂博矿区经历了华北克拉通2.5~1.8 Ga的前寒武纪构造演化过程;哥伦比亚超大陆裂解的最后阶段,约1.3 Ga在白云鄂博裂谷形成了巨型稀土矿床,与同期碳酸岩墙形成时代一致;受后期华北克拉通北缘古亚洲洋俯冲碰撞造山的影响,白云鄂博地区引发热液交代活动,形成了晚期稀土矿脉和原有稀土矿物的重结晶,导致H 8赋矿白云岩同位素系统受到扰动,呈现出多期次(1.0~0.2 Ga)的同位素年龄结果。总之,白云鄂博是一个在约1.3 Ga裂谷成矿并叠加了加里东和海西2期热扰动事件的巨型稀土矿床。

复合捕收剂浮选回收白云鄂博某尾矿中的铌及其机理分析

为提高白云鄂博铌矿物的浮选回收效率,研究了单一苯甲羟肟酸(BHA)及苯甲羟肟酸+NPs(羟肟酸类)复合捕收剂对含铌尾矿中铌的浮选分离效果及吸附机理。结果表明,复合捕收剂(BHA+NPs)对铌矿物浮选的最佳质量配比为m(NPs)∶m(BHA)=0.35∶0.65,浮选闭路实验可获得Nb_(2)O_(5)品位为3.24%、回收率为83.03%的铌精矿;与采用单一BHA相比,精矿回收率基本一致,精矿品位提高0.53百分点。复合捕收剂可以显著提高精矿中铌矿物的含量,说明其对含铌矿物具有强捕收能力。XPS分析发现,辅助捕收剂NPs的存在不能改变铌铁矿表面N元素的化学环境,NPs与BHA在铌铁矿表面共同吸附,并促进BHA在矿物表面的吸附。

Investigations on mineralogical characteristics of rare earth minerals in Bayan Obo tailings during the roasting process

This paper focused on the investigation of the mineralogical characteristics of rare earth minerals from Bayan Obo tailings during the roasting process in the presence of coal,Ca（OH）_2 and NaOH.Roasting experiments and leaching experiments were carried out to study the decomposition of rare earth minerals.The results indicated that bastnaesite and monazite could be completely decomposed at 650 ℃ and the leaching ratio of rare earths could reach 89.78%.The reaction mechanisms of bastnaesite and monazite at 650 ℃were analyzed.For bastnaesite,both the outer layer decomposition and inner core decomposition occurred simultaneously during the roasting.However,monazite was decomposed in a spatial sequence starting from the outer layer and proceeding to the inner core.

Thermal decomposition mechanism of low-content-fluorite Bayan Obo rare earth concentrate roasted with sodium carbonate and its consequent separation study

Thermal decomposition and phase transformation for the mixture of Bayan Obo rare earth concentrate(BORC)and sodium carbonate(Na2CO3)roasted at different temperatures with weight ratio of 100:20 were studied in detail in our study.The aim of our study is to reveal the nature of roasting reaction between BORC and Na2CO3 and thus providing a new method for processing BORC.The results indicate that BORC can be decomposed completely with Na2CO3 at around 600℃after 3 h.During the calcination process,Ce0.5Nd0.5O1.75,NaF,Na3PO4,and a rare earth double phosphate phase Na3RE(PO4)2 are formed after the decomposition of BORC with Na2CO3.In addition,the thermal decomposition mechanism is determined in the paper.Based on these facts,a clean technique processing BORC was developed.And a CeF3 powder,whose composition was measured and stability was also evaluated,was obtained for some potential application from the new technique.This research is of significance in terms of the Na2CO3-roasting BORC solid reaction study and sheds a light on a potential clean technique for BORC.

Geochemistry of Apatite from the Apatite-rich Iron Deposits in the Ningwu Region,East Central China

Four types of apatite have been identified in the Ningwu region. The first type of apatite is widely distributed in the middle dark colored zones （i.e. iron ores） of individual deposits. The assemblage includes magnetite, apatite and actinolite （or diopside）. The second type occurs within magnetite-apatite veins in the iron ores. The third type is seen in magnetite-apatite veins and （or） nodules in host rocks （i.e. gabbro-diorite porphyry or gabbro-diorite or pyroxene diorite）.The fourth type occurs within apatite-pyrite-quartz veins f＇dfing fractures in the Xiangshan Group. Rare earth elements （REE） geochemistry of apatite of the four occurrences in porphyry iron deposits is presented. The REE distribution patterns of apatite are generally similar to those of apatites in the Kiruna-type iron ores, nelsonites. They are enriched in fight REE, with pronounced negative Eu anomalies. The similarity of REE distribution patterns in apatites from various deposits in different locations in the world indicates a common process of formation for various ore types, e.g. immiscibility. Early magmatic apatites contain 3031.48-12080 ×10^-6 REE. Later hydrothermal apatite contains 1958 ×10^-6 REE, indicating that the later hydrothermal ore-forming solution contains lower REE. Although gabbro-diorite porphyry and apatite show similar REE patterns, gabbro-diorite porphyries have no europium anomalies or feeble positive or feeble negative europium anomalies, caused both by reduction environment of mantle source region and by fractionation and crystallization （immiscibility） under a high oxygen fugacity condition. Negative Eu anomalies of apatites were formed possibly due to acquisition of Eu^2＋ by earlier diopsite during ore magma cooling. The apatites in the Aoshan and Taishan iron deposits yield a narrow variation range of ^87Sr/^86Sr values from 0.7071 to 0.7073, similar to those of the volcanic and subvolcaulc rocks, indicating that apatites were formed by liquid immiscibility and differentiation of intermediate and basic magmas.

In-situ measurement of mineral phase transition and kinetics in roasting process of Bayan Obo mixed rare earth concentrate by sodium carbonate

In this study,the Bayan Obo rare earth concentrates mixed with Na_(2)CO_(3)were used for roasting research.The phase change process of each firing stage was analyzed.The kinetic mechanism model of the continuous heating process was calculated.This study aims to recover valuable elements and optimize the production process to provide a certain theoretical basis.Using X-ray diffraction(XRD),Fourier infrared spectroscopy,scanning electron microscopy with energy dispersive spectrometry,the reaction process and the existence of mineral phases were analyzed.The variable temperature XRD and thermogravimetric method were used to calculate the roasting kinetics.The phase transition results show that carbonate-like substances first decompose into fine mineral particles,and CaO,MgO,and SiO_(2)react to form silicates,causing hardening.Further,REPO_(4)and NaF can directly generate CeF_(3) and CeF_(4)at high temperatures,and a part of CeF_(4)and NaF forms a solid solution substance Na_(3)CeF_(7).Rare earth oxides calcined at a high temperature of 750℃were separated to produce Ce_(0.6)Nd_(0.4)O_(1.8),Ce_(4)O_(7),and LaPrO_(3+x).Then,BaSO_(4),Na_(2)CO_(3),and Fe_(2)O_(3)react to form barium ferrite BaFe_(12)O_(19);the kinetic calculation results show that during the continuous heating process,the apparent activation energy E reaches the minimum in the entire reaction stage in the temperature range of 440-524℃,and the reaction order n reaches the maximum,which indicates that the decomposition product REFO significantly impacts the reaction system and reduces the activation energy.The mechanism function is F(α)=[-In(1-α)]^(1/3).The reaction order n reaches the minimum in the temperature range of 680-757℃,and the apparent activation energy E is large.The difficulty of the reaction increases during the final stage.The reaction mechanism function is F(α)=[1-(1-α)^(1/3)]^(2).Observing the entire reaction stage,the step of controlling the reaction rate changes from random nucleation to three-dimensional diffusion(spherical symmetry).