Process mineralogy of Dalucao rare earth ore and design of beneficiation process based on AMICS
School of Materials and Chemistry and Chemical Engineering, Chengdu University of Technology
School of Science,Xichang University
Institute of Materials Science and Technology,Chengdu University of Technology
作者简介：*Ke-Hui Qiu,e-mail:qkh2188@163.com;
收稿日期：5 December 2019
基金：financially supported by the Science and Technology Support Project in Sichuan(No. 2017GZ0400);
Process mineralogy of Dalucao rare earth ore and design of beneficiation process based on AMICS
Yu Jiao Ke-Hui Qiu Pei-Cong Zhang Jun-Feng Li Wen-Tao Zhang Xian-Fei Chen
School of Materials and Chemistry and Chemical Engineering, Chengdu University of Technology
School of Science,Xichang University
Institute of Materials Science and Technology,Chengdu University of Technology
Abstract：
The test results of the automated mineral identification and characterization system(AMICS),including the mineral composition,particle size distribution,dissemination state and degree of liberation of the target minerals,could be used to improve the beneficiation process.Taking the Dalucao rare earth ore located in Dechang,Sichuan Province,China(with an average content of 2.40 wt%) as the research object in this paper,the chemical composition,phase composition and dissemination state of the minerals were tested by AMICS,and the minerals of different fineness were ground.The concentrate yield,grade and recovery rate of the minerals of different fineness were compared through flotation tests.When the grinding lasted for 5 min and 82.60% of mineral grains passed through the-74-μm sieve,the yield,grade and recovery rate could reach 20.19%,8.75% and 73.64%,respectively(as the best grinding fineness),under the same flotation conditions.
Keyword：
Automated mineral identification and characterization system(AMICS); Bastnasite; Dalucao; Flotation;
Received： 5 December 2019
1 Introduction
China is rich in rare earth mineral resources with superior metallogenic conditions and unique advantages.The Mianning-Dechang (MD) Himalayan REE belt in western Sichuan is approximately 270 km long and 15 km wide,hosting one giant (Maoniuping),one large (Dalucao),two small-medium-sized deposits (Muluozhai and Lizhuang)and numerous other mineralized occurrences and points
Dechang Dalucao REE deposit is classified into a rare earth (bastnasite) deposit,and the minerals have been seriously weathered.The rare earth minerals exist mainly in the form of bastnasite and parisite.The rare earth minerals have a small monocrystal grain size and are interlocked with other minerals such as barite,fluorite,celestite and calcite,eventually leading to a serious encapsulation phenomenon
Compared with other analysis means,automated mineral identification and characterization system (AMICS) is the latest generation (the third generation) of automated mineral identification and characterization system,followed by QEMSCAN and MLA
2 Experimental
2.1 Materials and instruments
Nitric acid,hydrochloric acid,perchloric acid,oxalic acid,ammonium chloride and ammonium hydroxide were analytical pure and were purchased from Chengdu CHRON Chemicals Co.,Ltd.Salicylhydroxamic acid (99.5%),sodium silicate (modulus 2.8) and turpentine (2#oil) were purchased from Shanghai Yuanye Bio-Technology Co.,Ltd.;Dechang Dalucao rare earth ores were harvested,crushed into-15 mm and packaged by Sichuan Hedi Mining Co.,Ltd.
The automated mineral identification and characterization systems (AMICS) were as follows:ZEISS (sigma 500)mineral liberation analyzer (German) for determining the chemical composition,phase composition,particle size distribution,dissemination state and degree of liberation);Epsilon 3 X-ray fluorescence spectrometer (XRF) produced by PANalytical B.V.is used for elemental composition and content analysis;planetary ball mill using a ball mill(XQM2L) from Tianjin Hongyang Machinery Equipment Co.,Ltd.,for reducing the mineral fineness;single-trough flotation machine with a 1-L single-trough flotation machine (XFD-111) from Shaoxing Shangyu Jinfeng Machinery Equipment Co.,Ltd.for flotation test.
2.2 Experimental process
AMICS test was as follows.The sample needed to be premade into a cylinder with a diameter of 30 mm.The samples were observed on a polished round surface with a diameter of 30 mm.Hence,the tested ore samples were crushed and then the particle samples were cold-mounted in a cylinder with a diameter of 30 mm using epoxy resin.
The grinding process is shown in flowchart (Fig.1).After mixing,300 g of ground minerals was poured into a1-L flotation tank,water was filled to the scale mark,and flotation was carried out at room temperature with a ventilation rate of 0.35 m3·h-1 and a stirring rate of 3000r·min-1.As the foam was blown out,water was continuously filled so as to ensure that the foam can be blown out.The total rare earth was determined by oxalate gravimetric method and was titrated with reference to GBT14635-2008.
3 Results and discussion
Through the electron microscope test and energy spectrum test of AMICS,as well as analysis of the quantitative analysis system,the chemical composition,phase composition,occurrence state of rare earth in the minerals,particle size distribution and degree of liberation can be obtained.
3.1 Process mineralogy analysis of ore samples
3.1.1 Main chemical composition and phase composition of ore samples
After the rare earth elements were listed,the chemical elements were sorted according to the content from high to low,as shown in Table 1.As seen,the rare earth elements in the ore mainly included Ce,La and a small amount of Y,and other elements were mainly Si,Ca,F,Sr,Al,K,S,Fe and Ba.Rare earths may exist in the form of oxides,fluorides,sulfides,sulfates,silicates or carbonates.
Fig.1 Flowchart of grinding process
Table 1 Main chemical composition of ore from XRF test (wt%)
Chemical composition only representing statistical results of mineral particles in scanning area;total content of 99.90 wt%
Table 2 Main mineral composition in raw bastnasite from MLA test
Phases with a mineral content below 1 wt%being included into column“Other”,including magnetite (0.54 wt%),limonite (0.52wt%),wollastonite (0.47 wt%),galena (0.15 wt%),manganese (0.14wt%),apatite (0.13 wt%),rutile (0.10 wt%) and unknown ores (2.22wt%)
After the rare earth occurrence phases were listed,the phases were sorted by content from low to high,as shown in Table 2.As seen,Ce and La mainly occurred in bastnasite-(La) and bastnasite.Si mainly occurred in feldspar minerals (30.09 wt%),quartz (12.49 wt%) and biotite (3.10wt%),and Ca mainly occurred in anorthite (1.35 wt%),calcite (14.82 wt%) and fluorite (10.04 wt%).F mainly occurred in bastnasite-(La)(4.99 wt%),bastnasite (1.01wt%) and fluorite (10.04 wt%),and Sr mainly occurred in celestite (10.35 wt%).Al mainly occurred in feldspar(30.09 wt%),biotite (3.10 wt%) and kaolinite (2.03 wt%).K mainly occurred in potassium feldspar (17.31 wt%),and S mainly occurred in celestite (10.35 wt%),barite (4.06wt%) and pyrite (2.41 wt%).Fe mainly occurred in biotite(3.10 wt%) and pyrite (2.41 wt%).Ba mainly occurred in celestite (10.35 wt%) and barite (4.06 wt%).The content of chemical elements in Table 1 was fully consistent with the phase content of the elements.
According to the main phases in the minerals from Table 2,the rare earth minerals of the Dechang Dalucao Rare Earth Mine are bastnasite-(La) and bastnasite,of which the bastnasite has a large density and can be separated from feldspar minerals (2.55-2.75 g·cm-3),calcite(2.6-2.8 g·cm-3),quartz (2.65 g·cm-3),fluorescence(3.175-3.56 g·cm-3),biotite (3.02-3.12 g·cm-3) and kaolinite (2.60-2.63 g·cm-3) through gravity separation.However,barite (4.2-4.5 g·cm-3) and celestite(3.9-4.0 g·cm-3) with a large density cannot be separated through gravity separation.As barite and celestite are nonmagnetic and bastnasite is weakly magnetic,they can be separated by strong magnetic separation.
Besides,hydroxamic acid collector which has a good collection effect for bastnasite can be used to separate bastnasite from gangue mineral by flotation.
3.1.2 Composition of bastnasite-(La) and bastnasite in ore samples
Typical particles of bastnasite-(La) and bastnasite were selected,respectively.Figure 2 shows energy spectrum analysis.The analysis results are shown in Tables 3 and 4.For bastnasite-(La)(molecular formula (Ce,La)[CO3]F),theoretical chemical composition consists of REO (rare earth oxides)(74.77%-74.88%) and F (8.72%).For bastnasite (Ce(CO3)F),theoretical chemical composition consists of REO (74.88%) and F (6.39%).As seen from Table 3,among five typical particles tested,the REO content of the bastnasite ranged between 84.25 wt%and86.87 wt%,with an average of 85.78 wt%,while the F content ranged between 5.34 wt%and 6.02 wt%,with an average of 5.65 wt%.The REO content was higher than the theoretical calculation value,but the F content was lower than the theoretical calculation value,possibly because some rare earth oxides were disseminated in the bastnasite phase.OH and F were in perfect isomorphism,and some F was replaced by OH in the bastnasite,which were similar to the results in Table 4.
3.1.3 Dissemination characteristics of bastnasite-(La)and bastnasite in ores
3.1.3. 1 Schematic diagram.for determination of ore samples by AMICS
Through phase analysis of the minerals,the main composition of the minerals was ascertained.According to different brightness of different minerals in the electron backscattering diagram,different minerals were identified as different colors after granulated graphic processing of the samples using the mineral characterization system;thus,the process diagram was obtained,as shown in Fig.3.
Fig.2 Typical phases and EDS spectra:a,b bastnasite-(La) and c,d bastnasite
Table 3 Chemical composition of bastnasite-(La) from MLA test (wt/%)
Table 4 Chemical composition of bastnasite from MLA test (wt/%)
3.1.3. 2 Dissemination characteristics of bastnasite-(La)and bastnasite
As seen from Fig.4,the bastnasite-(La)and bastnasite were encapsulated by various gangue minerals in the ore samples and formed a symbiotic,interlocked and encapsulated relationship with the gangue minerals.As seen from Table 5,when the ore was ground to-74μm,the degree of liberation of the bastnasite-(La)was as high as 79.45%,while that of bastnasite was as high as 72.62%,and the remaining rare earth ores and gangue minerals were under a symbiotic,interlocked and encapsulated relationship.In this case,the ores were beneficiated by gravity separation.Bastnasite-(La) and bastnasite were under intergrowth with feldspar,calcite,quartz,fluorite and biotite,and 18.79%and 23.61%of rare earth ores would be directly lost,respectively.In this case,the ores were beneficiated by magnetic separation.Bastnasite-(La) and bastnasite were under intergrowth with barite and celestite,and 1.76%and 3.14%of rare earth ores would be directly lost,respectively.During flotation of bastnasite-(La) and bastnasite using hydroxamic acid collector,some gangue minerals can also be collected.Therefore,if the ores were beneficiated by gravity separation,this would lead to a high grade but a very low recovery rate.Gravity separation and flotation may lead to a grade cutoff,but a higher yield could be guaranteed.
Fig.3 Schematic diagram for determination of ore samples by AMICS:a SEM image and b result diagram of mineral analysis
Fig.4 Backscattering diagram of dissemination characteristics of rare earth mineral particles:a bastnasite encapsulated by gangue minerals,b bastnasite and bastnasite-(La) showing mutual replacement and association,c needle-like bastnasite precipitated on gangue mineral surface,and d bastnasite particles under liberation
Table 5 Dissemination characteristics of rare earth ores and main minerals in-74-μm ore samples from MLA test (wt/%)
Fig.5 Particle size distribution of rare earth minerals of a bastnasite-(La) and b bastnasite
Table 6 Grinding test conditions
3.1.3. 3 Particle size distribution of bastnasite-(La) and bastnasite in the ores
As can be seen from Fig.4,the size of over 80%particles of bastnasite-(La) and bastnasite was mainly 10-75μm and 10-20μm,respectively,but the size of over 65%bastnasite-(La) was mainly 30-75μm;the size of over 90%bastnasite-(La) was mainly less than20μm.According to Table 2,the content ofthe bastnasite-(La) in the ore was 4.99 wt%,while that of the bastnasite was 1.01 wt%.The content of the bastnasite-(La) was higher than that of the bastnasite,and the particle size was larger than that of the bastnasite.If the grinding size was too large,the monomers would not be liberated.However,if the grinding size was too small,the target minerals were easily clustered with the gangue minerals.Therefore,in terms of grinding fineness,priority should be given to the monomer particle size of the bastnasite-(La).The grinding fineness should mainly range between 30 and 75μm.
3.2 Ore sample flotation test
The grinding time,costs and total beneficiation cost increased.Besides,the grinding fineness was closely related to the beneficiation indexes.According to the analysis results shown in Fig.5,the grinding process was developed,as shown in Table 6.The ground minerals were floated and verified,as shown in flotation process (Fig.6).The flotation results are shown in Table 7.
Fig.6 Flowchart of flotation process
Table 7 Flotation results at different flotation time
According to the results shown in Table 7,the grinding fineness had a significant effect on the recovery rate of the rare earth ore concentrates.With the increase in the grinding fineness and the degree of liberation of main rare earth minerals (bastnasite-(La) and bastnasite),the grade and recovery rate of rare earth ore concentrates would increase.However,as the grinding fineness further increased,the grade and recovery rate would begin to decline.The best grinding fineness occurred when the grinding lasted for 5 min and about 80%passed through the-74-μm sieve.
4 Conclusion
Through AMICS test and analysis,the rare earth minerals of the Dechang Dalucao ore were mainly bastnasite-(La)(4.99 wt%) and bastnasite (1.01 wt%).The main gangue minerals were feldspar minerals (30.09 wt%),calcite(14.82 wt%),quartz (12.49 wt%),celestite (10.35 wt%),fluorite (10.04 wt%),barite (4.06 wt%),biotite (3.10 wt%),pyrite (2.41 wt%) and kaolinite (2.37 wt%).
Judging from mineral types,the rare earth minerals,barite and celestite can be separated from feldspar minerals,calcite,quartz,fluorite,biotite and kaolinite by gravity separation,and the rare earth minerals were separated from barite and celestite by magnetic separation.The minerals formed a symbiotic,interlocked and encapsulated relationship.However,seen from the degree of liberation,the intergrowth of the rare earth ore and feldspar,as well as calcite,quartz,fluorite and biotite was severe.Gravity separation would lead to a low yield of rare earth,and highgrade minerals cannot be obtained if only magnetic separation was used.Therefore,the Dechang Dalucao ore was beneficiated by both gravity separation and magnetic separation at best.
During flotation of bastnasite-(La) and bastnasite using hydroxamic acid collector,some gangue minerals (especially those inter-grown with rare earth) can also be collected.Therefore,flotation could lead to a higher yield of the rare earth ore concentrates.
The grinding fineness had a significant effect on flotation.When the grinding lasted for 5 min and 82.60%of mineral grains passed through the-74-μm sieve,the main rare earth mineral (bastnasite) in the minerals could be liberated.The yield,grade and recovery rate of the rare earth ore concentrates could reach 20.19 wt%,8.75 wt%and 73.64 wt%,respectively (the optimum grinding fineness),under the same flotation conditions.
Acknowledgements This study was financially supported by the Science and Technology Support Project in Sichuan (No.2017GZ0400))
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