Occurrence State And Enrichment Mechanism Of Rare Earth During Processing Of Zhijin Phosphate Ore In Guizhou,China

Phosphorus and rare earth resources are strategic mineral resources in China.Rare earth resources are indispensable and important raw materials for developing strategic emerging industries.But with the massive exploitation and utilization of high-quality rare earth resources,the global share of rare earth resource reserves in China has decreased year by year.In recent years,the demand for rare earth resources in new technologies and equipment has continued to increase,and the recovery and extraction of associated rare earth elements from phosphate ore has attracted increasing attention.China is rich in rare earth resources.The reserves of rare earth containing phosphate ore in Zhijin,Guizhou,Southwest China,amount to millions of tons.As the occurrence state of the associated rare earth oxides in the phosphate ore is unclear,and the in-depth research has not yet made on the enrichment mechanism of rare earth elements in the processing.This research is expected to carry out the research on the efficient separation and extraction technology and mechanism of rare earth elements from Zhijin phosphate ore,and to identify the occurrence status of rare earth elements and reveal the enrichment mechanism of them during the processing of the ore.It will hopefully lay a theoretical foundation for the utilization of rare earth resources.It is of great significance for enhancing the resource protection of strategic emerging industries.Flotation is the main method for processing rare earth phosphate ores.This research focused on the difficulties in the development and utilization of rare earth resources associated with the phosphate ore in Zhijin.Mineralogical studies on the occurrence state of rare earth elements were conducted.It revealed the trend of rare earth elements in the flotation process through flotation experimental research,and determined the processing technology of phosphorus associated rare earth resources,and explored the enrichment mechanism of heavy metal elements in the processing of rare earth phosphate ores.This research will,hopefully,provide theoretical guidance for the comprehensive utilization of rare earth containing phosphorus ores.The rare earth containing phosphate ore from Zhijin,Guizhou,Southwest China,was taken as the research object.The mineralogical characteristics of the phosphate ore were studied through chemical composition analysis,polarizing microscope,X-ray diffraction analysis,and scanning electron microscope energy spectrum analysis.REEs may occurred in the form of isomorphism in fluorapatite.Under different flotation conditions（grinding fineness,reagent system,flotation process,etc.）to investigate the migration and enrichment of rare earth elements in the phosphate rock flotation process;The four rare earth elements（La,Ce,Nd and Y）with high content in the ore were used as the research object.The distribution,occupation number and structure occupation of REEs in apatite were studied by XRD refinement and scanning electron microscopy.Use DFT to calculate the substitution form and difficulty of La,Ce,Nd and Y entering the crystal of fluorapatite,carbonate-bearing fluorapatite and dolomite,and clarify the enrichment mechanism of rare earths in apatite.The heavy metal elements As and Pb enriched with phosphorus and rare earths during flotation were studied.The substitution forms of As and Pb in apatite and the adsorption structures of As and Pb on the surface of dolomite and apatite were studied using DFT calculations.The reasons for the migration of heavy metal in phosphate ore to phosphorus concentrate during flotation were revealed.（1）The main structures of the Zhijin rare earth phosphate ore were colloidal cryptocrystalline structure,fine-medium grain sand debris structure,fine-medium grain structure,inclusion structure,micro-scale structure,etc.The binding between mineral aggregates was relatively tight,with common phenomena of mutual cementation and encapsulation,while the mode of association was relatively simple.The main ore mineral was collophanite,and the main gangue mineral was dolomite,with a small amount of quartz.REEs accounted for 88.31%in collophanite,8.02%in dolomite,3.32%of carbon,and 0.08%of quartz and other minerals.No independent rare earth minerals were found in the ore.After screening analysis of rare earth-containing phosphate ore,it was found that the content of rare earth elements in each grade positively correlated with the content of P₂O₅.The content of heavy rare earth element Y was the highest in each particle size fraction,while the content of light rare earth elements La,Nd and Ce was higher.（2）Using SW as regulator for pH,and GJBM as collector can effectively enrich apatite and REEs.Using the“one coarse and one fine”flotation test process,the P₂O₅ content was 35.32%,the MgO was 0.71%,and theΣREE was 1507.77μg/g,the recovery rate of P₂O₅ was 85.75%.The REE recovery rate was 83.53%.The fitting relationship between∑REE and P₂O₅ content and Mg O content in flotation products showed that∑REE was positively correlated with P₂O₅ content,while∑REE was negatively correlated with MgO content.The flotation rate curves of P₂O₅ and∑REE showed high similarity under different conditions.The distribution area of rare earth elements in the SEM surface scan diagrams of flotation concentrate and tailings had a high coincidence degree with the distribution area of P,O and Ca.In the tailings,apatite mostly existed in the form of fine particles,and a small amount was associated with dolomite,indicating that the main reasons for apatite entering the tailings were mainly water entrainment and insufficient dissociation of minerals during grinding.Therefore,the co-recovery of P₂O₅ and REE can be achieved by“phosphorus enrichment and magnesium reduction”of rare earth containing phosphate ore.（3）In apatite single mineral,The contents of La,Ce,Nd and Y accounted for 83.29%of ∑REE content.The distribution area of Y element had a high degree of coincidence with fluorapatite.La,Ce,Nd and Y occupied the Ca1 and Ca2 sites in fluorapatite.The characteristic absorption peaks of CO₃^2-in the infrared spectrum of apatite split into a pair of sharp double peaks at 1459 cm^-1 and 1438 cm^-1,indicating that there may be CO₃^2-substitution in apatite.Although the single minerals of dolomite also contained a certain amount of rare earth,the total content of rare earth elements was only 13.62μg/g.The presence of CaPO₃⁺ions was also detected in the distribution area of rare earth ions.（4）The substitution of the four elements at Ca1/Ca2 sites of fluorapatite were similar and mostly negative.Four rare earth atoms replaced the adjacent atoms at the Ca2 site to form a more stable 6-coordinated structure,resulting in less coordination polyhedron distortion,leading to the tendency of REEs to preferentially occupy the Ca2 site.For carbonate-bearing fluorapatite,the substitution of PO₄^3-by CO₃^2-led to a more likely substitution of REEs at Ca sites.The bond population between REEs and adjacent atoms in carbonate-bearing increased,and the bonding effect of REE-O and REE-F is stronger than fluorapatite.For dolomite,the substitution energy of REEs in dolomite Ca and Mg sites was mostly positive,indicating that it was difficult for REEs to enter dolomite.（5）The reverse flotation method can efficiently enrich P₂O₅ and rare earth elements,but the heavy metal elements As and Pb are also enriched to concentrate.The substitution forms of As and Pb in apatite were studied by DFT calculation.The heavy metal element As mainly replaced the PO₄^3-position in apatite in the form of arsenate(AsO₄^3-).The substitution of heavy metal Pb at the Ca1 and Ca2 sites of apatite may require high temperature and high pressure conditions.The content analysis of heavy metal elements in single mineral showed that the content of As in apatite was higher,while the content of Pb in dolomite was higher,indicating that heavy metal elements migrate from dolomite to apatite during flotation.In the flotation pulp,heavy metals As and Pb existed in the form of H₂AsO₄^3-and Pb SO₄,respectively.DFT studies found that both H₂AsO₄ interacted with the metal sites on the mineral surface,with negative adsorption energies.However,the absolute value of the adsorption energy on the apatite surface was larger,indicating that H₂AsO₄ and Pb SO₄ were more easily adsorbed on the apatite surfacess.