Study On The Occurrence State Of Rare Earth Elements In Zhijin Phosphate Ore And Its Extraction And Separation

Zhijin phosphate rock is generally associated with rare earth elements,which is the largest area in China at present.As of 2014,Zhijin phosphate mine has identified3.518 million tons of rare earth oxide（RE₂O₃）resources associated with phosphate rock,with an average RE₂O₃grade of 0.1036%.The middle yttrium and europium rich ionic rare earth ore with the highest rare earth distribution value is an important medium and heavy rare earth reserve resource after the ionic rare earth ore.The content of rare earth in Zhijin rare earth containing phosphate rock is low,the crystallization degree of collophanite is poor,and the occurrence state of rare earth elements has been lack of direct and powerful evidence and scientific and clear conclusions,which seriously restricts the research on rare earth beneficiation enrichment and extraction and separation technology.The study on the occurrence of rare earth elements in Zhijin phosphate rock and their extraction and separation has very important scientific and practical significance for the development and utilization of rare earth containing phosphate rock.The paper takes Zhijin rare earth containing phosphate rock as the research object,systematically collects representative test samples,and conducts in-depth research on its process mineralogy and occurrence state of rare earth elements.On this basis,it carries out detailed research on physical beneficiation,chemical beneficiation and rare earth extraction and separation,and deeply analyzes the occurrence state of rare earth elements and the formation mechanism of rare earth containing phosphate rock,the mechanism of rare earth chemical beneficiation and the mechanism of rare earth leaching solution distillation,The main conclusions are as follows:（1）The main ore mineral in the rare earth phosphorus ore of Zhijin Dama plant is collophanite,the main associated beneficial components are rare earth and fluorine,and the main gangue minerals are dolomite,hydrobiotite,quartz,chalcedony,pyrite,etc.Ore minerals and gangue minerals have fine particle size and poor dissociation of collophanite.Phosphorus and rare earth are mainly contained in collophanite.Physical beneficiation cannot separate rare earth,and rare earth can only be enriched with phosphorus.The collophanite is separated from the raw ore.The highest grade of rare earth RE₂O₃is 0.21%,and the theoretical recovery is 87.15%.The highest grade of phosphorus P₂O₅is 35.85%,and the theoretical recovery is 90.18%.（2）In the rare earth containing phosphate rock of Zhijin damachang,the rare earth elements are mainly contained in collophanite,dolomite,quartz,chalcedony,feldspar,pyrite and other minerals in the form of phosphate ultramicro inclusions,accounting for 91.73%of the total rare earth elements,and 6.80%of the rare earth elements are contained in apatite,crystalline collophanite,phosphoalumino strontium and other minerals in the form of isomorphism,1.36%of rare earth elements are stored in clay minerals such as hydrobiotite in the form of adsorption,only 0.10%of rare earth elements are stored in monazite,bauxite and Cerite in the form of independent minerals,and the content of rare earth elements in the form of combination with organic matter is very small.The occurrence and formation mechanism of rare earth elements are mainly controlled by the solubility product and microenvironment of rare earth phosphate.The formation mechanism of collophanite is a"rare earth phosphate ultramicro inclusion nucleation calcium phosphate chemical coprecipitation"model.（3）The one roughing and three scavenging reverse flotation process was used to separate rare earth phosphate ore from Zhijin Dama plant.The flotation concentrate product with a yield of 52.55%,P₂O₅grade of 28.67%,recovery of 85.72%,RE₂O₃content of 0.22%,recovery of 82.58%,Mg O content of 0.89%and removal rate of92.56%was obtained.The grade of raw ore P₂O₅is 17.58%,the content of RE₂O₃is0.14%,the content of Mg O is 6.69%,and the content of Si O₂is 10.42%.The beneficiation ratio is 2.93,and the beneficiation index is good.（4）The three cycle leaching chemical beneficiation process is used to enrich the rare earth in the flotation concentrate of Zhijin motianchong rare earth containing phosphate ore.The content of RE₂O₃is increased from 0.13%to 0.92%,enriched by7.03 times,the recovery rate is 91.90%,the content of P₂O₅is reduced from 31.89%to1.87%,and the leaching rate is as high as 99.23%,realizing the efficient separation of phosphorus and rare earth.The mechanism of chemical beneficiation is that based on the fact that rare earth elements mainly exist in the form of phosphate ultramicro inclusions and that the solubility of rare earth phosphate is far lower than that of calcium phosphate,the chemical separation of phosphorus and rare earth can be realized by adjusting the chemical dissolution equilibrium conditions and selectively leaching phosphorus to keep rare earth in the slag.（5）Rare earth is extracted from rare earth chemical concentrate by hydrochloric acid atmospheric pressure heating leaching process.At the pilot scale level,good indexes of RE₂O₃leaching rate of 96.44%,P₂O₅leaching rate of 97.42%and f leaching rate of 88.83%are obtained,and the effect is better than the laboratory test results.The optimum technological conditions are as follows:the dosage of hydrochloric acid is105%of the theoretical dosage,the concentration of hydrochloric acid is 25%,the leaching temperature is 70℃,the leaching time is 30 minutes at room temperature and 180 minutes at elevated temperature.（6）A rare earth oxide product with a content of 56.69%of RE₂O₃was obtained by the process of rotary evaporation of rare earth leaching solution,acid removal,fluorine removal and desilication,ion exchange resin adsorption and separation,oxalic acid precipitation and roasting.The content of Ca O,Al₂O₃and Fe₂O₃in the product was42.54%,0.46%and 0.31%respectively.The mechanism of removing fluorine and desilication by rotary evaporation is to make use of the volatility of hydrochloric acid and the instability of fluorosilicic acid in strong acid to promote hydrochloric acid and silicon tetrafluoride gas to escape from the rare earth leaching liquid system and enter the gas phase through the movement of gas-liquid equilibrium and chemical equilibrium under the condition of reduced pressure heating,so as to achieve the purpose of reducing the acidity of the solution and removing fluorine and desilication.（7）The best technological route for rare earth beneficiation and smelting of rare earth containing phosphate ore is as follows:physical beneficiation magnesium reduction chemical beneficiation dephosphorization hydrochloric acid heating Leaching Rare Earth decompression heating rotary evaporation acid removal fluorine and desilication ion exchange separation impurity removal oxalic acid precipitation separation iron and aluminum roasting to prepare rare earth oxide.According to this technical route,the total recovery rate of rare earth beneficiation and smelting of Zhijin motianchong rare earth containing phosphate rock is 75.67%,which is significantly better than the achievement index of 55.60%of phosphoric acid method.The production cost is 151700yuan/ton of RE₂O₃products,significantly lower than the production cost of 400000 yuan/ton of RE₂O₃products by sulfuric acid method.