Study On The Occurrence State Of Rare Earths And Their Behavior In The Acid/pyrolysis Process Of Zhijin Rich Rare Earth Phosphate Rock In Guizhou

China is the largest producer,consumer and exporter of phosphate rock and phosphate in the world.Although the phosphate mineral resources are abundant in china,but the grade of most phosphate rock is not high.The Ministry of land and resources has listed it as one of the minerals that cannot meet the needs of the national economic development.It is of great significance to strengthen the development of the key technology of the middle and low grade phosphate rock for the sustainable development of the phosphoric industry in China.Zhijin phorphorus ore in Guizhou is an ultra-large middle and low grade phorphorus mine containing rare earth.The explored reserve of phosphorus mine is 1.334 billion of tons and the rare earth oxide reserve is 1.446 million of tons.Among them,heavy rare earth yttria accounts for 31.96%,which is equivalent to a large rare earth ore.Exploitation of this ore must consider comprehensive utilization of rare earth.A lot of research work has been carried out on the geological origin,ore structure,phase composition,the occurrence state of rare earth and ore selection of Zhijin phosphate rock,but there is still a lack of direct and powerful evidence on the form of the associated rare earth in the Zhijin phosphate rock.Many studies on migration and enrichment behaviors of rare earth in phosphorus ore have been reported,but most of them focus on wet phosphoric acid processing,and the research on other processing technology is still less,and the process is mostly in the stage of laboratory exploration.So that the Zhijin phosphate ore exploration report has been completed for nearly 50 years,but the mine has not been approved for exploitation and utilization for its indefinite industrial use index.Therefore,according to the specific characteristics of Zhijin phosphate rock,it is necessary to find out the occurrence characteristics of associated rare earth and master the law of rare earth migration and enrichment in the process of phosphate rock,and to develop the feasible extraction technology of the associated rare earth from phosphate rock,and realize the efficient extraction and utilization of phosphorus and rare earth resources.This is one of the important research topics of phosphorus chemical industry in our province.For this background,the research topic is put forward:Rare earth occurrence in Zhijin phosphate ore and its migration and separation behavior during acid or thermal decomposition process.In this paper,an experimental mineralogical method combined with molecular simulation method was used to systematically study the occurrence state of the associated rare earth in the phosphate rock.The rare earth migration behavior and the existence form of rare earth in the Phosphorite Acid/pyrolysis process were studied.The influence of processing conditions on the migration behavior of the associated rare earth in phosphate rock was investigated.The separation and recovery of rare earth in the acid solution of phosphate rock/phosphorus slag was studied and carried out.The study found that:Through the combination of chemical composition analysis,ICP-MS analysis,polarizing microscope,XRD and SEM,the mineral characteristics of Zhijin phosphate ore in Guizhou are studied.The results show that the main minerals in Zhijin phosphate rock are fluorapatite,dolomite and limestone,accompanied by hematite and clay minerals.The higher content of phosphate rock is P₂O₅,CaO,SiO₂,MgO,Al₂O₃,Fe₂O₃,F,P₂O₅ content is about 22%,and the content of rare earth is 0.07%.Phosphate rock has the characteristics of high impurity content and abundant trace elements.Through the study of phosphorite mineralogy and flotation of phosphate ore,acid leaching and ion leaching,the results show that there are three kinds of existence form of rare earth in phosphate rock,such as ion adsorption,independent minerals and doped in apatite,and more than 97%rare earth exist with fluorapatite,and the rare earth with independent minerals is not exceed 1.8%.The ion occupancy of the main rare earth elements,yttrium,lanthanum,cerium and neodymium in calcium fluoropite,is studied by molecular simulation method.The results show that the rare earth element can replace the calcium ion position in the fluorapatite arbitrarily,which shows that the rare earth does enter the fluorapatite mainly in the phase of the homogeneous phase and occupies the position of calcium ion.The lattice is most stable when the rare earth is completely substituted for the calcium ion position of fluorapatite,but the rare earth independent minerals are rarely found in the Zhijin phosphate mine,which further proves the genesis of the metallogenic mineralization of the Zhijin phosphate deposit.The hydrolysis of phosphate ore using hydrochloric acid was systematically studied through extensive testing.Thermodynamic and kinetic analysis showed that when the phosphate rock was decomposed by hydrochloric acid,the associated rare earth elements in the phosphate rock mainly entered the liquid phase.The reaction conforms to the characteristics of the shrinking core model,and the reaction kinetics shows that the reaction is controlled by chemical reaction and diffusion reaction process simultaneously.The leaching rate of P₂O₅ and rare-earth in phosphate ore was systematically studied under the conditions of expanded experiment.The results show that when 210 L of HCL per 100 kg of phosphorite is used at 30°C for 360 minutes,96.12%of the P₂O₅ and 95.04%of the rare earths are leached from the phosphorite..The sulfuric acid method was used for the hydrolysis of phosphate rock.It was found that the amount of sulphuric acid,the reaction temperature and the reaction time had a great influence on the morphology of phosphogypsum and the rare earth leaching rate;The distribution of rare earth elements in the liquid phase was consistent with the solubility law of the compound salt of sulphuric acid,and the thermodynamic analysis shows that the rare earth phosphate will react with sulphuric acid to produce sulphate,indicating that the rare earth in the process of sulphuric acid decomposition are in the form of rare earth sulphate.Due to the co precipitation of rare earth sulfate with a large amount of phosphogypsum in the system,the leaching rate of rare earth is low.Migration behavior of rare earth during thermal decomposition of Zhijin phosphorus ore was studied systematically.It found that in the thermal decomposition process of phosphorus ore,almost all of the associated rare earth enters into the phosphorus slag phase,but won't enter into ferrophosphorus phase and gas phase.Amorphous calcium metasilicate and calcium fluosilicate are major components of phosphorus slag and rare earth mainly exists as calsil solid solution.In phosphorus slag acidolysis by hydrochloric acid,it can make more than 95%rare earth in phosphorus slag enter into the liquid phase given 1.5 acid excess coefficient,50min reaction time and 50?reaction temperature.The separation and recovery experiments of rare earth in Hydrochloric acid hydrolysis solution of phosphate ore were carried out by liquid precipitation method.Hydrochloric acid phosphate hydrolysis solution was defluorinated using sodium chloride and was purified using sodium sulfide and calcium hydroxide.Sodium hydroxide was then used as the pH adjusting agent.When the pH value was 2.1,a rare earth enriched material with a rare earth content of 1.76%was obtained.The rare earth recovery reached90.1%.The rare earth material underwent multiple enrichment processes.After undergoing four enrichment processes,the rare earth content did not increase by more than 5%.