Fundamental Research On The Fractionation And High Efficiency Leaching Of Ion Adsorption Rare Earth

Rare earths are key materials in the field of high technology and defense industrial,and are also the advanced materials for energy conservation,environmental protection and meeting the requirements of a better life.In the past decade,extensive research on the discovery of rare earth functions and the preparation of new materials have been carried out with great attention to the environmental protection and rare earth utilization efficiency due to the implementation of the new pollutant emission standard for rare earth industrial.Ion adsorption rare earth(IARE)is a type of characteristic resource and basic material which is rich in medium and heavy rare earths with important strategic significance.Therefore,a system study for the green and high efficiency exploitation of IARE have been carried out in this paper,including the mineral characteristics,rare earth element(REE)migration and fractionation,leaching mechanism,high efficient green extraction method and wastewater treatment technique.The main achievements are as follow:1 Evaluation method of migration activity and fractionation of IAREsThe concept of relative fractionation value(RFV)and its calculation method are defined and used to evaluate the fractionation characteristics of IAREs.The results show that due to the inhomogeneity of the deposit,the erosion pH and the rare earth content as well as the enrichment ratio do not change regularly with the depth.However,the change of REE partition value(PV)and RFV shows a monotonous upward or downward trend.It means that these parameters are more suitable for describing the fractionation of REE and can be directly used to evaluate the migration and differentiation characteristics of REEs along a certain direction or in a certain region.Moreover,the RFV can also reflect the contribution of the unit REEs to the fractionation.Therefore,several representative IARE deposits in Longnan,Quannan,Anyuan and Xunwu are selected to evaluate the spatial distribution,migration activity and fractionation of REEs along vertical direction of the deposit and among mineral particles with different sizes by taking leachable RE ions as research object.It is proved that the fractionation of rare earth in the deposit has obvious regional characteristics,and the migration direction and fractionation degree of REEs are related to the direction of water flow and the erosion pH of mine.In order to obtain the migration activity of the REEs,the RFVs of REEs from depth of 1 to 6 m and 6 to 8 m in a deposit in Quannan were calculated respectively.It is shown that from the top to the bottom of the shaft,the migration of Ce,Pr,and Nd is inert,while the middle and heavy REEs after Sm are active.The fractionation boundary lies between Nd and Sm,and La demonstrates different migration properties in the upper and lower shaft.For the first time,a tetral-group phenomenon is observed in the dependence relationship between RFVs and REEs atomic number.It is concluded that the migration of REEs in the deposit is the comprehensive manifestation of their hydrolysis and adsorption characteristics,and the erosion pH is the key factor to determine the relative contribution of migration,adsorption and precipitation.The study results on the transport and adsorption of cerium show that the sharp decrease of the PV and RFV of cerium from the surface to the inner layer is really related to the ability of cerium to be oxidized.However,it is not due to the formation of cerium hydroxide as described in the literature.The fact that most of the cerium in the deposit can still be leached by neutral electrolyte solution shows that the oxidation of a small amount of cerium and the coexistence of tetra and trivalent cerium can greatly improve the adsorption ability of cerium and limit its migration.Therefore,the adsorption ability of clay minerals to rare earth ions not only varies monotonously with the radius of hydrated ions of trivalent rare earth ions,but also contributes to the enhancement and weakening of the adsorption capacity due to the trend of formation of tetravalent or bivalent ions.This redox ability is directly related to the number of electrons filled in their 4 f orbitals.The appearance of the tetral-group phenomenon indicates that there exist relatively stable states when filling 4f orbit with 3,7,10 electrons.It is considered that the mixed valence state of REEs also exists in aqueous solution and depends on the number of electrons in 4f orbits.In addition,according to the characteristics of cerium migration,it can be determined whether the region belongs to the primary or stacked weathered crust.Based on this,it is found that the central area of a deposit in Xunwu is a primitive weathered crust because the PV and RFV of cerium decrease obviously with the depth.While the edge area is a stacked weathered crust,the PV of cerium is higher,and there is no significant difference with the space position.2 Fractionation of REEs in different landscape positions and its significationThe fractionation of REE in different landscape positions(watershed,ridge beam,side slope and end slope)of a mountain in Guanxi town,Longnan county was investigated respectively.Meanwhile,the minerals in the ridge beam sampling wells were characterized by XRD,SEM,IR and particle size analysis as well as adsorption properties and some other factors influencing the fluid flow are also examined.The results show that the main minerals of the fine-grained level(-700mesh)are quartz,illite and kaolinite.The main minerals are quartz,illite and kaolinite for sample at 1 meter depth,and kaolinite,halloysite for sample at 7 meters depth.The abrasion pH of the sample in surface keeps a low level and then increases to at around 6.The variation of pH values with depth is not obvious.It is found that the REEs are light rightist type pattern,and are enriched in the near surface layer(0-3m).The fractionation shows typical regional migration characterization.A great difference is observed for different landscape.In the watershed,from the top to the bottom,the enrichment direction is totally different from most of the reported results.The PVs of Light REE increase with the depth increasing,heavy REEs seem to be migration inner elements.In fact,this fraction characteristics is the result of heavy REE lateral migration instead of moving from top to bottom.In the side slope and end slope position,the migration direction of the heavy rare earth fractionation indicates a 2-3 m region,and the high content of heavy REE in the lower position of side slope is attributed to the lateral water flow.The direction of water flow indicated by REE fractionation is related to the enrichment area,but is not completely matched.The area where heavy/light rare earth ratio is large should be smooth flow.3 Classification and high efficient leaching of IARE based on its pH dependence and leaching mechanismIt is proved that the leaching rate of various kinds of electrolyte leaching of rare earths is linearly related to the zeta potential of clay minerals,and the slope is correlated with the types of anions and cations.Based on the double-layer model of particle surface and the determination of zeta potential,the mechanism of exchange leaching of rare earths by electrolyte solution is proposed,which can be used to explain the order and mechanism of electrolyte ions to leaching of rare earth ions and the causes of landslide.A new method to improve the leaching rate of rare earth and to stabilize tailings and to reduce waste water discharge is put forward by using high valence ion electrolyte to leach and adding lime water to stabilize tailings.Based on the relationship between pH value of leaching solution and leaching rate of REEs and coexisting ions,the adsorbed rare earths are divided into two parts:easy to extract rare earths and hard to extract rare earths.It is proved that the ratio of these two parts of rare earth is related to the erosion pH(pHd)and exchange pH(pHt)of ore body.Based on the relationship between the above differentiation law and the pH value of ore body erosion,the ways and methods to improve the leaching efficiency of ion adsorbed rare earth are discussed.For ore samples with high abrasion pH and exchange pH,especially in fine clay,the ratio of rare earths difficult to exchange is higher.So it is necessary to increase the acid leaching section after leaching in pure inorganic salt solution to ensure the high leaching rate of rare earths.For this reason,a new process of leaching rare earth and protecting the tailings with lime water in stages is put forward.If aluminum sulfate is used in secondary leaching stage instead of acid solution,the residual ammonium in tailings can be recovered while the leaching rate of rare earth is increased,the concentration of pollutants in rain water leaching wastewater can be reduced,and the discharge requirements can be met.The results show that the amount of Th,U,Pb in simulated rainfall leaching wastewater is only 9%,4%,6.3%,which greatly improves the safety and stability of tailings.4 Treating waste water containing REEs and ammonium with clay minerals and aquatic plants as adsorbentsAs a aquatic plant,hyacinth is used to treat waste water with low concentration of REE and ammonium.A method for the absorption of rare earth from low concentration ammonia-containing wastewater is proposed and the technological conditions were determined.The designed multistage aquatic plant purification process is proved good for the purification of extremely low concentration of rare earth solution,with which ammonia and nitrogen has been reduced to 4.63ppm,and the concentration of REE can be controlled under the 0.5mg/L,indicating that the discharge of wastewater can meet the emissions requirements.REE can be recovered by a chemical process from the collected water hyacinth,while the biomass can be used for energy transformation.It is a new way for the wastewater treatment and resource recovery.Based on the adsorption characterization of clay mineral in tailings for REEs,a simple method for treating waste water containing low concentration of rare earth is proposed using clay mineral as adsorption materials.This method is the main technology in the second metallogenic model,its implementation can greatly improve the utilization rate of resource recyclingand reduce waste water discharge.Finally,according to the environmental engineering model of ion adsorbed rare earth resource exploitation,the present study puts forward the comprehensive process and technical basis including:resource exploration,direction prediction of water flow,selection of leaching agent and leaching mode,rare earth extraction and precipitation enrichment,tailings remediation and wastewater treatment.All in all,they lay a good foundation for the efficient green extraction of ion adsorbed rare earths and have broad application prospects.