Study of Rare Earth Recovery from Low-intensity Magnetic Tailings of Baotou

Author:Yang Zhi Ren

Supervisor:wu wen yuan


Degree Year:2017





At present,rare earth resources can not be effectively recovered from low-intensity magnetic tailings of Baotou,which causes the waste of resources.Therefore,the recovery of rare earth resources is researched in this paper,and a"flotation-calcification roasting-flotation" of the environmental friendly and combined with the new process of mineral processing and metallurgy was put ford ward.Firstly,the research of mineral processing technology of tailings indicated that rare earth can be effectively recovered from tailing by flotation.And then through structural chemistry theory,geochemical classification theory of elements and the characteristics of the ore gangue minerals in tailings,the representative hydroxamic acid as a collector(H205)to rare earh minerals was selected,and flotation mechanism of H205 to rare earth mineral was studied.Subsequently,the flotation technology of rare earth minerals in low-intensity magnetic tailings was studied,and qualified concentrate(above 50%REO)was obtained.Then,the decomposition mechanism and decomposition process of the calcified roasting were researched.At last,a large number of theoretical researches on the flotation separation of three kinds of artificial minerals have been made.Mineral processing technology of low-intensity magnetic tailings was studied by MLA,optical microscope,ore microscope,scanning electron microscope,XRD,laser particle size measurement and XRF.The results indicated that RE,Fe,Ca,Ba,F,P,Nb,Sc and Th are mainly recyclable elements in low-intensity magnetic tailings was studied.The major minerals are monazite,bastnaesite,fluorite,hematite,barite,apatite,sodium amphibole,sodium pyroxene,dolomite,calcite and quartz.The grade of the target element of RE(REO)has reached 19.60%,which can be used as an important raw material for the recovery of rare earth.The particle size of the mineral is 90%in less than 74μm,and the grinding process is not needed,which meets the requirements of particle size in mineral processing technology.Most of the major minerals exist in the form of liberation degree,such as rare earth minerals and fluorite,and the liberation degree of rare earth is 87.28%.Finally,the main mineral properties of low-intensity magnetic tailings were analyzed.The results indicated that rare earth minerals can be obtained by adjusting the floatability of rare earth minerals,fluorite,barite,sodium amphibole and sodium pyroxene in low-intensity magnetic tailings.Bastnasite and monazite are typical oxidized minerals,and the valence of rare earth elements on the surface of a crystal lattice is trivalent,which is a typical hard acid according to the hard and soft acids and bases theory(HSAB).Therefore,organic compounds that contain oxygen are good collectors for separation of rare earth minerals.According to this principle,hydroxamic acid collector(H205)was used as a collector for the flotation of rare earth minerals,flotation mechanism of H205 to rare earth minerals were studied.The results indicated that H205 exhibited superior collecting performance to rare earth and the best floatability at pH 8-9.The adsorption mechanism of H205 to rare earth was studied by solution chemistry analysis of flotation,infrared spectroscopy and the ζ-potential tests.The results showed that the collection of H205 to rare earth was a result of the chemical adsorption,which formed a five-membered ring chelate.In the laboratory,P8(the main ingredient is H205)was used for the collector of the rare-earth minerals and flotation tests were carried out on this low-intensity magnetic tailing samples.The results indicated that,under the conditions of 30%roughing pulp concentration,pH 9,65℃ pulp temperature,2.4 kg/t H2O5 dosage,5.6 kg/t water glass dosage and 0.36kg/t frother dosage,by adopting a closed-circuit flowsheet of single-stage roughing,three-stage concentrating,single-stage scavenging and middling sequential returning to treat the samples,the qualified rare-earth concentrate with the REO grade 50.3%and the recovery rate 78.6%was obtained.In this paper,Ca(OH)2-NaOH process roasting the flotation concentrate is studied by thermal analysis and X-ray diffraction analysis.The results show that the flotation rare earth concentrate decomposition process is divided into two phases by adding the Ca(OH)2-NaOH.The first stage in the range of 350~500℃ is the decomposition of bastnaesite,rare earth generated oxide and fluoride fixed in the form of calcium fluoride to the calcined product.The second phase in the range of 500~650 ℃ is mainly of Ca(OH)2,CaF2 and NaOH decomposition of monazite and generating rare earth oxide and fluoride calcium phosphate.The influences of the amount of Ca(OH)2 and NaOH,roasting temperature and roasting time on decomposition rate of flotation rare earth concentrate is studied in this paper.Obtaining the optimum conditions for:roasting temperature 630℃,the amount of Ca(OH)2 30%and NaOH 20%and roasting time is 30 min.Under these conditions,the rate of decomposition of rare earth concentrates is 97.7%.The calcined product was analyzed by scanning electron microscope,XRD and laser particle size measurement.The results indicated that the calcined products were mainly REO,CaF2 and Ca5F(PO4)3.The size of calcined artificial mineral was not changed compared with that before roasting.The rare earth oxides in calcined artificial mineral can be separated by adjusting floatability of REO,CaF2 and Ca5F(PO4)3.Rare earth concentrate produced REO,CaF2 and Ca5F(PO4)3 after roasting.In order to facilitate research and provide a scientific basis for the flotation separation of these three kinds of artificial minerals,REO,CaF2 and Ca5F(PO4)3 were synthesized by being roasted at high temperature in the laboratory.Then,through a large number of flotation tests,flotability of this three artificial minerals are researched by using sodium oleate(NaOI)and styrene phosphonic acid as collectors,and the effects of inorganic modifiers(water glass,sodium phosphate and sodium pyrophosphate),organic small molecular modifiers(citric acid,lactic acid and tartaric acid)and organic polymer compounds(corn starch,sodium carboxymethyl starch and cationic starch)to this three artificial minerals are studied.The results showed that this three artificial minerals had similar flotability,sodium oleate exhibited superior collecting performance to direct flotation recovery of them and floated out above 90%REO at pH 8-9.In the SPA flotation system,compared with CaF2 and CasF(PO4)3,SPA exhibited superior collecting performance to direct flotation recovery of REO and floated out above 90%REO at pH=5.However,the collecting ability of SPA to CaF2 and Ca5F(PO4)3 was extremely weak and the highest recovery was only 20%at pH 2-11.In the paper,these three types of depressants,citric acid and sodium pyrophosphate all have obvious depression on this artificial mineral flotation.Based on the experiment of single mineral flotation,the simulated roasting mixed minerals were carried out through the flotation separation experiment,which is in agreement with the results of the single flotation tests.The flotation mechanism of collectors,organic and inorganic depressants to artificial minerals was studied by solution chemistry analysis of collector,theζ-potential tests,infrared spectroscopy and X-ray photoelectron spectroscopy(XPS)analyses.The results indicated that the collection of NaOI to artificial minerals was a result of the chemical adsorption,which formed oleate precipitation in the sodium oleate flotation system.However,C8H7PO(OH)(O)-dominates when 2.0<pH<7.0,but REO is positively charged,so SPA was physically adsorbed on REO surfaces.C8H7PO32-dominates when pH>7.0.Since both REO and SPA are negatively charged at pH>7.0,the adsorption of SPA on REO surface had to overcome the electrostatic repulsion,so SPA was not adsorbed onto REO surfaces.In the depressant flotation systems,the depression reaction of citric acid and sodium pyrophosphate to artificial minerals was a result of the chemical reaction,which formed chelates to make artificial minerals hydrophilic.