Theory And Application Of Rare Earth Ore Flotation Of Alkaline Rocks

Rare earth elements (REEs) are a set of seventeen chemical elements that comprise the fifteen elements of the lanthanide series as well as yttrium and scandium. These elements, which are praised as "industrial monosodium glutamate", are important strategic resources of non-renewable and increasingly widely required for many different applications in field of new energy, new materials, cutting-edge technology, etc.. There are may be found in approximately250different minerals in the world to date, but the only REE bearing minerals that have been extracted on a commercial scales are bastnasite, monazite, xenotime and ion-adsorbed clays.The alkaline rock type rare earth ore in Maoniuping deposit, Sichuan, of which rare earth reserves after Bayan Obo rare earth ore. The most commonly utilized application of gravity separation with shaking tables as roughing or that combined with magnetic separation is in the beneficiation, such as gravity separation with shaking tables as roughing, drying and then dry magnetic separation. Those techniques just only recovered the rare earth bearing minerals, but a large number of barite, fluorite and other associated minerals are discarded as tailings instead of the comprehensive recovery. Because of the lag in beneficiation techniques, rare earth recovery rate is only about50%, resulted in an enormous waste of the valuable mineral resources. Meanwhile, the disadvantages of the combined beneficiation flowsheet are discontinuous operation and in the situation of full with dusts.As previously mentioned, based on a comprehensive study of mineralogy, a new wet combined beneficiation technique is developed to highly-efficiently recover the valuable minerals in this type of rare earth resource; in the meantime, basic theories of the bastnasite monomineral flotation are been systematically researched in order to provide a certain reference to the flotation separation of rare earth ore contains the bastnasite.In the beneficiation technique research, firstly, the process mineralogy is studied by means of Electron Microscope Energy Spectrum and Mineral Liberation Analyser, and several process characteristics such as composition as well as contents of the rare earth bearing minerals and gangue minerals, disseminating relationship and its state, degree of mineral liberation, occurrences of valuable elements, are determined. Then, a series of exploratory experiments including classification, magnetic, gravity and flotation separation are conducted. Consequently, a rational beneficiation process flowsheet is determined according to all of the performances above.The principle of beneficiation is in full compliance with the ore properties which could also be utilized. This dissertation has proposed that a technical route comprising magnetic separation combined with gravity separation plus flotation must be applied because valuable minerals in the ore should be recovered comprehensively in order to exploit the resource. Accordingly, a combined beneficiation flowsheet designed to concentrate rare earth bearing minerals. In the flowsheet, non-magnetic gangue including large amounts of slimes is discarded via wet high intensity magnetic separation, then gravity separation is used to discard any low specific gravity gangue and the final shaking table concentrate stream can be achieved. The middlings stream from shaking tables that remains contains a portion of the rare earth bearing minerals which are intergrowth as well as gangue minerals which are not removed in the first two steps. A flotation separation is then applied to exploit the different surface properties of the valuable bastnasite and gangue minerals and produce the final flotation concentrate stream. Consequently, it is not only achieved the highly effective recovery of the rare earth minerals and improved the final concentrate recovery, but also to take into account the concentration of barite and fluorite which should be recovered comprehensively in the successive beneficiation flowsheet.Magnetic and gravity separation are ineffective at separating very fine particles resulting in large losses of rare earths, but flotation separation is commonly applied to the beneficiation of rare earth ores is due to the fact that it is possible to process a wide range of fine particle size. Undoubtedly, flotation separation can be used to beneficiate the fine particles, which is of vital importance to the increase in overall recovery. In this connection, a series of parameters including grinding fineness, types and dosages of regulators, collectors and assistant collectors, pulp density, conditioning time, temperature, ratio of return water to new water and structure of flowsheet are all researched systematically by comparative trials. A selective hydroxamic acid collector, known as GSH, and sodium silicate as regulator are used to produce final flotation rare earth oxide concentrate with grade of65.11%at recovery of17.05%. The two concentration streams from shaking tables and flotation are combined to be the final REO concentration with grade of65.08%at overall recovery of84.61%, of which the contents of both REO and impurity meet No.000165product’s requirements in the rare earth industry standards (XB/T103-2010).In terms of the basic theory of flotation bastnasite, the basic flotation behaviors for the mineral are completed using sodium oleate and salicylhydroxamic acid as collector, respectively. The mechanisms of action between multiple regulators as well as collectors and minerals is analyzed systematically by means of solution chemistry calculation, zeta potential, infrared spectroscopy, adsorption measurements, dissolution measurements and Inductively Coupled Plasma (ICP) analysis. The necessity of regulating pulp before adding collectors and mechanism of selective adsorption are illuminated by a comparative analysis, which is provide references for further theoretical researches, but also offer guidance for practical application. Meanwhile, the effect of elevated temperatures on flotation is discussed.The calculation results of solution chemistry demonstrate that hydroxylated species produced from cations on the surface of bastnasite could influence the flotation. Because of active points, hydroxylated species RE(0H)2+and RE(OH)2+are propitious to the adsorption of collector on the surface of bastnasite. But it is clear that hydroxylated species RE(OH)3and RE(OH)4do not assist flotation and adsorption may be due to they are negative active points.The action mechanism research results of sodium oleate adsorbed on the bastnasite surface indicates that chemisorption plays the most important role as well as auxiliary electrostatic or molecular adsorption, which are due to the ion-molecular association originated from dissociated oleic acid radical ion during pH6-9. But in salicylhydroxamic acid terms, the results of this adsorption study indicate a surface reaction mechanism whereby the cations on the mineral surface form hydroxy complexies in solution, readsorb at the surface and then interact with the hydroxamate, namely the salicylhydroxamic acid group bonds with the hydroxylated species to generate stable five chelate ring to realize the selective flotation of bastnasite in the range of pH8-9.The investigation results demonstrate that depressing function of sodium carbonate relates to the coions effect of potential determining ions CO32-which originates both from bastnasite surface and the reagent in the water (these ions that can interact with both mineral surface and aqueous phase in forming the electrical double layer). There are adsorption on the bastnasite surface for sodium hexametaphosphate, sodium silicate and sodium hexafluorosilicate. There is no basically effect to increase the degree of solubility of bastnasite in water for sodium carbonate, sodium silicate and sodium hexafluorosilicate. The reasons for sodium hexametaphosphate exhibits significant inhibition are most likely twofold:(1) it adsorbs on the mineral surface that changing the mineral’s electrical properties and hydrophilic, directly reducing the collector adsorbs on the bastnasite;(2) the complexation reaction takes place between RE cations hydroxylated species on the mineral surface and hexametaphosphate anion and produces soluble complexes, which reduces the concentration of active points on the surface of minerals, therefore, the suppressing effect is presented.Cations Ca2+and Al3+in the solution reveal activation when sodium oleate as the collector, which could be attributed to these ions and their partial hydrolysates have adhered on the minerals surface that is beneficial to produce more oleate precipitates exhibiting hydrophobic. On the contrary, in the flotation solution system adding salicylhydroxamic acid as collector, the investigation demonstrates depressing for these two ions. In terms of Ca2+ion, the depression is attributed to the electrostatic adsorption on the bastnasite surface and the non-selective competitive adsorption among these RE3+ions as well as their hydroxy complexes and Ca2+ions with hydroxamic acid occur. Moreover, Ca2+ions have a certain effect on the solubility of bastnasite, which may be related to the ion pair (Ca2+,CO32-) effect. This inhibition of Al3+is mainly due to the complexes that reacted between salicylhydroxamic group and Al cations, which is more stable than that produced by rare earth cations. Both Ca2+and Al3+in solution may reduce the density of active points on the bastnasite surface, consequently, the mineral is depressed.It is established that elevated temperatures in the flotation system of single bastnasite component that using salicylhydroxamic acid or sodium oleate as collector promote selective adsorption of collectors. Just on the contrary, the results of floating the rare earth ore in Maoniuping with modified hydroxamic acid demonstrate that there are obvious drops both in concentrate grade and recovery observed during flotation above50℃. The reasons are preliminarily determined that there is no related to dissolution of minerals such as bastnasite, but may be connected with several parameters including particles movements, reagents action, bubbles collision and load, and surface tension of pulp, etc.. The real reasons are in need of further researches by decomposing the complex flotation system and establishing the models.