GB2102402A

GB2102402A - Method of and apparatus for treating a rare-earth mineral or concentrate

Info

Publication number: GB2102402A
Application number: GB08219010A
Authority: GB
Inventors: Kiyoshi Inoue
Original assignee: Inoue Japax Research Inc
Current assignee: Inoue Japax Research Inc
Priority date: 1981-07-03
Filing date: 1982-07-01
Publication date: 1983-02-02
Also published as: DE3224856A1; IT8248750A0; JPS586947A; FR2508931A1; IT1148195B; DE3224856C2; FR2508931B1; JPH0120214B2; GB2102402B

Abstract

A rare-earth mineral or concentrate, e.g. monazite or bastnaseite or a mixed ore thereof, as a muddy mass or the pulverized rare- earth mineral or concentrate mixed with an aqueous solution of an electrolyte, e.g. sodium hydroxide, is subjected to induction heating to facilitate dissociation and reduction of the rare-earth mineral or concentrate.

Description

SPECIFICATION Method of and apparatus for treating a rareearth mineral or concentrate The present invention relates generally to a dissociation technique customarily encountered in the refining of rare-earth mineral materials.

More particularly, it relates to a new and improved method of and apparatus for treating rare-earth minerals or concentrates, e.g. monazite and/or bastnaesite, to dissociate them into a rareearth compound, e.g. R(OH)3, from which the desired rare-earth element R, such as lanthanum, cerium, praseodymium, neodymium, samarium or gadolium, or a combination of them or "misch metal" (hereinafter referred to generally as rareearth substance) can readily be recovered.

It is known that rare-earth substances may be extracted from a variety of source minerals such as monazite, bastnaesite, gadolinite and xenotime which contain rare-earth concentrates in the form of (Th,R)PO4, RFCO3, (Be,Fe)R2Si2O10 and RPO4, respectively. In refining it is necessary therefore to treat each of these source materials or rare-earth concentrates to separate or free the rare-earth compound from the other component parts. This separation or dissociation step has heretofore been carried out purely chemically.Thus, monazite, bastnaesite or xenotime has been treated with sulphuric acid, sodium sulphate, sodium hydroxide, hydrogen chloride and ammonium chloride to yield the rare-earth compound in the form of R(OH)3 or R2O3, separated from thorium sulphate, hydrogen phosphate, sodium sulphate, carbon dioxide, silicon fluoride, hydrogen fluoride, sodium phosphate, sodium hydroxide, thorium hydroxide, thorium ions and sulphate and/or phosphate radicals.

Not only do these prior dissociation processes require a high concentration of the reactant, H2SO4, NaSO4, HCI, NH 3Cl, which adds to cost, but they also require a relatively high reaction temperature amounting to 200 to 2500C or around 1 500C to be maintained for a period of several hours. Furthermore, large amounts of noxious gases such as SO2 and HF and noxious alkaline mists may unavoidably be generated, necessitating a large and costly gas-treatment facility. It should be noted that the prior dissoaciation processes are undesirable or unsatisfactory not only from energy and resource saving standpoints but from an economic consideration of the equipment as well as the cost of the rare-earth elements that are produced thereby.

Another problem encountered heretofore in the rare-earth material field is that one existing dissociation process (e.g. the alkaline dissociation process) applicable to one particular rare-earth mineral (e.g. monazite) is generally not applicable to another mineral (e.g. bastnaesite). Thus, where two different types of the rare-earth source are present in the same mineral as, for example, that available from the Baiyun mine China, which contains 40% monazite and 60% bastnaesite, the prior-art techniques have been prohibitively inefficient or even impractical.

Accordingly, the present invention seeks to provide a new and improved method of dissociating rare-earth minerals or concentrations, e.g. monazite and/or bastnaesite, into rare-earth compounds, which method is relatively simple in procedural steps, efficient in energy and resource saving, less costly in operation, capable of producing desired rare-earth substances at a reduced cost, applicable even to mixed rare-earth mineral concentrates (e.g.

monazite plus bastnaesite) and, in practice, generally independent of the nature of the rareearth source.

The invention also seeks to provide a rare-earth mineral or concentrate dissociation method which produces a greater yield of a convenient rareearth compound such as a rare-earth hydroxide (R(OH)3), rare-earth sulphate (R(S04)3) or rareearth chloride (RC13), and which is capable of reducing the presence of noxious gases and fluid so as to eliminate costly and large-sized antipollution equipment.

The invention further seeks to provide a new and improved apparatus for dissociating rareearth minerals or concentrates into a desired rareearth component, which apparatus is relatively simple; and yet economical in operation, versatile in its operation capability of handling a variety of rare-earth source minerals and capable of eliminating environmental pollution problems.

The method according to the present invention resides in a physicochemical process and generally comprises: admixing a rare-earth mineral or concentrate with an aqueous solution of an electrolyte to form a muddy mass of the mixture; and induc;tively heating the mass to facilitate reduction of said mineral or concentrate with the electrolyte.

Specifically, the mass may be heated by passing therethrough a high-frequency electrical field of a frequency ranging between 50 Hz and 100 Hz generated by electrical induction.

Alternatively, the mass may be heated by radiating the mass with a beam of microwaves of a frequency ranging between 300 MHz and 300 GHz to inductively heat the mass.

The mineral or concentrate may contain a rareearth component in the form of an oxide of at least one rare-earth element.

The rare-earth mineral of concentrate may be at least one ore selected from the group which consists of monazite, bastnaesite, gadolinite and xenotime. For example, a mixture of monazite and bastnaesite can be efficiently treated according to the present method, in spite of the earlier belief that such a mixed rare-earth ore can be treated only with difficultly or at a great loss of efficiency.

The electrolyte may be at least one substance selected from the group which consists of potassium acetate, ammonia, ammonium, chloride, sodium chloride, sulfuric acid, sodium carbonate, sodium hydroxide and potassium hydroxide. It has been found that an alkaline compound such as sodium hydroxide is particularly suitable for use with the present invention.

The pulverized rare-earth mineral or concentrate should preferably have a particle size ranging between 100 and 400 mesh. The pulverization, as customarily, is effected in advance to mixing with the electrolyte, although the mineral or concentrate may also be pulverized after being mixed with electrolyte.

The invention also provides an apparatus for treating a rare-earth mineral or concentrate, which comprises: a treatment vessel, support means in the treatment vessel for retaining a muddy mass formed by mixing the rare-earth mineral or concentrate with an aqueous solution of an electrolyte, and means for inductively heating the mass to facilitate reduction of the rare-earth mineral with the electrolyte.

Specifically, the heating means may comprise coil means disposed to surround the mass and a power supply for passing a high-frequency electric current of a frequency ranging between 50 Hz and 100 KHz through the coil means to inductively heat the mass. Alternatively, the heating means may comprise a magnetron for radiating the mass with a beam of microwaves of a frequency ranging between 300 MHz and 300 GHz to inductively heat the mass.

These and other features of the present invention as well as advantages thereof will become more readily apparent from the following description when taken with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view illustrating a first embodiment of the present invention; and Figure 2 is a diagrammatic view illustrating a second embodiment of the present invention.

Referring now to Figure 1, an apparatus according to the present invention includes a treatment vessel 1 which is composed, at least along its inner surfaces, of an anti-acid and/or anti-alkaline material. The vessel 1 is also rigid and is constructed to tightly seal its inner space. A mass of material 2 to be treated is introduced into this space through an inlet opening 1 a. The inlet opening 1 a is provided with a door 3, which is closed for the operation of the apparatus. In the vessel 1 the material 2 to be treated, which is a mixture of a rare-earth mineral or concentrate previously pulverized into particle sizes ranging, for example, between 200 and 400 mesh with a liquid electrolyte and is in the form of a sludge or viscous mud sufficiently mixed or kneaded, is introduced into the vessel 1 and disposed in a trough 4 mounted on a table 5 therein.

Shown also in the vessel 1 is a coil 6 disposed to surround the material 2 and energized by a high-frequency power supply 7 for inductively heating the material 2 and generating electrical (micro or spark) discharges among the particles thereof. The coil 6 has cooling means not shown.

The power supply 7 is equipped with a control unit 8 for adjustably controlling the magnitude of the output current passed from the supply 7 through the coil 6 or the heating energy applied to the material 2 and the time of delivery of the heating current or energy. Thus, the output current of the power supply 7 may be pulsed and the pulse duration and interval as well as the magnitude thereof may be controlled by the control unit 8. Gases and mists produced during the inductive heating and discharge treatment of the material 2 are allowed to be discharged out of the vessel 1 through a conduit 9 by an exhaust unit 10 which may include a vacuum pump and a gas-treatment unit. A valve 11 is provided in the conduit 9.In addition a gas supply 12 is provided to furnish a suitable gas into the treatment vessel 1 via a conduit 13 for the purposes of promoting the treatment reactions in the vessel 1, diluting the produced gases and mists within the interest of anti-fire and anti-pollution, facilitating the treatment of these gases and mists in the unit 10 and/or holding the space in the vessel 1 in appropriate pressure and temperature conditions.

A valve 14 is provided in the conduit 13.

The rare-earth mineral or concentrate powder constituting the material 2 refers to a mass of rare-earth mineral previously pulverized and then subjected to gravity concentration to remove impurities such as silica sand and further to magnetic or electromagnetic concentration to remove iron ores so that the mineral may have a rare-earth concentration at least 60% by weight or volume. Such concentration pre-treatments are advantageous here for the sake of effective use of electric power consumed for the induction heating and discharge treatment in the vessel 1. It should be noted, however, that the method of this invention is applicable to a rare-earth mineral of a rare-earth concentration, say, less than 50% by weight or volume.Thus, the gravity concentration and the maghetic or electromagnetic concentration may be dispensed with if the cost for these concentration treatments is higher than the cost for the excess of electric power needed due to the greater concentration of the impurities in the practice of the present method.

While a rare-earth concentrate itself is highly resistive or dielectric, by admixing it with a liquid electrolyte a body of a moderate resistivity, viz.

in the order of ohm-cm, is provided and can effectively be induction-heated and can effectively develop electrical discharges among the particles thereof. When the mixed material or body 2 is heated at more than 1 000C or so, the aqueous liquid will evaporate and gasify, thus giving rise to development of gaseous bubbles among the interstices of the particles. Upon the development of these bubbles tending to expand outwards, the eddy current generated through the material 2 by passage of the high-frequency current through the coil 6 tends to be interrupted.

The result is a localized and dispersive development of micro or spark discharges (as viewed, assuming dotted blue-white and red coloured lights) among the particles throughout the mass 2. The rare-earth concentrate particles are thus exposed to localized adjacent discharge coiumns and, at a localized high temperature of the discharge and in the presence of the reactive electrolyte, undergo decomposition and reduction. As a result, with the electrolyte being, for example, caustic soda (NaOH), there is produced a rare-earth hydroxide (R(OH)3). Due to the presence of water content, the mixture 2 is, without supply of extraordinarily high energy or of heating energy with an extraordinarily high rate, not heated to so high a temperature as above 2000C.It can be assumed that at least a portion of the rare-earth concentrate particles is placed at a temperature around 1 000C in a state just ready to undergo dissociation with an acid or alkali.

When these particles come into contact with a spark or micro-discharge column, the required reactions are seen to be promoted.

In another embodiment of the invention shown in Figure 2, the inductive heating of a rare-earth mineral material 2 is achieved with microwaves emitted by a microwave tube, say, magnetron 1 5.

The microwave tube 1 5 is energized by a power supply 1 6 having a control unit 1 7. The power supply 1 6 is adjusted with the control unit 1 7 to provide a beam of microwaves of a frequency between 300 MHz and 300 GHz from the tube 1 5. The control unit 1 7 is also used to adjustably vary the energy of the microwaves as well as the time duration and interval of application of the microwaves. In the arrangement of Figure 2, same reference numerals are used to refer to same parts of functionally same parts as in Figure 1 and the material 2 is represented by three or more masses instead of one mass as in Figure 1.

Furthermore, the trough 4 is shown mounted on a rotary table 1 8 which is rotatably mounted on the base or table 5 and a fan 1 9 is provided, to make even the distribution of microwaves emitted from the tube 1 5 over the masses 2 in the trough 4.

The microwave tube 1 5 makes use of principles of electromagnetic induction heating or dielectric heating and customarily operates to emit the high-frequency waves in the frequency range between 1 and 3 GHz. When each of the masses 2 is radiated with a beam of microwaves, it is inductively heated due to the dielectric loss created therethrough. At the same time, electrical charges tend to accumulate on the surfaces of the rare-earth concentrate particles and result in local sparks or micro-discharges through the interstices thereof in each mass 2. When the mass 2 is inductively heated by dielectric heating to a temperature of 1 000C or more and held at the temperature, there result a vaporization of water content thereof and emission of gases entrapped therein.The continued vaporization and gas emission give rise to development of sparks or micro-discharges dispersed throughout the mass 2 as in the previous embodiment. The induction heating and the accumulation of electrical charges are carried out efficiently due to the fact that the rare-earth concentrate is of a high dielectric constant. The sparks or microdischarges are thoroughly produced throughout the mass 2 and, without so much elevating the temperature thereof, facilitate dissociation and reduction of the concentrate with a localized high thermal energy created by discharges and in the presence of the reactant electrolyte.

Both with the embodiments of Figures 1 and 2, the mass 2 itself is, as a whole, not so much elevated in temperature. This allows only a reduced amount of the mists and gases which are harmful and difficult to treat to be produced. This eventually makes it possible to select much less severe operating conditions as far as the treatment of these gases and mists is concerned and to make the treatment equipment less bulky and much simpler than in the conventional processes.

Depending on the type of the electrolyte used, it is also possible to supply higher energy and thus to allow the mass 2 to be heated to a higher temperature of 200 to 3000C or more (say, to 1 0000C) so that the reaction may proceed at a higher rate. Thus, using an alkaline electrolyte such as caustic soda (NaOH), which is capable of largely reducing harmful gases such as SOx (where x is an integer), greater supply energy may be employed to increase the rate of reactions.

Example I A liquid electrolyte consists of an aqueous solution containing 50% by weight of sodium hydroxide (NaOH) and each of various rare-earth concentrates identified below is mixed with the liquid electrolyte in a volume ratio of 1:2. The concentrate is in the form of particles having a particle size of 300 mesh. The mixture is subjected to induction heating as discussed hereinbefore and it is observed that minute electrical discharges of blue or green/blue colour develop dispersiveiy throughout the mixture. It has been found that: (1) When the rare-earth concentrate is monazite or senotime (RPO4), rare-earth hydroxide (R(OH)3) and sodium phosphate (Na2P04) are produced. No harmful gas is produced.

(2) When the rare-earth concentrate is bastnaesite, rare-earth hydroxide (R(OH)s), sodium fluoride (NaF) and sodium carbonate (Na2CO3) are produced. No harmful gas is produced.

(3) When the rare-earth concentrate is a mixture of monazite (4 parts) and bastnaesite (6 parts), rare-earth hydroxide (R(OH3), sodium phosphate (Na2PO4), sodium fluoride (NaF) and sodium carbonate (Na2CO3) are produced. No harmful gas is produced.

In each of the above, the yield appears to be as high as 90 to 95% or more. Thus, initially the content of rare-earth elements in each concentrate is measured. After the induction heating, the rare-earth hydroxide (R(OH)3) sediment is collected by filtration and washed with water at 1 000C. The washed rare-earth hydroxide is then treated with a 5% hydrochloric acid solution at 1 000C for 40 minutes to yield a solution: Upon adjustment of its pH value to 5.8 to 6.0, the solution is freed from sediment containing thorium hydroxide, yttrium compounds and a minor amount of rare-earth substance, and is condensed by boiling. Then, by drying the concentrate, the rare-earth chloride (RCl3) is obtained and measured, the yield of rare-earth substance being 92 to 93%.Alternatively, the above solution may be neutralized with sodium hydroxide to yield a sediment containing the rareearth hydroxide. This method also provides a yield of 92 to 93% of rare-earth substance.

Example II A liquid electrolyte consists of an aqueous solution of ammonium chloride (NH4CI) with a mixed rare-earth concentrate containing monazite (4 parts) and bastnaesite (6 parts) mixed therewith. It has been found that inductiveheating of this mixture and subjecting the particles thereof to the consequential minute electrical discharges produces rare-earth hydroxides (R(OH)3) and rare-earth chlorides (RCl3), and in addition harmful gases such as fluorine (F2), hydrogen fluoride (HF), chlorine (Cl2) and ammonium fluoride (NH4F) together with other harmful gases in smaller amounts including NH4HF2, PCI3 and POCI. Simultaneously, phosphoric acid is also produced.

Example Ill A liquid electrolyte consists of an aqueous solution of sodium chloride with monazite plus bastnaesite mixture mixed therewith. It has been found that inductive-heating of this mixture and subjecting the particles thereof to the consequential minute electrical discharges produce R(OH)3 and RCI3 together with small amounts of harmful gases including NaF, Cl2, PCI3 and POCI. Simultaneously, sodium phosphate (Na3PO4) is also produced.

Example IV A liquid electrolyte consists of sulphuric acid (H2SO4) or an aqueous solution thereof with monazite and bastnaesite mixture mixed therewith. It has been found that inductive heating of this mixture and subjecting the particles thereof to the consequential minute electrical discharges produces rare-earth sulphates (R2(SO4)3), phosphotic acid (H3PO4) and harmful gases including F2, HF and SOx (where is an integer).

Example V A liquid elctrolyte consists of an aqueous solution of sodium carbonate (NaCO3) with monazite and bastnaesite mixture mixed therewith. It has been found that inductiveheating of this mixture and subjecting the particles thereof to the consequential minute electrical discharges produces rare-earth hydroxides (R(OH)3) and sodium phosphate (Na3PO4). No harmful gas is produced.

Example VI A liquid electrolyte consists of an aqueous solution of potassium hydroxide (KOH) with monazite and bastnaesite mixture mixed therewith. It has been found that inductiveheating of this mixture and subjecting the particles thereof to the consequential electrical discharges produces rare-earth hydroxides (R(OHt)), potassium phosphate (K3PO4), potassium fluoride (KF) and potassium carbonate (K2CO3). No harmful gas is produced.

Example Vll A rare-earth mineral concentrate consisting of 30% monazite and 70% bastnaesite contains rare-earth complexes in an amount which is 60% by volume when calculated in terms of rare-earth oxides (R203). The concentrate is crushed into particles so that 99% of them have a particle size of 200 mesh. In weight proportion, 2 parts of the particles are mixed with 1 part of caustic soda and 0.4 part of water so that 1 mol of the rareearth concentrate is present for 3 mol of caustic soda in the mixture and suspended in the solution.

The muddy mixture of 60 grams in weight is shaped into separate disks each having a diameter of 30 mm and a thickness of 6 to 8 mm.

These disk-shaped masses are loaded in a highfrequency induction-heating furnace as generally shown in Figure 1 and are heated therein by a high-frequencv induction heating current of a frequency of 40 kHz passing through a coil 6 for a period of 10 minutes at a heating rate of 6.4 kcal/min. The sediment is washed with water at 1 OO"C or room temperature five times and then dried, there resulting an amount of 36.5 grams of rare-earth hydroxide. The latter is dissolved with an aqueous solution of 300 ml in volume containing 35 to 40% by weight of hydrogen chloride and is heated at a temperature of 1 050C for a period of 10 minutes. The sediment obtained after conducting this acid solubilization three times is dewatered to yield a residue of 0.8 gram in the form of rare-earth chloride.

Example VIII A mass of 83 grams of the muddy mixture referred to in Example VII is induction-heated by being radiated with a beam of microwaves of a frequency of 2.450 MHz from a mgnetron at a heating rate of 6.4 kcal/min for a period of 1 5 minutes. Then, as in Example VII, the treated mass is washed with water five times, subjected to filtration and then dried to yield an amount of 57.5 grams of rare-earth hydroxide. when the latter is dissolved, for a period of 10 minutes, with an aqueous solution of 400 ml containing 36% by weight hydrogen chloride heated at a temperature of 1 050C, a residue of 1.8 gram consisting of rare-earth chloride is obtained.

The X-ray analysis of the rare-earth hydroxide sediments obtained in Examples VII and VIII shows that they contain practically no trace of rare-earth oxides, indicating that the oxides are substantially completely reduced to the hydroxide.

Claims

1. A method of treating a rare-earth mineral or concentrate in a pulverized form, comprising the steps of: a) admixing the rare-earth mineral or concentrate with an aqueous solution of an electrolyte to form a muddy mass of the mixture; and b) inductively heating said mass to facilitate reduction of said mineral or concentrate with said electrolyte.

2. The method defined in Claim 1 wherein said mass is heated by passing therethrough a highfrequency electrical field of a frequency ranging between 50 Hz and 100 kHz generated by electrical induction.

3. The method defined in Claim 1 wherein said mass is heated by radiating said mass with a beam of microwaves of a frequency ranging between 300 MHz and 300 GHz.

4. The method defined in any one of the preceding claims wherein said mineral or concentrate contains a rare-earth component in the form of an oxide of at least one rare-earth element.

5. The method defined in any one of the preceding claims wherein said rare-earth mineral or concentrate is at least one ore selected from the group which consists of monazite, bastnaesite, gadolinite and xenotime.

6. The method defined in any one of claims 1 to 4 wherein the rare-earth mineral or concentrate is a mixture of monazite and bastnaesite.

7. The method defined in any one of the preceding claims wherein said electrolyte is at least one substance selected from the group which consists of potassium acetate, ammonia, ammonium chloride, sodium chloride, sulphuric acid, sodium carbonate, sodium hydroxide and potassium hydroxide.

8. The method defined in any one of claims 1 to 6 wherein said electrolyte contains at least one alkaline compound.

9. The method defined in Claim 8 wherein said alkaline compound is sodium hydroxide.

10. The method defined in any one of the preceding claims wherein said pulverized rareearth mineral or concentrate has a particle size ranging between 100 and 400 mesh.

11. An apparatus for treating a rare-earth mineral or concentrate in a pulverized form, the apparatus comprising: a treatment vessel; support means disposed in said vessel for retaining a muddy mass formed by said mineral or concentrate mixed with an aqueous solution of an electrolyte; and means for inductively heating said mass to facilitate reduction of said rare-earth mineral or concentrate with said electrolyte.

12. The apparatus defined in Claim 11 wherein said means comprises coil means disposed to surround said mass and power supply for passing a high-frequency electric current of a frequency ranging between 50 Hz and 100 kHz through said coil means to inductively heat said mass.

1 3. The apparatus defined in Claim 11 wherein said means comprises a microwave tube for radiating said mass with a beam of microwaves of a frequency ranging between 300 MHz and 300 GHz to inductively heat said mass.

14. A method of treating a rare-earth mineral or concentrate in a pulverized form, the method being substantially as hereinbefore described with reference to Examples I to VIII and/or with reference to Figure 1 or Figure 2 of the accompanying diagrammatic drawings.

1 5. An apparatus for treating a rare-earth mineral or concentrate in a pulverized form, the apparatus being constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in Figure 1 or Figure 2 of the accompanying diagrammatic drawings.

1 6. A rare-earth mineral or concentrate which has been dissociated or reduced by a method defined in any one of Claims 1 to 10 or Claim 14, or in apparatus defined in any one of Claims 11 to 13 or Claim

15.