CA1077682A

CA1077682A - Methods of desulphurizing fluid materials

Info

Publication number: CA1077682A
Application number: CA297,627A
Authority: CA
Inventors: D. Alan R. Kay; William G. Wilson
Original assignee: MOLYCORP
Current assignee: MOLYCORP
Priority date: 1977-10-03
Filing date: 1978-02-23
Publication date: 1980-05-20
Also published as: DE2756201A1; FR2404676A2; DE2756201B2; IT7847733A0; GB1570776A; JPS5451976A; IT1155781B; DE2756201C3

Abstract

ABSTRACT OF THE DISCLOSURE
A method for desulphurizing fluid materials such as molten iron, steel, stack gases, synthetic natural gases, boiler gases, coal gasification and liquification products and the like is provided in which one of the groups rare earth fluorocarbonates, rare earth oxyfluorides and mixtures thereof, including bastnasite concentrates are reacted at low oxygen potential, with the sulphur to be removed to form one of the group consisting of rare earth sulphides, rare earth oxysul-phides and mixtures thereof. The low oxygen potential can be achieved by carrying out the reaction in the presence of vacuum, reducing gases, carbon, etc.

Description

1077~

Ihis invention relates to methods of desulphurizing fluid materials and particularly to a method of external de-sulphurizing fluids such as molten iron and steel, stack gases, coal gases, coal liquification products, and the like using rare earth fluorocarbonates or rare earth oxyfluorides in an essentially dry process.
According to the invention, there is provided a method of desulphurizing fluid materials comprising the steps of:
(a) reacting a member from the group consisting of rare earth fluorocarbonates and rare earth oxyfluorides at low oxygen potential with sulphur to be removed from the fluid material to form one of the groups consisting of rare earth sulphides and rare earth oxysulphides and mixtures thereof, and (b) removing said oxysulphides and sulphides.
As we have indicated above this method is adapted to the desulphurization of essentially any fluid material. We shall, however, discuss the method in connection with the two most pressing problems of desulphurization which industry presently faces, i.e. the desulphurization of molten iron and steel baths and the desulphurization of stack gases.
External desulphurization of molten iron and steel has been practiced for quite some time. It is a recognized, even necessary practice, in much of the iron and steel produced today. In current practices for desulphurization of iron and steel it is common to add magnesium metal, mag-coke, calcium oxide, calcium carbide or mixtures of calcium oxide and calcium carbide as the desulphurizing agent. Unfortunately, there are serious problems, as well as major cost items involved, in the use of all of these materials for desulphurization. Obviously, both CaO and CaC2 must be stored under dry conditions, since D ~

76~Z

CaO will hydrate and CaC2 will liberate acetylene on contact with moisture. Magnesium is, of course, highly incendiary and must be carefully stored and handled. There are also further problems associated with the disposal of spent desulphurization slags containing unreacted CaC2.
We have found that these storage, material handling and disposal problems are markedly reduced by using rare earth fluorocarbonates or oxyfluorides in a low oxygen content bath of molten iron or steel. The process is adapted to the desul-phurization of pig iron or steel where carbon monoxide, evolvedby the reaction, where carbon is used as a deoxidizer, is di-luted with an inert gas such is used as a deoxidizer, is diluted with an inert gas such as nitrogen or by vacuum degassing the melt in order to reduce the oxygen potential and thereby increase the efficiency of the reaction by reducing the likelihood of forming oxysulphides. The principle may also be used for de-sulphurizing stack gases from boilers, etc., as we shall discuss in more detail hereafter.
In desulphurizing molten iron and steel in the practice of this invention we preferably follow the steps of reacting rare earth oxyfluorides, rare earth fluorocarbonates and mixtures thereof including bastnasite concentrates in the presence of a deoxidizing agent with the sulphur to be removed to form one of the groups consisting of rare earth sulphide and rare earth oxysulphide and mixtures thereof.
Preferably, hot metal is treated in a ladle or trans-fer car with rare earth oxyfluorides or fluorocarbonates, by the simple addition and mixing of the rare earth oxides, by an injection technique in which the rare earth compounds are in-jected into the molten bath in a carrier gas such as argon ornitrogen or by the use of an "active lining" i.e., a rare earth

- 2 -compound lining in the vessel.
Similarly, the problem of desulphurizing gases is one of the oldest recognized problems in environmental chemistry.
It dates back to the beginning of the utilization of fossil fuels for home heating and for industrial power. Sulphur dioxide is the primary sulphur compound which has been recognized as the problem in environmental control. Sulphur dioxide is a constit-uent in many waste gases such as flue gases, off gases from various chemical manufacturing processes, stack gases from coal and oil burning furnaces and boilers, smelter gases, ore roaster gases, coke gases and the like. Contamination of the atmosphere by sulphur dioxide, whether present in dilute concentrations of 0.05 to 0.3 volume percent as in power plant flue gases or in higher amounts of up to 10% as in ore roaster gases, has been a public health and environmental problem for many years due to its effect on the respiratory system of animals and humans, its destructive effect on plant life and its corrosive attack on metals, fabrics and building materials.
The reduction or elimination of the sulphur dioxide from gases emitted into the atmosphere is an essential key to the successful use of the world's abundant fuels (coal and high sulphur oils). Thus many methods have been proposed for the de-sulphurization of gases. Most methods which have been proposed are technically feasible but their expense is in most cases ; completely prohibitive. The most commonly proposed methods in-volve scrubbing the gases with water and precipitation of the sulphur dioxide with lime as calcium sulphate or sulphite, de-pending upon the process involved. Unfortunately, the expense of scrubbing the vast amounts of gas involved and disposing of the resulting precipitate is extremely expensive.
The present invention lies in the discovery that rare ~ - 3 -. ?~ '``

' 107768Z

earth fluorocarbonates and rare earth oxyfluorides will, at lowoxygen potential, remove sulphur from gases and will in turn give up the sulphides at high oxygen potential so that they may be regenerated with the production of a gas high in sulphur oxides from which elemental sulfur, sulfuric acid and like useful prod~cts can be obtained.
rhe ability of ~astnasite - 3a - :
. . .

- . ..... - - ~ . :
.. : . . . . . . : - . .

1o776b?z concentrates (complex rare earth fluorocarbonates and rare earth oxyfluorides) to transform to oxysulphide and sulphide under conditions of low oxygen potential has been established thermodynamically and experimentally by applicants.
In all cases the chemical reactions are as follows:
I. Desulphurization at low oxygen potential, 2CeO2(s) = Ce2o3(s) + l/2 2(g~ ~-2 3(s) l/2 S2(g) = RE2O2S( )+l/2 O

RE O S + S = RE S +O
2 2 (s) 2(g) 2 3 2(g) II. Regeneration at high oxygen potential, 2 3(s) 3 2(g) = RE2O2S( )+ 2 SO2( ) 2 2 (s) / 2(g) RE2O3(s)+so2(g) e23(s) + l/2 2(g) = CeO2(s) In the case of liquid reactors, such as molten iron or steel, the product sulphide or oxysulphide will either be fixed in an 'active' lining or removed by flotation and absorbed into the slag cover and vessel lining depending upon the process used for introducing the rare earth oxide.
The products of desulphurization of carbon saturated iron with RE oxides is dependent on the partial pressure of CO, pCO, and the Henrian sulphur activity in the metal, hs~
Using cerium as the representative rare earth, the following standard free energy changes the equilibrium constants at 1500C for different desulphurization reactions can be calculated from thermodynamic data in the literature:

~o776s2 - - - ---REACTION ~ G cal. K1773 ...
2CeO2(s)+[c] = ce2o3(s) C (g) 66000-53,16T pCO = 3041 Ce2O3(s~+[C]+[s]lw/O Ce22s(s) C (g) 18220-26,43T pCO~hs=3395 Ce22S(S)+2[C]+2[S]lW/o=Ce2S3(5)+2CO(g) 66180-39~86T P / S

3/2 Ce2o2s(s)+3[c]+5/2[s]l = Ce S4 +3CO( 127050-72.lT p3CO/h 5/2=1.25 Ce22S(S)+2[C]+[S]lW/o = 2CeS(s)+ 2CO(120,860-61.0l p2CO/hs=.027 (s) / 2(g) CO(g)-28200-20.16T pCO/p O2=7.6x10 _ -31520~5.27T hS/pl/ S2=5.4x10 The thermodynamics of desulphurization with lanthan-ium oxide, La2O3, are similar although, in this case, LaO2 is unstable and there will be no conversion corresponding to CeO2~ Ce2O3.
In the case of desulphurization of gases, such as stack gases, assuming the following gas composition at 1000C:
Component Vol.

H2S 0.3 3 (200 grains/100 ft .) This equilibrium gas composition is represented by point A
on the diagram illustrated as Figure 6 where CO/CO2 = 2.5 and H2/H2S = 133. This point lies within the Ce2O2S phase field and at constant CO/CO2 desulphurization with Ce2O3 will take place up to point B. At point B, H2/H2S -104 and the 5.

-- . . . : . .
. .: :: . : : : : ,. .
''~ , . ' :: ' ' : . . : ' 1~77682 concentration of H S is 0.004 vol.% (~3 grains/100 ft. ).
Beyond this point, desulphurization is not possible.
The basic theory for this invention is supported by the standard free energies of rare earth compounds likely to be involved. Examples of these appear in Table I which follows:

w~ o ~ ~ u~ WU~ ~U ~n w w ~

~ ~ _ ~ ~ ~
~ ~ ~ ~ u~ ~ w w ~, ~
U~ ~ ~D
~u~ ~ ~ ~o ~o ~ ~ ~D' ~ O
~ . , O ~~ ~ W ~ ~ ~ ~
`I O W 1-- W ~ ~0 Ul ~ ~
O W (.rl C~ CO CO Ul N O X O
* ~ ~

~ 9 ~C ~
O o w o ~ ~ o o ~n *-*
WI~-~WI~ IWI
O O O O O O O O O --O
g g o g g og g g g 7 D
I+ I+ I+ I+ I+ I+ I+ I+ I+ ~ ~ ~) ~ 0- 10- ~ w W W 0~ ~

~ . . . ,_ ~ ~ ' ~h ' .
, ' 6.

: . - ., :

lv7768z The three phase equilibria at 1273K for the Ce-O-S System is set out in Table II as follows:

. . . . _ . _ ~ ~ ~ 2 2 2 2 2 W~ ~
_ _ æ

.q~ 2N ~æ

~ _ tn . .':
+
~ ~ .
(D
I I I 00 CO ~ h3 ~ ~-, a~ n ~ co Q ~ T ~

~ w o ~ ~ o 1~
. ,~ _ W

.; ~ n _ ~
,~,o~ X X X 1- o 11 ~1 1l !1 1l ~ '- W X o x x ~ x ~ ~ l --- ~ -:: -~07768Z

Typical calculations of energy changes involved inthe systems involved in this invention are as follows:

2(~ + Ce22s(s~ = Ce2S3( ) + O

Ce2S3(s) = 2ce(~) + 3/2 S2( ) ~G = 351160 - 76-0T cal-Ce2o2s(s) = 2Ce(Q) + 2(g) + 1/2 S2( ) : ~ G = 410730 - 65 OT cal Ce O S( ) + S2(g) = ce2s3(s) + 2(g) ~ 1273K aG = 73573 cal. and pO2/pS2 = 2.33 x 10 ';
. . . _. _ ~

23(s) + 1/2 S2(g) = Ce202S + 1/2 2( Ce23( ) = 2ce(~) + 3/202( ) ~ G = 425621 - 66-OT cal-10~ Ce22s(s) = 2Ce(~) + 2(g) + 1/2 S2(g) ~ G = 41n730 - 65-0T cal-O + 1/2 S = Ce202s(s) + 1/2 2(g) ~1273K ~G = 13618 cal. and (pO2,~pS2) / = 4.6 x 10 :

Ce22s(s) + 1/2 S2(g) = 2CeS(s) + 2( ) Ce22s(s) = 2ce(~) + 1/2 S2(g) + 2(g) ~ G = 410730 - 65-0T cal-2Ces(s) = 2Ce(~) + S2( ) : ~ G = 264960 - 49.8T cal.

~077682 Ce O S( ) + 1/2 S2( ) = 2CeS(s) 2(g) 1273K ~ G = 126420 cal. and po2/pl/ S2= 1.96 x 10 2 2_(s) + 5/2 S2(q) = 2ce3s4( ) + 3 0 2Ce3S4( ) = 6Ce(~) + 4S2( ) : a G = 966360 - 196.4T cal.

3ce2O2S(S) = 6Cet~)+ 3 2(g)+ 3/2 S2( ):L~G = 1232190 - 195.0T cal.

.

2 2 (s) / S2(g) 2Ce3S4(s)+ 3 2(g) ~G = 265830 + 1.4T caL
1273K ~ G = 267612 cal and p 02/P5/ S2 = 1.12 x 10 Ce3S4( ) = 3CeS(s) + 1/2 S2(g) ce3s4( ) = 3Ce(~) + 2S3( ) : ~ G = 48318 - 98.2T cal.

10 3CeS(s) = 3Ce(D) + 3/2 S2( ) : ~ G = 397,440 - 74-7T cal-. ~ . .

Ce3s4(s) = 3ces(s) + 1/2 S2( ) ~ G = 85740 - 23-5T cal-1273X ~G = 55824 cal pl/ S2 = 2.6 x 10 ~ ' 2 3(s) 2ce3s4( ) + 1/2 S2( 2Ce3S4( = 6Ce(~) + 4 S2( ) : ~ G = 966360 - 196.4T cal.

~077682 3ce2S3( ) = 6Ce(~) + 9/2 S2( ) : ~G = 1053480 - 228.0T cal.

.

2 3(s) 3 4(s) + 1/2 S2( ) ~ G = 87120 @ 1273K A G = 468893 cal. and p / S2 = 8.9 x 10 9 2(g) 2(g) 2 (g) . _ .

H2( ~ + 1/2 S2(g) = H2S( ) : ~G =-21580 + 11.80T cal.

@ 1273K ~G =-6559 and pH2S/(pH2.p / S2) = 13-4 pH2/pH2S log PS2 1 - 2.25 1o2 - 6.25 104 -10.25 6 -14.25 8 -18.25 -22.25 2 -26.25 (g) 2(g) 2 (g) H2( ) + 1/2 2( ) = H2O : ~ G = -58900 + 13.1T cal.

@ 1273K ~G =-42223 cal. and (pH2/pH2O) pl/202 = 5.6 x 10 8 10 .

t 077682 pH2/pH2O log PO2 10 4 - 6.5 ~2 -10.5 1 -14.5 2 ~18.5 104 -22.5 6 -26.5 8 -30.5 (g) / 2(g) CO2(g) CO(g) + 1/2 2( ) = C2(g) : ~ G = -67500 + 20.75T. cal.

1273K a G = -41085 and pC02/(pCO.pl/202) = 1.1 x 107 PCO/pCO2 log PO2 - 6.1 10-2 -10.1 ~ - ',,' 1 -14.1 2 -18.1 104 -20.1 6 -24.1 lo8 -30.1 In the foregoing general description of this invention, certain objects, purposes and advantages have been outlined.
Other objects, purposes and advantages of this invention will be apparent, however, from the following description and the accompanying drawings in which~

~` , . . .

Figure 1 is a stability diagram showing w/o sulphur as partial pressure of CO;
Figure 2a and 2b show Ce2S3 and Ce2O2S layers on a pellet of CeO2;
Figure 3 is a graph of the theoretical CeO2 required for removal of 0.01 w/o S/THM;
Figure 4 is a graph showing the volume of nitrogen required to produce a given partial pressure of CO;
Figure 5 is a graph showing the CeO2 requirements as a function of partial pressure of CO; and Figure 6 is a stability diagram for stack gas systems treated according to this invention.
Referring back to the discussion of free energy set out above, it is clear that these free energy changes may be used to determine the fields of stability of Ce2O3, Ce2O2S, : -Ce2S3, Ce3S4 and CeS in terms of the partial pressure of CO and the Henrian sulphur activity of the melt at 1500C. The resultant stability diagram is shown in Figure 1, the boundaries between the phase fields being given by the following relation-ships:
. --~
BOUNDARY EQUATION

Ce23 ~ Ce O S log pCO = log hS + 3.53 Ce O S - Ce S log pCO = log hS + 0.28 Ce2O2S - ce3s4 log pCO = 0.83 log hS + 0 03 Ce2O2S CeS log pCO = 0.5 log hS ~ 0 79 Ce2S3 - Ce3S4 log hS = ~ 1.47 _ log hS = ~ 2.45 12.

~o~6~Z

The phase fields in Figure 1 are also shown in terms of the Henrian activity of oxygen, ho~ and the approximate [w/o S]
in the iron melt using an activity coefficient fs~ 5.5 for graphite saturated conditions.
The coordinates of the points B, C, D and E on the diagram are given below:

. _ COORDINATES B C D E
~ ._ pCO atm.9.8 x 10-36.5 x 10-2 1.0 -1 1.0 hS 3.5 x 10 3.4 x 10-2 5.3 x 10 2.9 x 10-4 Approx. [w/o S] 6.2 x 10 3 9.6 x 10 2 5.3 x 10 5 -The points B and C represent simultaneous equilibria between the oxysulphide and two sulphides at 1500C. These univariant points are only a function of temperature. The points E and D represent the minimum sulphur contents or activities at which oxysulphide and Ce2S3 can be formed, respectively, at pCO =
1 atm. Thus, carbon saturated hot metal cannot be desulphurized by oxysulphide formation below hs~ 2.9 x 10 4 ([w/o S] ~ 5.3 x 10 5) at pCO = 1 atm. However, lower sulphur levels may be attained by reducing the partial pressure of CO.
The conversion of CeO2-~Ce2O3-~Ce2O2S-~Ce2S3 is illustrated in Figures 2a and 2b which show Ce2S3 and Ce2O2S
layers on a pellet of CeO2 (which first transformed to Ce2O3) ~-on immersion in graphite saturated iron at ~1600C, initially containing 0.10 w/o S, for 10 hours. The final sulphur content was ~ 0.03 w/o S and the experiment was carried out under argon, where pCOC~l atm.
The conversion of the oxide to oxysulphide and sulphide 13.

1077~8;~

is mass transfer controlled and, as in conventional external desulphurization with CaC2, vigorous stirring will be required for the simple addition process and circulation of hot metal may be required in the 'active' lining process.
From Eigure 1 it is apparent that the external desulphurization of graphite saturated iron is thermodynamic-ally possible using RE oxides. For example the diagram indicates that hot metal sulphur levels of ~0.5 ppm (point E) can be achieved by cerium oxide addition even at pCO = 1 atm.
Desulphurization in this case will take place through the transformation sequence CeO~Ce203-~Ce202S which required 2 moles of CeO2 to remove 1 gm. atom of sulphur. The efficiency of sulphur removal/lb. CeO2 added can, however, be greatly increased by the formation of sulphides. 1 mole CeO2 is required per g.
atom of sulphur for CeS formation and 2/3 moles CeO2 for Ce2S3 formation. The theoretical CeO2 requirements for the removal of 0.01 w/o S/THM for the various desulphurization products are given below and expressed graphically in Figure 3.

. ~
PRODUCT lb CeO /0.01 w/o S.THM ft3CO/lb CeO2 ft3CO/0.01 w/o S.THM
? _ _ -Ce2O2S 2.15 2.1 4.5 CeS 1.1 4.2 4.5 Ce3S4 0.8 4.2 3.4 Ce2S3 0.7 ~__ _ _ 3.0 The volume of carbon monoxide produced in ft CO/lb CeO2 and ft3CO/0.01 w/o S.THM are also given in the above table for each desulphurization product. For efficient desulphurization the partial pressure of carbon monoxide should be sufficiently low to avoid oxysulphide formation. For example, 1~ .

~07768Z

Figure 1 shows that oxysulphide will not form in a graphite saturated melt until [w/o S] C 0.01 when pCO ~0.1 atm. It will form however when [w/o S]~ 0.10 at pCO = 1 atm. Thus by reducing the pCO in the desulphurization process to 0.1 atm., hot metal can be desulphurized to 0.01 w/o S with a CeO2 addition of 0.72 lb/0.01 w/o S removed for each ton hot metal.
The choice of the method of reducing the partial pressure of carbon monoxide depends on economic and technical considerations. However, in an injection process calculations can be made for the volume of injection gas, say nitrogen, required to produce a given pCO.
Thus: -VN2 = Vc (l-pCO)/pCo where VCO is the scf of CO formed/lb CeO2 added VN is the scf of N2 required/lb CeO2 added and pCO is the desired partial pressure of CO in atm.
The results of these calculations for Ce2S3 formation are shown in Figure 4, which also shows the [w/o S] in equilibrium with Ce2S3(s) as a function of pCO. From this figure it is apparent that the volume of N2/lb CeO2 required to form Ce2S3 is excessive and if an injection process were used a balance would have to be struck between sulphide and oxysulphide formation. When, for example, hot metal is to desulphurize from 0.05 to 0.01 w/o S at pCO = 0.2 atm., ~16 scf N2/lb CeO2 would be required for Ce2S3 formation and the sulphur content would drop to 0.02 w/o. The remaining 0.01 w/o S would be 15.

1077~8~2 removed by oxysulphide formation. From Figure 3, lt can be seen that _2 lbs of CeO2/THM would be required for Ce2S3 formation and 2 lbs for Ce2O2S formation giving a total require-ment of 4 lbs CeO2/THM.
Calculations similar to the one above have been used to construct Figure 5 where the CeO2 requirements in lbs/THM
are shown as a function of pCO.
When large volumes of nitrogen are used in an injection process the heat carried away by the nitrogen, as sensible heat, is not large but the increased losses by radiation may be excessive. Injection rates with CaC2 for example are in the order of 0.1 scf N2/lb CaC2.
Vacuum processing is an alternative method of reducing the partial pressure of carbon monoxide. This is impractical in hot metal external desulphurization but not in steelmaking (see below).
Still another alternative approach to external desulphurization using rare earth oxides is the use of active linings which would involve the 'gunning' or flame-spraying of HM transfer car linings with rare earth oxides. Here the oxides would transform to oxysulphides during the transfer of hot metal from the blast furnace to the steelmaking plant, and the oxide would be regenerated by atmospheric oxidation when the car was emptied. It is estimated that for a 200 ton transfer car, conversion of a 2 mm layer (~ 0.080") of oxide to oxysulphide would reduce the sulphur content of the hot metal by ~ 0.02 w/o S. This process has the following advantages:
1) continuous regeneration of rare earth oxide by atmospheric oxidation when the car is empty, 2) reaction times would be in the order of hours, 16.

-, ~ : :
- : :

31 the absence of a sulphur rich desulphurization slag, and

4) the absence of suspended sulphides in the hot metal.
The mechanical integrity and the life of an "active" lining is, of course, critical and some pollution problems may be associated with oxide regeneration by atmospheric oxidation.
With regard to steelmaking applications, vacuum desulphurization could be carried out by an "active" lining in the ASEA-SKF process and circulation vacuum degassing processes.
As an example of desulphurization of a stack gas, assuming the following gas composition at 1000C.:
Component Vol.%

I~2S 0.3 3 (200 grains/100 ft .) This equilibrium gas composition is represented by point A on the diagram illustrated as Figure 1 where CO/CO2 = 2.5 and H2/H2S = 133. This point lies within the Ce2O2S phase field and at constant CO/CO2 desulphurization with Ce2O3 will take place up to point B. At point B, H2/H2S ~104 and the concentra-; tion of ~l2S is 0.004 vol.~ (~3 grains/100 ft3). Beyond this point, desulphurization is not possible.
In the foregoing specification~ we have set outcertain preferred practices and embodiments of our invention, however, it will be understood that this invention may be other- -~-wise embodied within the scope of the following claims.

-

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of desulphurizing fluid materials comprising the steps of:
(a) reacting a member from the group consisting of rare earth fluorocarbonates and rare earth oxyfluor-ides at low oxygen potential with sulphur to be removed from the fluid material to form one of the group consisting of rare earth sulphides and rare earth oxysulphides and mixtures thereof, and (b) removing said oxysulphides and sulphides.

2. The method of desulphurizing fluid materials as claimed in claim 1 wherein Bastnasite concentrates (complex rare earth fluorocarbonates and rare earth oxyfluorides) are reacted with sulphur.

3. The method of desulphurizing fluid materials as claimed in claim 1 wherein the oxygen potential is maintained at a low level by reducing the partial pressure of CO.

4. The method of claim 3 wherein the partial pressure of CO is maintained below about 0.1 atmosphere.

5. The method of desulphurizing fluid materials as claimed in claim 1 wherein at least one of the groups of rare earth fluorocarbonates and rare earth oxyfluorides is added to the fluid material by injecting the rare earth oxide into the fluid material in a stream of inert gas sufficient to dilute carbon monoxide formed in the reaction of a level below about 0.1 atmosphere.

6. The method of desulphurizing fluid material as claimed in claim 5 wherein the inert gas is nitrogen.

7. The method of desulphurizing fluid material as claimed in claim 1 wherein one of the groups of rare earth fluorocarbonates and rare earth oxyfluorides is added to said fluid material subject to a vacuum sufficient to maintain the partial pressure of carbon monoxide below about 0.1 atmosphere.

8. The method of desulphurizing fluid material as claimed in claim 1 wherein the rare earth sulphide and oxy-sulphide is removed from the fluid material, regenerated with oxygen and returned to the fluid system for further desulphuriza-tion.

9. A method of desulphurizing gases comprising the steps of:
(a) reacting a member from the group con-sisting of rare earth fluorocarbonates and rare earth oxyfluorides at low oxygen potential with sulphur to be removed to form one of the group consisting of rare earth sulphides and rare earth oxysulphides and mixtures thereof, and (b) removing said oxysulphides and sulphides.

10. The method of desulphurizing gases as claimed in claim 9 wherein Bastnasite concentrates (complex rare earth fluorocarbonates and rare earth oxyfluorides) are reacted with sulphur.

11. The method of desulphurizing gases as claimed in claim 9 wherein the oxygen potential is maintained at a low level by controlling the CO/CO2 or H2/H2O ratios.

12. The method of desulphurizing gases as claimed in claim 9 wherein the removed rare earth oxysulphides and sulphides are regenerated at high oxygen potential to rare earth oxides.