AU606607B2 - The recycling of fluoride in coal refining - Google Patents

Description

lil -7 COMMQNWEALTH OF AUSTRALIA Patent Act 1952 SP RE C C 6T O SEC Q UC (Tno 7 C M P L E TE

(ORIGINAL)

Class Int. Class Application Number PH07489 Lodged 14 August 1986 Complete Specification Lodged

C

0 0O Accepted Published amendments made under Section 49 and is correct for printing.

Priority Related Art Name of Applicant Address of Applicant Actual Inventor Address for Service S COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANISATION Limestone Avenue, Campbell, Australian Capital Territory, Commonwealth of Australia S HORST ROTTENDORF F.B. RICE CO., Patent Attorneys, 28A Montague Street, BALMAIN. 2041.

Complete Specification for the invention entitled: The Recycling of Fluoride in Coal Refining The following statement is a full description of this invention including the best method of performing it known to us:- S2 BACKGROUND TO THE INVENTION CHEMICAL DEMINERALISATION WIHT DILUTE SOLUTIONS OF HYDROFLUORIC ACID It has been shown by earlier investigators that aqueous solutions of hydrofluoric acid can reduce the ash content of brown and bituminous coal dramatically. Whereas "ordinary" mineral acids such as sulphuric, hydrochloric, phosphoric or nitric acid show only attack on carbonates, and to some extent on phosphates and oxides, they leave other mineral matter like silicates and silicoaluminates with coal undissolved. In contrast, dilute solutic;s of hydrofluoric acid or its ammonium salt (ammonium bifluoride) dissolve complex silicates and aluminates with ease at ambient C temperature. However, the direct treatment of coal as mined c eC 15 gives quite often disappointing results when contacted with HF. The reason for this is the formation of insoluble c c silicofluorides of mainly Ca, K and Na which are sparingly soluble and cannot be removed from the coal by washing: Sc

C

Si02 4HF SiF 4 2H 2 0 c e SiF 4 2HF-4 H 2 SiF 6 .0 0 S(3) H 2 SiF 6 CaCO3 CaSiF 6

CO

2 H 0 c C c c ea 1 Thus, calcite on the coal will react with i o hydrofluoric acid to give not only calcium fluoride I C c o (insoluble), but also calcium silicofluoride. The same Sgoo. holds true with sodium and potassium or magnesium.

30 Ammonium silicofluoride, however, is soluble.

It is therefore a necessary pre-requisite for the successful application of reactions and to remove cations from coal prior to fluoride treatment. Then, in the presence of excess hydrofluoric acid, the initially formed silicon tetrafluoride, a gaseous substance at room 3 temperature, dissolves to form silicofluoric acid,

H

2 SiF 6 which is the compound known by its trivial name "fluoride" when added to the major water supplies in a number of Australian cities. H 2 SiF 6 being water-soluble, can thus be washed out from the coal.

Similarly, aluminium oxide found on coal reacts with HF to give soluble complexes, such as H 3 AlF 6 (see equation S4), which can also be washed out together wiht silica, thus leaving a highly demineralised coal: A2 03 12 2 H3AIF 6 3 In previous laboratory work, cations interfering with Sthe successful demineralisation of coal were easily solubilised by hot hydrochloric acid 9 It could now be shown that the pre-treatment of coal with cod sulphuric acid as outlined in Part 1 of this report is also quite effective for this purpose. If this pre-treatment is ignored, HF will not be efficient enough in demineralising coal to the desired low levels. A recent publication 31 has suggested using 10% aqueous NH 4

HF

2 in conjunction with an organic acid and HC1 for ash removal from coal.

I However, this might only apply if the silica-alumina i c content is a minor constituent of the mineral matter.

In order to meet more than the stoichiometric requirements of the reaction, an excess of HF has been Sused throughout this work, aqueous solutions of S HF (40% commercial grade diluted with water). This, however, does not mean that the acid could not be used in more dilute form or as ammonium bifluoride. It would be left to the experimenter to determine the optimum concentration, especially with regard to possible safety hazards. Solid ammonium bifluoride could have some advantage in handling or storage over the aqueous acid, commercially available. However, plastic materials 4must be used instead of glass or earthen-ware since HF attacks these materials.

The reaction between the mineral matter and HF is slightly exothermic and dissolution of silica/alumina is fast. In small-scale laboratory work plastic beakers and a magnetic rod (Teflon coated) can be used for stirring.

Filtration is best carried out on polycarbonate or polypropylene Buchner flasks and funnels, using hardened filter paper (Whatman No. 54). Other techniques which can be used are centrifugation of excess acid in plastic tubes, or, less sophisticated, washing by decantation.

After complete acid removal for recovery, the coal can now be used for low ash coke manufacture or ground very finely ac for use in coal slurry combustion. Although the use of c 15 ultraclean coal as a substitute for fuel oil looks cso promising, it would take a good deal of persuasion for 0 industry to initiate demineralising of coal by chemical 0°° o methods. Low-ash coke manufacture could be a good start, coo followed k large scale, brown coal demineralisation by chemical methods, and finally by de-ashing bituminous coals. The export of large shipments of demineralised °coal suspensions, which have been stabilised by additives Soo 0 in conventional oil tankers, should pose no major problem Ssince the behaviour of coal suspensions in simulated "o 25 shipping trials was well under study as witnessed by the author in Japan as far back as 1978.

on o THE RECYCING OF FLUORIDE AND BYPRODUCTS OF THE PROCESS o 0 In the previous section it was mentioned that SiF 4 "o oa" is a gas at room temperature, soluble in excess HF. On evaporation of the solution, or by passing through the solution a warm or hot carrier gas, SiF4 can be removed from a partially closed reaction vessel. Subsequent hydrolysis gives pure silica as a gel and more silicofluoric acid in pure form: 7i:, 5 3SiF 4 4H 2 0-4 Si(OH) 4 2H 2 SiF 6 This reaction, however, does not recycle any fluoride and it would be necessary to modify the chemical pathway accordingly to achieve this. One of the numerous possibilities is to neutralize the silicofluoric acid with ammonia, and add an excess in order to precipitate silica:

H

2 SiF 6 6NH 4 0H- 6NH 4 F 2H 2 0 Si(OH) 4 The ammonium fluoride is filtered from the silica and can be re-used for HF recovery in two ways: a) The ammonia acts as a recyclable intermediate and can 0" be liberated by lime addition to give insoluble calcium 0 15 fluoride and ammonia gas. The latter is liberated from the solution by heating: SC 0 2NH 4 F Ca(OH) 2 CaF 2 2NH 3 2H 2 0 The calcium fluoride thus formed, which is free from silica, can be converted to hydrofluoric acid, using known 00 0 ooo techniques: 0 00 00 0 0 ooo b) The ammonia acts as a vehicle for HF, ammonium bifluoride has in solution the demineralising power B o similar to HF according to equations and The 0 O" intermediate silicofluoride complex formed is converted back to fluoride by addition of excess ammonia (see equation and silica can be removed by filtration. The excess ammonia can be recoved by distillation or used for in situ generation of bifluoride according to:

NH

4 F HF-> NH 4

HF

2 I- 1 6 (9a) NH 3

(H

2 O) 2HF -N'NH 4 F.HF (H 2 0) This would mean that ammonium bifluoride is continuously generated by addition of hydrofluoric acid and ammonia.

However, ammonia fluoride is fortunately not very stable and disintegrates on heating of a solution to give ammonia and ammonium bifluoride according to 2NH 4

F--,NH

3

NH

4

HF

2 This would allow the ammonia to be recovered by distillation, and the ammonium bifluoride solution would then just undergo a concentrating treatment to the stage where it would regain its dissolving power for the minerals on coal.

Hydrofluoric acid distills at 111 C as a constant boiling azeotrope (43.2% HF). This would simplify its recovery from the filtrate, if waste heat was available, by first expelling SiF 4 (see above) and distillation of the azeotrope. If no pure silica was required, the filtrate, containing HF and H 2 SiF 6 from the coal treatment step, could be neutralized with ammonia, giving silica gel, contaminated with other compounds.

The chemistry of fluoride recycling with regard to cc 25 aluminium is not quite as straightforward, since aluminium fluoride reacts with ammonium ions to form the insoluble a ammonium-analog to cryolite: i bo0 (11) 3 NH 4 OH H 3 AlF 6

(NH

4 3 A1F 6 3 H 2 0 This precipitation of aluminium occurs already at low pH values and would allow a selective preparation of coal-derived aluminium from silica, which would precipitate mainly in the alkaline region. It is possible to convert the ammonium cryolite to the sodium compound, 7 by simple alkali treatment: (12) (NH 4 3 A1F 6 3 NaOH -2 Na 3 AlF 6 3 NH4 OH Cryolite is the electrolyte used for electrolysis of alumina. Cryolite can be regarded as the sodium salt of the hypothetical aluminofluoric acid. It is technically prepared by dissolving aluminium oxide in HF and treatment with soda: (13) A1203 12HF-' 2H 3 A1F 6 3H 2 0 (14) 2H 3 A1F 6 3Na 2 C03-- 2Na 3 AlF 6 3H20 3C0 2 t 15 If the recovery process was geared for pure silica (equation silicon tetrafluoride would be removed from the coal leaving behind ideally aluminofluoric acid in S c solution, from which cryolite would form according to equation (14).

RECYCLING OF FLUORIDE USING THE AMMONIUM BIFLUORIDE ROUTE The use of ammonium bifluoride as a vehicle for HF in i CC coal demineralisation requires the modified stoichiometry c acQof equation oon 25 SiO 2 4NH 4 F x HF-> SiF 4 2H 2 0 4NH 4

F

S0 SiF 4 2NH 4 F x HF H 2 SiF 6 2NH 4

F

S0 0 0*0 0 (16) SiO 2 6NH 4 F x HF H 2 SiF 6 2H20 6NH 4

F

The silicofluoric acid formed as intermediate is destroyed by ammonia addition (equation 6) and the silica removed by filtration. Excess ammonia is recovered by distillation and the remaining ammonium fluoride can either be converted by addition of hydrofluoric acid to I 8 give ammonium bifluoride or by further evaporation of the filtrate, whence decomposition to ammonia bifluoride occurs (equations 9 and Thus, fluoride recycling is much simplified and requires only a heating step after the removal of silica by filtration. The recovery of the demineralizing reagent and its regeneration using this route has the potential to substantially reduce the processing costs.

The present invention relates to an improvement in methods for demineralizing carbonaceous materials and more particularly to improved methods in which fluoride etchant solutions are recovered, regenerated and recycled.

It is widely known that derivatives of fluorine such as hydrofluoric acid, HF, or its salts, in particular its S 15 ammonium salts such as NH 4 where x 1, 2, 3 or 4, attack silicious material commonly practised in glass etching. This attack is not restricted to silica 0 C o c but can be observed on other oxides, such as alumina in particular, if the latter forms part of the molecular structure in silicates. Aqueous solutions containing fluorine compounds which are effective in dissolving silica and/or alumina, and/or other mineral oxides are ou. hereinafter called "aqueous fluoride etchant solutions".

Such silicates are present in coals, and hence can be o 25 removed partially or totally from coal by leaching with fluoride solutions under moderate conditions. Depending on the composition of ash forming constituents in coal a pre-treatment of this coal with acidic reagents such as o mineral acids might or might not be necessary. A previous patent (Australian Patent 472,900) describes the demineralization of brown coals down to low ash levels with aqueous solutions including the use of fluorides.

The latter are used as a final step in order to remove residual mineral matter from coal which cannot be removed by any other type of aqueous reagents.

1~ -9- Other processes for producing low ash coal involve dissolving mineral constituents in molten alkalis or in aqueous alkaline solutions at elevated temperatures and pressures and the removal of thereby formed aklali-stable minerals by subsequent acid leaching of the coal. The low-ash coal thus obtained may, in some circumstances, contain more silica or alumina than is desirable, and it may therefore be expedient to give it a final treatment with fluoride solutions.

Major problems which have prevented the large scale production of ultraclean coal and its derivative such as coke by the fluoride route have arisen from either the cost or the chemical properties of hydrofluoric acid and 'a fluorides. These problems which cover economic, S 15 environmental and health aspects, would largely disappear if a simple, efficient and economic method were available to recover, regenerate and recycle the fluorine compounds.

Fluorine recovery schemes previously proposed, although not after coal refining, usually require high temperature processing to release hydrogen fluoride gas, followed by its collection as an aqueous solution which a 0? may well be more concentrated and hence more corrosive than is actually required for re-use in the demineralizing process. This could cause operating problems and thus S 25 preclude its use in coal refining.

A major object of the present invention is to provide a practical means of achieving good recovery and re-use of 0 reagents under mild and easily manageable conditions after 0 coal refining so that the fluoride route could be used industrially to produce low-ash coal, and concurrently to recover the inorganic constituents either as useful byproducts or as innocuous wastes, The fluoride route could also be employed in the final ash removal from black coals which have undergone an alkali-acid purification step and for brown coal which had J I undergone an ion-exchange treatment step with mineral or other inorganic or organic acids.

The present invention consists in a process for demineralizing bituminous coal or other mineral containing carbonaceous material by leaching the carbonaceous material with an aqueous fluoride etchant solution, the improvement comprising reacting the spent leachant with a mi-feAsoluble hydroxide ion source to precipitate at least some of the minerals dissolved in the leachant, removing the precipitate therefrom and treating the resultant fluoride solution to regenerate an effective fluoride etchant solution.

The process to be described may be applied to the treatment of a wide range of coals, either in the as-mined co co Sc «15 condition or after preliminary cleaning by other methods.

c U The use of acidic heavy media as described in a co-pending COga Australian patent application No. PI1784 has been found c 0c very suitable for this purpose.

oc In its broadest form the present invention is 0" 20 applicable to spent aqueous fluoride leachants derived from the demineralization of coal or other carbonaceous go, materials. These leachants contain silicon, aluminium and o0 Qec C o other elements in solution as complex compounds or 0 otherwise. For instance silicon which is usually a major oo~0 25 inorganic component is present wholly or partially as o 00 fluorosilicic acid, H 2 SiF 6 or its salts. Likewise, aluminium is present wholly or partially as fluoroaluminic 0 og acid H 3 AlF 6 or its salts. The composition of the S leachant should be optimized so that it gives the best S 30 demineralizing effect and facilitates reagent recovery, regeneration and recycling. The invention includes the use of fluorides which can be seen as mixtures of ammonium fluorides, as stated earlier with hydrofluoric acid which demineralize coal on contact with the latter by forming the aforementioned complexes. This contact is preferably r 11 facilitated in vessels inert to fluoride and the time of contact may vary depending on the granular size of the coal. Dissolution of minerals is achieved accordingly within a matter of minutes on finely crushed coal or within a matter of hours on coarser material. The temperature of the solution may be kept ambient or can be elevated to just below boiling point of the solution.

According to the invention the spent leachant, after separation from the leached and largely demineralized coal, is treated with ammonia gas or ammonium hydroxide, preferably at or near ambient temperature to decompose the soluble inorganic compounds and thereby to precipitate silica, alumina, and other oxides present in hydrated or gel form.

I) 3[SiF 6 12 OH' 3 Si(OH) 4 18F' II) 3[AlF 6 9 OH' 3 Al(OH) 3 18F' Other forms of hydroxyl-ion supply which can be used for this reaction are found in hydroxides of Li, Na, K.

Rb, Cs, Ca, Mg, Ba, Sr or in form of organic bases or quaternary hydroxides such as tetramethyl ammonium hydroxide etc.

After separating the precipitated hydroxides from the remaining soluble fluoride, the latter is heated to its boiling.point or a temperature approaching boiling point, whereby, in the case of ammonia (as preferred base) it is driven off. On further concentration of the solution, the thereby present ammonium fluoride undergoes decomposition J according to 0 (III) 2 NH 4 F- NH 3

NH

4

F.HF

and more ammonia is generated which is collected in (pure) water for re-use. The remaining liquid contains most of the fluoride ions used in the original leaching step and can be regarded as a mixture of ammonium fluoride, ammonium bifluoride and hydrofluoric acid. It can be concentrated to its desired strength by distilling off 12 water, and both water and leachant can be used over and over again.

If a hydroxide other than ammonium hydroxide is used the hydroxide cations may be removed by chemical means or by ion exchange to regenerate the fluoride etchant solution.

The process may be presented in more detail by the flowsheet (Fig. 1) which illustrates one version of the fluoride recovery method in relation to the whole demineralization process. Variations of this process, involving alternative types of reactors, filters, centrifuges, evaporators, stills, condensers, absorbers and other equipment, fall within the scope of the invention.

Feed coal 1, suitably sized and optionally precleaned by physical methods or otherwise to remove part of the j mineral matter, is contacted in an extraction reactor 2 with an aqueous fluoride reagent 3 which acts as a i leachant for minerals in the coal. The extraction reactor may operate continuously or batchwise at ambient temperature or thereabouts, although any temperature between 0 antd 100 0 C is feasible. A residence time of 1-12 hours at 20 0 C has been found appropriate in laboratory batch tests, but the optimum conditions vary with coal type, particle sizing and reactor design and are not limited to these ranges. The reaction mixture is then separated in a filter or centrifuge 4, appropriately coated with non-mineral containing, and thus fluoride j resistant material, with washing to produce leached coal 30 as a solid product and a filtrate 6 plus washings. The leached coal 5 may be further purified in 7 by countercurrent washing with water, applied in conjunction with other reagents if required, or by other known methods, to produce a low-ash coal 8 which has been substantially freed of mineral matter and or residual i r 13 leaching reagents, especially fluorides.

The filtrate and washings from 4 and 7 enter a precipitation reactor 9 to which ammonia or ammonium hydroxide 10 is also admitted in quantities sufficient to deposit silicon, aluminium, and other elements in the form of hydroxides, hydrated oxides or their variants (eg.

silicic acids or silica gel). After a sufficient time in this reactor, which may operate continuously or batchwise, the reaction mixture comprises a slurry of solid particles in the presence of the co-product solution. This slurry passes to a filter or centrifuge 11 or equivalent device, preferably equipped with cake-washing facilities, where the mineral matter is separated from the filtrate containing soluble fluorides. The filtrate passes to a heated decomposer 12 operating either batchwise or continuously at a temperature between ambient and the boiling point of the solution. Under these conditions the equilibrium in the ammonium fluoride/hydrofluoric acid system in substantially shifted, ammonia is liberated, and the residual liquid phase can be regarded as a solution of ammonium fluoride, ammonium bifluoride and hydrofluoric acid. The vapour leaving 12 contains ammonia gas and steam which can be recovered in a condenser 13 as a solution of ammonium hydroxide 10, suitable for recycling to 9.

After removing substantially all displacable ammonia in 12, the liquid may be subjected to evaporation or fractional distillation 14 to concentrate the fluoride Ssolution to any desired concentration before recycling it as 3 to 2. The overhead product is high-purity water vapour which, upon condensing in 15, yields high-purity water for washing purposes in 7 and 11. If there is an unacceptably high level of specific contaminants such ag fluoride ions in this water, it may be passed through an ion-exchange column 16 containing anionic exchange 14 materials before re-use.

Before concentration the recycled fluoride solution is monitored for undesirable impurities. In case of presence of iron or other cationic materials which may have passed through the precipitation reaction, the solution can optionally be purified by precipitating these impurities with ammonium carbonate. This precipitate can be removed by filtration and the solution can them be concentrated, whereby excess ammonium carbonate will undergo decomposition through loss of carbon dioxide and finally on concentration through loss of ammonia giving the desired ammonium bifluoride solution.

The invention as outlined provides a simple, low-temperature, atmospheric-pressure method for avoiding contamination of air and water resources while effectively recovering and reqycling fluorides, ammonia and high-purity water. Only small losses of these materials in the cleaned coal and mineral byproduct need result, thus requiring only low expenditures for make-up chemicals and water. The mineral byproduct may have economic value or it may be disposed of an an innocuous landfill or minefill.

The results obtainable by application of the invention may be further understood from the following example: Example of fluoride recovery in coal refining.

64 g of moist (21% H20) Liddell coal (approx. 50 g dry basis) which had been previously up-graded in a float/sink separation step, using 1.5 gravity sulphuric acid at room temperature, was mixed in a plastic beaker with 75 cc hydrofluoric acid The mixture was left at room temperature for two hours with occasional stirring, using a plastic rod. After removal of the acid by vacuum filtration, using plastic filtration equipment, the filter cake was washed with 25 cc HP and then with 10 lots 15 of 50 cc pure water, giving a total filtrate of approximately 700 cc. The coal was allowed to dry at room temperature. Its ash content was reduced from an initial to The total amount of hydrofluoric acid used in this operation was 50cc of 40% w/w HF or 20 g HF (100%= 1 mole). The combined filtrates were neutralised with semi-concentrated aqueous ammonia liquor. After addition of 117 cc of ammonia, a pH value of 5 was reached (indicator paper), and a fine-crystalline precipitate began to form. The crystals were allowed to settle overnight and were removed by filtration to give 3.5 g dry material analysed as triammonium hexafluoro-aluminate

(NH

4 3 A1F 6 also known under its trivial name ammonium cryolite. Thereby, a selective recovery of aluminium from solubilised ash constituents of coal is possible.

The further addition of ammonia liquor (20cc) brought about a rapid change in pH value, and silica precipitated out as a gel. The precipitate was washed several times with water to remove adhering fluoride solution, and the combined filtrate was evaporated in a platinum dish until a solid crust formed on the surface of the solution. On cooling, a crystalline precipitate of ammonium fluoride formed, which was removed by filtration. The mother 25 liquors were concentrated further and the total crystalline product was heated for a short period to remove as much adhering water as possible. Obtained were 34.1 g crystals of ammonium fluoride of unknown composition. The fluoride content was analysed to be 47.3%, which constitutes a recovery of 16.1 g F in soluble form and 2 g F (in the ammonium cryolite) in insoluble form. The total recovery is therefore 18.1 g out of 19 g F or 95.2%.

In a blank experiment, hydrofluoric acid was neutralised with ammonia and evaporated as described 16 before. The crystals obtained (16.5g) had 44.7% F content, giving a somewhat lower recovery. A total recovery of all fluoride in soluble form was probably not achieved in this case due to losses from the open system which can be avoided, if a suitable closed system is available.

Other Examples 1. A coking coal from the Bulli seam was floated with sulphuric acid as under Example l(a) Part 1. The water-washed floats, while still wet with an ash content of 5.5% d.b. were suspended in a plastic beaker with 20% aqueous hydrogen fluoride and left 3 hours. The coal was washed by addition of water, filtered in a plastic Buchner funnel using hardened Whatman Filter 0. .paper. The coal was vacuum dried and its ash content found to be 0.36%.

S0,: When the same coal was ball-milled and then c 2treated as for Example 1(a) the fluoride treatment lowered the ash result to only 1.05%.

2. Coking coal from the Bulli seam (see Example 2 Go Part 1) having 5.9% ash value after initial CoO upgrading was treated with 20% HF solution and worked up as specified under Example The 25 coal was demineralised to an ash value of 0.36%.

3. A soft coking coal from the Hunter Valley (Liddell) with an ash yield of 3.6% after °o oCo upgrading was treated with aqueous HF at 0 9 o room temperature and worked up as previously described. The ash value obtained was 0.25%.

4. A coking coal from southern N.S.W. (Wongawilli) was upgraded by ball-milling and acid extraction to an ash value of When this coal was then digested with 20% aqueous HF at room temperature and the acid removed after 3 hours, 17 the coal had an ash content of 0.26%.

A steaming coal from N.S.W. (Ulan) with a particle size range of -250 75 microns had an ash value of 9.5% after sink-float treatment at SG 1.5 in either perchloroethylene (admixed with heavier liquid) or sulphuric acid. The dried product free from organic liquid or the acid-free wet coal was left with 20% HF at room temperature overnight, and then filtered and washed. The ash content of the coal was lowered to 0.25% in each case.

6. The coal from Example with a particle size range from -125 to +63 micron had an ash content of 8.5% after gravity separation. When treated 15 as under Example the ash content was found to be 0.25%.

It will be recognised by persons skilled in the art that numerous variations and modifications may be made to the invention as described above without departing from the spirit or scope of the invention as broadly described.

0 0 0o 0 S9 0 0 03 a o o o o 0 90 O 0 Q QOB 00 0010 o o 9 9 90 id O Q 99 30 @0 0 0 0 0

O

6 0

I

Claims (12)

1. A process for recycling fluoride following deminecalizing bituminous coal or other mineral containing carbonaceous material by leaching the carbonaceous material with an aqueous fluoride etchant solution, the improvement comprising reacting the spent leachant with a wast4 soluble hydroxide ion source to precipitate at least some of the minerals dissolved in the leachant, removing the precipitate therefrom and treating the resultant fluoride solution to regenerate an effective fluoride etchant solution. 00 OQ 08 0 0 08 *440 00 C 0ccc C 000 C o 0000 aCt Q0 a iCO 000 0 O 0 tO 0 O 0p 00 A 11j 18 C OC C C I C C CC C C C C C C C C C C C CC 00 o oc 0000 6 0 00 0 00 0 o *90400 0 I. In a process for demineralizing bituminous coal- or other mineral containing carbonaceous materia-1-by leaching the carbonaceous material with an aqueou; fluoride etchant solution, the improvement comprislng reacting the spent leachant with a waste solublre hydroxide ion source to precipitate at leastome of the minerals dissolved in the leachant, removing the precipitate therefrom and treating the resultant fluoride solution to regenerate an effective lidp atcan..nf~

2. The process according to claim 1 wherein the aqueous fluoride leachant is a solution of ammonium fluoride or bifluoride with or without hydrofluoric acid, and with or without other salts or organic materials.

3. The process according to claims 1 and 2, in which the precipitation reaction is conducted between ambient temperature and the boiling point of the solution with sufficient time to ensure that all or most of the dissolved minerals are deposited in a form that enables them to be readily removed by filtration or centrifugation.

4. The process according to claim 3 in which the precipitation reaction is conducted over a period of 0.2 to 5 hours.

The process according to claims 1 and 2 in which the recovered fluoride solution may be purified, if necessary, by precipitating out impurities with ammonium carbonate or by introduction of carbon dioxide into the basic fluoride solution and the separation of these impurities from the fluoride solution by filtration or centrifugation.

6. The process according to claims 1 and 2 in which the decomposition of the recovered fluoride solution to yield ammonia and water vapour is conducted at a temperature substantially above ambient.

7. A process according to claim 6 in which the temperature is between 5 0 0C and the boiling point of the 19 solution under atmospheric pressure.

8. The process according to claim 6 whereby water and ammonia are substantially removed above ambient temperature by applying a vacuum.

9. The process according to claims 1 and 2 in which the regenerated fluoride leachant is concentrated under normal pressure or in vacuo to the extent necessary to make it suitable for recycling as a coal demineralizing reagent.

The process according to claims 1 and 2 in which the recovery and recycling of reagents and wash water is conducted in such a way as to approximate a closed system with respect to these materials.

11. A clean coal product with a typical ash yield between 0.1 and 1% on a dry basis, but not restricted to these limits, made by a process defined by any preceding claim.

12. A mineral-bearing byproduct or products derived therefrom, made by extracting ash-forming mineral matter from coal by a process defined by any preceding claim. DATED this 13th day of August 1987 CC 0 COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANISATION Patent Attorneys for the *b Applicant; t S