CA1126483A - Recovering string-like agglomerates of chrysotile asbestos fibrils from crude asbestos - Google Patents

Abstract

Abstract of the Disclosure This application is directed to a method of recovering string-like agglomerates of unit, or near unit, chrysotile asbestos fibrils from crude asbestos. The method includes the steps of forming a stable mixture of individual asbestos fibrils by mixing the crude asbestos with an aqueous solution of an asbestos dispersing agent which is effective to disperse the fibres to form a stable gel structure. The concentration of the asbestos dispersing agent in the gel structure is rapidly diluted and the dispersion, during or immediately after the dilution step, is subjected to an orienting flow. The string-like agglomerates of unit, or near unit, fibrils formed are recovered.

Description

~Z6483 The present invention relates to processes for the openins of crude chrysotile asbestos and the recovery of string-like agglomerates of unit, or néar unit, chrysotile asbestos fibrils, and to the products obtained from these processes.
As used in this specification the expression "asbestos"
is taken to mean chrysotile asbestos unless a contrary intent-lon appears. Asbestos oocurs as bundles or seams of indivldual fibrils within a matrix of serpentine rock. The unit fibrils have a diameter of between about 100 and 500 angstoms and a length which is very large relative to the diameter of the fibrils. The bundles of asbestos fibrils, whether in the rock matrix or partially or fully liberated therefrom, are termed crude asbestos. The present inven~ion is concerned with the opening of crude asbestos to separate the fibrils from one another and to reaggregate the fibrils into string-like agglomerates.
Conventionally asbestos is liberated from its ore by crushing the ore and winnowing the crushed material such that the llberated asbestos is carrled away in air currents. The associated rock is sub~ected to further crushing and winnowlng before belng eventually discarded. This process has the dual disadvantage that the process may tend to break the crude fibre lnto short lengths without adequately separating the unit fibrils from one another and that the process creates environmental dust problems.
The value of asbestos depends largely upon the length of the fibrils and thelr degree of separation~ Fibres of relatively great length, e.g. 1/4" upwards, are very . valuable as they can be spun to produce asbestos yarns and like goods. Shorter grades of asbestos whieh are unsplnable but which have sufficient ibrous character to relnforce con-crete are less valuable than the spinable fibrils or fibril bundles but more valuable than dust like particles which are difficult to recover and are of very little, if any, value.
The conventional processes for the recovery of asbestos either leave in the rock, or liberate but do not effectively recover, quite a lot of dust like short asbestos crudes.
It has been proposed that crude asbestos could be opened by a wet process involving the separation of the fibrils

- 2 -6~L~33 usin~ an asb~stos dispersing agent such as a surfactant. This . process has been used to produce relatively long spinable fibres obtained from certain of the higher grades of asbestos.
The present process is designed to allow the production of asbestos aggregates useful in making asbestos/cement products and/or in spinning from grades of crude asbestos which would yield little or no long or intermediate length fibre by conventional processes.
The present invention consists in a ~ethod for producing agglomerates of unit, or near unit, fibrils of chrysotile asbestos from crude chrysotile asbestos, comprising the steps of:-(a) forming a stable gel structure of unit, or near unit, fibrils of asbestos by mixing the crude asbestos with an aqueous solution of an asbestos dispersing agent to - disperse the fibrils to form the stable gel structure;
(b) diluting the gel structure dispersion with water in a first dilution step to form a readily pourable dispersion without diluting the concentration of the asbestos dispersing agent to a level where it is ihsufficient to maintain the asbestos fibrils in a dispersed state; and (c) rapidly diluting the dispersio~ wlth water in a second dilution step sufficient to reduce the concentration of the asbestos dispersing agent to a level where lt is insufficient to maintain the dispersion s~ch that the dlspersion of the fibrils collapses and aggomerates of the fibrils are formed.
The present invention further consists in a method of - recovering string-l.i.ke agglomerates of unit, or near unit, chrysotile asbestos fibrils from crude asbestos comprising the steps of:-(a) forming a stable gel structure of individual asbestos fibrils by mixing the crude asbestos with an aqueous solution of an asbestos dispersing agent effective to disperse the fibres to form a stable gel structure:
(b) rapidly diluting the concentration of the asbestos dispersing agent in the gel structure:
(c) subjecting the dispersion, during or immediately after said dilution step, to an orienting flow, and - (d) recovering the string-like agglomerates of unit, _ 3 --~ 6~83 or near unit, asbestos fibrils formed in said orienting flow. In a still further aspect the present invention consists in string-like agglomerates chrysotile asbestos fibrils produced by the method according to this invention.
The present inventors have found that the formation of a stable gel state upon mixing the crude asbestos material with the solution of dispersing agent is facilitated by applying a shearing force to the asbestos to separate the fibrils from one another. In the simplest case this shearing force can be applied by merely stirring the mixture vigorously as with a spatula. In larger scale operations or with more firmly bonded crude asbestos bundles more complex procedures are required to bring about the desired shearing action.
It has been found that a colloid mill, or similar type of mill such as a paper pulp refiner is particularly suitable for the application of a suitable shearing force to the crude asbestos.
It appears that the application of more work to the crude asbestos than the minimum necessary to separate the fibrils from one another is not unduly deleterious to the fibrils. It therefore appears possible to ensure complete separation of the fibrils by passing the crude asbestos and the asbestos dispersing agent solution through a suitable mill of sufficient diameter and of a suitable gap width that more than the minimum shear force is applied to the mixture.
It appears that the dispersing agent solution has the effect of wetting the surfaces of individual asbestos fibrils on the surface of the crude asbestos but will not penetrate into the crude material until the previously wetted fibres are removed from its ~2~483 surfaces. This can be demonstrated by placing a sizeable lump of crude asbestos i~ a suitable solution of a colloidising agent.
Even after some hours the asbestos will only show wetting and loosening, i.e. opening of fibres on the surface of the lump if it is left stationery in the solution. If, however, the lump is subjected to an applied shearing force in the solution such as vigorous stirring or rubbing between the fingers it is found that the lump will disperse into a colloidal gel state very rapidly e.g. within five minutes. This explanation of the phenomenon observed by the present inventors is given by way of explan-~4a-~2~33 ation ar~ ic; no~ i o b~ take1l as ]i~ iN( ~)road scope of th~ present invention.
The asbestos dispersing a~ents u~e~l to bring about the dispersion of the asbestos may be ionic or nonionic in character or mixtures of the two types. They are character-ised in that they react with or are adsorbed on the surface of asbestos fibres and consequently facilitate the opening of the fibres under the influence of the mechanically applied shear forces and maintaln the fibres in stable dispersion.
Preferably the d~spersing agents are surfactants, and are selected from the classes of anionic, cationic, nonionic, and amphoteric surfactants. It has been found that ionic surfactants or mixtures containing them are particularly useful. The most preferred surfactants are of the anionic type and mixture of anionic and non-ionic types. Where mixtures of surfactants are used they may be added together in the processing or added in sequence when this is beneficial to either the fiberising, the subsequent coagulation, or t~le properties of the final product. In the latter case, for example, the mixture of surfactants may be chosen to facilltate the redispersion of the fi~res in making cementitious com-positions such as asbestos cement.
In the case of the preferred sufactants, some of the surfactant remains strongly adsorbed even after extensive dilution of the fiberising dispersion.
The concentration and conditions required for optimum fiberising vary according to both the nature of the surfactant and of the asbestos. Because of its effects on the surface charge of the asbestos, the pH of the solution influences the surfactant adsorption. Amphoteric types of surfactants may display either anionic or cationic character according to the pH of the system. Mixtures of surfactants of the same type, for example, anionic, can be beneficial in optimising the overall process, but may tend to complicate aspects of reagent recycle.
The surfactant or surfactants for our process may be selected from among the following groups of anionic sufactants: carboxylates, N-acylsarcosinates, alkanesulphon-ates, linear and branched alkylarylsulphonates, dialkyl sulphosuccinates, arylsulphonates, naphthalenesulphonates, ., ~

N-acyl-N-alkyl-laurates, 2-sulpoethyl esters of atty acid,, olefin sulphonates, alkyl sulpha-tes, sulphated natural oils, sulphated alkyl-phenol alkoxylates, and phosphate esters o~
alkanols and phenol and alkylphenol alkoxylates.
The carboxylates, sulphates, sulphonates, and phosphates may be in any of the derlvative forms known to those skilled in the art, as for example, the free acid, metal salts such as the magnesium and sodium salts, ammonium and substituted arnmonium salts, and esters. Typical substituted ammonium salts are those derived frorn mono-, di- and triethanolamine.
We prefer to use the sodium salts since they are readily avilable and generally are convenient to use because they have good water solubility.
The preferred anionic surfactants are those with long chain alkyl groups such as, for example, nonyl, decyl dodecyl, tridecyl, stearyl, cetyl, palmityl and myristyl.
Thus typical carboxylates that give good results with our process are sodium oleate and sodium laurate. Preferred N-acylsarcosinates are those with the acyl group selected from the group consisting of cocoyl, lauroyl, stearoyl and tall oil acyl.
Typical examples of suitable sulphates and sulphonates are ammonium lauryl sulphate, diethanolamine lauryl sulphate, sodium cetyl sulphate, dodecylbenzene-sulphonic acid, sodium dodecylbenzenesulphonate, triethanolamine dodecylbenezene sulphonate, tridecylbenzene-sulphonic acid, nonylnaphthalene-sulphonic acid, sodium butylnaphthalenesulphonate, sodium tetrahydronaphthalene-sulphonate, andcy~- olefin sulphonate.
The most preferred sulphonates are those derived from sulphosuccinic acid. They are conveniently used in the form of sodium salts of the esterlfied acids. Specific members of this group that we have found very useful are sodium dihexyl sulphosuccinate, sodium di- (isobutyl) sulphosuccinate, sodium dioctyl sulphosuccinate, disodium N-octadecylsulphos-uccinamate, tetrasodium N-(1,2-dicarbethoxyethyl)-N-octadecyl sulphosuccinamate, and the sodium sulphosuccinate esters of lauric mono- and di-ethanolamides or of ethoxylated lauryl or decyl alcohols.
Suitable phosphate esters include "Teric" 305 and 306 (alkyl ether phosphates, "Teric" is a Registered Trade Mark).
.....

~%6~83 Suitable cationic surfactants comprise the mono-, di-, and polyamines, amine oxides, alkoxylates of alkyl and alicyclic amines, 2-alkyl-1-(hydroxyethyl)-2-imidazolines, tetrakis-substituted ethylenediamines, amide-linked amines, and quaternary ammonium salts. The amine oxides are of the general formula.

Rl-N-O

wherein A ls hydrogen or hydroxyl, and R1 is selected from the ~roup consisting of cetyl, lauryl, myristyl, stearyl, coco, decyl, hexadecyl and octadecyl, The amide-linked amines are of the general formula (CH2) B-NH2 R2-CO-N \

~CH2) B-NH2 wherein R2-CO-N is derived from the group consisting of coconut, oleic, stearic, and tall oil acids, and B is 2 or 3.
The qllaternary ammonium salts are of the general formula ~0 +

4 I CH3 l X -wherein R3 and R4, which may be the same or different, are selected from the group consistiny of methyl, benzyl, tallow, - stearyl, cetyl, lauryl, and myristyl, dodecylphenyl, and stearyl, and X is bromide, chloride, methanesulphonate, or toluene-sulphonate.
The dialkylpyridinium salts comprise compounds of the general formula _ - :

R5-N ~ X

. . ~

wherein R5 is cetyl or lauryl, and X is as hereinbefore defined~
Cationic surfactants which we have found particularly useful .
include "Cetrimide" (cetyltrimethylammonium bromide), "Vantoc"
CL (lauryl-dimethyl benzylammonium chloride), "Monofluor" 71, and "Fixinol"(cetyl pyridinium bromide). "Cetrimide'1, "Vantoc", Monofluor" an~ "Fixinol" are Registered Trade Marks.
Suitable non-ionic surfactants for the process of our inven-tion may be selected from among fatty acid esteres, alkoxylated aliphatic alcohols and alkylphenols, alkoxylates fatty acids and fatty acid amides, and natural fats and oils.
Preferred aliphatic alcohols are selected from the group consisting of ethylene glycol, propylene glycol, glycerol, oleyl alcohol, lauryl alcohol, cetyl alcohol, stearyl alcohol, tridecyl alcohol, myristyl alcohol, trimethylnonyl alcohol, primary Cl2-Cl3 and C -C15 alcohols, secondary Cll-Cl5 alcohols, tallow, and sorbitan, and preferred alkylphenols are selected from the group consisting of nonylphenol, dodec~lphenol, octylphenol, isooctyl-phenol, and ~8-C12-alkyl-phenols. The preferred fatty acids are lauric acid, stearic acid, oleic acid, coco acid, capric acid and myristic acid.
The carboxylic esters are those prepared from carboxylic acids selected from the group consisting of lauric acid, stearic acid, oleic acid, coco acid, palmitic acid ricinoleic acid, tall oil, soybean oil, rosin, tallow, lard, cottonseed, safflower oil, and from alcohols selected from the group consisting of glycerol, sor~itan, ethylene glycol, diethylene glycol, propanediol and poly(oxyethylene).

,~ "~

~%6~83 It is preferred that the alkoxylates be ethoxylates which contain from 1 to 50 ethyleneoxy (-CH2CH2-0-) units per molecule.
The amlnes used to prepare the fatty acid amides are selected from the group consisting of ethanol-amine, diethanolamine, and isopropanolamine.
Non-ionic surfactants which have been found to be particularl~
useful include the glycol esters of oleic and lauric acid, ethoxylated nonyl phenols, polyethylene-glycol methacrylate, and "Teric" 9A8 (an ethoxylated aliphatic alcohol; "Teric" is a Registered Trade Mark).
Suitable amphoteric surfactants are substitued amino acids, such as N-coco-3-aminopropionic acid disodium N-laur~1-3-imino-dipropionate, N-carboxymethyl-N-cocoalkyl-N,N, dimethylammonium hydroxide, the sodium sàlb of N-hydroxyethyl-N-lauromido-P-alanine, and substituted 2-imidazolinium h~droxides.
Other chemical agents that may be used for the process of our invention include tannin, dextrin, alkanoic acids, and ligno-sulphates such as sodium lignin sulphonate and calcium ligno-sulphate. The latter are closely related to the sulphonates surfactants described hereinbefore, but are not usually considered "surfaciants" by those skilled in the art.

The dispersing agent is preferably added to the asbestos agglomerates as an aqueous solution containing from 0.8% to 10%
most preferably 5% of the dispersing agent. The solution is pre-erably added in an amount which will allow the asbestos to be thoroughly wetted and such that the surfactant is able to form layers on the surfaces of the indiviaual fibres as the crude _g_ 6~3 asbestos is opened up in order to ensure the stability of the gel structure formed. In preferred examples three parts by weight of the solution are added to one part by weight of asbestos con-taining material.
It will be realised that the processes according to the invention may be applied to the raw asbestos containing ore or to concentrates of such asbestos obtained e.g. by conventional crushing and winnowing procedures or by wet processing techniques.
The processes may also with advantage be applied to open up purified asbestos in order to increase the surace area of the asbestos as an alternative to conventional carding or fiberizing processes known to those skilled in the art.
Once a stable gel-like dispersion of the asbestos fibres has been obtained it is then necessary to treat the dispersion to recover the asbestos fibres in a useful form. It has been found by the present inventors that it is possible to recover the asbestos in the form of string-like agglomerates of ibrils.
The parameters which appear to be critical to the recovery of the aforementioned string-like agglomerates are that the gel like dispersion should be rapidly diluted without destruction of the physical involvement and that upon, or -9a-6~3 immediately after, dilution the diluted dispersion should be subjected to an orienting flow.
It is believed, although applicant do not wish to be bound by this explanation, that the effect of the rapid dilution of the dispersion is to allow the dispersing agent to diffuse away from the fibrils, while retàining the fibrils in sufficiently close proximity, that the fibre structure of the gel can collapse such that an agglomerate of fibrils is formed. If this formation of an agglomerate takes place in an orienting flow field then the new agglomerate will take 'the 'form o'~ an elonga`te string of'asbestos .
fibres in which each ~ibre is overlapped with, and entagled with or adhered to, the next adjacent fibres in the string.
The orientation of the flow ~ield may be brought about in the simplest form of the invention by stirring the water into which the gelled dispersion is poured. As the dilution takes place strings of fibrils form and can be readily recovered from the dilù'ed dispersion. In one sophisticated arrangement the gelled dispersion may be brought about by extruding the gel like dispersion under pressure through a suitable orifice into a dilution bath to simultaneously bring about the dilution and the oriented flow field.
It has been found that substantiall~ improved results are obtained in the present process if the dilutio~ of the dispersion is carried out in two stages. The first dilution is preferably to a fibre/liquid ratio of from 1 : 10 to 1 : 80 more preferable 1 : 15 to 1 : 50, however, as'long as the dilution is sufficient to render the dipsersion pourable improvea results are obtained provided that the dilution is not sufficient to reduce the con-centration of the dipsersing agent to a level wherein the dispersion ~10--6~33 is no longer maintained.
After the first dilution the dispersion may be readily tested to determine the degree of opening of the asbestos which has been achieved. If the diluted dispersion is centrifuged three layers are normally observed, the lowermost layer being comprised of particles ofthe rock matrix surrounding the asbestos; the inter-mediate layer comprises particles of asbestos which ahve not been reduces to unit, or near unit, fibrils; and the supernatant comprises a -lOa-,~ ~
t 64~33 dispersion of ~ibri~ The supernal~nt dispersion is particularly suitable ~or use in the formation of string-like agglomerates in the second dilution stage. The centrifugation technique may be useful in comrnercial production to enabling the recycling of the unopened asbestos particles.
The second dilution step must be carried out rapidly for the reasons discussed above. The degree of dilution is preferably sufficient to give a fibre/liquid ratio of from 1 : 100 to 1 : 400.
It is, however, sufficient to dilute the dispersion until agglomeration takes place. While it is desirable that the second dilution takes place into an orienting stream, however, this is not essential to this aspect of the present invention. It is possible to form agglomerates having useful properties merely by appropriately diluting the dispersion.
While the various aspects of this invention have been described with reference to chrysotile asbestos it is believed that this invention could have utility with crocidil-ite and amostie asbestos forms as well. The statement of the essential features of this invention are to be read to include the treatment of crocidilite and amosi~e asbestos forms within their scope.
Hereinafter described by way of example are experiments exemplifying the processes according to the present invention:-25 gram samples of chrysotile asbestos crudes obtained by the dry processing of asbestos ore were mixed with a predetermined quantity of 20% by volume aqueous solution of Matexil WA-OT (Registered Trade Mark) a surfactant having asbestos dispersing properties, in a Silverson blender.
The dispersions formed are detailed in Table I.
TABLE I_ ___ _ _ _ _ _ __ Test No. Reagent Conc. Reagent Addition Added Matexil/
1 5.0% 75 ml 8.75g 0.15 2 125 ml 6.25g 0.25

3 2.5% 75 ml 1.88g 0.075

4 _ 125 ml 3.13g 0.125 -.

6~3 lO gram samples of each of the gels listed in Table 1 were diluted separately in 100, 200, 500, 1000 and 2000 ml aliquots of water to produce the dispersion shown in Table II.
TABLE II
Final Conc. of Reagent (Nominal)*
Dilution Volume IA ~ C In_ 1~ ' Test No. ¦ 100 200 500 l 1000 ¦ 2000 ~ I 1 _I .
1 1 0.35 0.18 0.073 1 0.037 1 0.019 2 1 0.38 0.20 0.082 1 0.041 1 0.021 3 0.18 0.09 0.037 ~ 0.019 1 0.009 L _ _ ~ ~ 0.041 1 0,.0~1 1 0.010 1 *Note: Matexil OT as supplied consists of only 50% active reagent.
Concentrations are expressed in terms of the whole chemical add-ition.
It was found that when the dilution had be~n carried out a rough measure could be made of the average length of the string like agglomerations of fibrils by catching the strings on a spatula and measuring the length draped on each side of the spatula. Table III gives the results of a measurement of an average length on one side of the spatula.

~6~3 TABLE I I I
Approximate Fibre Lengths (mm) . h ~ . . . ~
. Test N~lution A B C D E .
/ Volume 100 200 500 1000 2000 / 1 --~ _ I 10 12- 15 .
2 _ _ Viscose 14 20 . Gelatin- , 3~j i~

-12a--- " -~.~

~26~83 1 The dilutions for tests lA, lB, 2A, 2B, 4A, 5A and 5B did not produce any apparent fibre. Rather the gel broke into lumps and dispersed to give a lumpy fluid. When these were blended using the Silverson mixer a smooth gelatinous fluid was obtained similar ', to that from text 2C. A11 of these fluids poured readily, and when introduced as a thin stream into swirling water long ge,latinous, filaments coagulated which condensed into fibre strings (not 4A).
Fibre strings of exceptional length could be produced consistently in this way ~30-35 mm).
Reference to Table II shows that ~he minimum concentration of Matexil above which the fibre could be maintained in a dispersed state was about 0.08%. Slow dilution by stirring in small incr-ements of water produced apparently poor fibre ( ~ 2mmj.
The fibre produced by tests lC - E, 2D - E, and 5C - E, was all very similar and of reasonable quality. That from tests 4B - E
was relatively poor. It would appear that the fi~erizing treatment in forming the gel of test 4 was inade~uate and the fibre was not opened enough to be N form extended flbre strings.
If the first stage dilution is carried out without due care localised areas of the dispersion may be caused to collapse due ~o the concentration of the asbestos dispersing agent being allowed to fall below the concentration necessary to maintain the disper-sion. It has been found that the agglomerates formed by such point agglomeration within the'dispersion are hard to redisper~e in the diluted solution of the asbestos dispersing agent. In order to avoid such undesirable point agglomeration it is preferred that the dilution is carried out with a very dilute solution of the asbestos dispersing agent rather than wlth pure water. Most pre-_~3-~, , ~6~

ferably the concentration of the asbestos dispersing agent in thedilutent solution is the minimum necessary to prevent point agg-lomeration of the asbestos fibrils in the dispersion. In the case of the dipsersing agent used in the foregoing examples, "Matexil WA ~T" a concentration of 0.2~ by weiyht is desirable in the dilutent solution.
E~AMPLE 5 25 grams of C 30 asbestos fibre were mixed with 125 ml of 5%
by weight solution of Matexil WA-OT in a Silverson blender to produce a dispersion having a.liguid to solid ration on a weight basis of 5 : l and a Matexil to fibre ratio. on a weight basis of 0.25 : 1.
10 grams of the dispersion were diluted into 1000 ml of water with moderate stirring to produce string-like agglomerates of fibrils. The diluted dispersion had a Matexil concentration of 0.04% by weight and a liquid to solid ratio on a weight basis of 600 : 1.
The string-like asglomerates of fibrils were found to have an apparent average length of 3 cm.

25 grams of C 30 asbestos fibre were mixed with 75 ml of a

5% by weight solution of Matexil WA-OT in a Silverson blender.
The dispersion so produced had a liquid to solid ratio on a weight basis of 3 : l and a Matexil to fibre ratio: on a weight basis of 0.15 : l.
100 mls of water were blendea into the dispersion with stirring and the diluted dispersion again passed through the S.ilverson blender. The diluted dispersion was found to have / , . .

8;3 a liquid to solid ratio- of 43 : 1 and a Matexil concentration of 0~35% by weight.
The diluted dispersion was poured into 6.5 1. of swirling water to produce string-like agglomerates of an apparent average length of 7 cm. This final mixture showed a liquid to solid ratio of 300 : 1 and a Matexil concentration of 0.05%.

400 grams of C 30 asbestos fibre were blended with 1000 ml of a 5% by weight solution of Mate~il WA-OT with a spatula. The mixture was passed through a "Van Gelder" plate mill set with the plates virtually touching to produce a stiff gel.
The gel was diluted stirring in 8 1. of an 0.2% by weight solution of Matexil. The diluted dispersion, which showed no point agglomeration during the dilution step, had a liquid to solid ratio on a weight basis of 23 : 1 and a Matexil concentration of 0.73% by weight.
The dilut~d dispersion was centrifuged at 3000 r.p.m. at a radius of 50 cm for 2 minutes to produce 5 1. of an opalescent supernatant liquid.

-14a-- ~26~
~ rhen ~h~ supernatant was poured in a t?lin strearn ir,to 40 l. of swirling water string-like agglomerates having an apparent average length of 10 cm were produced. This mixture had a Matexil concentration o~ 0. 08~o by weight.

A fibre concentrate (670 g) was added to a 5~ solution of "Matexil" WA-OT (2000 ml), preheated to 90C, and the mixture fiberised for a short time in a high speed macerator in several batches. 400 g of the mixture was removed and dumped with minimal stirring into 20 litres of water. The remaining recombined slurry was diluted with 13.5 litre of 0.25~
"Matexil" WA-OT and split into six identical parts, each of which was diluted further to agglomerate the fibres by adding to 20 litres of water in different ways. The coagulated products were each collected using a centrifuge.
Five of the coagulation stage experiments were carried out with different combinations of pumps linXed with various sprays and ~ets. In a sixth case the fibre dispersion was dumped rapidly into the dilution water with minimal stlrring.
All of the methods showed good flexural strength values for asbestos cement plaques, and similar Bauer-McNett sizing characteristics, and were better in both respects than the fibre concentrate used as raw material and the dumped gel.
The results are recorded below.
Pump (A) was of conventional impeller drive, while pump (B) was of peristaltic design to provide a gentle pulsating flow. Jet (1) produced a fan-shaped stream and jet (2) was a length of rubber tubing that could be directed to various parts of the diluted slurry. Spray (a) was a device giving a multiplicity of fine spray jets and spray (b) differed in that there were fewer fine spra~ ~ets and in that the jets were essentially parallel to one another.

~269~83 .. ~ _ ~ilution Method Flexural % FSU Bauer McNett Sizing Strength Fibre _ __ . kg/cm2 in +4 +14 -200 Plaques _ _ .
Pump (A), Jet ~l) 307 11.0 lO038.446.1 41.2 Pump (~), Spray (a) 297 11.0 9740.948.7 38.7 Pump tB), Spray (b) 266 ll.0 8844.049~ 38.1 Pump (B), Spray (a) 294 11.0 9543.751.7 36.9 Pump (B), Jet (2) 316 11.4 9938.246.3 43.0 ~d fibre dispersio 276 11.0 89 34.1 43.0 40.8 Dumped fibre gel 307 15.1 7314.433.8 55.8 Fibre Concentrate 286 17.4 57 1.4 4.1 72.0 _ . ._ . .. _ .. _ . _ It will be seen that the dumped fibre gel, i.e. the undiluted dispersion, performed much more poorly than any of the other samples which were given a two stage dilution. This example serves to show the advantages obtainable using the two stage dilution according to the present invention.

.
A pilot scale plant was constructed which followed the following flow diagram ~26~
~O D ~ L

CYCLONE
1, CYCLON~ (small) ~ REJECT ROCK
l PARTICLES
HUMPHREY'S SPIRAL
I

THICKENER
DISPERSING
~GENT DISC MILL FIBE~IZER
DILUTE DISPERSING
AGENT MIXING PUMP CIRCUIT (Primary Dilution) WATER _~ ~
DILUTING VESSELS

CYCLONES- , CYCLONE UNDER~LOW
tGrit and Fibre , Bundles) CENTRIFUGE OR
OTHER PRODUCT
COLLECTOR
From 2 tonnes of chrysotile ore from the Woodsreef Mine at .
Barraba, New South Wales, passed through this plant the following results were achieved:-Reject Rock 7 ~
Finished Product 10%
Cyclone Underflow 7æ ( 50% fibre bundles to be returned to process) Other waste products 9~
The average flexure strength 236 at 12l~% fibre 25 ~ FSU value approximately 70 It is to be noted that the above :re treated by the conventional dry process yields approximately 3% recoverable asbestos.
In the pilot plant referred to above the dilution vessels in which floculation took place consisted generally of two stirred tanks in series and a stream of dispersion is introduced into the swirling flow. The flows were ad~usted so that an overall dilution rate of 200 : 1 was achieved and a primary dilution rate of 15.1~

Claims (8)

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

1. A method of recovering string-like agglomerates of unit, or near unit, chrysotile asbestos fibrils from crude asbestos comprising the steps of:-(a) forming a stable gel structure of individual asbestos fibrils by mixing the crude asbestos with an aqueous solution of an asbestos dispersing agent effective to disperse the fibres to form a stable gel structure;
(b) rapidly diluting the concentration of the asbestos dispersing agent in the gel structure;
(c) subjecting the dispersion, during or immediately after said dilution step, to an orienting flow, and (d) recovering the string-like agglomerates of unit, or near unit, asbestos fibrils formed in said orienting flow.

2. A method as claimed in claim 1 in which the asbestos dispersing agent is selected from a group of anionic surfactants, non-ionic surfactants and mixtures thereof.

3. A method as claimed in claim 2 in which the anionic surfactant is selected from the group comprising carboxylates, N acylsarcosinates, alkanesulphonates, linear and branched alkylarylsulphonates, dialkyl sulphosuccinates, arylsulphonates, naphthalenesulphonates, N-acyl-N-alkyl-laurates, 2-sulphoethyl esters of fatty acids, olefin sulphonates, alkyl sulphates, sulphated natural oils, sulphated alkyl-phenol alkoxylates, and phosphate esters of alkanols and phenol and alkylphenol alkoxylates.

4. A method as claimed in claim 3 in which the anionic surfactants are sulphates and sulphonates selected from the group comprising ammonium lauryl sulphate, diethanoloamine lauryl sulphate, sodium cetyl sulphate, dodecylbenzenesulphonic acid, sodium dodecylbenzenesulphonate, triethanolamine dodecylbenzene sulphonate, tridecylbenzene-sulphonic acid, nonylnaphthalene-sulphonic acid, sodium butylnaphthalene-sulphonate, sodium tetrahydronaphthalene-sulphonate, and .alpha.-olefin sulphonate.

5. A method as claimed in claim 4 in which the sulphonate surfactants are derived from sulphosuccinic acid.

6. A method as claimed in claim 5 in which the sulphonated surfactants derived from sulphosuccinic acid are selected from the group comprising sodium dihexyl sulphosuccinate, sodium di-(isobutyl) sulphosuccinate,sodium dioctyl sulphosuccinate, disodium N-octadecylsulphosuccinamate, tetrasodium N-(1,2-dicarbethoxyethyl)-N- oetadecyl sulphosuccinamate, and the sodium sulphosuccinate esters of lauric mono- and di-ethanolamides or of ethoxylated lauryl or decyl alcohols.

7. A method as claimed in claim 1 in which a shearing force is applied to the mixture of the crude asbestos and the aqueous solution of the asbestos dispersing agent to facilitate the formation of the stable gel structure.

8. A method as claimed in claim 7 in which the shearing force is applied to the mixture by passing it thorugh a device selected from the group comprising colloid mills and paper pulp refiners.