Method for treating shale

A method for producing a kerogen concentrate from oil shale comprises treating shale with an aqueous caustic treating solution to produce a shale product of substantially transformed mineral content, and then treating the shale product with an aqueous acid solution to produce a kerogen concentrate. The acid solution extracts minerals from the shale product to lower the ash content of the kerogen concentrate. A spent acid solution containing the extracted minerals can be treated to recover minerals therefrom.

FIELD OF THE INVENTION 
The invention relates generally to chemical treatments of oil shale rock to 
facilitate extraction of minerals contained in the shale ore. More 
specifically, it relates to a method for treating shale with an aqueous 
caustic solution to transform minerals present in the shale into 
extractable forms which are not extracted into the caustic solution. 
BACKGROUND OF THE INVENTION 
Oil shale rock represents a large hydrocarbon resource base from which 
energy can be recovered. The hydrocarbon constituents in shale rock are 
known as kerogen which is a mixture of hydrocarbons, in either dry or 
solidified form, produced by sedimentation of organic substances. The 
kerogen is contained within the interstices of the shale rock matrix and 
is generally about 15-25 weight percent of the rock. The kerogen is 
typically converted into shale oil by high temperature retorting of shale. 
Shale rock also contains other valuable inorganic mineral values such as 
uranium, copper, nickel, cobalt, molybdenum, vanadium, titanium, iron and 
aluminum. For example, western Colorado shale generally contains about 3 
to about 6 wt. percent aluminum. 
Because of the value of shale's kerogen and minerals, methods for 
extracting kerogen or the minerals are important. Thus, chemical treating 
methods other than retorting for concentrating the kerogen contained in 
oil shale have been disclosed. Chemical treatments of oil shale to recover 
mineral values contained in the shale have also been disclosed. 
For example, Hunter, U.S. Pat. No. 3,238,038 discloses a method for 
recovering a precious metals such as gold and silver from a bituminous 
shale ore by treating the shale with an aqueous alkaline solution to 
increase solubility of the precious metal in an aqueous acid solution. The 
insoluble residue from the alkaline digestion step is then separated and 
contacted with an aqueous acid solution, which must contain sulfate, 
nitrate, chloride and iron ions. A solution containing the precious metal 
is then separated. Hunter does not disclose a technique for concentrating 
the kerogen in shale nor a technique for recovering minerals other than 
precious metals. 
Huang, U.S. Pat. No. 4,069,296, discloses a method for recovering aluminum 
from raw or spent oil shale by contacting the shale with aqueous 
hydrochloric acid, removing the insoluble residues from the acid treating 
solution, and then precipitating hydrated aluminum hydroxide from the acid 
treating solution by contacting with an alkaline agent. 
Haas, U.S. Pat. No. 3,859,413 extracts some of the alumina from a 
previously retorted dawsonite-bearing oil shale. Dawsonite is a sodium 
aluminum carbonate mineral, NaAlCO.sub.3 (OH).sub.2, having aluminum 
concentrations greater than 4 weight percent. Haas employs a dilute 
alkaline leaching solution containing 5 to 25 grams solid caustic per 
liter, at temperatures of 5.degree. to 40.degree. C. for short leach 
periods up to 1 minute. 
Rust, et al., U.S. Pat. No. 4,130,627, discloses a method for recovering 
minerals from fly ash, not shale, by treating a fly ash water slurry with 
a sodium hydroxide solution at pH 11-14, recovering a solid residue, and 
then leaching the solid residue with hydrochloric or hydrofluoric acid to 
form dissolved chloride or fluoride salts of iron, aluminum, and other 
metals. The solution containing the dissolved salts is then electrolized 
to plate out at least iron and optionally one or more other metals, and to 
recover silicone dioxide by precipitation from the electrolysis solution. 
The electrolysis solution free of silicone dioxide is then treated to 
precipitate aluminum hydroxide by raising the pH of the electrolysis 
solution. 
Drinker, U.S. Pat. No. 4,026,360, discloses an in situ method for producing 
a shale oil from a subterranean oil shale deposit. The method comprises 
contacting the shale deposit with a hot aqueous alkaline solution to form 
clay-like materials in the deposit which can swell when subsequently 
contacted with water. Fresh water relatively free of electrolytes is then 
injected into the deposit to form flow barriers and reduce permeability of 
the shale deposit. The flow barriers then direct the flow of subsequently 
injected fluids to produce shale oil. 
Fahlstrom, U.S. Pat. No. 4,176,042, discloses a method for recovering 
kerogen from bituminous sedimentary rock by crushing and finally dividing 
the rock in a plurality of grinding stages to a sufficient fineness to 
free the major part of the kerogen present in the rock. The kerogen can 
than be separated from the rock by emulsification, flotation or 
density-separation processes. To enable the rock to be finely divided more 
readily, the rock at least prior to the final one of the grinding stages 
is subjected to a leaching treatment to weaken mechanical bonds between 
minerals contained in the sedimentary rock. The leaching treatment is 
performed at temperatures above 50.degree. C. with acid solutions, 
"although basic solutions may also be used". Fahlstrom discloses chemical 
treating only as an aid to a physical separation of kerogen by grinding of 
the shale rock. Moreover, acid and basic solutions are disclosed as 
equivalent for kerogen concentration, but acid solutions are preferred by 
Fahlstrom. 
International Patent Application No. WO82/03484, Meyers et al., assigned to 
TRW, Inc., published Oct. 14, 1982, and titled "Extraction and Upgrading 
of Fossil Fuels Using Fused Caustic and Acid Solutions" describes a 
two-step treating method for raw shale ore. The oil shale is first 
contacted with a fused alkali at a temperature within the range of 
250.degree.-400.degree. C. The solid residue obtained is then washed with 
a dilute aqueous acid solution to obtain a kerogen concentrate. In this 
method, the severity of the fused alkali treating conditions is such that 
no water is present in the treating solution nor is any water maintained 
within the shale being treated. In addition, there is no disclosure of 
mineral recovery carried out in conjunction with the kerogen 
concentration. 
There are also numerous disclosures involving treating shale which has been 
previously retorted, roasted, or pyrolyzed with acid or base solutions. 
Typical such disclosures are found in Van Nordstrum, U.S. Pat. No. 
3,389,975; Hite, U.S. Pat. No. 3,481,695; Paul et al., U.S. Pat. No. 
3,510,255; Van Nordstrum, U.S. Pat. No 3,516,787; Templeton, U.S. Pat. No. 
3,572,838; Ellington, U.S. Pat. No. 3,586,377; Hoss, U.S. Pat. No. 
3,859,413. For example, Hite, U.S. Pat. No. 3,481,695 discloses a process 
in which oil shale is mixed with sodium carbonate or bicarbonate salt, the 
resulting mixture is retorted to drive off the shale oil, and the solid 
residue is then leached with water or dilute acid or base to extract some 
of the aluminum values from the solid residue. 
Applicants are not, however, aware of any integrated method for 
concentrating kerogen contained in raw or spent shale in conjunction with 
recovering the mineral values contained within the shale. The disclosed 
methods also do not focus on obtaining a kerogen concentrate of reduced 
ash content. Therefore, one object of the invention is to obtain an 
improved kerogen concentrate of reduced mineral content as measured by its 
ash content. Another object is to recover minerals such as aluminum 
contained within the shale rock to improve the economics of the treating 
method. 
SUMMARY OF THE INVENTION 
The invention comprises a method for treating oil shale by digesting the 
shale with an aqueous caustic solution under conditions sufficient to 
transform minerals present in the shale to extractable form without 
substantial extraction of the minerals into the caustic treating solution 
to produce a shale product of transformed mineral content. The caustic 
digestion of the invention has the advantage of maximizing the eventual 
removal of minerals from the shale to produce a kerogen concentrate of low 
ash content. The kerogen concentrate can then be retorted in a much 
smaller retort because of the mineral removal. Moreover, the invention has 
the advantage of high mineral recovery to improve the economics of shale 
treating because the shale minerals are not substantially extracted into 
the concentrated aqueous caustic solution from which mineral removal is 
more costly due to the large volumes of solution. Not extracting minerals 
into the caustic treating solution is further advantageous because the 
minerals can interfere with regeneration of the caustic solution. Instead, 
the invention permits the minerals in the shale product to be extracted 
with a dilute acid solution from which mineral recovery is easier. For 
example, aluminum can be recovered in high yields with the invention from 
shales which previously were not susceptible to aluminum extraction. 
In one aspect the invention thus comprises contacting raw shale with an 
aqueous caustic treating solution under conditions sufficient to transform 
minerals present in the shale into acid extractable form without 
substantial extraction of the minerals into the aqueous caustic treating 
solution; separating a shale product having a substantially transformed 
mineral content; contacting the shale product with an aqueous acid 
solution to extract minerals from the shale product and produce a kerogen 
concentrate of reduced ash content; and recovering the kerogen 
concentrate. If desired, the mineral-containing acid solution is subjected 
to further separation techniques for minerals recovery, and the acid and 
caustic treating solutions can be regenerated if necessary.

DETAILED DESCRIPTION OF THE INVENTION 
This invention comprises a method for treating shale rock containing 
kerogen. The shale starting material can be raw shale which has been mined 
in a conventional manner. Raw shale from many different deposits can be 
treated according to the invention. Shale which has been previously 
beneficiated to upgrade kerogen content or treated to extract kerogen can 
also be used as the starting material. For example, spent shale from a 
retort or shale beneficiated in a flotation process which removes gangue 
material from the shale can be used. It is preferred, however, to use raw 
shale as the starting material. 
The invention broadly comprises digesting shale ore with an aqueous caustic 
treating solution under conditions which are sufficient to transform 
minerals present in the shale into extractable forms without substantial 
extraction of the minerals into the caustic treating solution to produce a 
shale product of substantially transformed mineral content. The shale 
product can then be treated to produce a kerogen concentrate of low ash 
content. 
A low ash content in the kerogen concentrate is highly desirable because 
the size of retort to process the concentrate is related to ash content. 
Decreases in ash content lower the retort size at significant cost 
savings. 
Applicants have found that the treating conditions in the caustic digestion 
determine ash content of the kerogen concentrate obtained from the shale 
product. This is so because the ash content of the kerogen concentrate 
depends on the amount of minerals left unextracted in the concentrate, and 
the amount of unextracted minerals in turn depends on the effectiveness of 
the treating conditions in the caustic digestion for transforming the 
minerals into extractable forms. In short, the greater the mineral 
extraction, the lower the ash content in the kerogen concentrate. 
The caustic treating conditions are controlled by maintaining water 
concentration during the caustic digestion within specified limits. The 
water concentration, which includes both water present in the caustic 
treating solution and water present in the shale being digested, 
determines the amount of minerals which are transformed into extractable 
forms. For example, sufficient water must be present to produce 
extractable cancrinite, a hydrated alumina-silicate, or other extractable 
minerals, from the unextractable alumina minerals present in shale. The 
method of the invention therefore maintains the water concentration above 
about 5%, preferably within about 5 to about 25%, although greater amounts 
can be used, by control of caustic concentration in the caustic treating 
solution, of digestion pressures and of digestion temperature. By such 
control of the water concentration, a kerogen concentrate with a reduced 
ash content can be produced with concomitant recovery of the extracted 
minerals. 
This significance of the water concentration is illustrated in Examples 
1-20 and FIG. 3, which are discussed below. Briefly, in these examples 
shale was treated with a 50% aqueous caustic treating solution in the 
caustic digestion, and the water loss during the digestion was measured. 
The kerogen concentrates with lower ash contents were seen in those 
examples where the water concentration, as measured by water lost during 
the digestion, was within about 10 to about 18%. 
As noted, one purpose of the caustic digestion is to substantially 
transform the minerals contained in the matrix of the shale rock to 
different extractable forms in the resulting shale product. Then, in a 
further aspect of the invention, treating of the shale product extracts 
the minerals to produce the kerogen concentrate of low ash content which 
can be upgraded directly in a retort. 
The subsequent treating is an acid digestion wherein the shale product 
having a substantially transformed mineral content obtained from the 
caustic digestion is treated with an aqueous acid solution. The acid 
solution extracts minerals in ionic form from the shale product into the 
acid treating solution. The residue separated from a spent acid treating 
solution containing the minerals is the kerogen concentrate which has a 
reduced ash content due to the mineral extraction. 
In a further aspect the spent acid treating solution which contains the 
minerals is processed to recover the minerals and to regenerate the acid 
solution. The mineral recovery and acid regeneration can be performed in 
conjunction with regeneration of the spent caustic treating solution. 
FIG. 1 illustrates the caustic then acid digestion aspect of the invention. 
Here, shale 1 is shown as feed to caustic digestion 2, and caustic 
treating solution 3 is fed into the caustic digestion where it contacts 
the shale. The minerals in the shale are transformed by the digestion into 
an extractable form, but the minerals are not substantially extracted into 
the caustic treating solution. 
The resulting shale product 5 having a transformed mineral content is 
separated from the spent caustic solution 4. The spent caustic solution is 
regenerated in caustic regeneration 10. Caustic 12 from the caustic 
regeneration is used to make additional caustic treating solution 3. 
The shale product 5 is fed to acid digestion 7 where it is contacted with 
dilute aqueous acid solution 6, and the minerals in the shale product are 
extracted into the acid treating solution. The kerogen concentrate 8 is 
separated from the mineral laden spent acid solution 9. The mineral laden 
acid solution is sent to mineral recovery and acid regeneration 11. Here 
minerals 14 are recovered and the acid treating solution 13 is 
regenerated. 
To prepare the aqueous caustic treating solutions of the invention, Group 1 
or Group 2 metal hydroxides such as sodium, lithium, potassium, or calcium 
hydroxide can be used. Other alkaline materials such as sodium sulfide, 
sodium tetrasulfide, sodium hydrosulfide, sodium carbonate, sodium 
bicarbonate, and sodium silicate can also be used as the caustic to 
prepare the caustic treating solution. However, sodium hydroxide is 
preferred because it is easier to subsequently regenerate sodium hydroxide 
solution for additional treatments of fresh shale than to regenerate other 
caustic solutions. Calcium hydroxide, for example, may entail operating 
problems in the regeneration due to the formation of calcium sulfate where 
sulfate ions are present. 
The concentration of caustic on a dry solids weight basis in the aqueous 
caustic treating solution is the amount which yields a treating solution 
containing at least about 5 weight % water, and preferably about 5 to 
about 25 weight % water. The preferred range was determined in Examples 
1-20 and FIG. 3, and additional tests by measuring water concentration in 
the caustic digestion, correlating water concentration to ash content, 
noting that within the range the ash content of the kerogen concentrate 
obtained is relatively the lowest and correlating water concentration to 
the caustic concentration. 
Less concentrated solutions of the caustic of about 10 to about 75 weight % 
caustic can be used with lower reagent costs. However, use of caustic 
treating solutions containing less than about 75 weight % caustic can 
require elevated pressure conditions in the caustic digestion, for 
example, a digestion pressure of about 50 psi to about 250 psi, although 
higher pressures can be used. The 50 to 250 psi range should be used where 
the caustic concentration is about 40 to about 60 weight %. 
For the preferred caustic, NaOH, the solid NaOH used is thus within the 
range of about 15 to about 24 molal, and more preferably within the range 
of about 20 to about 24 molal because the range yields a lower ash content 
in the kerogen concentrate. 
The caustic digestion treating time is about 2 to about 6 hours, although 
it can be longer. However, contacting times above 24 hours are probably 
unacceptable for economic reasons. 
The caustic digestion is performed at ambient pressure up to about 500 psi, 
preferably at ambient to about 50 psi. As noted, at caustic concentrations 
above 75 weight %, the digestion does not require high pressure and is 
thus performed at about ambient to about 50 psi. This lower pressure 
condition is preferred, along with high caustic concentrations, in the 
method of the invention to produce the kerogen concentrate of less than 
20% ash content. 
The digestion can also be performed under an inert atmosphere, instead of 
air, to prevent oxidation of the shale product, although this is not 
essential to the practice of the invention since oxidation does not occur 
to a substantial extent. 
The caustic digestion is performed at about 140.degree. to about 
200.degree. C. Below 140.degree. C. the mineral transformation reactions 
of the digestion are kinetic controlled and require excessive digestion 
times. At temperatures above 200.degree. C., essentially no water is 
present in the caustic solution which severely reduces the desired mineral 
transformations. It is preferred to perform the digestion at about 
160.degree. to about 180.degree. C., because over this range water vapor 
pressure is sufficient to maximize mineral transformations in the shale. 
At 160.degree. to 180.degree. C., the mineral transformation is 
equilibrium controlled, but the water concentration is at a level which 
ensures the transformations are high. 
The weight ratio of caustic in the treating solution to the shale is 
preferably about 0.75 to about 2.5, and was determined by noting that a 
20% ash content in the kerogen concentrate is a desired upper limit of 
ash. To stay below 20% ash, 0.75 is the minimum treating ratio of caustic 
to shale. The 0.75 weight ratio is also close to the amount of caustic 
which is stoichometrically necessary to transform silica present in the 
shale into cancrinite, which can subsequently be extracted. The upper 
limit on the caustic to shale weight ratio is preferably about 2.5 to 
permit treating of differing shale deposits, although greater ratios can 
be used. Examples 21-25 and Table III illustrate the weight ratio range. A 
more preferred weight range of the caustic to shale is about 1.0 to about 
1.5 as seen in results with western Colorado oil shale which showed no 
decrease in ash content of the kerogen concentrate at treating ratios 
outside this range. 
Thus the caustic digestion preferably comprises contacting oil shale with 
an aqueous caustic solution of sodium hydroxide, at a temperature in the 
range of from about 140.degree. C. to about 200.degree. C., with the ratio 
of the weight of caustic to the weight of oil shale being in the range of 
from about 0.75 to about 2.5, and with the caustic concentration being in 
the range of from about 15 to about 24 molal, and at a pressure of about 
ambient to about 50 psi. 
At the end of the caustic digestion, the shale product is separated from 
the spent caustic treating solution, and is cooled and water washed. The 
amount of wash can be that equal to the amount of spent caustic solution, 
and is preferably a minimal amount of water to keep the spent caustic 
solution as a concentrated solution. The shale product can be dried before 
further treatment, although the shale product is preferably treated in the 
acid digestion while it is still damp because higher mineral extraction 
from the damp shale product occurs. 
The shale product differs substantially from the original shale because the 
minerals in the shale have been substantially transformed. Table I shows 
the mineral transformations as determined by X-ray diffraction caused by a 
caustic digestion. The caustic digestions of a Colorado oil shale were 
performed as in the caustic digestions of Examples 1-20 using 50% on a dry 
solids weight basis aqueous NaOH treating solution at a temperature of 
about 165.degree.-175.degree. C. The shale product from two runs under 
pressure and one at atmospheric pressure were analyzed, and relative 
amounts of different minerals found in the starting shale were compared to 
those amounts in the separated shale products. 
TABLE I 
__________________________________________________________________________ 
MINERALS IN SHALE AND KEROGEN CONCENTRATES 
Composition.sup.a 
Quartz 
Dolomite 
Albite 
Analcime 
Calcite 
Cancrinite 
Tobermorite 
__________________________________________________________________________ 
Medium Shale 
Major 
Major 
Major 
Major 
Minor 
-- -- 
Autoclave Product.sup.c 
-- -- -- -- Major 
Major Major 
Autoclave Product.sup.c 
-- Minor 
-- -- Minor 
Major Intermediate 
Atmospheric Product.sup.c 
-- -- -- -- .sup. Major.sup.d 
-- -- 
__________________________________________________________________________ 
.sup.a Chemical compositions of the crystalline minerals are as follows: 
aQuartz, SiO.sub.2 ; Dolomite, CaMg(CO.sub.3).sub.2 ; Albite, NaAlSi.sub. 
O.sub.8 ; Analcime, NaAl(SiO.sub.3).sub.2 --H.sub.2 O; Calcite, CaCO.sub. 
; Cancrinite, (Na, Ca, Al).sub.8 (Si, Al).sub.12 O.sub.24 (CO.sub.3).sub. 
--3H.sub.2 O; Tobermorite, Ca.sub.5 (OH).sub.2 Si.sub.6 O.sub.16 
--4H.sub.2 O. 
.sup.b Pass14-mesh mediumrich shale. 
.sup.c Mediumrich shale caustictreated with 50% aqueous NaOH. 
.sup.d Plus several weak unidentified peaks. Under infrared, cancrinite 
minerals present. 
As the data show, the minerals present in the shale were substantially 
transformed into calcite, cancrinite and tobermorite, all of which are 
extractable by acid solutions and are not present in the original shale. 
Although total amounts of minerals were not measured, the data show 
substantially complete mineral transformations caused by caustic digestion 
under high caustic concentration with low pressure and under lower caustic 
concentration with higher pressure. The same substantial mineral 
transformations to cancrinite, tobermorite and calcite were seen in shale 
treated at autoclave pressure with both 25 and 35 weight % caustic 
solutions. 
That mineral transformations, not extractions, occur during the caustic 
digestion is further seen in Examples 26-29. In these, the spent caustic 
treating solutions and spent acid treating solutions of two shale 
treatments performed with the method of Examples 1-20 were analyzed by 
atomic absorption for mineral content. Only six out of 24 minerals had a 
lower concentration in the acid solution than in the caustic solution. 
The mineral transformations due to the caustic digestion is an advantage of 
the invention. All aluminates and aluminosilicates present in shale 
including feldspar, are converted into soluble forms. Thus, aluminum 
recovery can be made from all shales with the invention and is not 
restricted to Dawsonite-rich shales. 
In effect, the shale product separated from the caustic digestion is a 
silica gel upon which acid soluble minerals and kerogen are deposted. That 
the shale product's structure appears to be silica gel supporting kerogen 
and mineral as seen in infrared analysis of the product. All bands 
corresponding to silica gel (3400, 1625, 1085, 950, 800, and 460 cm-1) 
were seen in the IR spectrum plus only those associated with kerogen. 
Because of the shale product's structure, it can thus be used as an active 
adsorbent for removing acidic and neutral sulfur-containing compounds from 
liquids or gases such as a flue gas. 
The kerogen contained in the shale product showed some changes in elemental 
and IR analyses after the caustic digestion. It was expected that the 
severe hydrolysis conditions used in the digestion would hydrolyze the 
large number of ester and amide links in kerogen to produce a much 
different kerogen, but the changes observed were chiefly a 5-10% increase 
in aromatic carbon content, and some slight oxidation of sulfur present. 
After the caustic digestion, the washed shale product is then treated in 
the acid digestion. The purpose of the acid digestion is to extract the 
minerals which were converted into extractable form by the caustic 
digestion with an aqueous acid treating solution. The acid digestion 
destroys the crystalline nature of the shale product to produce an 
amorphous kerogen concentrate which is separated from the spent acid 
treating solution. The spent acid treating solution contains the extracted 
minerals which can be recovered. 
The aqueous acid solutions useful in the acid digestion include H.sub.2 
SO.sub.3, H.sub.2 SO.sub.4, HCl, HF, HNO.sub.3, glacial acetic acid and 
formic acid. It is preferred to use H.sub.2 SO.sub.3 because bisulfite ion 
does not precipitate metals, thereby preventing subsequent downstream 
regeneration problems. Hydroflouric acid in particular presents 
possibilities of metal salt precipitation. 
For any acid used, the concentration is at least about 0.5 molar. In using 
certain acids the concentration of the acid can affect the success of the 
acid digestion, as measured by ash content in the kerogen concentrate. Too 
low an acid concentration does not extract the extractable minerals; too 
high an acid concentration, on the other hand, can polymerize silicic acid 
present instead of extracting it. 
Thus, for certain acids, the acid treating solution should be maintained 
within a concentration range of about 0.5 molar up to about 2.0 molar. 
Acids which should be controlled in this manner are HCl, HNO.sub.3 and HF. 
For H.sub.2 SO.sub.3, glacial acetic and formic acids however, a 
concentration of about 0.5 molar up to saturated solutions can be used. 
H.sub.2 SO.sub.3 is further preferred for the acid digestion because it 
does not exhibit the problems of acid concentration. However, when using 
above about 1.5 molar H.sub.2 SO.sub.3, no additional mineral extraction 
occurred compared to weaker solutions. Thus, for H.sub.2 SO.sub.3 the 
preferred concentration range is about 0.5 to about 1.5 molar. 
The treating time of the acid digestion is preferably about 1 to about 3 
hours, and more preferably about 2 hours. The temperature of the acid 
digestion was not found to be critical. The acid digestion can be 
performed at a temperature of about ambient up to about the boiling point 
of the aqueous acid treating solution used, and lower temperatures in that 
range are preferred. 
For maximum extraction of mineral values from the shale product, vigorous 
stirring of a slurry of the shale product in the acid treating solution is 
preferred over a leach or percolation treatment. Vigorous stirring ensures 
that all extractable minerals and silica are swept into solution and not 
precipitated to remain in the kerogen concentrate. 
After the digestion is terminated, the final kerogen concentrate is 
separated and fresh water washed. The wash is combined with the spent acid 
treating solution. The amount of wash is not as important as in the 
caustic digestion work-up because of the low acid concentrations used. The 
separated kerogen concentrate is a mixture of silica gel and kerogen; the 
organic (non-ash) content of the concentrate can be upwards of 80%. The 
concentrate can be used directly in a retorting process of lower retorting 
capacity than that used to retort raw shale for conversion of the kerogen 
to hydrocarbon compounds. 
After separating the kerogen concentrate, further increases in the 
economics of the invention are yielded by recovery of the minerals 
contained in the spent caustic and acid treating solutions with a 
concomitant regeneration of the caustic and acid treating solutions FIG. 2 
shows a preferred embodiment of a regeneration and mineral recovery 
technique of the invention. 
Spent caustic solution 4 is shown as feed to silica gel production zone 20 
where excess CO.sub.2 21 is bubbled into the spent caustic solution. 
Silica gel 22 precipitates leaving sodium carbonate solution 23 which is 
sent to a caustic treating solution regeneration 24. 
The mineral laden spent acid solution 9 containing, for example, aluminum, 
iron, and calcium enters another silica gel production zone 30 where the 
solution is heated to about 50.degree.-60.degree. C., air is bubbled in 
and silica gel 22 precipitates. The resulting acid solution is fed into 
iron and aluminum recovery zone 31. Here, the pH of the solution is 
sequentially adjusted for selective precipitation of iron 32 and 
particularly aluminum 33 in a conventional manner. Other minerals wherre 
present in significant amounts are recovered in a similar manner at this 
point. The resulting solution 36 is then fed to carbonate production 37, 
where CO.sub.2 21 is bubbled into the solution, preferably under neutral 
to slightly basic pH, to precipitate calcium carbonate and magnesium 
carbonate 38. Neutral or basic pH is preferred to avoid use of large 
amounts of CO.sub.2. From the carbonate production zone 37, the resulting 
SO.sub.2 solution 38 is removed and acidified 39 to produce the acid 
treating solution which is returned to the acid digestion 41. 
The filtered calcium carbonate and magnesium carbonate 42 is fed to 
alkaline earth oxide production 43, where heat is supplied to produce 
mainly calcium oxide 25 since only small amounts of magnesium carbonate 
are present in feed 42. The calcium oxide reacts with Na.sub.2 CO.sub.3 23 
in caustic treating solution regeneration 24 to form sodium hydroxide and 
calcium carbonate solution 26. Calcium carbonate is precipitated and the 
sodium hydroxide solution is sent to caustic digestion 40. 
The following examples illustrate the method of the invention. 
EXAMPLES 1-20 
Examples 1-20 were run using a western Colorado oil shale. This shale is a 
lean shale having about 18.0 gallons of oil per ton (determined by 
modified Fischer assay). All runs started with pass-100 mesh shale. 
Mineral content of the lean shale included about 5.3% Al, 17.0% Si, 2.4% 
Fe, 3.5% K, 6.8% Ca, and 0.8% S. 
The caustic digestions proceeded by mixing the 100 mesh shale in a tared, 
stainless steel beaker with a measured amount of 50% on a dry solid weight 
basis aqueous NaOH solution. In all runs, the NaOH/shale weight ratio was 
1.5. The mixture was stirred until the shale was wet, about 5 minutes, the 
beaker was covered, and placed in a preheated oven. After a selected time, 
the beaker was cooled and weighed to determine water lost during the 
caustic digestion. The resulting shale product was then filtered and water 
washed. The time, temperature and water loss of each run are shown in 
Table 2. 
The damp shale products were passed through a No. 14 sieve and then treated 
with acid digestions with sulfurous acid. The acid concentration and the 
acid digestion procedure for each example are listed in Table 2. Seven 
digestion procedures were used: (1) the shale product was washed 
repeatedly with acid; (2) excess SO.sub.2 was bubbled through a water 
slurry of shale product, and the solids were filtered and washed with 1.0 
molar H.sub.2 SO.sub.3 and water; (3) as in (2) except the slurry was also 
stirred; (4) the shale product was slowly stirred with acid solution and 
the supernatant liquid was filtered off; (5) as in (2) except the shale 
product was treated in a percolation column; (6) as in (5) except the 
final H.sub.2 SO.sub.3 wash was omitted; and (7) damp shale product was 
rapidly stirred with excess 1.0 molar H.sub.2 SO.sub.3, filtered, again 
stirred with acid, and then fresh water washed. The resulting kerogen 
concentrate for each run was then filtered, air dried, and its ash content 
was measured. The ash contents are in Table 2. 
TABLE 2 
______________________________________ 
EFFECT OF CAUSTIC-TREATMENT 
ON KEROGEN QUALITY 
Caustic-Treatment 
Time, Temp., % H.sub.2 O 
Acid-Treat. 
Run hrs. .degree.C. 
off Conc. Procedure 
% Ash 
______________________________________ 
1 16.5 171 82.5 Sat. 5 45.4 
2 16.0 180 92.2 " 6 59.5 
3 18.0 175 93.1 1.0 M 1 60.2 
4 " " 90.6 1.0 M 1 54.3 
.sup. 5.sup.b 
" " 97.6 Sat. 2 73.6 
.sup. 6.sup.b 
" " 99.6 " 2 65.1 
.sup. 7.sup.b 
" " 98.2 " 2 69.4 
.sup. 8.sup.b 
" " 99.7 " 2 71.4 
.sup. 9.sup.b 
" " 99.6 " 2 71.5 
10.sup.c 
18.5 " 101.9 Sat.sup.c 
2 70.3 
11 16.0 170 98.8 " 2 70.1 
12 5.3 180 81.1 " 2 71.8 
13 5.1 185 81.8 " 3 68.5 
14 4.8 190 81.6 1.0 M 1 52.7 
15 16.0 161 86.7 " 3 44.5 
16 57.5 153 82.1 " 3 48.0 
17 30.0 160 87.5 " 4 63.9 
18 40.0 165 84.2 " 4 65.6 
19 40.0 " 84.0 " 7 26.9 
20 22.9 175 88.4 " 7 24.1 
______________________________________ 
.sup.a Weight loss expressed as percent of H.sub.2 O in caustic solution 
charged. 
.sup.b Shale product was washed with dilute NaOH solution instead of with 
H.sub.2 O. 
.sup.c Acetonewater mixture saturated with SO.sub.2 
FIG. 3 is a plot of percent water lost during the caustic digestion versus 
the percent ash in the kerogen concentrate. As seen in FIG. 3, when the 
percent water lost is between about 82 to 90%, the ash content is 
relatively the lowest. These results indicate that the desired ash content 
is obtainable by control of water concentration during the base digestion. 
Later examples will show that ash content is reducible to below 20% with 
the caustic-acid procedure used in Examples 1-20 . 
A comparison of Examples 17-18 to 19-20 also show the effect of vigorous 
stirring during the acid digestion. At about the same water loss 
condition, 17 and 18, poorly stirred, had much greater ash content than 19 
and 20, vigorously stirred. Vigorous stirring or contact during the acid 
digestion thus yields lower ash content. 
EXAMPLES 21-25 
Examples 21-25 demonstrate the effect of the caustic solution to shale 
weight ratio using the same shale in the above examples. The caustic 
digestions were performed as in Examples 1-20 but were performed at 
165.degree. C. for 17 hours. The acid digestions were by stirring well 
with 1.0M H.sub.2 SO.sub.3. Table 3 shows the weight ratio, and the % ash 
and % unextracted aluminum in the kerogen concentrate. As can be seen, at 
a weight ratio below 0.75, the ash and unextracted aluminum content 
remains high. 
TABLE III 
______________________________________ 
EFFECT OF CAUSTIC-TO-SHALE 
RATIO ON ASH CONTENT 
Run NaOH/Shale % Ash % Unextracted Al 
______________________________________ 
21 1.5 27 1.1 
22 1.0 31 3.1 
23 .75 31 3.4 
24 .5 68 34 
.sup. 25.sup.a 
.5 60 22 
______________________________________ 
.sup.a Higher severity run: 17 hrs. at 180.degree. C. 
EXAMPLES 26-29 
Examples 26-29 are atomic absorption analysis of the spent caustic and 
spent acid solutions, respectively, from two shale treatments, with 26 and 
27 of the acid, and 28 and 29 of the caustic. Examples 26 and 29 are from 
one shale treatment wherein the acid digestion used 1.0M H.sub.2 SO.sub.3, 
and 27 and 28 from the other wherein the digestion used 1.0N HCl. The 
caustic digestions were performed as in Examples 1-20 with 50% NaOH 
solution, 1.5 NaOH/shale ratios and at 165.degree. for 17 hours. The acid 
digestions were performed by stirring a slurry of the shale products with 
the acid. Table IV lists the parts per million parts concentration of 
twenty-four minerals, and the amounts listed for caustic and acid 
solutions are on an equal volume of spent treating solution basis. 
TABLE IV 
__________________________________________________________________________ 
Example 
Zn Mn Pb Cd Cr Fe V Co Cu Ni K Li 
__________________________________________________________________________ 
26 1.85 
3.41 
1.39 
0.067 
4.25 
230 0.181 
0.117 
3.06 
1.56 
5.1 
0.29 
27 2.99 
11.9 
3.11 
0.132 
78 700 0.55 
0.91 
1.91 
34.5 
11.2 
0.60 
28 1.06 
0.058 
0.52 
0.045 
0.075 
2.62 
0.77 
0.075 
0.30 
0.10 
88 0.55 
29 0.485 
0.039 
0.52 
0.045 
0.113 
1.25 
0.56 
0.075 
0.30 
0.10 
50 0.35 
__________________________________________________________________________ 
Example 
Ca Mo Mg Al Ti P Si B Ba Se Sb Sr 
__________________________________________________________________________ 
26 960 0.085 
400 285 12.8 
2.22 
700 6.2 
0.64 
1.06 
0.84 
5.6 
27 1260 0.347 
590 600 24.5 
4.33 
1120 
5.8 
10.9 
3.42 
1.99 
8.7 
28 0.67 0.68 
0.52 
16.8 
0.18 
4.85 
670 8.5 
0.045 
0.83 
0.45 
0.030 
29 1.26 0.227 
0.64 
57 0.18 
3.42 
480 8.8 
0.045 
0.83 
0.45 
0.030 
__________________________________________________________________________ 
As is seen in the table, all minerals but vanadium, potassium, lithium (one 
run), molybdenum (one run), silicon, and boron had higher concentrations 
in the acid solution than in the caustic solution. In particular, iron, 
aluminum, magnesium and calcium show much greater concentration in the 
spent acid. Approximate material balances showed that about 50% silica is 
extracted into the caustic along with about 86% of the associated 
potassium; iron, calcium and magnesium were not extracted into the 
caustic; and aluminum showed 5% (one run) and 25% (the other) extraction 
into the caustic. The results show no substantial extraction of minerals, 
particularly non-silicaceous minerals, into the caustic treating solution. 
EXAMPLES 30-35 
Examples 30-35, detailed in Table V and VI, show the preparation of a 
kerogen concentrate having less than 20% ash content with the method of 
the invention. The caustic digestions are in Table V, and all, unless 
noted, used 50% by weight aqueous NaOH solution, 1.5 NaOH/shale ratios, 
the lean shale of the earlier examples, 1 atmosphere pressure, and an air 
atmosphere. Also shown is the amount of damp shale product obtained. 
Table VI shows the acid digestions conditions used. Unless noted, all used 
a slurry treatment of the damp shale products in the acid with good 
stirring. The weight of kerogen concentrate, % yield, and % ash in the 
concentrate are also shown. 
TABLE V 
______________________________________ 
CAUSTIC-TREATMENT 
Time, Temp., Shale, 
Product, 
Run hrs. .degree.C. gr. gr. 
______________________________________ 
.sup. 30.sup.a 
6.0 175 15.0 40.2 
31 6.0 175 15.0 40.2 
32 23.0 175 15.0 36.9 
33 16.0 177 80.0 197.1 
34 16.0 177 80.0 197.1 
.sup. 35.sup.b 
-- 185 150.0 412.0 
______________________________________ 
.sup.a Caustic/shale ratio of 5.0. 
.sup.b -- means not measured. 
TABLE VI 
______________________________________ 
ACID TREATMENT 
Kerogen Concentrate 
Vol., Wt., % 
Run Acid Conc. cc gr Yield % Ash 
______________________________________ 
30 H.sub.2 SO.sub.3 
Sat'd. 500 .99 6.6 12.5 
31 HCl 1.0N &gt;200 1.10 9.1 18.7 
32.sup.a,b 
HCl 1.0N -- .67 4.5 15.4 
.sup. 33.sup.a 
HCl 1.0N -- 1.15 9.7 17.2 
34 HCl 1.0N -- 5.05 9.7 12.6 
35 H.sub.2 SO.sub.3 
1.0M 8000 10.5 7.0 18.3 
______________________________________ 
.sup.a Percolation treatment; volume not measured. 
.sup.b Shale product was unwashed. 
As seen in the % ash, all runs had organic content greater than 80%, and 
two with organic content greater than 85%. The method of the invention can 
successfully prepare a kerogen concentrate of less than 20% ash content. 
The above examples and specification are intended as merely illustrative; 
the scope of the invention is given by the claims.