CA1137290A - Ascorbic acid or erythorbic acid for prevention of formation of ferric compound - Google Patents
Ascorbic acid or erythorbic acid for prevention of formation of ferric compoundInfo
- Publication number
- CA1137290A CA1137290A CA000372741A CA372741A CA1137290A CA 1137290 A CA1137290 A CA 1137290A CA 000372741 A CA000372741 A CA 000372741A CA 372741 A CA372741 A CA 372741A CA 1137290 A CA1137290 A CA 1137290A
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- acid
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- formation
- erythorbic
- aqueous
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Abstract
ABSTRACT
The formation and subsequent precipitation of undesirable ferric compounds during the acid treatment of wells is substantially eliminated by incorporating in said treating acid an inhibiting amount of a monobasic alkanoic and/or alkenoic acid having at least four carbon atoms and bearing at least two alcoholic hydroxyl groups per molecule, and/or a soluble salt or .gamma.-lactone of said acid. E.g. ascorbic acid or erythorbic acid.
27,986-F
The formation and subsequent precipitation of undesirable ferric compounds during the acid treatment of wells is substantially eliminated by incorporating in said treating acid an inhibiting amount of a monobasic alkanoic and/or alkenoic acid having at least four carbon atoms and bearing at least two alcoholic hydroxyl groups per molecule, and/or a soluble salt or .gamma.-lactone of said acid. E.g. ascorbic acid or erythorbic acid.
27,986-F
Description
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METHOD FOR PREVENTING THE PRECIPITATION OF FERRIC
COMPOUNDS DURING THE ACID TREATMENT OF WELLS
This invention pertains to methods of sub-stantially eliminating problems arising from the presence of ferric ions which occur during the acidization of wells.
Various acids have long been used to increase the permeability of a subterranean formation surrounding a wellbore. In these treatments, the acid is normally pumped from the surface through iron pipe under pressure into the formation to dissolve various parts of the formations. Such acid treatments have been particularly effective in calcareous formations and have been effective in increasing the production of oil, gas, brine, or even water wells.
, During such acid treatments, the treatment acid dissolves iron scale in pipes and iron-containing minerals in the formation. The dissolved iron normally remains in solution until the acid is spent whereupon ferric hydroxide begins ~o precipitate causing a plugging up of the formation. Complete precipitation of ferric hydroxide is reached at a pH of about 3.2. Ferrous 27,986-F -1-. . . .. . .
.~ ; ~ ..
~3~
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METHOD FOR PREVENTING THE PRECIPITATION OF FERRIC
COMPOUNDS DURING THE ACID TREATMENT OF WELLS
This invention pertains to methods of sub-stantially eliminating problems arising from the presence of ferric ions which occur during the acidization of wells.
Various acids have long been used to increase the permeability of a subterranean formation surrounding a wellbore. In these treatments, the acid is normally pumped from the surface through iron pipe under pressure into the formation to dissolve various parts of the formations. Such acid treatments have been particularly effective in calcareous formations and have been effective in increasing the production of oil, gas, brine, or even water wells.
, During such acid treatments, the treatment acid dissolves iron scale in pipes and iron-containing minerals in the formation. The dissolved iron normally remains in solution until the acid is spent whereupon ferric hydroxide begins ~o precipitate causing a plugging up of the formation. Complete precipitation of ferric hydroxide is reached at a pH of about 3.2. Ferrous 27,986-F -1-. . . .. . .
.~ ; ~ ..
~3~
-2-hydroxide, being more soluble, does not begin to pre-cipitate until a pH of approximately 7.7 and is not generally a problem.
The deleterious effects of ferric hydroxide S in wells was recognized by Grebe in USP 2,175,081 as early as 1937. Grebe used a strong acid containing sulphurous acid to counter the precipitation problem.
N~nerous other procedures have been proposed for avoiding the ferric hydroxide problem. For example, USP 2,175,09S suggests including within the acidizing fluid a material such as lactic acid, ammonium acetate, glycine, glycollc acid, citric acid, or the like, which is capable of preventing the precipitation of iron or aluminum hydrates at normal precipitation pH values.
USP 2,335,689 suggests adding an iron sequestering agent, such as a polyhydric phenol into the injected acids. USP 3,142,335 suggests the use of a sequestering agent containing a mixture of ingredients that function as a pH bufer, such as citric acid or a citrate salt mixed with acetic or formic acids or their salts. USP
The deleterious effects of ferric hydroxide S in wells was recognized by Grebe in USP 2,175,081 as early as 1937. Grebe used a strong acid containing sulphurous acid to counter the precipitation problem.
N~nerous other procedures have been proposed for avoiding the ferric hydroxide problem. For example, USP 2,175,09S suggests including within the acidizing fluid a material such as lactic acid, ammonium acetate, glycine, glycollc acid, citric acid, or the like, which is capable of preventing the precipitation of iron or aluminum hydrates at normal precipitation pH values.
USP 2,335,689 suggests adding an iron sequestering agent, such as a polyhydric phenol into the injected acids. USP 3,142,335 suggests the use of a sequestering agent containing a mixture of ingredients that function as a pH bufer, such as citric acid or a citrate salt mixed with acetic or formic acids or their salts. USP
3,150,081 suggests using mixtures of hydroxyacetic and citric acids; the mixtures are alleged to be cheaper and more effective than the use of either acid alone.
The most common iron sequestering agents in commercial practice are citric acid, ethylenediamine tetraacetic acid (EDTA), nitrilotriacetic acid (NTA), acetic acid, lactic acid, and citric acid/acetic acid mixtures. Data on these sequestering agents is found in the paper by Smith et al. Paper No. SPE 2358, Society of Petroleum Engineers of AIME, (presented November 7-8, 1968).
27,986-F -2-. . , : ~ ~
. . ..
' . : ' !
'~'' ~ "
~L~.3~
The problem with most iron se~uestering agents is that they are not particularly effective at temperatures above about 125-lS0F. OI11Y citric acid and EDTA have shown any effectiveness at higher tempera-tures. And of these, EDTA is the only practical seques-tering agent because citric acid tends to form insoluble citrates during the course of the well treatment. Such citrates can block the well production almost as effec-tively as the ferric hydroxide.
The presence of ferric ions in the treatment acid solution is known to cause other serious problems as well. For example, USP 4,096,914 teaches that ferric iron reacts with asphaltenic oil to form insoluble iron-asphaltene compounds. These compounds are insoluble precipitates which likewise plug the formation channels and inhibit production of the well. The patent teaches that the problem can be solved by incorporating salicylic acid into the treatment acid.
Ferric ion corrosion can also be a problem.
Each mole of ferric ions react with base metal to form two moles of ferrous ions. Almost any oxidizing source readily converts the ferrous ions to ferric ions, and an undesirable cycle is established. Additives used to control problems associated with ferric ions in treat~
ment of wells have been called "iron stabilizersi' by practitioners in the field.
Accordingly, the state of the art is such that there is a substantial need to prevent the formation of ferric ions during acid treatment of wells and there is a particular need to prevent the formation and precipitation of ferric compounds as the acid is spent.
27,986 ~ -3-, ~.:3L3~
A method has now been discovered for preventing the undesirablé formation and precipltation of ferric com-pounds from spent acid solutions containing dissolved iron following the acidizin~ treatment of subterranean forma-tions surrounding wellbores.
The invention resides in a method for preventing the undesirable formation and precipitation of ferric com-pounds from a spent treatement acid containing dissolved iron following an acidizing treatment of subterranean for-mations surrounding a wellbore, said method comprising adding to said treatment acid prior to contact with the formation an amount of ascorbic acid and/or erythorbic acid, and/or a soluble salt of said acid, sufficient to prevent the formation and precipitation of ferric com-pounds from the treatment acid upon spending.
The invention also resides in an ungelled aque-ous treatment acid composition for acidizing subterranean formations comprising an aqueous acid at a pH less than about 1.5, and ascorbic acid and/or erythorbic acid, and/or a soluble salt of said acid, in an amount suffi-cient to inhibit the formation and precipitation of ferric compounds in said treatment acid during conditions of use and in the spent treatment acid.
The inhibitors used herein are a known class of organic compounds, each member of which is suitable for use herein so long as the selected compound(s) is compatible with the treatment acid or treatment acid system and is effective in inhibiting the production of ferric ions and/or is effective in inhibiting or prevent-ing the formation and precipitation of insoluble ferric compounds during conditions of use. Members of this 27,986-F -4-, .:
~ ~3~7~
known class of compounds include ascorbic acid, erythor-bic acid and other isomers of the general formula (HOCH2-CH(OH)-CH-C(OH)=C(OH)-C(O)-O);dehydroascorbic acid (HOCH2CH(OH)CHCH2(0H)CH2(0H)-C(O)O); 2,3 diketo-L-gluconic acid ~-lactone (HOCH2=CH(OH)CH-C(O)-C(O)-C(O)-O); and the corresponding acid-threonic acid (HOCH2CH(OH)C(OH)-COOH), and the like. In many instances, it is a procedural advantage to add such inhibitors to the treatment acid as the alkali metal or ammonium salts thereof because of the faster dissolution rate of the salts. Of course, when the salts are dissolved in the treatment acid, the salts are converted to the corresponding organic acid.
The inhibitors of the invention are added in an amount sufficient to substantially inhibit or prevent the 27,986-F -4a-,~, .~
' , 7~
formation of ferric ions and/or the formation and precipitation of insoluble ferric compounds during conditions of use. Normally, the inhibitors will be added in an amount of from 0.1 to 400 pounds of inhibitor per 1,000 gallons of treatment acid. Preferred limits normally are from 1 to 100 pounds per 1,000 gallons of treatment acid. The preferred inhibitors are ascorbic acid and erythorbic acid, with erythorbic acid being the most preferred.
The treatment acid can be any of the conven~
tional treating acids. Examples of such acids include hydrochloric acids, fluoboric acid, hydrofluoric acid, hydrochloric/ hydrofluoric acid mixtures, sulfamic acid, formic acid, acetic acid, hydroxyacetic acid, and the like~ Mixtures of acids are used in many instances and are also suitable for use herein. Preferred treating acids are hydrochloric acid, HCl/HF mixtures known as mud acid, and fluoboric acid. The most preferred treatment acid is hydrochloric acid at concentrations of from 5 to 15 weight percent and mud acid which is typically a mixture of about 12 percent hydrochloric acid and about 3 percent hydrofluoric acid. The aqueous treating acid used in the present invention can be substantially any which is capable of dissolving solid materials located within a subterranean earthen formation in a manner which increases the permeability of that formation and it can be either a solution or a homogeneous dispersion in which the aqueous water phase is an aqueous acid. The oil phase of such acid dispersions is usually a liquid hydrocarbon, such as light petroleum crude oil, toluene, etc. which is compatible with the formation.
27,986-F -5 In many instances, the dispersed acids ~or acid dispersions) have very desirable viscosity properties.
Viscosity of acid treating solutions can also be adjusted by the incorporation of various thickening agents (e.g.
polysaccharides, galactomannans, xanthan gums, etc.).
The use of the lnstant inhibitors and treatment acids thickened with xanthan gums is particularly effective due to the unigue nature of such formulations. Such formulations are the su~ject matter of U.S. Patent
The most common iron sequestering agents in commercial practice are citric acid, ethylenediamine tetraacetic acid (EDTA), nitrilotriacetic acid (NTA), acetic acid, lactic acid, and citric acid/acetic acid mixtures. Data on these sequestering agents is found in the paper by Smith et al. Paper No. SPE 2358, Society of Petroleum Engineers of AIME, (presented November 7-8, 1968).
27,986-F -2-. . , : ~ ~
. . ..
' . : ' !
'~'' ~ "
~L~.3~
The problem with most iron se~uestering agents is that they are not particularly effective at temperatures above about 125-lS0F. OI11Y citric acid and EDTA have shown any effectiveness at higher tempera-tures. And of these, EDTA is the only practical seques-tering agent because citric acid tends to form insoluble citrates during the course of the well treatment. Such citrates can block the well production almost as effec-tively as the ferric hydroxide.
The presence of ferric ions in the treatment acid solution is known to cause other serious problems as well. For example, USP 4,096,914 teaches that ferric iron reacts with asphaltenic oil to form insoluble iron-asphaltene compounds. These compounds are insoluble precipitates which likewise plug the formation channels and inhibit production of the well. The patent teaches that the problem can be solved by incorporating salicylic acid into the treatment acid.
Ferric ion corrosion can also be a problem.
Each mole of ferric ions react with base metal to form two moles of ferrous ions. Almost any oxidizing source readily converts the ferrous ions to ferric ions, and an undesirable cycle is established. Additives used to control problems associated with ferric ions in treat~
ment of wells have been called "iron stabilizersi' by practitioners in the field.
Accordingly, the state of the art is such that there is a substantial need to prevent the formation of ferric ions during acid treatment of wells and there is a particular need to prevent the formation and precipitation of ferric compounds as the acid is spent.
27,986 ~ -3-, ~.:3L3~
A method has now been discovered for preventing the undesirablé formation and precipltation of ferric com-pounds from spent acid solutions containing dissolved iron following the acidizin~ treatment of subterranean forma-tions surrounding wellbores.
The invention resides in a method for preventing the undesirable formation and precipitation of ferric com-pounds from a spent treatement acid containing dissolved iron following an acidizing treatment of subterranean for-mations surrounding a wellbore, said method comprising adding to said treatment acid prior to contact with the formation an amount of ascorbic acid and/or erythorbic acid, and/or a soluble salt of said acid, sufficient to prevent the formation and precipitation of ferric com-pounds from the treatment acid upon spending.
The invention also resides in an ungelled aque-ous treatment acid composition for acidizing subterranean formations comprising an aqueous acid at a pH less than about 1.5, and ascorbic acid and/or erythorbic acid, and/or a soluble salt of said acid, in an amount suffi-cient to inhibit the formation and precipitation of ferric compounds in said treatment acid during conditions of use and in the spent treatment acid.
The inhibitors used herein are a known class of organic compounds, each member of which is suitable for use herein so long as the selected compound(s) is compatible with the treatment acid or treatment acid system and is effective in inhibiting the production of ferric ions and/or is effective in inhibiting or prevent-ing the formation and precipitation of insoluble ferric compounds during conditions of use. Members of this 27,986-F -4-, .:
~ ~3~7~
known class of compounds include ascorbic acid, erythor-bic acid and other isomers of the general formula (HOCH2-CH(OH)-CH-C(OH)=C(OH)-C(O)-O);dehydroascorbic acid (HOCH2CH(OH)CHCH2(0H)CH2(0H)-C(O)O); 2,3 diketo-L-gluconic acid ~-lactone (HOCH2=CH(OH)CH-C(O)-C(O)-C(O)-O); and the corresponding acid-threonic acid (HOCH2CH(OH)C(OH)-COOH), and the like. In many instances, it is a procedural advantage to add such inhibitors to the treatment acid as the alkali metal or ammonium salts thereof because of the faster dissolution rate of the salts. Of course, when the salts are dissolved in the treatment acid, the salts are converted to the corresponding organic acid.
The inhibitors of the invention are added in an amount sufficient to substantially inhibit or prevent the 27,986-F -4a-,~, .~
' , 7~
formation of ferric ions and/or the formation and precipitation of insoluble ferric compounds during conditions of use. Normally, the inhibitors will be added in an amount of from 0.1 to 400 pounds of inhibitor per 1,000 gallons of treatment acid. Preferred limits normally are from 1 to 100 pounds per 1,000 gallons of treatment acid. The preferred inhibitors are ascorbic acid and erythorbic acid, with erythorbic acid being the most preferred.
The treatment acid can be any of the conven~
tional treating acids. Examples of such acids include hydrochloric acids, fluoboric acid, hydrofluoric acid, hydrochloric/ hydrofluoric acid mixtures, sulfamic acid, formic acid, acetic acid, hydroxyacetic acid, and the like~ Mixtures of acids are used in many instances and are also suitable for use herein. Preferred treating acids are hydrochloric acid, HCl/HF mixtures known as mud acid, and fluoboric acid. The most preferred treatment acid is hydrochloric acid at concentrations of from 5 to 15 weight percent and mud acid which is typically a mixture of about 12 percent hydrochloric acid and about 3 percent hydrofluoric acid. The aqueous treating acid used in the present invention can be substantially any which is capable of dissolving solid materials located within a subterranean earthen formation in a manner which increases the permeability of that formation and it can be either a solution or a homogeneous dispersion in which the aqueous water phase is an aqueous acid. The oil phase of such acid dispersions is usually a liquid hydrocarbon, such as light petroleum crude oil, toluene, etc. which is compatible with the formation.
27,986-F -5 In many instances, the dispersed acids ~or acid dispersions) have very desirable viscosity properties.
Viscosity of acid treating solutions can also be adjusted by the incorporation of various thickening agents (e.g.
polysaccharides, galactomannans, xanthan gums, etc.).
The use of the lnstant inhibitors and treatment acids thickened with xanthan gums is particularly effective due to the unigue nature of such formulations. Such formulations are the su~ject matter of U.S. Patent
4,317,735 (C. W. Crowe) which issued March 2, 1382.-Other conventional additives can be included in the instant formulations as desired. Acid corrosion lnhibitors are typically included in treatment acids and are beneficial in the instant method as well. Such acid corrosion inhibitors are known class of compounds and include, for example, acetylenic alcohols and nitrogen-based corrosion inhi~itors.
In the practice of the invention, the inhibitors 23 will be formulated with the treatment acid ~and any optional additives) at the surface and injected into the well by conventional techniques. Since at least a substantial quantity OI the ferric ions are usually derived from contact of the treatment acid with iron 2~ process equipment used in making or handling the acid or the wellbore pipelines, it is clearly desirable that at least the first injected portion of the treatment acid contain enough of the inhibitor to offset such ferric ions initially. Treatment acid without the present inhibitors can be subsequently injected into the well following the initial inhibited acid provide,d that the treatment acid itself is substantially free of ferriç ions and the formation has few iron-containing 27,98~-F -6-compounds. In many acidizing treatments, the initial volume of treatment acid is preceded and/or followed by other fluids (e.g. dilute ammonium chloride) which do not react with the iron scale to produce ferric ions.
These fluids are used to establish injectivity and/or provide a spacer between treatment 1uids in most instances. Such technigues are likewise suitable for use with the instant ferric inhibited acids.
Where the sub-terranean formation being treated is relatively unconsolidated, the procedure for injecting acidizing fluids and returning the well to production can advantageously be that described by USP 3,948,324.
Where the formation is siliceous and its permeability may be impaired by clay or silica fines, at least a portion of the acidizing acid should be a mud acid (normally containing 12 percen~ hydrochloric and 3 percent hydrofluoric) and may include pretreatment slugs of ammonium chloride. The treatment of forma-tions containing clay and siliceous fines is maximized by the processes of Thomas in USP 4,151,878 and 4,151,879. If the Thomas procedure(s) is followed, the present ferric inhibitors can be included in the initial treatment acid or in both the initial treatment acid and any or all of the following fluids, includiny the -~
fluoboric acid.
A series of tests was conducted with acid solutions (15 percent aqueous hydrochloric acid) con-taining 8000 milligrams of dissolved ferric ions per liter of acid on Indiana limestone for 18 hours at 150F. A blank of the above acid solution was prepared containing no ferric inhibitor. Examples 1 and 2 contained ascorbic acid and erythorbic acid, respec-tively, at a concentration of 2400 mg/l (i.e. 20 pounds 27,986-F -7-~ .
:
`
"` ` ~ ::
3~2~
per 1000 gallons) of treatment acid. In examples 1 and 2, the dissolved iron was retained in solution as ferrous (Fe 2) iron and very little, if any, ferric hydroxide precipitated. The blank contained very little dissolved iron and large quantities of insoluble ferric hydroxide. The results are summarized in Table I.
TABLE I
Dissolved Iron Example (Fe 2, Mg/l) Blank 140 Similar results were obtained in tests con-ducted at 100, 125, 150 and 200F. By way of com-parison, it took almost 16-20 times as much citric acid, EDTA, or acetic acid ~on a per weight basis) to achieve essentially the same result. Both ascorbic and erythorbic acid are substantially less expensive on a cost performance basis than EDTA. Accordingly, the present invention has potential economic as well as substantial technical advantages.
27,986-F -8-' ' 9
In the practice of the invention, the inhibitors 23 will be formulated with the treatment acid ~and any optional additives) at the surface and injected into the well by conventional techniques. Since at least a substantial quantity OI the ferric ions are usually derived from contact of the treatment acid with iron 2~ process equipment used in making or handling the acid or the wellbore pipelines, it is clearly desirable that at least the first injected portion of the treatment acid contain enough of the inhibitor to offset such ferric ions initially. Treatment acid without the present inhibitors can be subsequently injected into the well following the initial inhibited acid provide,d that the treatment acid itself is substantially free of ferriç ions and the formation has few iron-containing 27,98~-F -6-compounds. In many acidizing treatments, the initial volume of treatment acid is preceded and/or followed by other fluids (e.g. dilute ammonium chloride) which do not react with the iron scale to produce ferric ions.
These fluids are used to establish injectivity and/or provide a spacer between treatment 1uids in most instances. Such technigues are likewise suitable for use with the instant ferric inhibited acids.
Where the sub-terranean formation being treated is relatively unconsolidated, the procedure for injecting acidizing fluids and returning the well to production can advantageously be that described by USP 3,948,324.
Where the formation is siliceous and its permeability may be impaired by clay or silica fines, at least a portion of the acidizing acid should be a mud acid (normally containing 12 percen~ hydrochloric and 3 percent hydrofluoric) and may include pretreatment slugs of ammonium chloride. The treatment of forma-tions containing clay and siliceous fines is maximized by the processes of Thomas in USP 4,151,878 and 4,151,879. If the Thomas procedure(s) is followed, the present ferric inhibitors can be included in the initial treatment acid or in both the initial treatment acid and any or all of the following fluids, includiny the -~
fluoboric acid.
A series of tests was conducted with acid solutions (15 percent aqueous hydrochloric acid) con-taining 8000 milligrams of dissolved ferric ions per liter of acid on Indiana limestone for 18 hours at 150F. A blank of the above acid solution was prepared containing no ferric inhibitor. Examples 1 and 2 contained ascorbic acid and erythorbic acid, respec-tively, at a concentration of 2400 mg/l (i.e. 20 pounds 27,986-F -7-~ .
:
`
"` ` ~ ::
3~2~
per 1000 gallons) of treatment acid. In examples 1 and 2, the dissolved iron was retained in solution as ferrous (Fe 2) iron and very little, if any, ferric hydroxide precipitated. The blank contained very little dissolved iron and large quantities of insoluble ferric hydroxide. The results are summarized in Table I.
TABLE I
Dissolved Iron Example (Fe 2, Mg/l) Blank 140 Similar results were obtained in tests con-ducted at 100, 125, 150 and 200F. By way of com-parison, it took almost 16-20 times as much citric acid, EDTA, or acetic acid ~on a per weight basis) to achieve essentially the same result. Both ascorbic and erythorbic acid are substantially less expensive on a cost performance basis than EDTA. Accordingly, the present invention has potential economic as well as substantial technical advantages.
27,986-F -8-' ' 9
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for preventing the undesirable formation and precipitation of ferric compounds from a spent treatment acid containing dissolved iron following an acidizing treatment of subterranean formations surround-ing a wellbore, said method comprising adding to said treatment acid prior to contact with the formation an amount of ascorbic acid and/or erythorbic acid, and/or a soluble salt of said acid, sufficient to prevent the formation and precipitation of ferric compounds from the treatment acid upon spending.
2. The process of Claim 1 in which the aqueous acid is hydrochloric acid, HCl/HF mixtures or fluoboric acid.
3. The method of Claim 2 wherein said aqueous acid is from 5 to 15 percent hydrochloric acid or a mix-ture of about 12 percent hydrochloric and about 3 percent hydrofluoric acid.
4. The method of Claim 1 in which said acid is ascorbic acid or erythorbic acid.
5. The method of Claim 3 in which said acid is erythorbic acid.
6. An ungelled aqueous treatment acid compo-sition for acidizing subterranean formations comprising an aqueous acid at a pH less than about 1.5, and ascorbic acid and/or erythorbic acid, and/or a soluble salt of said acid, in an amount sufficient to inhibit the 27,986-F -9-formation and precipitation of ferric compounds in said treatment acid during conditions of use and in the spent treatment acid.
7. The composition of Claim 6 wherein said aqueous acid is from 5 to 15 percent HCl and said acid is erythorbic acid.
8. The composition of Claim 6 wherein said aqueous acid is hydrochloric acid, HCl/HF mixtures or fluoroboric acid.
9. The composition of Claim 8 wherein said aqueous acid is from 5 to 15 percent hydrochloric acid or a mixture of about 12 percent hydrochloric acid and 3 percent hydrofluoric acid.
10. The compositions of Claims 6, 8 or 9 in which said acid is ascorbic acid or erythorbic acid.
27,986-F -10-
27,986-F -10-
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US13129880A | 1980-03-18 | 1980-03-18 | |
| US131,298 | 1980-03-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1137290A true CA1137290A (en) | 1982-12-14 |
Family
ID=22448806
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000372741A Expired CA1137290A (en) | 1980-03-18 | 1981-03-11 | Ascorbic acid or erythorbic acid for prevention of formation of ferric compound |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1137290A (en) |
-
1981
- 1981-03-11 CA CA000372741A patent/CA1137290A/en not_active Expired
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