CA1195443A - Removal of iron from chelant solutions - Google Patents
Removal of iron from chelant solutionsInfo
- Publication number
- CA1195443A CA1195443A CA000415046A CA415046A CA1195443A CA 1195443 A CA1195443 A CA 1195443A CA 000415046 A CA000415046 A CA 000415046A CA 415046 A CA415046 A CA 415046A CA 1195443 A CA1195443 A CA 1195443A
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- CA
- Canada
- Prior art keywords
- iron
- liquid
- aqueous liquid
- process defined
- liquid effluent
- Prior art date
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- Removal Of Specific Substances (AREA)
- Treatment Of Water By Oxidation Or Reduction (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process is described for removing dissolved iron from an aqueous liquid containing iron in the form of a soluble complex with alkylenepolyamine poly-acetic acids or salts thereof. The process comprises the steps of (a) adjusting the pH of said aqueous liquid to at least about 12.5, (b) adding sufficient quantities of a soluble calcium salt to facilitate the growth of insoluble iron hydroxide particles, and (c) separating the resulting insoluble mass containing iron hydroxide from the liquid effluent.
A process is described for removing dissolved iron from an aqueous liquid containing iron in the form of a soluble complex with alkylenepolyamine poly-acetic acids or salts thereof. The process comprises the steps of (a) adjusting the pH of said aqueous liquid to at least about 12.5, (b) adding sufficient quantities of a soluble calcium salt to facilitate the growth of insoluble iron hydroxide particles, and (c) separating the resulting insoluble mass containing iron hydroxide from the liquid effluent.
Description
REMOVAL OF IRON FROM CHELANT SOLUTIONS
This invention pertains to a procPss for removing dissolved iron from an a~ueous li~uid con-taining i.ron chelated by alkylenepolyamine polyacetic acid. More particularly, this invention pertains to a treatment process for removing dissolved iron from certain liquid waste.
The alkylenepolyamine polyacetic acid chelan-ts form a known class of compounds having many members.
The most common of these are ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DEPA); and of these, EDTA is by far the most widely used compound on a commercial scale. Because -the materials are relatively insoluble in the acid form, such compounds are normally used as their soluble salts.
The alkali metal (e.g. sodium) salts and -the ammoniated salts are the best known.
There are many chelant uses for the alkylene-polyamine polyacetic acids, but one such u~ility is in cl~aning iron oxide containing scale from steam gener-ating equipment. In almost any type of metal equipment 29,653-F -l-~2 in which water is evaporated or heat transfer occurs, insoluble salts deposit upon the surface to form a scale. The composition of the scale will vary depending upon the water which has been used, the 5 type of equipment, the operating temperature, etc.
The scale may be very dense or coa.rse, tightly bound ko the base metal or not. In most steam generating units, the scale usually consists of o~ides of iron, which include magnetite together with red iron oxide.
And when the steam generating unit is fabricated using parts containing copper or copper alloys, as for example, in the condenser units, the scale will normally contain copper and/or contains copper oxide(s~.
Several investigators have addressed the problem of scale removal. Lesinksi described in U.S. Patent No. 3,308,065 a unique way of removing iron oxide containing scale from ferrous metal sur~
faces and for passivating the clean surface. Lesinski discovered that ammoniated salts of alkylenepolyamine polycarbo~ylic acids were particularly efficien-t in scale removal when used at an alkaline pH (generally above about a pH of 8). Ammoniated EDTA used at a pH of from 8 to ll, preferably about 9, was said to be a preferred solvent.
Harriman et al. in U.S. Patent No. 3,438,811 discovered that an aqueous solution of a ferric chelate of an alkylenepolyamine polycarboxylic acid at an alkaline pH was unusually effective in removing copper--containing encrus-tations of elemental ccpper from ferrous metal surfaces.
29,653-F -2---3~
Teumac ln U.S. Patent No. 3,413,160 then descxlbed a method of passivatlng ferrous metal sur-faces which had been cleaned using an alkylenepoly amine polycarboxyl1c acid at an alkaline pH to remove 5 iron-oxide containing scale and/or copper encrusta~
tions from steam generating equipment. In this pro cess, an o~idlzing agent was added at the end of the cleanlng process and the oxidation potential of the aqueous solution was carefully monitored to achieve the desired deyree of passlvation.
The technology described by Lesinski, Harrlman, and Teumac represent the state of the art.
All use alkylenepolyamine polycarboxylic acids or sal~s ~hereof at an alkaline p~ and all generate waste solutions which contain dissolved iron as an iron chelate with the alkylenepolyamin~ polycar-boxylic acids. ~nd, in most instances, the a~ue~us solu~ions also contain dissolved copper as a copper chelate.
Waste-disposal is a significant problem in today's industrial e~vironment. Thus, the problem of how to safely deal with a liquid waste containlng dissolved complexes of iron and/or copper and Qther heav~ metals with alkylenepolyamlrle polyacetlc acid chelates is a ~uestion that must be faced after each cleaning job. It has been demonstrated that the liquid was-te can be safely and efficiently incinerated, but with increasingly stringen~ contxols on incin-eration, this is also becoming less acceptable.
Thus, there exists a strong and incre~sing need for a safe and efficient method for removing heavy met~ls 29,653-F -3-_4.
from such a~ueous liquids prior to other trea-tment methods.
The invention resides in a process for removing iron from an aqueous liquid containing dissolved iron in the form o~ a soluble chelate with an alkylenepolyamine polyacetic acid and/or soluble chelating salts of said acid, said process comprising the steps of: ~a) adjusting the pH of said aqueous liq~lid to at least about 12.5, (b) aclding sufficient quantities of a soluble calcium salt to facili-~ate the growth of insoluble colloidal iron hydroxide par~icles, and (c) separating the resulting insoluble mass containing iron hydroxide from the liquid effluent.
The novel process is highly efective in reducing the amount of dissolved iron in solu~ion and, in addition, the insoluble ma~s resul-ting from the process is easily separated from -the liquid effluent.
.
Iron hydroxide is normally formed as a gelatinous mass which is difficult to deal with.
In this process, however, the iron hydroxide is formed as a floc and is easily separable from the liquid.
~5 The invention also resides in a waste treat~
ment p.rocess for removin~ iron and copper ions from an aqueous liquid waste in whi.ch said ions exist as ~oluble chelates with ethylen2diaminetetraace-tlc acid ~EDTA) and/or a soluble chelating sal-t of EDTA, said process comprising the steps of: (a) adjusting the 29,653-F ~4-pH of said aqueous liquid waste to at leas-t abou-t 12.5 with sodium hydroxide, (b) adding from 0.25 to 1 weight percent calclum hydroxide as an aqueous slurry, (c) adding a substantially stoichiometric amount of sodium N,N-diethyldithiocarbamate related ko the amount of copper ions present in said aqueous liquid waste, (d) adding from 2 to 10 ppm of an anionic water soluble polyacrylamide, and (e~ separating the solids in said liquid waste from the liquid effluent.
The general class of alkylenepolyamine polyacetic acid chelants is, of course, a well known class of compounds. The types of metals that are chelated by these compounds are likewise well known and include, iron, chromium, copper, nickel, etc.
The instant process is highly effec-tive in removing dissolved iron from solutions of such chelant com-plexes.
Step (a) is a pH adjustment st~p in which the pH of the solution is adjusted to a-t least about 12.S. This is conveniently done by adding an alkali metal oxide or hydroxide to the aqueous liquid.
Sodium hydroxide or potassium hydroxide would typically be used; ancl, sodium hydroxide would be the alkali me-tal hydro~ide of choice based upon commercial avail-ability and cost.
In step ~b) a soluble calcium salt is addedin amounts sufficient to facilitate the particle growth of the iron hydroxide floc. Usually amounts of from 0.25 to 5 weight percent are satisfactory.
Substantially any inorganic calcium salt can be used, but calcium chloride, calcium bromide, and calcium 29,653~F -5~
hydroxide are common calcium salts and -they would typically be used. Calcium hydroxide is the calcium salt of choice because it is alkaline and the present process is conducted at a basic pH. An anionic water-5 -soluble, high molecular weight polymer such as poly~
acrylamide and the like, can also be added to facilitate rapid flocculation; such addition is preferred. Usually the anionic polymer is added in the amounts of from 2 to 10 parts per million.
In step ~c) the solid mass is separated from the liquid ef1uent. This can be an active process or a passive process. For example, one can use high pressure filtration techniques, centri-fugation techniques, settling ponds, etc. The par-ticular means used in step ~c) will largely depend upon the eguipment available to the ar-tisan.
If one desires to also remove copper ions from the aqueous liquid, dimethyl and/or diethyl-dithiocarbamate is added in essentially stoichiometric 29 amounts, relative to the amount of dissolved copper.
The reaction with the dialkyldithiocarbamate is almost instantaneous and the copper is removed in almost quantitative yield~ The solid precipitate containing -the copper is then removed from the liquid effluen-t by techniques as described or step (c).
If one desires to purify the effluent even further, the liquid effluent can be passed through a bed of activated charcoal to remove organics and to decolorize the liquid. The activated charcoal is also effective in removing trace amounts of heavy me-tals. After this "polishing" step, the liquid 29,653-~ -6-effluent contains the alkylenepolyamine polyacetic acid, usually as the primary ingredient dissolved in water. The alkylenepolyamine polyacetic acid can be removed from solution by lowering the pH. For example, ethylenediamin~-tetraacetic acid will pre~
cipitate at a pH of approximat~ly 1.8 or below.
Experimental The following e~periments will further illustrate the invention.
Example 1 A representative "waste" solution was prepared using ammoniated EDTA buffered at a p~ of about 9.2 with ammonia to dissolve iron sulfate (5100 ppm iron) and copper sulfate (1000 ppm copper). The pH of the solution was raised to about 12.5 using 50 percent aqueous sodium hydroxide, followed by the addition of two weight percent calcium hydroxide, followed by the addition of one weight percent sodium dlethyl-dithiocarbamate. The precipitated solids were removed by filtration and the liquid effluent was tested for dissolved metals using conven~ional analytical tec~miques (eOg. atomic absorption). It was found that the clear liquid effluent contained less than one part per million dissolved iron and less than one part per million dissolved copper.
Example 2 A representative "waste" was prepared by dissolving iron sulfate (1500 ppm iron) wlth an ammoniated EDTA buffered at a pH of from 4 to 6 with formic acid. This solution was then treated with 50 percen-t sodium hydroxide to a pH of about 12.5, 29,653-F -7-followed by the addition of one weight percent calcium hydroxide. The solid precipitate was removed by fil-tration and the clear liquid effluent analyzed for dissolved metal content. It was found that the effluent contained less than one part per million dissolved iron.
Exam ~e 3 The waste from cleaning an industrial boiler at a utility company in California had been discharged to a holding pond. The commercial solvent used to clean the steam generating equipment was an inhibi~ted ammoniated EDTA solution buffered with ammonia at a pH of approximately 9.2. The liquid waste conkained chelated iron, chromium, copper, and nickel. Treat-ment of this waste to remove metals was a continuoustreatment in which the liquid waste was pumped from the holding pond into a mixing tank at an average rate o about 35 yallons per minute. The treatment chemicals (50 percent aqueous sodium hydroxide, 35 weight percent calcium chloride, and 25 weight per~
cent sodium diethy.ldithiocarbamate~ were likewise continuously added to the mixing tank. The waste and the trea-tment chemicals were mixed in this 700 gallon mixing tank and allowed to reac-t and overflow into the bottom of a 30,000 gallon clarifier. In the clarifier, the treated mixture was con-tacted wi-th a polyacrylamide (AP 273 from The Dow Chemical Company) to enhance flow formation and ~ettling rates. As the solids coagulated in the clarifier, the solids separated from the treated solution by gravi-ty. The clarified solution rose to the top of the clarifier and overflowed to a polishing filter. The solids - were withdrawn from the bottom of the clarifier slowly 29,653-F -8~
i~ order to maintain a st~ble sludge "blanket". The ~ sludge blanket was quite dense (4-5 weight percent solids) and acted as a "sieve" to provide efficient solid/liquid separation.
The solids were transferred into a thickener uni-t - (basically a holdlng tank) where the solids continu2d to condense and precipitate. After the solids were accumulated, they were processed in-to filter cakes using a commercial filter press and disposed of safely.
The clear liquld effluent flowing from the clarifier was decolori~ed in the polishing filter.
Me-tal analysls (by atomic absorptlon spectroscopy) on the polished ef~luent provided the information in Table I.
TABLE I
Before ~fter %
MetalsTreatment Trea~men-t Removal __ ___ Iron1040 ppm 0.09 ppm 99.99 Copper 114 0.04 99.96 Chromium0.73 0.13 82.2 Nic~el 80 14 82.5 The total treatment chemicals used to treat 150,000 gallons of waste were: 1350 gallons of 50 weight percent sodium hydroxide, 4500 pounds of calcium hydroxide (dry weight basis), and 370 gallons of 25 weight percent sodium diethyldithlocarbama-te.
29,653-F -9-
This invention pertains to a procPss for removing dissolved iron from an a~ueous li~uid con-taining i.ron chelated by alkylenepolyamine polyacetic acid. More particularly, this invention pertains to a treatment process for removing dissolved iron from certain liquid waste.
The alkylenepolyamine polyacetic acid chelan-ts form a known class of compounds having many members.
The most common of these are ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DEPA); and of these, EDTA is by far the most widely used compound on a commercial scale. Because -the materials are relatively insoluble in the acid form, such compounds are normally used as their soluble salts.
The alkali metal (e.g. sodium) salts and -the ammoniated salts are the best known.
There are many chelant uses for the alkylene-polyamine polyacetic acids, but one such u~ility is in cl~aning iron oxide containing scale from steam gener-ating equipment. In almost any type of metal equipment 29,653-F -l-~2 in which water is evaporated or heat transfer occurs, insoluble salts deposit upon the surface to form a scale. The composition of the scale will vary depending upon the water which has been used, the 5 type of equipment, the operating temperature, etc.
The scale may be very dense or coa.rse, tightly bound ko the base metal or not. In most steam generating units, the scale usually consists of o~ides of iron, which include magnetite together with red iron oxide.
And when the steam generating unit is fabricated using parts containing copper or copper alloys, as for example, in the condenser units, the scale will normally contain copper and/or contains copper oxide(s~.
Several investigators have addressed the problem of scale removal. Lesinksi described in U.S. Patent No. 3,308,065 a unique way of removing iron oxide containing scale from ferrous metal sur~
faces and for passivating the clean surface. Lesinski discovered that ammoniated salts of alkylenepolyamine polycarbo~ylic acids were particularly efficien-t in scale removal when used at an alkaline pH (generally above about a pH of 8). Ammoniated EDTA used at a pH of from 8 to ll, preferably about 9, was said to be a preferred solvent.
Harriman et al. in U.S. Patent No. 3,438,811 discovered that an aqueous solution of a ferric chelate of an alkylenepolyamine polycarboxylic acid at an alkaline pH was unusually effective in removing copper--containing encrus-tations of elemental ccpper from ferrous metal surfaces.
29,653-F -2---3~
Teumac ln U.S. Patent No. 3,413,160 then descxlbed a method of passivatlng ferrous metal sur-faces which had been cleaned using an alkylenepoly amine polycarboxyl1c acid at an alkaline pH to remove 5 iron-oxide containing scale and/or copper encrusta~
tions from steam generating equipment. In this pro cess, an o~idlzing agent was added at the end of the cleanlng process and the oxidation potential of the aqueous solution was carefully monitored to achieve the desired deyree of passlvation.
The technology described by Lesinski, Harrlman, and Teumac represent the state of the art.
All use alkylenepolyamine polycarboxylic acids or sal~s ~hereof at an alkaline p~ and all generate waste solutions which contain dissolved iron as an iron chelate with the alkylenepolyamin~ polycar-boxylic acids. ~nd, in most instances, the a~ue~us solu~ions also contain dissolved copper as a copper chelate.
Waste-disposal is a significant problem in today's industrial e~vironment. Thus, the problem of how to safely deal with a liquid waste containlng dissolved complexes of iron and/or copper and Qther heav~ metals with alkylenepolyamlrle polyacetlc acid chelates is a ~uestion that must be faced after each cleaning job. It has been demonstrated that the liquid was-te can be safely and efficiently incinerated, but with increasingly stringen~ contxols on incin-eration, this is also becoming less acceptable.
Thus, there exists a strong and incre~sing need for a safe and efficient method for removing heavy met~ls 29,653-F -3-_4.
from such a~ueous liquids prior to other trea-tment methods.
The invention resides in a process for removing iron from an aqueous liquid containing dissolved iron in the form o~ a soluble chelate with an alkylenepolyamine polyacetic acid and/or soluble chelating salts of said acid, said process comprising the steps of: ~a) adjusting the pH of said aqueous liq~lid to at least about 12.5, (b) aclding sufficient quantities of a soluble calcium salt to facili-~ate the growth of insoluble colloidal iron hydroxide par~icles, and (c) separating the resulting insoluble mass containing iron hydroxide from the liquid effluent.
The novel process is highly efective in reducing the amount of dissolved iron in solu~ion and, in addition, the insoluble ma~s resul-ting from the process is easily separated from -the liquid effluent.
.
Iron hydroxide is normally formed as a gelatinous mass which is difficult to deal with.
In this process, however, the iron hydroxide is formed as a floc and is easily separable from the liquid.
~5 The invention also resides in a waste treat~
ment p.rocess for removin~ iron and copper ions from an aqueous liquid waste in whi.ch said ions exist as ~oluble chelates with ethylen2diaminetetraace-tlc acid ~EDTA) and/or a soluble chelating sal-t of EDTA, said process comprising the steps of: (a) adjusting the 29,653-F ~4-pH of said aqueous liquid waste to at leas-t abou-t 12.5 with sodium hydroxide, (b) adding from 0.25 to 1 weight percent calclum hydroxide as an aqueous slurry, (c) adding a substantially stoichiometric amount of sodium N,N-diethyldithiocarbamate related ko the amount of copper ions present in said aqueous liquid waste, (d) adding from 2 to 10 ppm of an anionic water soluble polyacrylamide, and (e~ separating the solids in said liquid waste from the liquid effluent.
The general class of alkylenepolyamine polyacetic acid chelants is, of course, a well known class of compounds. The types of metals that are chelated by these compounds are likewise well known and include, iron, chromium, copper, nickel, etc.
The instant process is highly effec-tive in removing dissolved iron from solutions of such chelant com-plexes.
Step (a) is a pH adjustment st~p in which the pH of the solution is adjusted to a-t least about 12.S. This is conveniently done by adding an alkali metal oxide or hydroxide to the aqueous liquid.
Sodium hydroxide or potassium hydroxide would typically be used; ancl, sodium hydroxide would be the alkali me-tal hydro~ide of choice based upon commercial avail-ability and cost.
In step ~b) a soluble calcium salt is addedin amounts sufficient to facilitate the particle growth of the iron hydroxide floc. Usually amounts of from 0.25 to 5 weight percent are satisfactory.
Substantially any inorganic calcium salt can be used, but calcium chloride, calcium bromide, and calcium 29,653~F -5~
hydroxide are common calcium salts and -they would typically be used. Calcium hydroxide is the calcium salt of choice because it is alkaline and the present process is conducted at a basic pH. An anionic water-5 -soluble, high molecular weight polymer such as poly~
acrylamide and the like, can also be added to facilitate rapid flocculation; such addition is preferred. Usually the anionic polymer is added in the amounts of from 2 to 10 parts per million.
In step ~c) the solid mass is separated from the liquid ef1uent. This can be an active process or a passive process. For example, one can use high pressure filtration techniques, centri-fugation techniques, settling ponds, etc. The par-ticular means used in step ~c) will largely depend upon the eguipment available to the ar-tisan.
If one desires to also remove copper ions from the aqueous liquid, dimethyl and/or diethyl-dithiocarbamate is added in essentially stoichiometric 29 amounts, relative to the amount of dissolved copper.
The reaction with the dialkyldithiocarbamate is almost instantaneous and the copper is removed in almost quantitative yield~ The solid precipitate containing -the copper is then removed from the liquid effluen-t by techniques as described or step (c).
If one desires to purify the effluent even further, the liquid effluent can be passed through a bed of activated charcoal to remove organics and to decolorize the liquid. The activated charcoal is also effective in removing trace amounts of heavy me-tals. After this "polishing" step, the liquid 29,653-~ -6-effluent contains the alkylenepolyamine polyacetic acid, usually as the primary ingredient dissolved in water. The alkylenepolyamine polyacetic acid can be removed from solution by lowering the pH. For example, ethylenediamin~-tetraacetic acid will pre~
cipitate at a pH of approximat~ly 1.8 or below.
Experimental The following e~periments will further illustrate the invention.
Example 1 A representative "waste" solution was prepared using ammoniated EDTA buffered at a p~ of about 9.2 with ammonia to dissolve iron sulfate (5100 ppm iron) and copper sulfate (1000 ppm copper). The pH of the solution was raised to about 12.5 using 50 percent aqueous sodium hydroxide, followed by the addition of two weight percent calcium hydroxide, followed by the addition of one weight percent sodium dlethyl-dithiocarbamate. The precipitated solids were removed by filtration and the liquid effluent was tested for dissolved metals using conven~ional analytical tec~miques (eOg. atomic absorption). It was found that the clear liquid effluent contained less than one part per million dissolved iron and less than one part per million dissolved copper.
Example 2 A representative "waste" was prepared by dissolving iron sulfate (1500 ppm iron) wlth an ammoniated EDTA buffered at a pH of from 4 to 6 with formic acid. This solution was then treated with 50 percen-t sodium hydroxide to a pH of about 12.5, 29,653-F -7-followed by the addition of one weight percent calcium hydroxide. The solid precipitate was removed by fil-tration and the clear liquid effluent analyzed for dissolved metal content. It was found that the effluent contained less than one part per million dissolved iron.
Exam ~e 3 The waste from cleaning an industrial boiler at a utility company in California had been discharged to a holding pond. The commercial solvent used to clean the steam generating equipment was an inhibi~ted ammoniated EDTA solution buffered with ammonia at a pH of approximately 9.2. The liquid waste conkained chelated iron, chromium, copper, and nickel. Treat-ment of this waste to remove metals was a continuoustreatment in which the liquid waste was pumped from the holding pond into a mixing tank at an average rate o about 35 yallons per minute. The treatment chemicals (50 percent aqueous sodium hydroxide, 35 weight percent calcium chloride, and 25 weight per~
cent sodium diethy.ldithiocarbamate~ were likewise continuously added to the mixing tank. The waste and the trea-tment chemicals were mixed in this 700 gallon mixing tank and allowed to reac-t and overflow into the bottom of a 30,000 gallon clarifier. In the clarifier, the treated mixture was con-tacted wi-th a polyacrylamide (AP 273 from The Dow Chemical Company) to enhance flow formation and ~ettling rates. As the solids coagulated in the clarifier, the solids separated from the treated solution by gravi-ty. The clarified solution rose to the top of the clarifier and overflowed to a polishing filter. The solids - were withdrawn from the bottom of the clarifier slowly 29,653-F -8~
i~ order to maintain a st~ble sludge "blanket". The ~ sludge blanket was quite dense (4-5 weight percent solids) and acted as a "sieve" to provide efficient solid/liquid separation.
The solids were transferred into a thickener uni-t - (basically a holdlng tank) where the solids continu2d to condense and precipitate. After the solids were accumulated, they were processed in-to filter cakes using a commercial filter press and disposed of safely.
The clear liquld effluent flowing from the clarifier was decolori~ed in the polishing filter.
Me-tal analysls (by atomic absorptlon spectroscopy) on the polished ef~luent provided the information in Table I.
TABLE I
Before ~fter %
MetalsTreatment Trea~men-t Removal __ ___ Iron1040 ppm 0.09 ppm 99.99 Copper 114 0.04 99.96 Chromium0.73 0.13 82.2 Nic~el 80 14 82.5 The total treatment chemicals used to treat 150,000 gallons of waste were: 1350 gallons of 50 weight percent sodium hydroxide, 4500 pounds of calcium hydroxide (dry weight basis), and 370 gallons of 25 weight percent sodium diethyldithlocarbama-te.
29,653-F -9-
Claims (12)
1. A process for removing iron from an aqueous liquid containing dissolved iron in the form of a soluble chelate with an alkylenepolyamine poly-acetic acid and/or soluble chelating salts of said acid, said process comprising the steps of: (a) adjust-ing the pH of said aqueous liquid to at least about 12.5, (b) adding sufficient quantities of a soluble calcium salt to facilitate the growth of insoluble colloidal iron hydroxide particles, and (c) separating the resulting insoluble mass containing iron hydroxide from the liquid effluent.
2. The process defined by Claim 1 wherein said soluble calcium salt is calcium hydroxide.
3. The process defined by Claim 2 wherein said calcium hydroxide is added in amounts of from 0.25 to 5 weight percent.
4. The process defined by Claim 1 wherein said process is a continuous process in which iron is continuously removed from a flowing stream of said aqueous liquid.
5. The process defined by Claim 1 wherein said aqueous liquid is an aqueous liquid waste produced by the cleaning of ferrous oxide-containing encrusta-tions from ferrous metal surfaces with a solvent con-taining ammoniated EDTA at an alkaline pH; the pH being measured at 20°C.
6. The process defined by Claim 1 comprising the additional step of adding a water soluble high molecular weight anionic polymer to facilitate floc-culation of the insoluble colloidal iron hydroxide particles.
7. The process defined by Claim 1 comprising the additional step of: (d) adding an alkali metal N,N-dimethyl- or N,N-diethyldithiocarbamate to the aqueous liquid in essentially a stoichiometric amount, relative to dissolved copper in said aqueous liquid to thereby remove copper as a solid precipitate.
8. The process defined by Claim 7 comprising the additional steps of: (e) contacting said liquid effluent with activated carbon, and (f) thereafter separating the liquid effluent from the activated carbon.
9. The process defined by Claim 8 comprising the additional steps of: (h) adjusting the pH of the liquid effluent from step to less than about 1.8, and (i) separating any solids precipitated from the liquid effluent by the change in pH.
10. A waste treatment process for removing iron and copper ions from an aqueous liquid waste in which said ions exist as soluble chelates with ethylene-diaminetetraacetic acid (EDTA) and/or a soluble chelating salt of EDTA, said process comprising the steps of: (a) adjusting the pH of said aqueous liquid waste to at least about 12.5 with sodium hydroxide, (b) adding from 0.25 to 1 weight percent calcium hydroxide as an aqueous slurry, (c) adding a sub-stantially stoichiometric amount of sodium N,N-diethyldithiocarbamate related to the amount of copper ions present in said aqueous liquid waste, (d) adding from 2 to 10 ppm of an anionic water soluble polyacrylamide, and (e) separating the solids in said liquid waste from the liquid effluent.
11. The process defined by Claim 10 comprising the additional steps of: (f) contacting said liquid effluent with activated carbon, and (g) separating the activated carbon from the liquid effluent to thereby remove organic contaminants from said liquid effluent.
12. The process defined by Claim 11 comprising the additional steps of: (h) adjusting the pH of the liquid effluent from step to less than about 1.8, and (i) separating any solids precipitated from the liquid effluent by the change in pH.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US31951881A | 1981-11-09 | 1981-11-09 | |
| US319,518 | 1989-03-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1195443A true CA1195443A (en) | 1985-10-15 |
Family
ID=23242580
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000415046A Expired CA1195443A (en) | 1981-11-09 | 1982-11-08 | Removal of iron from chelant solutions |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1195443A (en) |
-
1982
- 1982-11-08 CA CA000415046A patent/CA1195443A/en not_active Expired
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