CA1083272A - Treatment of mercury contaminated aqueous media - Google Patents
Treatment of mercury contaminated aqueous mediaInfo
- Publication number
- CA1083272A CA1083272A CA269,686A CA269686A CA1083272A CA 1083272 A CA1083272 A CA 1083272A CA 269686 A CA269686 A CA 269686A CA 1083272 A CA1083272 A CA 1083272A
- Authority
- CA
- Canada
- Prior art keywords
- mercury
- sulfide
- polysulfide
- effluent
- elemental
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT
TREATMENT OF MERCURY CONTAINING AQUEOUS MEDIA
A technique for removing substantially all the elemental mercury from a mercury containing aqueous media by adjusting the pH of the liquid to the range of 7 - 13, adding a polysulfide in an amount sufficient to combine with the elemental mercury to form a mercury sulfide which is precipi-tated and preventing the mercury from being resolublized.
TREATMENT OF MERCURY CONTAINING AQUEOUS MEDIA
A technique for removing substantially all the elemental mercury from a mercury containing aqueous media by adjusting the pH of the liquid to the range of 7 - 13, adding a polysulfide in an amount sufficient to combine with the elemental mercury to form a mercury sulfide which is precipi-tated and preventing the mercury from being resolublized.
Description
~83Z72 FIELD OF THE INVENTION
The present invention relates to a technique for precipitating mercury from mercury containing aqueo~ media.
DESCRIPTION OF PRIOR ART
Many methods have been investigated in the attempt to remove mercury from aqueous media, for example solid particles including many ion exchange resins, activated carbon, zinc particles, and solutions of sodium borohydride or stannous chloride (see Mercury Recovery from Contaminated Waste Water and Sludges by Richard Perry, EPA-660/2-74-086 December 1974). None of the above methods were found able to achieve efficient mercury levels below 100 ppb when the starting solutions contained about 2 to 25 ppm. or their capacity was limited so that their effective life was general-ly shortened by concentrated mercury feeds. Ion exchange resins and activated carbon appear to be most effective as polishing step~ after a first ~tage treatment has removed the bulk of the mercury and are able to treat solutions in the range of 40-100 ppb down to 1-5 ppb.
The generally accepted commercial technique for - removal of mercury from a~ueous media is to convert the mercury to mercury sulfide which precipitates. This techni-que generally employs sodium sulfide or sodium hydrosulfide which is added to the contaminated medium under mild alkaline conditions and the mercury sulfide which precipitates may be separated from the liquid by ~iltering, decanting or the like.
Generally as used throughout the specification the term sulfide is intended to include hydrosulfide.
The present invention provides an improved tech-nique for significantly increasing the amount of elemental
The present invention relates to a technique for precipitating mercury from mercury containing aqueo~ media.
DESCRIPTION OF PRIOR ART
Many methods have been investigated in the attempt to remove mercury from aqueous media, for example solid particles including many ion exchange resins, activated carbon, zinc particles, and solutions of sodium borohydride or stannous chloride (see Mercury Recovery from Contaminated Waste Water and Sludges by Richard Perry, EPA-660/2-74-086 December 1974). None of the above methods were found able to achieve efficient mercury levels below 100 ppb when the starting solutions contained about 2 to 25 ppm. or their capacity was limited so that their effective life was general-ly shortened by concentrated mercury feeds. Ion exchange resins and activated carbon appear to be most effective as polishing step~ after a first ~tage treatment has removed the bulk of the mercury and are able to treat solutions in the range of 40-100 ppb down to 1-5 ppb.
The generally accepted commercial technique for - removal of mercury from a~ueous media is to convert the mercury to mercury sulfide which precipitates. This techni-que generally employs sodium sulfide or sodium hydrosulfide which is added to the contaminated medium under mild alkaline conditions and the mercury sulfide which precipitates may be separated from the liquid by ~iltering, decanting or the like.
Generally as used throughout the specification the term sulfide is intended to include hydrosulfide.
The present invention provides an improved tech-nique for significantly increasing the amount of elemental
- 2 ~
1(~83272 mercury that may be removed by precipitation from a contami-nated medium.
The mercury present ~n ~uch contaminated media may~ be in addition to other form~ as elemental mercury and it was believed that the added sulfide reacts, relatively rapidly with the mercury. It has now been found that ele-mental mercury does not react a~ quickly as was heretofore thought to form the mercury sulfide, and it i8 believed for thi~ reason, prior to the present invention proces-~es for precipitating mercury from contaminated media have produce variable results probably dependent on the elemental mercury content in the media.
BRIEF DESCRIPTION OF THE INVENTION
Broadly, the pre~ent invention provides a technique for precipitating ~ubstantially all of the elemental mercury in a mercury contaminated aqueous medium by adjusting the p~
of the medium to the range of 7 - 13 and then adding a poly-sulfide in an amount to combine with the mercury to form mercury sulfide which precipitates. When a process stream i~ so treated, the mercury sulfide formed may be separated by decantation or filtration.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Further features, objects and advantages will be evident from the following detailed description of the pre-ferred embodiments of the present invention.
Treatment of a contaminated sample containingmercury either in elemental or ionic form, first require~
adjustment of the pH into the range of between 7 and 13, preferably 9 to 12. A soluble polysulfide is then added.
The soluble polysulfide may be added in the form of say a 40% sodium sulfide or sodium hydrosulfide solution to which
1(~83272 mercury that may be removed by precipitation from a contami-nated medium.
The mercury present ~n ~uch contaminated media may~ be in addition to other form~ as elemental mercury and it was believed that the added sulfide reacts, relatively rapidly with the mercury. It has now been found that ele-mental mercury does not react a~ quickly as was heretofore thought to form the mercury sulfide, and it i8 believed for thi~ reason, prior to the present invention proces-~es for precipitating mercury from contaminated media have produce variable results probably dependent on the elemental mercury content in the media.
BRIEF DESCRIPTION OF THE INVENTION
Broadly, the pre~ent invention provides a technique for precipitating ~ubstantially all of the elemental mercury in a mercury contaminated aqueous medium by adjusting the p~
of the medium to the range of 7 - 13 and then adding a poly-sulfide in an amount to combine with the mercury to form mercury sulfide which precipitates. When a process stream i~ so treated, the mercury sulfide formed may be separated by decantation or filtration.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Further features, objects and advantages will be evident from the following detailed description of the pre-ferred embodiments of the present invention.
Treatment of a contaminated sample containingmercury either in elemental or ionic form, first require~
adjustment of the pH into the range of between 7 and 13, preferably 9 to 12. A soluble polysulfide is then added.
The soluble polysulfide may be added in the form of say a 40% sodium sulfide or sodium hydrosulfide solution to which
- 3 -is a~ded exce~s ~ulphur to form polysulfide in situ. Poly-sulfide from any other suitable source ma~f be used. The amount of such polysulfide added should be sufficient to col~ine with ~ubstantially all the elementaxy mercury present to form mercury sulfide.
In the event that both elemental mercury and ionic mercury are pre~ent in the contaminated media, it i8 preferred to use polysulfide together with sulfide. Both polysulfide and ~ulfide may be used to precipitzte ionic mercury. However, a greater weight of polysulfide than sulfide i5 required to precipitate the same amount of ionic mercury and, for this reason, a medium containing both ionic and elemental mercury is more economically treated by adding both sulfide and poly-sulfide.
If there i~ too great an exces~ of sulfide ions in the treated medium some of the mercury sulfide precipitated may react with excess sulfide ions to form a soluble mercuric disulfide complex.
HgS t S _ HgS2 The reactions to form mercury sulfide and the mercu-ry disulfide complex are pH dependent and therefore the amount of exces~ sulfide ion that may be tolerated is dependent on the pH of the media being treated, unless precautions are taken to ensure that the mercury sulfide is not converted into a soluble mercury disulfide complex. Such precautions would include the removing the mercury sulfide precipitate e.g. by filtration, before it can react with the excess sul-fide ion or the removing of the excess sulfide ions, e.g. by reaction with ferric chloride or the like. Thiq i8 facilita-ted by the fact that the formation of the mercury sulfide occurs more rapidly than the formation of the 801uble mer-cury di~ulfide complex.
~C~83272 In many cases, where the amount of mercury in the aqueous medium is small, the precautions may be superfluou~.
While it is preferred to use sodi~lm as the poly-su;Lfide cation, obviously other ~oluble polysulfides ~uch as potassium, ammonium, magnesium and calcium may be used provided they do not have other deleterious effects on the materialc being treated.
Dilute polysulfide solu~ions are unstable and therefore care must be taken to ensure that the effective-ness of the polysulfide solution is not prematurely des-troyed.
The present invention i9 particularly applicable to chlor-alkali plants using mercury cells and may be used to decontaminate the variou~ effluents from such a plant.
In a mercury cell, the mercury acts as the cathode and flows over the bottom of the cell which slopes slightly towards one end. Saturated brine solution is carried over the mercury and carbon anodes are inserted through the top of and cell and extend into the brine. The electrical potential between the anode and cathode draws the chloride ions to the anode where they form elemental chlorine which leaves the cell through a special outlet. The sodium ions are drawn to the mercury cathode where they form elemental sodium which immediately forms an amalgam with a some of the mercury. The mercury solution of the amalgam i9 carried to a separate compartment referred to as the denuder where water iB added to regenerate the mercury from the amalgam while at the same time forming sodium hydroxide and hydrogen gas. The mercury is returned to the cell and the sodium hydroxide and hydrogen ga~ are removed from the denuder.
The partially depleted brine is also removed from _ 5 _ the cell and carries with it 30me mercury. The depleted brine is fortified by the addition of fresh sodium chloride.
The impurities from the fre~h sodium chloricle are separated in a settling tank and the supernatant (fortified brine) is ret:urned to the cell while the dregs (brine ~ludge) are car-ried away for further treatment and di~posal. The mercury in the fortified brine return~ to the cell and is reused.
However the mercury in the brine sludge must be stabilized so that it cannot contaminate the environment.
The major source of mercury contaminated aqueous media from such chlor-alkali plants i9 the effluent from the cell sewers which collects all of the water from floor wash-ings, spills, purge streams from end boxes in the cells, wash waters, drainage from the caustic filtration area and from tank cleaning. The brine sludge referred to hereinabove is another source and is normally in the form of a sludge (up to about 40% suspended solids). The perimeter sewer which collects a liquid run off from an area adjacent to the plant forms yet another medium that requires treatment.
The following examples relate to treatment of speci-fic effluents from a chlor-alkali plant.
EXAMPLE I
Samples from the holding tank that collects the cell sewer effluent in a chlor-alkali plant were pH adjusted and treated according to the invention by adding polysulfide and sulfide plus a minor a unt of ferri~chloride and fil-tered. The pH was then set at 9 and the treatment repeated with and without sodium polysulfide ~Na2Sx when x is greater than 1). The results given in Table I.
10t~3Z72 T~LE I
TREATMENT OF CELL SEWER EE'FLUENT
TREATMENT METHOD Mercury After Removal of Effficiency Na2Sx NaH~ FeC13 Filtration (ppb) of Hg (%) pH ppm ppm ppm Elemental Total Elemental Total 9 control 140 570 - -9 50 50 ~00 4 4 97 99 100 2 2 9~ 99f 11 50 50 1~0 1 1 ggt 99t 12 50 50 100 1 97 99~ 83 It is apparent that the efficiency i 8 considerably better when Na2Sx is added and that the treatment is pH.
dependent. However the optimum pH will vary from plant to plant depending on the overall composition of the media being treated.
EXAMPLE II
Sample~ from the holding tank which collects the effluent cell sewer in a chlor-alkali plant, were adjusted to different~ pH values and treated with polysulfide (50 ppm), NaHS ~50 ppm) and FeC13 (100 ppm). The mercury level before treatment was 11.0 ppm the values after treatment are shown in Table II.
10~3Z7Z
TABLE I I
. .. ~
POLYSULFIDE PRECIPITATION OF MERCURY AT DIFFE~H
% Efficiency Elemental HgTotal Hg for removal of pH (ppb) ~ppm) total mercury . ~
8 <1 0.13 99 9 ~1 0.04 99 ~1 0.04 99 11 ~1 0.03 99 12 Sl 0.02 99 EXAMPLE III
In a specific plant trial at a chlor-alkali plant, polysulfide was used to treat the effluent from the cell sewer. This effluent has been traditionally treated by adding NaHS and FeC133, allowing the solids to settle in a decanter and then filtering.
During the plant trial polysulfide was also added during the treatment of this effluent. This was accompli~hed by simply adding polyculfide to a 5% NaHS solution which is continually metered into a treatment vessel. The polysulfide, NaHS and FeC13 concentrations in the water being treated were 20, 37, and 74 ppm respectively.
The average mercury losses in the two weeks prior to polysulfide addition was 0.087 ppm7 after polysulfide addition co~menced the level dropped to 0.011 ppm which represents an 86.9% reduction in mercury losses from this source. The efficiency of treatment with sulfide averaged 97.84~ and when polysulfide was added it increased to 99.71~.
EXAMPLE IV
_ In a chlor-alkali plant, samples of brine sludge were taken from the brine sludge tank. The major sources of 1~8327Z
this brine sludge are the brine clarifier, and the brine saturator. A con~iderable portion of the mercury from these source~ i5 elemental mercury. These samples of brine ~ludge at pH 10.7, were treated with varying quantitie~ of sodium polysulfide and the solids were then removed by filtration.
The mercury in soluble form (in the filtrate) was measured and the result~ are shown in Table III. ~ub~tantially all the mercury in the filtered solids from the sludge is fixed in the form of mercuric sulfide.
TABLE III
REMOVAL OF MERCURY FROM BRINE SLUDGE
FI~TRATE WITH POLYSULFIDE
BRINE SLUDGE SAMPLE "A"
Na SElemental Total Efficiency of Removal ad~e~ Hg Hg(%) ___ (ppm)(ppb) (ppb~ Elemental Total Control 720 1390 - -13 90 g8 94 ~1 30 99~ 98 50* ~1 20 ggf 99 100 <1 60 99~ 96 100* ~1 30 99~ 98 250 ~1 60 99~ 96 *Samples analyzed again 30 hours after the first analysis.
BRINE SLUDGE SAMPLE ~B~
Na S NaHs Total Efficiency of Removal ad~e~ added Elemental Hg Hg of Hq (%) (ppm) (ppm) (ppb)(ppb) Elementa~ Total Control 150 5,200 _ _ 30 430 80 92 - ~3 65 98t 99 ~3 53 98~ 99 As can be seen from the Table, the present invention reduces the mercury concentration in the filtrate (supernatant) to a value lower, by an order of magnitude, than that attained by the prior art.
_ g _ ~083Z72 ~MPLE V
. . .
In a specific pilot plant trial on the use of polysulfide to precipitate mercury from brine sludge, 4 Imp.
gallons of polysulfide solution (about 10% solution, based on dissolved sulfur) were added to the brine sludge tank containing 12,000 Imp. gallons of brine sludge (approximately 2% ~uspended 801ids)o The elemental mercury content of the sludge before treatment was 17 ppb and this was reduced to less than 2 ppb with treatment (88.3~ removed). The total mercury in the supernatant was reduced from 3900 ppb to about 60 ppb. (98.5% removed).
EXAMPLE VI
A sa~ple from the perimeter sewer was treated at a pH of 9.5 as indicated in Table IV. A flocculating agent in the amount of 4 ppm was added and time was provided for settling before the treated sample was tested.
TABLE IV
PERIMETER SEWER
Hg in Supernatant Na S Na~S Elemental ~otal Removal Efficiency ad~eYd added Mercury Mercury for Hg ~) (ppm) (ppm) (ppb) (ppb) Elemental Total ~ 5 28 95 89 It will be apparent that the present invention provides a very effective way of reducing the mercury conta-mination of a wide variety of aquous media. The exampleshave all been directed to effluent media from a chlor-alkali 1~83Z72 plant but obviously the invention need not be limited to suc:h media.
Modifications may be made without departing from the spirit of the invention as defined in the appended claims.
In the event that both elemental mercury and ionic mercury are pre~ent in the contaminated media, it i8 preferred to use polysulfide together with sulfide. Both polysulfide and ~ulfide may be used to precipitzte ionic mercury. However, a greater weight of polysulfide than sulfide i5 required to precipitate the same amount of ionic mercury and, for this reason, a medium containing both ionic and elemental mercury is more economically treated by adding both sulfide and poly-sulfide.
If there i~ too great an exces~ of sulfide ions in the treated medium some of the mercury sulfide precipitated may react with excess sulfide ions to form a soluble mercuric disulfide complex.
HgS t S _ HgS2 The reactions to form mercury sulfide and the mercu-ry disulfide complex are pH dependent and therefore the amount of exces~ sulfide ion that may be tolerated is dependent on the pH of the media being treated, unless precautions are taken to ensure that the mercury sulfide is not converted into a soluble mercury disulfide complex. Such precautions would include the removing the mercury sulfide precipitate e.g. by filtration, before it can react with the excess sul-fide ion or the removing of the excess sulfide ions, e.g. by reaction with ferric chloride or the like. Thiq i8 facilita-ted by the fact that the formation of the mercury sulfide occurs more rapidly than the formation of the 801uble mer-cury di~ulfide complex.
~C~83272 In many cases, where the amount of mercury in the aqueous medium is small, the precautions may be superfluou~.
While it is preferred to use sodi~lm as the poly-su;Lfide cation, obviously other ~oluble polysulfides ~uch as potassium, ammonium, magnesium and calcium may be used provided they do not have other deleterious effects on the materialc being treated.
Dilute polysulfide solu~ions are unstable and therefore care must be taken to ensure that the effective-ness of the polysulfide solution is not prematurely des-troyed.
The present invention i9 particularly applicable to chlor-alkali plants using mercury cells and may be used to decontaminate the variou~ effluents from such a plant.
In a mercury cell, the mercury acts as the cathode and flows over the bottom of the cell which slopes slightly towards one end. Saturated brine solution is carried over the mercury and carbon anodes are inserted through the top of and cell and extend into the brine. The electrical potential between the anode and cathode draws the chloride ions to the anode where they form elemental chlorine which leaves the cell through a special outlet. The sodium ions are drawn to the mercury cathode where they form elemental sodium which immediately forms an amalgam with a some of the mercury. The mercury solution of the amalgam i9 carried to a separate compartment referred to as the denuder where water iB added to regenerate the mercury from the amalgam while at the same time forming sodium hydroxide and hydrogen gas. The mercury is returned to the cell and the sodium hydroxide and hydrogen ga~ are removed from the denuder.
The partially depleted brine is also removed from _ 5 _ the cell and carries with it 30me mercury. The depleted brine is fortified by the addition of fresh sodium chloride.
The impurities from the fre~h sodium chloricle are separated in a settling tank and the supernatant (fortified brine) is ret:urned to the cell while the dregs (brine ~ludge) are car-ried away for further treatment and di~posal. The mercury in the fortified brine return~ to the cell and is reused.
However the mercury in the brine sludge must be stabilized so that it cannot contaminate the environment.
The major source of mercury contaminated aqueous media from such chlor-alkali plants i9 the effluent from the cell sewers which collects all of the water from floor wash-ings, spills, purge streams from end boxes in the cells, wash waters, drainage from the caustic filtration area and from tank cleaning. The brine sludge referred to hereinabove is another source and is normally in the form of a sludge (up to about 40% suspended solids). The perimeter sewer which collects a liquid run off from an area adjacent to the plant forms yet another medium that requires treatment.
The following examples relate to treatment of speci-fic effluents from a chlor-alkali plant.
EXAMPLE I
Samples from the holding tank that collects the cell sewer effluent in a chlor-alkali plant were pH adjusted and treated according to the invention by adding polysulfide and sulfide plus a minor a unt of ferri~chloride and fil-tered. The pH was then set at 9 and the treatment repeated with and without sodium polysulfide ~Na2Sx when x is greater than 1). The results given in Table I.
10t~3Z72 T~LE I
TREATMENT OF CELL SEWER EE'FLUENT
TREATMENT METHOD Mercury After Removal of Effficiency Na2Sx NaH~ FeC13 Filtration (ppb) of Hg (%) pH ppm ppm ppm Elemental Total Elemental Total 9 control 140 570 - -9 50 50 ~00 4 4 97 99 100 2 2 9~ 99f 11 50 50 1~0 1 1 ggt 99t 12 50 50 100 1 97 99~ 83 It is apparent that the efficiency i 8 considerably better when Na2Sx is added and that the treatment is pH.
dependent. However the optimum pH will vary from plant to plant depending on the overall composition of the media being treated.
EXAMPLE II
Sample~ from the holding tank which collects the effluent cell sewer in a chlor-alkali plant, were adjusted to different~ pH values and treated with polysulfide (50 ppm), NaHS ~50 ppm) and FeC13 (100 ppm). The mercury level before treatment was 11.0 ppm the values after treatment are shown in Table II.
10~3Z7Z
TABLE I I
. .. ~
POLYSULFIDE PRECIPITATION OF MERCURY AT DIFFE~H
% Efficiency Elemental HgTotal Hg for removal of pH (ppb) ~ppm) total mercury . ~
8 <1 0.13 99 9 ~1 0.04 99 ~1 0.04 99 11 ~1 0.03 99 12 Sl 0.02 99 EXAMPLE III
In a specific plant trial at a chlor-alkali plant, polysulfide was used to treat the effluent from the cell sewer. This effluent has been traditionally treated by adding NaHS and FeC133, allowing the solids to settle in a decanter and then filtering.
During the plant trial polysulfide was also added during the treatment of this effluent. This was accompli~hed by simply adding polyculfide to a 5% NaHS solution which is continually metered into a treatment vessel. The polysulfide, NaHS and FeC13 concentrations in the water being treated were 20, 37, and 74 ppm respectively.
The average mercury losses in the two weeks prior to polysulfide addition was 0.087 ppm7 after polysulfide addition co~menced the level dropped to 0.011 ppm which represents an 86.9% reduction in mercury losses from this source. The efficiency of treatment with sulfide averaged 97.84~ and when polysulfide was added it increased to 99.71~.
EXAMPLE IV
_ In a chlor-alkali plant, samples of brine sludge were taken from the brine sludge tank. The major sources of 1~8327Z
this brine sludge are the brine clarifier, and the brine saturator. A con~iderable portion of the mercury from these source~ i5 elemental mercury. These samples of brine ~ludge at pH 10.7, were treated with varying quantitie~ of sodium polysulfide and the solids were then removed by filtration.
The mercury in soluble form (in the filtrate) was measured and the result~ are shown in Table III. ~ub~tantially all the mercury in the filtered solids from the sludge is fixed in the form of mercuric sulfide.
TABLE III
REMOVAL OF MERCURY FROM BRINE SLUDGE
FI~TRATE WITH POLYSULFIDE
BRINE SLUDGE SAMPLE "A"
Na SElemental Total Efficiency of Removal ad~e~ Hg Hg(%) ___ (ppm)(ppb) (ppb~ Elemental Total Control 720 1390 - -13 90 g8 94 ~1 30 99~ 98 50* ~1 20 ggf 99 100 <1 60 99~ 96 100* ~1 30 99~ 98 250 ~1 60 99~ 96 *Samples analyzed again 30 hours after the first analysis.
BRINE SLUDGE SAMPLE ~B~
Na S NaHs Total Efficiency of Removal ad~e~ added Elemental Hg Hg of Hq (%) (ppm) (ppm) (ppb)(ppb) Elementa~ Total Control 150 5,200 _ _ 30 430 80 92 - ~3 65 98t 99 ~3 53 98~ 99 As can be seen from the Table, the present invention reduces the mercury concentration in the filtrate (supernatant) to a value lower, by an order of magnitude, than that attained by the prior art.
_ g _ ~083Z72 ~MPLE V
. . .
In a specific pilot plant trial on the use of polysulfide to precipitate mercury from brine sludge, 4 Imp.
gallons of polysulfide solution (about 10% solution, based on dissolved sulfur) were added to the brine sludge tank containing 12,000 Imp. gallons of brine sludge (approximately 2% ~uspended 801ids)o The elemental mercury content of the sludge before treatment was 17 ppb and this was reduced to less than 2 ppb with treatment (88.3~ removed). The total mercury in the supernatant was reduced from 3900 ppb to about 60 ppb. (98.5% removed).
EXAMPLE VI
A sa~ple from the perimeter sewer was treated at a pH of 9.5 as indicated in Table IV. A flocculating agent in the amount of 4 ppm was added and time was provided for settling before the treated sample was tested.
TABLE IV
PERIMETER SEWER
Hg in Supernatant Na S Na~S Elemental ~otal Removal Efficiency ad~eYd added Mercury Mercury for Hg ~) (ppm) (ppm) (ppb) (ppb) Elemental Total ~ 5 28 95 89 It will be apparent that the present invention provides a very effective way of reducing the mercury conta-mination of a wide variety of aquous media. The exampleshave all been directed to effluent media from a chlor-alkali 1~83Z72 plant but obviously the invention need not be limited to suc:h media.
Modifications may be made without departing from the spirit of the invention as defined in the appended claims.
Claims (7)
1. A process for the treatment of aqueous effluent from a chlor-alkali plant containing elemental mercury and other undissolved solids to convert substantially all said elemental mercury to a stable form that does not contaminate the environment consisting essentially of: adding a water-soluble polysulfide to said solids containing effluent at a pH in the range 7-13 in an amount sufficient to combine with substantially all said elemental mercury to form insoluble mercury sulfide and separating solids from said effluent.
2. A method as defined in claim 1 wherein said polysulfide is a sodium polysulfide.
3. A method as defined in claim 1 wherein said effluent also includes ionic mercury and wherein a soluble sulfide is also added to said effluent, said polysulfide and said sulfide being present in the amount to combine with substantially all of said elemental mercury and ionic mercury in said effluent.
4. A method as defined in claim 3 wherein said sulfide and said polysulfide are sodium polysulfide and sodium sulfide.
5. A method as defined in claim 3 wherein said pH is in the range of 9 to 12.
6. A method as defined in claim 3 further comprises separating the mercury sulfide from said effluent before a significant portion of said mercury sulfide has time to re-solublize.
7. A method as defined in claim 6 wherein said mercury sulfide is separated from said effluent immediately after said mercury sulfide is formed.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA269,686A CA1083272A (en) | 1977-01-13 | 1977-01-13 | Treatment of mercury contaminated aqueous media |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA269,686A CA1083272A (en) | 1977-01-13 | 1977-01-13 | Treatment of mercury contaminated aqueous media |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1083272A true CA1083272A (en) | 1980-08-05 |
Family
ID=4107725
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA269,686A Expired CA1083272A (en) | 1977-01-13 | 1977-01-13 | Treatment of mercury contaminated aqueous media |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1083272A (en) |
-
1977
- 1977-01-13 CA CA269,686A patent/CA1083272A/en not_active Expired
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