CA1072412A - Chrome removal and recovery - Google Patents
Chrome removal and recoveryInfo
- Publication number
- CA1072412A CA1072412A CA255,874A CA255874A CA1072412A CA 1072412 A CA1072412 A CA 1072412A CA 255874 A CA255874 A CA 255874A CA 1072412 A CA1072412 A CA 1072412A
- Authority
- CA
- Canada
- Prior art keywords
- acetate
- barium
- chromium
- acid
- barium carbonate
- 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.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
- C02F1/54—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using organic material
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
- C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/20—Heavy metals or heavy metal compounds
- C02F2101/22—Chromium or chromium compounds, e.g. chromates
Landscapes
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Removal Of Specific Substances (AREA)
- Chemical Treatment Of Metals (AREA)
Abstract
Abstract of the Disclosure The present invention is directed to a process for removing and optionally recovering hexavalent chromium from chromium waste water. The invention involves the use of a treatment mixture comprising the combination of barium carbonate and/or barium hydrate, plus one or more certain specified acetates. The process involves contacting the chrome waste water to be treated with the treatment mixture at an acetic pH not e .g 6.0, and usually from 4.0 to 6.0, followed by filtration through an acid-resistant filter.
The chromium removed by this filter in the form of barium chromate can be regenerated into chromic acid by backwashing the filter into an agitated tank and treating to produce chromic acid and barium sulfate. The thus-generated chromic acid can then be returned to the chrome plating tank for re-use after passing through a filter to remove the barium sulfate.
The chromium removed by this filter in the form of barium chromate can be regenerated into chromic acid by backwashing the filter into an agitated tank and treating to produce chromic acid and barium sulfate. The thus-generated chromic acid can then be returned to the chrome plating tank for re-use after passing through a filter to remove the barium sulfate.
Description
~)t'~%~ ~L%
Back~ound of t~e Invention __ _ This invention is directed to treatment of in-dustrial waste waters containing hexavalent chromium in the form o~ chromic acid, metallic chromate salts, etc. Such chrome materials can no longer be discharged directly into sewers, rivers or streams due to various legal requirements and regulations imposed by environmental authorities. Also, chromium is an expensive metal and it is economically desir-able to recover the chromium values contained in the plating and rinse tanks. A process for removing the chromium from waste water and reco~ering it economically and efficiently has long been desired.
Prior art methods ~or removing chromium from indus-trial waste waters containing hexavalent chromium involve re-ducing the pH of the chromium waste water to a highly acid condition, e.g., 2.0 to 3.0, using a strong acid such as sul-furic acid or sodium bisulfite or sulfur dioxide (by adding it to a system through an S02 feeder), while agitating the treated solution by mechanical means, or by air. Then caustic ~` 20 soda, lime or another basic substance is added to elevate the ;' pH to a neutral or slightly basic condition, eOg., approximately 7.0 to 8.0, which then effects precipitation of the chrome in ~; the trivalent form. The thus precipitated solution is then permitted to settle for four to six hours, after which water is pumped to the sewer and sludge is discarded to landfill.
In many of these priorprocedures, the settlement of the pre-cipitatè is accomplished with one or more clarifiers which serve to reduce the volume of the sludge ~or discarding at a landfill. In recent years it has become increasin~ly diffi~
cult to discard this sludge to landfills because the chrome ~ "
': . , ~ .
, material present therein tends to leach Oll-t and thus find its way back into the soil and into the streams, causing water pollution. Moreover, in addition to great difficulty in meeting current environmental protection standards, these methods are costly and comparatively inefficient.
Another prior process involves the use of ion ex-change materials to remove chrome. The ion exchange proce-dures are extremely costly and not practical due to the large amounts of water required in such processes.
United States Patent No. 3,371,034 to Richards, illustrates a direct precipitation process utilizing great quantities of barium carbonate and aqueous solutions acldified with strong acids, such as nitric or hydrochloric acid, or their salts. Such procedures encountered difficulties in separation of the chromium solids which are precipitated from the liquid water media, thereby necessitating the use of one or more settling tanks which can be required to handle the excessive amounts of sludge produced. Moreover, the require-ment for large amounts of barium carbonate increases the - 20 amount of sludge generated.
Another prior process, set forth in ~nited States Patent No. 3,869,386 to Izdebski~ provides for direct re-moval of hexavalent chromium by adding aqueous barium ace--tate thereto. Izdebski states that this precipitation can be accomplished from neutral or slightly acid solutions in ` cases of precipitating both chromic acid and dichromates.
Disadvantages encountered with the Izdebski use of barium acetate only are that the acetate becomes more than is needed, thus having acetates in the water effluent and having to add more barium acetate to get the desired barium radical that is needed to form barium chromate. At this point barium chromate ' : ' ~ - , .. . . . . . . . ....... . . .
",`.'. ~ ' '-~ ' : ' . ' ~ . . .. . .
~V~JZ~ ~
is discarded. No reuse o~ the chrome is contemplated by Izdebski.
Accordingly, the need exists ~or a total recovery system which is economical and efficient, which permits reuse of both the recovered chromium and clarified water, and which may be installed as a single treatment unit in present plating systems.
Summary -of th~e Inve _ ion The present invention meets these needs by pro-viding a total recovery process whereby the chrome in thewaste is effectively precipitated, treated and reused, and the clarified water is either directed to the sewer or it-self reused in the plating operation. Basically, the process utilizes a combination of barium carbonate and/or barium hydrate along with an acetate compound. Preferably a dry ~ pre-mix of barium carbonate and/or barium hydrate and a pow-`~ dered inorganic acetate (for example calcium acetate) is utilized.
The total additives, whether pre-mixed or not, should be used in the range from 1:1 to 6:1, addltive to parts chrome in the waste water to be treated. Within the treatment mixture, the ratio of carbonate-hydrate to `~ acetate should generally range from 3:1 to 15:1 parts by weight.
The process involves contacting the chrome waste water to be treated with the treatment mixture at an acetic pH, generally 4.0 - 6.0 followed by filtration through an acid-resistant filter. The chromium deposited on -this filter ~- in the form of barium chromate is regenerated into chromium acid by backwashing into an agitated tank where it is treated to provide chromic acid and barium sulfate. The barium _ 4 _ .
~ , . .
.
%
sulfate is removed by a second acid-resistant ~ilter and the chromic acid is reused in the plating operation.
The clarified water from the first filtration may itself also be reused in the plating process. It may be re-used as is, may be treated with sul~uric acid first followed by filtration and neutralization, or may be disposed of as is or again after treatment with sulfuric acid and/or neutrali-zation.
Accordingly, it is an object of the present in-vention to provide an e~ficient, economical process for re-covering and reusing chromium from industrial waste solutions through the addition of barium carbonate and/or barium hydrate in mixture with an acetate materialO
Another object of the present invention is to clarify chromium containing waste waters to the extent that the clarified water may also be reused in the plating process.
A further object of the invention is to provide ` a pre-mixed treatment composition for use in clarifying `
chromium containing waste waters.
Other objects and advantages of the invention will be apparent from the following description, the ac-companying drawings and the appended claims.
. .
Brief Description of the Drawings Figs. 1 and 2 of the drawings are both flow charts ` showing the alternative variations in which the process may " be conducted.
Description of the Preferred Embodiments As a result of a chromium plating process plated parts, after being removed from the plating tank(s), are -`- placed in one or more aqueous rinse tanks. As parts are rinsed in the rinse tank(s), water counterflows backwards ,' ~ .: . ~ ' ' ~: ' ' ' - . . ' ':
-`: ' . ' . ' .
~ t2 toward the first rinse tank for concentrated contamination.
The rinse solution contained in the ~irst rinse tank thus contains a greater concentration of chromium due to this build-up.
In accordance with the process indicated in Fig. 1, the chrome contaminated rinse water in tank 2 is removed for treatment through line 3, or by free flow from the rinse tank to a chrome treatment tank 4. To the rinse water in this treatment tank has been added the treating composition of this invention, viz, the barium carbonate and/or barium hydrate, plus one or more specified acetates in the con-centration specified herein below. The weight ratio of the barium carbonate and/or barium hydrate to the specified acetate ranges from 3 to 15 weight parts of barium carbonate and/or barium hydrate to one weight part of the specified acetate. The cornbination is added to the waste water in sufficient amounts to provide 1 to 6 weight parts of the combination per weight part of chrome to be removed from the waste water. The pH of the treatment tank subsequent to the addition of the treating compositions of this invention, is acidic. Usually the pH in the treatment tank after addition of the barium carbonate and/or barium hydrate, plus speci-fied acetate(s), is within the range of 4.0 to 6.0, more preferably from 5.0 to 6Ø Most preferably, the weight ratio of barium carbonate and/or barium hydrate to the specified acetate(s) is around 4:1. Similarly, the preferred ratio of the treating composition to the amount of chrome present in the waste water is around 2:1.
In order to receive the benefits attainable in ac-cordance with this invention, not only must the concentration of the barium carbonate and/or barium hydrate to the specified ' . ,, . ' : -J~fll~
acetate be observed, buk also it is important that the pH
considerations be maintained. If the pH is permitted to exceed 6.0 during treatment, acetic acid is added in suffi-cient quantity to bring the pH down to 6.0 or below. If the pH of the chrome waste water, after contacting it with the treatment mixture of this invention, is below 6.0 and within the range of 4.0 to 6.0, it is not necessary to add the acetic acid.
The thus treated chrome waste water is then passed `~ lO to filter 6, which is preferably a 2 to 4 micron ~ilter, al- ;
though it may vary from 0.5 to lO microns, where the precipi-tated barium chromate is collected. The collected barium chromate is then removed from filter 6 by backwashing the filter through line 7 into an agitated holding tank 8. There it is treated with a sulfur containing material to produce ` chromic acid and barium sulfate. This may be by adding sul-furic acid or by using the plating solution in the plating (dip) tank 1, passed to line 12, in order to lower the pH i and add sulfate, thereby accelerating and enhancing conversion of the barium chromate to chromic acid at a pH ranging from l `-to 1.5. Chromic acid can then be taken from agitated tank 8 ` via line 9 through filter lO, a polyester filter having aver-age openings preferably of about 0.5 to l micron, although it could range from 0.5 - 3 microns. The thus Eegenerated chromic acid can then be added to plating tank l by passing it through line ll. Tank 8 is usually equipped with conven-tional agitation equipment.
The effluent from filter 6 can be moved directly to a sewer, river or stream, or can be recycled back to the original rinse tank for reuse.
In accordance with the flow chart of Fig. 2, and .
` :-` ` :.
' ' `
t)q,~
ra~her than usiny a separate ~hro~e treatment tank, the treatment mixture of this invention can be added to the chrome rinse tank 2, in which case it becomes a combined rinse and treatment -tank. Otherwise, the process according to Fig. 2 is the same as illustrated in Fig. 1. Actually, the use of the Fig. 2 process is preferred since not only can the separate treatment tank and accompanying inlet and outlet lines be eliminated, but surprisingly the rinse is more effective in obtaining removal of more of ~he chromium from the plating operation when the rinse tank is also used as a treatment tank.
While the pH of the chrome rinse tanks and that occurring in the chrome treatment tank 4 (Fig. 1) prior to the addition of the treating composition of this invention can vary widely, the pH before addition usually is about 3.0 + 0.5.
A very important aspect of the process and composi-tion of this invention is its ability to recover the chromium, which is removed as barium chromate in a simple two step procedure involving backwashing barium chromate removed by filter 6 into an agitated tank to which there is added re-presentative chromic acid plating solution. This plating solution contains about 100 to 200 weight parts of chromic acid per weight part of sulfate, which is typically present as sodium sulfate, sulfuric acid, etc. The volume ratio of a typical plating bath which is added to tank 8, in which the backwashed barium chromate is agitated, ranges from about 3.5 to ~.5 to 1 molar, or preferably ~ to 1 at a p~
of 1 to 1.5. This chromic acid from plating tank 1 can be pumped from the plating tank directly to the agitated barium chromate-containing tank~
Thus, there is provided a chromium removal and re-covery process wherein chromiu~, is removed as barium chro-mate by direct precipitation using the oomposi~ion of this invention in a process environment permitti~g its compara-tively inexpensive and direct regeneration to chromic acid in a condition in whi~h i-t is suitable for direct reuse in the chromic acid plating process tanks.
As previousl~ stated, this invention involves the carefully controlled use of a combination of barium carbonate and/or barium hydrate, plus selected acetate(s) wherein the weight ratio of the combination of barium carbonate and/or barium hydrate to the selected acetate ranges from about 3 -15 to 1, and preferably about 4 to 1. The acetate may be one or more acetates selected from the group consisting of barium acetate, calcium acetate, strontium acetate, ethyl acetate, ethylidene diacetate, ferric acetate, isobutyl acetate, isopropyl acetate, methyl acetate, aluminum acetate, stannous acetate, cerous acetate, cobalt acetate, cupric acetate, magnesium acetate, manganese acetate, nickel acetate, ~-~ , , .
uranyl acetate, sodium diacetate, zinc acetate, or mixtures ` thereof. Acetic acid can also be used as the acetate com-pound. However, it is preferred that the acetate radical be in dry ~orm so that it can be premixed with the barium car bonate and/or barium hydrate, which are also available as powders. Accordingly, the preferred acetates are those of barium, calcium, strontium, iron (~erric) aluminum, tin (stannous), cerium (cerous), cobalt, copper (cupric), magnesium, manganese, nickel, uranium (uranyl), sodium, zinc and mixtures thereof.
The acetate radical is only added to this in-vention composition to make the chromium solution slightly _ g _ . ~ .
- ' ~
~2 acetic and or,ly ~or this result. Since metallic impurities are not af~ected by this procedure, and remain soluble, -they flo~ through with the water e~luent, thus eliminating the impurity return to the chrome platin~ solution. This leaves a pure ~orm o~ chromic acid returning to the chromium plating solution.
In accordance with this invention it is important that the stated concentrations of barium carbonate and/or barium hydrate and the specified acetate be carefully observed.
When the acetate(s) are employed in excess, metals will be in aqueous effluent, such metals as barium and chromium, to an unduly high extent which would prevent the direct dis-charge of the aqueous effluent into rivers and streams.
While the variety of acid-resistant filtering media tresistant to pH ranges of about 2 to 5~ can be employed for filter 6, the use of synthetic organic plastic fibrous materials having requisite .5 to 10 micron openings is usually employed. Thus such synthetic organic plastic fibrous mater-ials as polyesters, polyamides, or polyethylenes, for example "Dacron" fiber filters or equivalent are preferred. Such filters should have openings ranging from 0.5 to 10 microns, `
and more preferably openings within the range from 2 to 4 microns.
As stated, the removed chromium values recovered `
in accordance with khis invention by backwashing the chrome removal filter 6 containing chromium in the form of barium chromate into an agitated holding tank 8 into which chromic ~i acid in the form of plating bath in tank 1 is added, concen-tration ratio of chromic acid being 100 to 200 to 1 sulfate.
The volume ratio of the plating solukion to barium chromate ranges about 4 to 1, or even as high as 10 to 1, depending ,;' ' - 10 -.' ` '' ' ~ ~ ~
on the concentration of chrome plating solution. This re-generated chromic acid solution is then filtered through the 0.5 to 1 micron filter 10 leaving an insoluble barium sulfate precipitate on the filter. This precipitate can be removed from the ~ilter by washing with water until the precipitate is clear. Alternatively, the barium sulfate filter cartridge can be discarded because barium sulfate is non-toxic and, therefore, more readily disposable.
In order to obtain intimate contact bètween the chromium material present in the industrial waste solution and the treating composition of this invention, it is pre-ferable to agitate the solutions as they are combined in the chrome treatment tank 4 (Fig. l), and chrome rinse and treatment tank(s) (Fig. 2). The reactant materials must be agitated vigorously by the use of air agitation, mechani~
cal agitation, or any other suitable agitation procedure.
- The process of this invention permits the direct precipitation, removal and recovery of substantially all of the chromium present in the waste aqueous media. The re-covery procedure is substantially sludge-free and permits the removal and recovery process to be conducted without undue clogging of filters and without the necessity for using secondary or settling tanks to assist in the removal and re-covery procedure. This process permits ready and swift fil-tration removal of chromium in one simple step. Any concen-tration of chromium in any volume of a~ueous waste media can be removed. The chromium can be precipitated, filtered and removed without re~uiring considerable periods of time and additional processing apparatus, secondary holding or settling ` 30 tanks. The process can be utili~ed in a continuous removal and recovery procedure and the chromium can be recycled for .' - 11 -~, ~
direct use to the primary industrial processes of plating.
EXAMPLE I
500 gallons o~ chromium rinse water containing 2 pounds of chrome was subjected to treatment in accordance with this invention. Four pounds of barium carbonate and one - pound of calcium acetate (as a five pound dry pre-mix of the two) were added to the chrome rinse water and agitated vigorously for a period of approximately five minutes. The resulting chromium solution was filtered through a 2 to 4 micron filter while the same was continuously agitated. The effluent water resulting from the filtration was clear and analysis taken of chrome content was 0.001 parts per million.
This is far beyond the acceptable analysis for direct dis-charge into rivers and streams in accordance with environ-mental regulations.
EXAMPLE II
The procedure of Example 1 is repeated with the added stage of regeneration of the remo~ed chromium by `
backwashing the 2 to 4 micron filter with water. The back-wash solution is passed to a tank in which the agitation is vigorously maintained by air. Approximately ten gallons of chromic acid from the chrome plating bath was then pumped to the agitated tank and the pH dropped to 1.5. Solution was then filtered through a 0.5 to 1 micron filter and found to be sufficiently pure to permit its direct reuse in the - chrome plating process.
:.
EXAMPLE III
` The procedure of Example 1 is duplicated except -~ utilizing four pounds of an equal (by weight) mixture of barium carbonate and/or poly hydrated barium hydrate, viz, BaOH~H2O. Likewise, other acetates were substituted totally for the calcium acetate of Example I. The results obtained . :
Z~ ~Z
were subs-tantially the same as that of Example I in respect to the concentration of chrome present in the ~iltered solution.
EX~MPLE IV
_ __~_ This procedure was performed utilizing actual contaminated chrome waste water from a K-35-Z Udylite chrome plating process.
The chrome content of the waste water was analyzed to be approximately 5-1/2 ounces of chrome in the 5 gallon sample.
The treating aqueous media was prepared by mixing 11 ounces of barium carbonate in a pint of water. Then four ounces of acetic acid was added thereto and the mixture was dumped into the chrome waste water (approximately five gallons ' of waste water). The waste water-treating media was agitated `, for two to three minutes and the pH was then measured and de-', termined to be approximately 4.5-4.6. No ammonium hydroxide ;, was added to elevate the pH as this was in the preferred range for conducting the process.
Filtration was started as the agitation of the ;l 20 chrome water-treatiny media mixture was continued. The first test sample was pulled after filtration of 1/2 gallon of the treated waste water through the "Dacron" filter having openings wi~hin the 2 to 4 micron range. The second test sample was pulled after filtering approximately two gallons thereof.
The third test sample was pulled after filtering approximately four gallons thQreof and the fourth and final test sample was ` pulled when about 1/2 gallon o~ the waste water-treating media mixture was left to undergo filtration. These test samples were analyzed in accordance with the procedure and utilizing the analyzer as set forth in Example I above.
The test results are tabulated hereinbelow in - . :.
Table IV.
T LE-IV
Sample Test Reading Wt. % Chrome One 100 None Two 100 None Three 100 None Four 100 None While the method herein described constitutes a preferred embodiment of the invention, it is to be under-stood that the invention is not limited to ~his precise method, and that changes may be made therein without de- .. -parting from the scope of the invention which is defined in the appended claims. '-, . .
:'.`
' ,:~
, 30 :
.'' ~
~ 14 -. - , , . ~ .
:
Back~ound of t~e Invention __ _ This invention is directed to treatment of in-dustrial waste waters containing hexavalent chromium in the form o~ chromic acid, metallic chromate salts, etc. Such chrome materials can no longer be discharged directly into sewers, rivers or streams due to various legal requirements and regulations imposed by environmental authorities. Also, chromium is an expensive metal and it is economically desir-able to recover the chromium values contained in the plating and rinse tanks. A process for removing the chromium from waste water and reco~ering it economically and efficiently has long been desired.
Prior art methods ~or removing chromium from indus-trial waste waters containing hexavalent chromium involve re-ducing the pH of the chromium waste water to a highly acid condition, e.g., 2.0 to 3.0, using a strong acid such as sul-furic acid or sodium bisulfite or sulfur dioxide (by adding it to a system through an S02 feeder), while agitating the treated solution by mechanical means, or by air. Then caustic ~` 20 soda, lime or another basic substance is added to elevate the ;' pH to a neutral or slightly basic condition, eOg., approximately 7.0 to 8.0, which then effects precipitation of the chrome in ~; the trivalent form. The thus precipitated solution is then permitted to settle for four to six hours, after which water is pumped to the sewer and sludge is discarded to landfill.
In many of these priorprocedures, the settlement of the pre-cipitatè is accomplished with one or more clarifiers which serve to reduce the volume of the sludge ~or discarding at a landfill. In recent years it has become increasin~ly diffi~
cult to discard this sludge to landfills because the chrome ~ "
': . , ~ .
, material present therein tends to leach Oll-t and thus find its way back into the soil and into the streams, causing water pollution. Moreover, in addition to great difficulty in meeting current environmental protection standards, these methods are costly and comparatively inefficient.
Another prior process involves the use of ion ex-change materials to remove chrome. The ion exchange proce-dures are extremely costly and not practical due to the large amounts of water required in such processes.
United States Patent No. 3,371,034 to Richards, illustrates a direct precipitation process utilizing great quantities of barium carbonate and aqueous solutions acldified with strong acids, such as nitric or hydrochloric acid, or their salts. Such procedures encountered difficulties in separation of the chromium solids which are precipitated from the liquid water media, thereby necessitating the use of one or more settling tanks which can be required to handle the excessive amounts of sludge produced. Moreover, the require-ment for large amounts of barium carbonate increases the - 20 amount of sludge generated.
Another prior process, set forth in ~nited States Patent No. 3,869,386 to Izdebski~ provides for direct re-moval of hexavalent chromium by adding aqueous barium ace--tate thereto. Izdebski states that this precipitation can be accomplished from neutral or slightly acid solutions in ` cases of precipitating both chromic acid and dichromates.
Disadvantages encountered with the Izdebski use of barium acetate only are that the acetate becomes more than is needed, thus having acetates in the water effluent and having to add more barium acetate to get the desired barium radical that is needed to form barium chromate. At this point barium chromate ' : ' ~ - , .. . . . . . . . ....... . . .
",`.'. ~ ' '-~ ' : ' . ' ~ . . .. . .
~V~JZ~ ~
is discarded. No reuse o~ the chrome is contemplated by Izdebski.
Accordingly, the need exists ~or a total recovery system which is economical and efficient, which permits reuse of both the recovered chromium and clarified water, and which may be installed as a single treatment unit in present plating systems.
Summary -of th~e Inve _ ion The present invention meets these needs by pro-viding a total recovery process whereby the chrome in thewaste is effectively precipitated, treated and reused, and the clarified water is either directed to the sewer or it-self reused in the plating operation. Basically, the process utilizes a combination of barium carbonate and/or barium hydrate along with an acetate compound. Preferably a dry ~ pre-mix of barium carbonate and/or barium hydrate and a pow-`~ dered inorganic acetate (for example calcium acetate) is utilized.
The total additives, whether pre-mixed or not, should be used in the range from 1:1 to 6:1, addltive to parts chrome in the waste water to be treated. Within the treatment mixture, the ratio of carbonate-hydrate to `~ acetate should generally range from 3:1 to 15:1 parts by weight.
The process involves contacting the chrome waste water to be treated with the treatment mixture at an acetic pH, generally 4.0 - 6.0 followed by filtration through an acid-resistant filter. The chromium deposited on -this filter ~- in the form of barium chromate is regenerated into chromium acid by backwashing into an agitated tank where it is treated to provide chromic acid and barium sulfate. The barium _ 4 _ .
~ , . .
.
%
sulfate is removed by a second acid-resistant ~ilter and the chromic acid is reused in the plating operation.
The clarified water from the first filtration may itself also be reused in the plating process. It may be re-used as is, may be treated with sul~uric acid first followed by filtration and neutralization, or may be disposed of as is or again after treatment with sulfuric acid and/or neutrali-zation.
Accordingly, it is an object of the present in-vention to provide an e~ficient, economical process for re-covering and reusing chromium from industrial waste solutions through the addition of barium carbonate and/or barium hydrate in mixture with an acetate materialO
Another object of the present invention is to clarify chromium containing waste waters to the extent that the clarified water may also be reused in the plating process.
A further object of the invention is to provide ` a pre-mixed treatment composition for use in clarifying `
chromium containing waste waters.
Other objects and advantages of the invention will be apparent from the following description, the ac-companying drawings and the appended claims.
. .
Brief Description of the Drawings Figs. 1 and 2 of the drawings are both flow charts ` showing the alternative variations in which the process may " be conducted.
Description of the Preferred Embodiments As a result of a chromium plating process plated parts, after being removed from the plating tank(s), are -`- placed in one or more aqueous rinse tanks. As parts are rinsed in the rinse tank(s), water counterflows backwards ,' ~ .: . ~ ' ' ~: ' ' ' - . . ' ':
-`: ' . ' . ' .
~ t2 toward the first rinse tank for concentrated contamination.
The rinse solution contained in the ~irst rinse tank thus contains a greater concentration of chromium due to this build-up.
In accordance with the process indicated in Fig. 1, the chrome contaminated rinse water in tank 2 is removed for treatment through line 3, or by free flow from the rinse tank to a chrome treatment tank 4. To the rinse water in this treatment tank has been added the treating composition of this invention, viz, the barium carbonate and/or barium hydrate, plus one or more specified acetates in the con-centration specified herein below. The weight ratio of the barium carbonate and/or barium hydrate to the specified acetate ranges from 3 to 15 weight parts of barium carbonate and/or barium hydrate to one weight part of the specified acetate. The cornbination is added to the waste water in sufficient amounts to provide 1 to 6 weight parts of the combination per weight part of chrome to be removed from the waste water. The pH of the treatment tank subsequent to the addition of the treating compositions of this invention, is acidic. Usually the pH in the treatment tank after addition of the barium carbonate and/or barium hydrate, plus speci-fied acetate(s), is within the range of 4.0 to 6.0, more preferably from 5.0 to 6Ø Most preferably, the weight ratio of barium carbonate and/or barium hydrate to the specified acetate(s) is around 4:1. Similarly, the preferred ratio of the treating composition to the amount of chrome present in the waste water is around 2:1.
In order to receive the benefits attainable in ac-cordance with this invention, not only must the concentration of the barium carbonate and/or barium hydrate to the specified ' . ,, . ' : -J~fll~
acetate be observed, buk also it is important that the pH
considerations be maintained. If the pH is permitted to exceed 6.0 during treatment, acetic acid is added in suffi-cient quantity to bring the pH down to 6.0 or below. If the pH of the chrome waste water, after contacting it with the treatment mixture of this invention, is below 6.0 and within the range of 4.0 to 6.0, it is not necessary to add the acetic acid.
The thus treated chrome waste water is then passed `~ lO to filter 6, which is preferably a 2 to 4 micron ~ilter, al- ;
though it may vary from 0.5 to lO microns, where the precipi-tated barium chromate is collected. The collected barium chromate is then removed from filter 6 by backwashing the filter through line 7 into an agitated holding tank 8. There it is treated with a sulfur containing material to produce ` chromic acid and barium sulfate. This may be by adding sul-furic acid or by using the plating solution in the plating (dip) tank 1, passed to line 12, in order to lower the pH i and add sulfate, thereby accelerating and enhancing conversion of the barium chromate to chromic acid at a pH ranging from l `-to 1.5. Chromic acid can then be taken from agitated tank 8 ` via line 9 through filter lO, a polyester filter having aver-age openings preferably of about 0.5 to l micron, although it could range from 0.5 - 3 microns. The thus Eegenerated chromic acid can then be added to plating tank l by passing it through line ll. Tank 8 is usually equipped with conven-tional agitation equipment.
The effluent from filter 6 can be moved directly to a sewer, river or stream, or can be recycled back to the original rinse tank for reuse.
In accordance with the flow chart of Fig. 2, and .
` :-` ` :.
' ' `
t)q,~
ra~her than usiny a separate ~hro~e treatment tank, the treatment mixture of this invention can be added to the chrome rinse tank 2, in which case it becomes a combined rinse and treatment -tank. Otherwise, the process according to Fig. 2 is the same as illustrated in Fig. 1. Actually, the use of the Fig. 2 process is preferred since not only can the separate treatment tank and accompanying inlet and outlet lines be eliminated, but surprisingly the rinse is more effective in obtaining removal of more of ~he chromium from the plating operation when the rinse tank is also used as a treatment tank.
While the pH of the chrome rinse tanks and that occurring in the chrome treatment tank 4 (Fig. 1) prior to the addition of the treating composition of this invention can vary widely, the pH before addition usually is about 3.0 + 0.5.
A very important aspect of the process and composi-tion of this invention is its ability to recover the chromium, which is removed as barium chromate in a simple two step procedure involving backwashing barium chromate removed by filter 6 into an agitated tank to which there is added re-presentative chromic acid plating solution. This plating solution contains about 100 to 200 weight parts of chromic acid per weight part of sulfate, which is typically present as sodium sulfate, sulfuric acid, etc. The volume ratio of a typical plating bath which is added to tank 8, in which the backwashed barium chromate is agitated, ranges from about 3.5 to ~.5 to 1 molar, or preferably ~ to 1 at a p~
of 1 to 1.5. This chromic acid from plating tank 1 can be pumped from the plating tank directly to the agitated barium chromate-containing tank~
Thus, there is provided a chromium removal and re-covery process wherein chromiu~, is removed as barium chro-mate by direct precipitation using the oomposi~ion of this invention in a process environment permitti~g its compara-tively inexpensive and direct regeneration to chromic acid in a condition in whi~h i-t is suitable for direct reuse in the chromic acid plating process tanks.
As previousl~ stated, this invention involves the carefully controlled use of a combination of barium carbonate and/or barium hydrate, plus selected acetate(s) wherein the weight ratio of the combination of barium carbonate and/or barium hydrate to the selected acetate ranges from about 3 -15 to 1, and preferably about 4 to 1. The acetate may be one or more acetates selected from the group consisting of barium acetate, calcium acetate, strontium acetate, ethyl acetate, ethylidene diacetate, ferric acetate, isobutyl acetate, isopropyl acetate, methyl acetate, aluminum acetate, stannous acetate, cerous acetate, cobalt acetate, cupric acetate, magnesium acetate, manganese acetate, nickel acetate, ~-~ , , .
uranyl acetate, sodium diacetate, zinc acetate, or mixtures ` thereof. Acetic acid can also be used as the acetate com-pound. However, it is preferred that the acetate radical be in dry ~orm so that it can be premixed with the barium car bonate and/or barium hydrate, which are also available as powders. Accordingly, the preferred acetates are those of barium, calcium, strontium, iron (~erric) aluminum, tin (stannous), cerium (cerous), cobalt, copper (cupric), magnesium, manganese, nickel, uranium (uranyl), sodium, zinc and mixtures thereof.
The acetate radical is only added to this in-vention composition to make the chromium solution slightly _ g _ . ~ .
- ' ~
~2 acetic and or,ly ~or this result. Since metallic impurities are not af~ected by this procedure, and remain soluble, -they flo~ through with the water e~luent, thus eliminating the impurity return to the chrome platin~ solution. This leaves a pure ~orm o~ chromic acid returning to the chromium plating solution.
In accordance with this invention it is important that the stated concentrations of barium carbonate and/or barium hydrate and the specified acetate be carefully observed.
When the acetate(s) are employed in excess, metals will be in aqueous effluent, such metals as barium and chromium, to an unduly high extent which would prevent the direct dis-charge of the aqueous effluent into rivers and streams.
While the variety of acid-resistant filtering media tresistant to pH ranges of about 2 to 5~ can be employed for filter 6, the use of synthetic organic plastic fibrous materials having requisite .5 to 10 micron openings is usually employed. Thus such synthetic organic plastic fibrous mater-ials as polyesters, polyamides, or polyethylenes, for example "Dacron" fiber filters or equivalent are preferred. Such filters should have openings ranging from 0.5 to 10 microns, `
and more preferably openings within the range from 2 to 4 microns.
As stated, the removed chromium values recovered `
in accordance with khis invention by backwashing the chrome removal filter 6 containing chromium in the form of barium chromate into an agitated holding tank 8 into which chromic ~i acid in the form of plating bath in tank 1 is added, concen-tration ratio of chromic acid being 100 to 200 to 1 sulfate.
The volume ratio of the plating solukion to barium chromate ranges about 4 to 1, or even as high as 10 to 1, depending ,;' ' - 10 -.' ` '' ' ~ ~ ~
on the concentration of chrome plating solution. This re-generated chromic acid solution is then filtered through the 0.5 to 1 micron filter 10 leaving an insoluble barium sulfate precipitate on the filter. This precipitate can be removed from the ~ilter by washing with water until the precipitate is clear. Alternatively, the barium sulfate filter cartridge can be discarded because barium sulfate is non-toxic and, therefore, more readily disposable.
In order to obtain intimate contact bètween the chromium material present in the industrial waste solution and the treating composition of this invention, it is pre-ferable to agitate the solutions as they are combined in the chrome treatment tank 4 (Fig. l), and chrome rinse and treatment tank(s) (Fig. 2). The reactant materials must be agitated vigorously by the use of air agitation, mechani~
cal agitation, or any other suitable agitation procedure.
- The process of this invention permits the direct precipitation, removal and recovery of substantially all of the chromium present in the waste aqueous media. The re-covery procedure is substantially sludge-free and permits the removal and recovery process to be conducted without undue clogging of filters and without the necessity for using secondary or settling tanks to assist in the removal and re-covery procedure. This process permits ready and swift fil-tration removal of chromium in one simple step. Any concen-tration of chromium in any volume of a~ueous waste media can be removed. The chromium can be precipitated, filtered and removed without re~uiring considerable periods of time and additional processing apparatus, secondary holding or settling ` 30 tanks. The process can be utili~ed in a continuous removal and recovery procedure and the chromium can be recycled for .' - 11 -~, ~
direct use to the primary industrial processes of plating.
EXAMPLE I
500 gallons o~ chromium rinse water containing 2 pounds of chrome was subjected to treatment in accordance with this invention. Four pounds of barium carbonate and one - pound of calcium acetate (as a five pound dry pre-mix of the two) were added to the chrome rinse water and agitated vigorously for a period of approximately five minutes. The resulting chromium solution was filtered through a 2 to 4 micron filter while the same was continuously agitated. The effluent water resulting from the filtration was clear and analysis taken of chrome content was 0.001 parts per million.
This is far beyond the acceptable analysis for direct dis-charge into rivers and streams in accordance with environ-mental regulations.
EXAMPLE II
The procedure of Example 1 is repeated with the added stage of regeneration of the remo~ed chromium by `
backwashing the 2 to 4 micron filter with water. The back-wash solution is passed to a tank in which the agitation is vigorously maintained by air. Approximately ten gallons of chromic acid from the chrome plating bath was then pumped to the agitated tank and the pH dropped to 1.5. Solution was then filtered through a 0.5 to 1 micron filter and found to be sufficiently pure to permit its direct reuse in the - chrome plating process.
:.
EXAMPLE III
` The procedure of Example 1 is duplicated except -~ utilizing four pounds of an equal (by weight) mixture of barium carbonate and/or poly hydrated barium hydrate, viz, BaOH~H2O. Likewise, other acetates were substituted totally for the calcium acetate of Example I. The results obtained . :
Z~ ~Z
were subs-tantially the same as that of Example I in respect to the concentration of chrome present in the ~iltered solution.
EX~MPLE IV
_ __~_ This procedure was performed utilizing actual contaminated chrome waste water from a K-35-Z Udylite chrome plating process.
The chrome content of the waste water was analyzed to be approximately 5-1/2 ounces of chrome in the 5 gallon sample.
The treating aqueous media was prepared by mixing 11 ounces of barium carbonate in a pint of water. Then four ounces of acetic acid was added thereto and the mixture was dumped into the chrome waste water (approximately five gallons ' of waste water). The waste water-treating media was agitated `, for two to three minutes and the pH was then measured and de-', termined to be approximately 4.5-4.6. No ammonium hydroxide ;, was added to elevate the pH as this was in the preferred range for conducting the process.
Filtration was started as the agitation of the ;l 20 chrome water-treatiny media mixture was continued. The first test sample was pulled after filtration of 1/2 gallon of the treated waste water through the "Dacron" filter having openings wi~hin the 2 to 4 micron range. The second test sample was pulled after filtering approximately two gallons thereof.
The third test sample was pulled after filtering approximately four gallons thQreof and the fourth and final test sample was ` pulled when about 1/2 gallon o~ the waste water-treating media mixture was left to undergo filtration. These test samples were analyzed in accordance with the procedure and utilizing the analyzer as set forth in Example I above.
The test results are tabulated hereinbelow in - . :.
Table IV.
T LE-IV
Sample Test Reading Wt. % Chrome One 100 None Two 100 None Three 100 None Four 100 None While the method herein described constitutes a preferred embodiment of the invention, it is to be under-stood that the invention is not limited to ~his precise method, and that changes may be made therein without de- .. -parting from the scope of the invention which is defined in the appended claims. '-, . .
:'.`
' ,:~
, 30 :
.'' ~
~ 14 -. - , , . ~ .
:
Claims (13)
1. A process for removing chromium from chromium-containing waste water from chromium plating processes com-prising contacting said chromium-containing waste water with a treatment mixture of barium carbonate and/or barium hydrate and an acetate compound at a pH of 6 or less utilizing a weight ratio of treatment mixture to chromium present rang-ing from 1:1 to 6:1 and a weight ratio of barium carbonate and/or barium hydrate to acetate compound ranging from 3 to 15:1 parts by weight, thereafter filtering with a first acid-resistant filter media to remove the resultant in-soluble barium chromate, recovering the filtered barium chromate, contacting said barium chromate with sulfuric acid to produce a chromic acid solution containing insoluble barium sulfate, passing said solution from said sulfuric acid contact through a second acid-resistant filter material to remove insoluble barium sulfate therefrom, collecting the filtrate effluent from said second filter, and reusing its chromium content in said chromium plating process.
2. The process as in Claim 1 wherein said first acid-resistant filter media had openings within the range of 0.5 to 10 microns.
3. The process as in Claim 2 wherein said second acid-resistant filter material has openings within the range of 0.5 - 1.0 microns.
4. The process as in claim 2 wherein said first acid-resistant filter media has openings of 2-4 microns.
5. The process as in claim 4 wherein said acetate compound is selected from the group consisting of barium acetate, calcium acetate, strontium acetate/ ethyl acetate, ethylidene diacetate, ferric acetate, isobutyl acetate, iso-propyl acetate, methyl acetate, aluminum acetate, stannous acetate, cerous acetate, cobalt acetate, cupric acetate, magnesium acetate, manganese acetate, nickel acetate, uranyl acetate, sodium diacetate, zinc acetate, and mixtures thereof.
6. The process as in claim 5 wherein said barium carbonate and/or barium hydrate is barium carbonate and said acetate is calcium acetate and wherein said barium carbonate and calcium acetate are utilized as a dry powder pre-mix.
7. The process as in claim 6 wherein said pre-mix is added directly to a chrome rinse.
8. The process as in claim 4 wherein said acetate compound is acetic acid.
9. The process as in Claim 1 wherein said sulfuric acid treatment comprises contacting said filtered chromium with a plating solution containing sulfuric acid.
10. The process as in Claim 1 wherein said effluent from said first acid-resistant filter is also reused in said chromium plating process.
11. A treatment composition for use in removing chromium from chromium containing water comprising a dry powder mixture of components: a) barium carbonate and/or barium hydrate and (b) a water-soluble acetate salt selected from the group consisting of the acetates of barium, calcium, strontium, iron, aluminum, tin, cerium, cobalt, copper, magnesium, manganese, nickel, uranium, sodium, zinc, and mixtures thereof, said components being present in the ratio of 3-15 parts by weight barium carbonate and/or barium hydrate to 1 part water-soluble acetate salt.
12. A treatment composition as in Claim 11 wherein said component (a) is barium carbonate and said component (b) is calcium acetate.
13. A treatment composition as in Claim 12 wherein said mixture of components contains four parts by weight barium carbonate and one part calcium acetate.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/657,885 US4054517A (en) | 1974-08-06 | 1976-02-13 | Chrome removal and recovery |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1072412A true CA1072412A (en) | 1980-02-26 |
Family
ID=24639057
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA255,874A Expired CA1072412A (en) | 1976-02-13 | 1976-06-28 | Chrome removal and recovery |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5298630A (en) |
| AU (1) | AU498353B2 (en) |
| CA (1) | CA1072412A (en) |
| DE (1) | DE2630544A1 (en) |
| GB (1) | GB1537914A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1130595B (en) * | 1980-05-12 | 1986-06-18 | Stoppani Luigi Spa | CONTINUOUS PROCEDURE FOR THE ELEMINATION OF CHROME FROM WASTE WATER AND THE VALORISATION OF RECOVERED CHROME |
| JPS57186008U (en) * | 1981-05-21 | 1982-11-26 | ||
| CN114016119B (en) * | 2021-12-02 | 2023-04-04 | 徐州徐工液压件有限公司 | Electroplating bath solution comprehensive management device |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5027313B2 (en) * | 1971-11-15 | 1975-09-06 |
-
1976
- 1976-06-28 CA CA255,874A patent/CA1072412A/en not_active Expired
- 1976-07-07 DE DE19762630544 patent/DE2630544A1/en not_active Ceased
- 1976-07-12 JP JP8282876A patent/JPS5298630A/en active Granted
- 1976-07-12 GB GB2897176A patent/GB1537914A/en not_active Expired
- 1976-07-13 AU AU15827/76A patent/AU498353B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2630544A1 (en) | 1977-08-18 |
| JPS5643120B2 (en) | 1981-10-09 |
| AU1582776A (en) | 1978-01-19 |
| GB1537914A (en) | 1979-01-10 |
| JPS5298630A (en) | 1977-08-18 |
| AU498353B2 (en) | 1979-03-08 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4332687A (en) | Removal of complexed heavy metals from waste effluents | |
| US3575854A (en) | Rapid setiling of gelatinous precipitates | |
| DE1517730C3 (en) | Process for purifying water | |
| US4014787A (en) | Wastewater treatment | |
| JPS62253738A (en) | Removal of dangerous metal waste sludge | |
| US4943377A (en) | Method for removing dissolved heavy metals from waste oils, industrial wastewaters, or any polar solvent | |
| EP0168752A2 (en) | Method of treating liquid wastes containing heavy metal chelate compounds | |
| Christensen et al. | Removal of heavy metals from electroplating rinsewaters by precipitation, flocculation and ultrafiltration | |
| US3869386A (en) | Removal of heavy metal ions from plating wastes | |
| US4157942A (en) | Method for recovery of metals from metal plating baths and neutralizing toxic effluents therefrom | |
| US4629570A (en) | Removal of iron from chelant solutions | |
| DE69416645T2 (en) | Process for the treatment of photographic waste water | |
| CN208362040U (en) | A kind of system for processing chrome-containing wastewater | |
| US4171255A (en) | Apparatus for recovery of metals from metal plating baths and neutralizing toxic effluents therefrom | |
| US4054517A (en) | Chrome removal and recovery | |
| Lochyński et al. | Research on neutralization of wastewater from pickling and electropolishing processes | |
| CA1072412A (en) | Chrome removal and recovery | |
| US3969246A (en) | Chromium removal and recovery process | |
| US5273661A (en) | Method for processing aqueous wastes | |
| DE2319244B2 (en) | Process for the recovery of chromium (VI) in the form of a concentrated sodium dichromate solution | |
| US4204973A (en) | Treatment composition for use in chrome removal and recovery | |
| JPH0714512B2 (en) | Treatment method of wastewater containing heavy metals | |
| Hassan et al. | Treatment technology evaluation for aqueous metal and cyanide bearing hazardous wastes (F007) | |
| US3371034A (en) | Process for removal of chromium in industrial waste waters | |
| CN108483715A (en) | A kind of processing method of Electroplating Wastewater, nickel |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |