June 1988

DISPOSAL OF CHROMIUM LABORATORY WASTES

Dr. Fay Thompson Todd Biewen

University of Minnesota Department o f Environmental and Occupational Health

Minneapolis, MN 55455

Project Officer

James S. Bridges Office of Environmental Engineering and Technology Demonstration

Cincinnati, OH 45268 Hazardous Waste Engineering Research Laboratory

This study was conducted through

Minnesota Waste Management Board St. Paul, MN 55108

and the

Minnesota Technical Assistance Program University of Minnesota Minneapolis, MN 55455

HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY OFFICE OF RESEARCH AND DEVELOPMENT

U . S . ENVIRONMENTAL PROTECTION AGENCY CINCINNATI, OH 45268

This project was partially supported with a United States Environmental Protection Agency cooperative agreement through the Minnesota Waste Management Board and the Minnesota Technical Assistance Program.

Although the research described in this report has been funded in part by the United States Environmental Protection Agency through a cooperative agreement, it has not been subjected to Agency review, and therefore doe8 not neceaaarily reflect the views of the Agency and no official endorsement should be inferred.

Project Summary

Disposal of Chromium Laboratory Wastes

F. M. Thompson and T. Biewen

Alternative reduction, recycling, treatment and disposal methods for chromium laboratory me? - specifically, sulfuric acid- potessium dichromate cleam ng sol utiom - Yere imestipated.

PI reduction method w23 shwn to be effective for precipitation of chromium from soiution. The effluent from this procedure contained (2 ppmchromium. The residue i s a mixture of chromium oxide and fi l ter media.

ton exchange was also proven effective et remwing chromium from solution, yielding a severable effluent (<2 ppm). Hovsvsr, the method i s exc#ively expem-ve.

Recycling and rscwery of chromium from these va$tt?s w shown to be infeasible under the current market confitions i n the US.

Waste minimization practica were also imdigated. A survey of local laboratorimindicated that alternatives to chromic acid cleaning sol utiom are frequently end effectirely used.

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Introduction sCqpdSut4

The overall objective of this study vas to examine a variety of alternative reduction, recycling, treatment, and disposal techniques for chromic acid cleaning solution wastes generated i n laboratories.

In the electroplating industry, where chromium-containing wetestreams are generated i n large volumes, recycliq practicm includingionexchamgeare usedvith frequency. Clearly, for any w t e stream the preferred solution i s rawer y and recycling; therefore the applicability of this mthod to chromic acid recovery vas mal uated. In addition, reduction end stabilization by formation o f the oxide YBS studied. I n each case, the feasibility of the method for in-lab treatment versus the cost of commerical treatment w mnsideral. In-lab feasibility considerations included nzrtard to techniCi81~, mt, time, practicality for very small generators, and mnageebility of the end-prodvct.

The 1984Amndmnb to ths Resource Comemtion and Recaverg Act established several guidelines for banningdisposl ofoertain v8stes i n landfills. The deadline for restricting liquid vadm containing heavy metals from landfills, which incluks chromium, vent into effect i n July 1987. Therefore chromium-containing wtes tlwt hwe not t e n stabilized are no longer acceptable for land dispusal. .

Chromium i s a multi-valent metal and can be found i n compounds i n a divalent (+2), trivalent (+3), o r hsxmlent (+6 ) state. The

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properties and toxicity of chromium differ for each o f these states. Hexawlent chromium i s considered the most toxic to humans and i s also thought to be a carcinogen.

Chromium i s used i n a variety of forms i n laboratories , mast common1 y m chromic acid cleaning solution, a mixture o f sulfuric acid and potassium dichromate that m a b a very strong agent for r e m 1 of organic material from laboratory glrrssvare. The typical chromic acid cleaning bath contains about 20,000 ppm chromium, vhich i s initially all present i n the hexavalent state. cls the material i s wed for cleaning glassme, the chromium i s reduced to the trivalent form. A spent solutioncontains both tri- and h e m l e n t form of chromium, i n wrying ratios depending on degree of use.

Disposal of these spent solutions hm posed a significant problem for axkmic, clinical , industrial and commercial labratorim, and the mod commn disspcssal practice has bean landfilling by the lab pack method. The landfill option, although urdesirable, i s generally a l l thst vas commercially available i n the past. With the July 1987 landfill ban cam the development o f a limited number o f commercial treatment optiom and a r e m d interest i n proeedum for treating chromic acid cleaning solution v" i n the laboratory.

Praxdurw

Data vas collected via laboratory experiment on ion

rebuctionlpreci pitation treatment methods. Information on commercial recycling and treatment options vas gathered through a series of telephocw, interview.

. excharge and chemical

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Results and Discusion

This process successfully precipitated the chromium from sol ution , lwi ng an effl usnt o f severable quality. Chromium was undetectable (< 2 ppm) using AAS analysis. The residue from this process i s a vel1 - mixed solid made up of trivalent chromium oxide, filtration media and some sodium wlfate. The quantity of residue produced i s six times greater than the theoretical yield of chromi um oxide, due to incorporation of f i l ter media.

Ion exchange treatment wm also found to be capable of producing a severable effluent ((2 ppm) . In addition, ion exchange requires less time and effort than does the previous method. Hmmer, this process i s very expensive because of the speed v i t h vhich tbe ion exchange column h m e s exhawted; one column y85 spent before a total of 100 ml of chromic acid solution could be psssed through it.

Chromium, a o m tenuously svailable commodity i n the US., i s current1 y i n adequste supply. k a result , metal recyclers shwed little interest i n small scale recycling ventures. To companies used to hendli ng t houssnds of gallom of vaste, the coat of transporting and managing small qmntities of chromic acid wastes ex- the revenue potential of the recovered chromium. This i s especially true today 8s the market price of chromium i s only about 50

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cents/pound. In addition, m n y recycling firm are set up to handle only hexavalent chromium. Consequently no firms vere lmted that would vil l ingly recycle spent chromic acid cleaners.

Tvo local firms seeking small quantity generator businem vi11 soon be on line i n the Minmpol isf i t . Paul area. Both expect to collect chromium vastes, but vi11 treat them for dispoal rather than recycling. It appears that contracting v i t h this type of f i rm for treatment and disposal of spent chromic acid cleaning solutions vi11 be the mwt cost effective option for handling

. labratory quantities of this w t e .

A survey i ndicatal that a majority of laboratories are using substitutes for chromic acid cleaners. The types of substitutes i n me include detergents, potsssi um hydroxide, sonic htb o r a combination of t b . The &tan- of substitutes is that they are less hatsrdous to work v i t h and i n most cases are smerable. Therefore, although the cost of substitutes i s comparable to chromic acid solutions, the winp on disposal costs are whtantial.

Several d e reduction, recycling and treatment alternatiw Vere examined for small quantities of chromic acid cleaning sol utions

important conclusions that can be dravn from this study are as follom:

. gemrated i n laboratories. The

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( 1 1 Recycling o f chromium from small quantities of W e such BS laboratory cleaners i s rat practical for metal recycling firms. The effort required to collect these w t e s 8101~~ with the lw volums and the current market price of chromium (about SOC/pourd) create a disincentive for recycling firm to pursue chromium recycling.

(2) An effectivt in-lab reduction method for chromic acid h a application for small quantity generators because it i s of moderate cost, i s simple to perform, and can be carried out safely by using good laboratory techniques.

(3) Ion exchsn~e wm ahwn to be effective at remwing chromium from solution, wlng disptrsable ion exchange columns, but thecostofthecolumnsmkesthis prows prohibitively expensive, due to the fact that the columns become saturated very quickly.

(4) Where contractors are available, utilizing them to collect vast- i s uorthvhils, Ths a d w n t e o f cont racti ng for YBSfG collection include cost SBYj rigs, ti me saviw, and reduced hazard for personnel.

(5) A survey of labs i n the Tvin Ci t ies area indicates that alternativm to chromic acid cleaning solutions are bei IMJ used frequent1 y. Theseinclude datergents, ptamum hydroxide and sonic baths. Advantm of the alternative include cost swings, no disposa\ comrns,

- and r e d d hazard to personnel.

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fkatmmendations

The follwing recommended management practices are directed particularly at the small quantity generator of chromic acid cleaning solutions.

( 11 The generator should make an effort to minimize the amount of chromic acid wte produced. This can best be accomplished by matching the cleaning 8gent to the degree of soil on glziware, by utilizing substitutes vhemr possible, and by adopting techniques that extend the l i f e o f the chromic acid cltani ng tmth.

(2) If space i s wailable for storage of chromic acid wte, look for local montrsctors v b vi11 collect and treat the waste. This process vi11 very likely be 1- expensive than in-lab treatment and i s especially vise for laboratone3 generating more than one l i ter per veek.

(3) h e a chemical reduction method when in-18b treatment is rmmmry. This method should be used i n t h laboratories not generating enough &e to make USG of regular collection (less than about one liter per veek).

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ABSTRACT

Alternative reduction, recycling, treatment and disposal methods fo r chromium laboratory wastes - specifically, sulfuric acid-potassium dichromate cleaning solutions - were investigated.

A reduction method was shown to be effective for precipitation of chromium from solution. Hexavalent chromium i s reduced t o the less toxic trivalent state and precipitated as an oxide. The effluent from this procedure was determined by atomic absorption spectroscopy t o be sewerable (<2 ppm). The residue i s a mixture of chromium oxide and f i l t e r media.

Ion exchange was also proven effect ive at removing chromium from solution. Spent chromic acid solution containing hexavalent and trivalent species was run through a mixed bed column of cation and anion resins. The chromium was removed by the column, yielding a sewerable effluent (<2 ppm). However, the cost of the column and the speed with which i t becomes exhausted negate the practicality of ion exchange fo r recovery of chromium from waste chromic acid cleaning solution.

The possibility of recycling these wastes was determined. Metal recyclers throughout the U.S. were contacted. In general they showed l i t t l e interest, due to the small volumes of waste in question, the problems associated with recycling wastes containing both hexavalent and trivalent species, and the current low market price of chromium.

Waste minimization practices were also investigated. A survey of local laboratories indicated that alternatives t o chromic acid cleaning solutions are frequently used. Reasons fo r the use of alternatives include: less hazard, comparable cost and effectiveness, and ease of disposal. Also, methods for the pretreatment of glassware, t o help prolong the l i f e of chromic acid solutions, are discussed.

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CONTENTS

Abstract

Introduction

Conclusions

Recommendations

Procedures

Chromium reduction method

Ion exchange

Metal recyclers/waste disposal firms

Subs tit utedwaste mini mi zation

Results and Discussion

Chromium reduction method

Ion exchange

Metal recyclers/waste disposal firms

Subst i tutes/wast e mini mi zati on

References

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INTRODUCTION

RCRA AMENDMENTS AND OTHER BACKGROUND

The 1984 Amendments t o the Resource Conservation and Recovery Act established several guidelines for banning disposal o f certain wastes i n landfills. The deadline for restricting liquid wastes containing heavy metals from landfills, which includes chromium, went into effect i n July 1987. Therefore chromium-containing wastes that have not been stabilized are no longer acceptable fo r land disposal.

Chromium i s a multi-valent metal and can be found in compounds in a . divalent (+2), trivalent (+3), o r hexavalent (+6) state. The properties and

tox ic i ty of chromium di f fer f o r each of these states (1). Hexavalent chromium i s considered the most toxic to humans and i s also thought t o be a carcinogen (2).

Chromium i s used in a variety of forms in laboratories, most commonly as chromic acid cleaning solution, a mixture of sulfuric acicl and potassium dichromate that makes a very strong agent fo r removal of organic material from laboratory glassware. The typical chromic acid cleaning bath contains about 20,000 ppm chromium, which i s in i t ia l l y a l l present i n the hexavalent state. As the material i s used for cleaning glassware, the chromium i s reduced t o the trivalent form. A spent solution contains both tri- and hexavalent forms of chromium, i n varying ratios depending on degree of use.

Disposal of these spent solutions has posed a significant problem for academic, clinical, industrial and commercial laboratories, and the most common disposal practice has been landfilling by the lab pack method. The landfill option, although undesirable, i s generally a l l that was commercially available i n the past. With the July 1987 landfill ban came the development of a limited number of commercial treatment options and a renewed interest in procedures fo r treating chromic acid cleaning solution wastes i n the laboratory. -

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SCOPE OF STUDY

The overall objective of this study was t o examine a variety of a1 temat ive reduction, recycling, treatment, and disposal techniques for chromic acid cleaning solution wastes generated in laboratories.

In the electroplating industry, where chromi um-cont aini ng wastestreams are generated in large volumes, recycling practices including ion exchange, electrolytic recovery and evaporation are used with frequency. Clearly, for any waste stream the preferred solution i s recovery and recycling; therefore the applicability of these methods t o chromic acid recovery was evaluated. In addition, reduction and stabilization by

method f o r in-lab treatment versus the cost of commerical treatment was considered. ln-hb feasibility considerations included hazard t o technicians, cost, time, practicality fo r very small generators, and manageability of the end-product.

. formation of the oxide was studied. In each case, the feasibility of the

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CONCLUSIONS

Several waste reduction, recycling and treatment altematives were examined f o r small quantities of chromic acid cleaning solutions generated i n laboratories. The important conclusions that can be drawn from this study are as follows:

( 1 ) Recycling of chromium from small quantities of waste such as laboratory cleaners i s not practical fo r metal recycling firms. The e f fo r t required t o collect these wastes along with the low volumes and the current market price of chromium (about SOC/pound) create a disincentive f o r recycling firms t o pursue chromium recycling.

(2) An effective in-lab reduction method fo r chromic acid has application for small quantity generators because it i s of low cost, i s simple t o perform, and can be carried out safely by using good laboratory techniques. The end product of this procedure i s a trivalent chromium residue. There i s a cost associated with the disposal of the residue since i t does require lab-packing, but the volume of waste i s significantly reduced and the acidic nature i s neutralized. There i s also a cost associated with the chemicals used for neutralization and the time spent carrying out the reduction, but overall this laboratory method does allow small generators t o carry out their own laboratory reduction process.

(3) Ion exchange was shown t o be effective a t removing chromium from solution, using dlsposable ion exchange columns, but the cost of the columns makes this process prohibitively expensive, due t o the fact that the columns become saturated very quickly.

(4) Where contractors are available, utilizing them t o collect wastes i s worthwhile. The advantages of contracting for waste collection include the following:

lower cost - A local f i rm (not yet i n operation) quoted a price of - 41t/gallon of waste (41, although there i s some question whether this

price would really apply t o the strongly acidic, high concentration chromium waste from cleaning solutions.

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time S8Ved - Time spent treating wastes i s eliminated.

0 reduced hazard - Exposure to waste i s minimized.

A disadvantage of dealing with outside contractors i s that large quantities of waste may have t o be collected t o real ize economical prices. Long term storage increases the hazard associated with chromic acid cleaning baths.

(5 ) A survey of labs i n the Twin Cities area indicates th8t a1 ternatives t o chromic acid cleaning solutions are being used frequently. These include detergents, potassium hydroxide and sonic baths. The scope of this study did not allow for an evsluation of the effectiveness of these alternatives. However, responses indicate that the advantages of a1 tematives include:

0 less costly fo r purchase and disposal

0 no disposal concerns (most alternatives can be sewered)

0 reduced hazard to personnel

0 as effective as chromic acid fo r most cleaning jobs

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RECOMMENDAT IONS

The following recommended management practices are directed particularly at the small quantity generator of chromic acid cleaning solutions.

( 1 ) The generator should make an effort t o minimize the amount of chromic acid waste produced. This can best be accomplished by the f o l 1 owing:

Evalutlte soiled glassware to determine the strength of cleaning agent required.

0 Ut i l ize substitutes whenever possible.

If chromic acid cleaner i s required, prolong i t s effectiveness by precleaning glassware in detergents and dying thoroughly prior t o soaking i n chromic acid.

(2) If space i s available fo r storage of chromic acid waste, look f o r local contractors who w i l l collect and treat the waste. This process w i l l very likely be less expensive than in-lab treatment and i s especially wise for laboratories generating more than one l i t e r per week.

(3) Use the reduction method of Armour, Browne and Weir when in-lab treatment i s necessary. This method should be used i n those laboratories not generating enough waste t o make use of regular collection (less than about one l i t e r per week).

(4) Further study i n the following areas should be carried out to assist i n making decisions on in-lab YS. contractor disposal options.

e Options for and cost of disposal of the residue from in-lab reduction should be determined.

0 Purification of the in-lab reduction residue should be pursued i f i t appears that this would improve the possibility of recycling the chromium.

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PROCEDURES

CHROMIUM REDUCTION METHOD

The reduction method of Armour, Browne and Weir (5) i s designed fo r the disposal of chromic acid wastes. These solutions, when fresh, contain the hexavalent chromium species. Upon exposure t o soiled glassware, hexavalent chromium i s reduced t o the trivalent state. Not a l l of the hexavalent chromium i s reduced however. Spent solutions are made up of both trivalent and hexavalent forms. Therefore, further reduction i s necessary t o get a l l the chromium into the less toxic trivalent state before i t i s precipitated out of solution. The primary concern when working with chromic acid wastes i s to avoid direct contact with the solution. With a pH

. of less than one and considerable oxidizing power, chromic acid solutions are reactive enough t o cause skin ulcerations and allergic dermatitis when contacted. Also, inhalation of chromic acid mist can cause damage t o nasal passages, but this can be avoided through careful manipulations i n a well venti 1 ated area.

Method: In’the fume hood, the spent waste was added slowly t o a beaker of water, using a 1:l ratio. So that complete reduction would take place, this mixture was brought to a pH of 1 using soda ash. The reductant, solid sodium thiosulfate, was then added (about 13.5 g for 100 ml of cleaning solution) until the solution became cloudy and blue. Immediately, with continued stirring, the solution was neutralized with soda ash. A f te r a few minutes, a blue precipitate formed. This solution WQS filtered immediately through Celite. The f i l t rate was analyzed using atomic absorption spectroscopy (AAS). The residue was washed in warm water t o remove much of the sodium sulfate, dried, weighed, and dissolved in 25% nitr ic acid i n preparation fo r AAS analysis.

ION EXCHANGE

The procedure for ion exchange involved using a disposable column containing both cation and anion resins. Cation resins remove trivalent chromium, while anion resins remove hexavalent chromium (dichromate). The chromic acid solution was neutralized with soda ash before being run

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through the column. During operation, the effectiveness of the column at removing the chromium was monitored by observing the appearance of a blue color i n the effluent, an indication that chromium had broken through.

METAL RECYCLERS/WASTE DISPOSAL FIRMS

Metal recyclers throughout the country were contacted by phone t o determine whether they were equipped t o recycle chromium from waste containing both trivalent and hexavalent chromium. Quantity constraints of these firms were also questioned t o determine whether their processes were applicable t o small quantity generators.

Waste disposal firms were contacted as well. Questions asked of . these firms were geared toward gathering information on the cost of the collection and disposal of raw chromic acid wastes, costs of residue collection and disposal, frequency of collection, and minimum quantity constraints fo r collection.

SUBST ITUTES/ W ASTE MI N IN1 Z AT I ON

Information on the types and prevalence of use of substitutes f o r chromic acid cleaners was gathered through a phone survey of testing laboratories and college science departments in the Twin Cities area. Laboratories were asked whether they used chromic acid solutions, how much they used, whether substitutes were in use, the types of substitutes i n use, and their effectiveness relative to chromic acid cleaners. Where chromic acid cleaners were in use, laboratories were asked if any waste minimization techniques were employed.

Additional information on substitutes fo r chromic acid cleaners, including cost, disposal methods, hazard t o workers, chemical composition, and effectiveness, was gathered from scientific catalogs and via phone conversations with representatives of these firms.

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RESULTS AND DISCUSSION

CHROMIUM REDUCTION METHOD

This process successfully precipitated the chromium from solution, leaving an effluent of sewerable quality. Chromium was undetectable (< 2 ppm) using AAS analysis.

The residue from this process is a well-mixed solid made up of trivalent chromium oxide, f i l tration media and some sodium sulfate. A 100 gram sample of cleaning solution should yield about 2.9 grams of chromium oxide; however, the weight of the solid residue was approximately 18 grams, indicating that a very significant amount of inert residue (largely . fi lter media) i s incorporated into the process. This i s a six-fold increase in the quantity of residue t o be handled as a hazardous waste.

ION EXCHANGE

Ion exchange treatment was also found to be capable of producing a sewerable effluent (<2 ppm). In addition, ion exchange requires less time and effort than does the previous method. However, this process i s very expensive because o f the speed with which the ion exchange column becomes exhausted; one column was spent before a to ta l of 100 ml of chromic acid solution could be passed through it.

A cost breakdown comparing chromium reduction versus ion exchange i s shown in Table 1. Note that the column makes up virtually al l of the cost of the ion exchange process. In addition, the disposal of a spent ion exchange column w i l l c a y a higher cost than lab-packing of the residue from chromium reduction. The actual cost difference was not determined, but w i l l be substantial simply due to the volume difference between the column and the reduction residue, and also because the column contains both hexavalent and trivalent chromium, while the residue contains only the 1 ess hazardous t ri V a l ent species.

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TABLE 1. COST COMPARISON OF IN-LA5 TREATMENT METHODS

Met hod Item cost *

Chromium reduction Soda ash a 1 .oo and precipitation Sodium thiosulfate a0.50

F i l t e r material a 1 .oo $ 2.50

Ion exchange Disposable ion exchange $ 47.00

Soda ash =: 1 .oo $48.00

column

*Costs are based on treatment of 100 ml sample of spent chromic acid cleaning solution and do not include the cost of disposal of the residues. Prices are taken from current catalogs.

METAL RECYCLERS/WASTE DISPOSAL FIRMS

Chromium, a once tenuously available commodity in the U S , i s currently i n adequate supply. As a result, metal recyclers showed l i t t l e interest in small scale recycling ventures. To companies used t o handling thousands of gallons of waste, the cost of transporting and managing small quantities of chromic acid wastes exceeds the revenue potential of the recovered chromium. This i s especially true today as the market price of chromium i s only about 50 centdpound (3). In addition, many recycling firms are set up t o handle only hexavalent chromium. Consequently no firms were located that would willingly recycle spent chromic acid cleaners.

Two local firms seeking small quantity generator business w i l l soon be on line i n the Minneapolis/St. Paul area. Both expect to collect chromium wastes, but w i l l treat them for disposal rather than recycling. It appears that contracting with this type of f i rm f o r treatment and

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disposal of spent chromic acid cleaning solutions w i l l be the most cost effective option for handling laboratory quantities of this waste. The actual cost, according t o the firms, i s dependent on a number of factors, including 1) the concentration of the hexavalent chromium in the waste, 2) the quantity of business from the customer, 3) the organic content of the waste, and 4) the travel time required for collection. Neither f irm w i l l be operative unti l mid-summer, 1988, but one quoted a price of 41 cents per gallon of waste collected f o r 8 chromium-containing plating solution.

In addition t o raw waste, residues w i l l also be collected. The cost of this service has not yet been projected; however, the firms expect i t t o be reasonable because of the volume reduction that has taken place before the waste i s received.

One last problem associated with storage and handling of spent chromic acid cleaning solutions should be recorded here. Chemists i n the author’s hbOr8tOQ have experienced two separate instances where 8 spent solution has been agitated during transfer from a large beaker t o a bottle prior t o storage fo r disposal. Both bottles were capped af ter filling. Agitation of the solution apparently brought unreacted organic material in contact wi th oxidizer and a reaction took place. In the f i rs t instance, a one l i t e r bottle exploded about one hour after filling, spraying chromic acid and glass over much of the empty laboratory. In the second instance, the bottle cap was loosened (after the f i rst explosion), relieving an obvious build-up of pressure. It i s clear that bottles of spent chromic acid cleaning solution should not be capped until a l l reaction has subsided.

SUEST ITUTES/WASTE MI NlMlZAT I ON

The local survey indicated that a majority of laboratories are using substitutes for chromic acid cleaners. The types of substitutes in use include detergents, potassium hydroxide, sonic baths or a combination of these. The advantage of substitutes i s that they are less hazardous t o work with and i n most cases are SeWer8ble. Therefore, although the cost of substitutes i s comparable to chromic acid solutions, the savings on

. disposal costs are substantial.

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The effectiveness of substitutes i s not clear. Some laboratories surveyed fe l t they were as effective as chromic acid cleaners while others disputed that observation. A few laboratories used chromic acid only for the most dif f icult pieces of glassware, indicating that chromic acid i s s t i l l seen as the most effective cleaner for the hardest cases.

Those laboratories that were using chromic acid cleaners minimized their waste by prolonging the l i f e of their solution. This was accomplished by t ) prewashing the glassware as thoroughly as possible with detergents, and 2) preventing dilution by soaking only dry glassware in the cleaner. A summary of the advantages and disadvantages of the treatment methods, disposal options and substitutes for chromic acid cleaners i s shown in Table 2.

TABLE 2. ADVANTAGES AND DISADVANTAGES OF TREATMENT AND DISPOSAL METHODS AND ALTERNATIVES TO CHROMIC-ACID SOLUTIONS

Met hod Disadvantages

Chromium Moderate cost Some hazard to reduction Effective chromium removal lab personnel

Stable product Volume reduction

Ion exchange Effective Quick, simple

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Very high cost Left with column

for disposal

Substitutes Low cost of disposal Hay not be as Sewerable effective Low personnel hazard

Commerci a1 l o w to moderate cost Extra storage space coll ec t i on Useful f o r raw waste or needed

residue

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REFERENCES

1. Clayton, G. and F. Clayton. Patty’s Industr ia l Hygiene and Toxicology. Wiley-Interscience, New York. 198 1.

2. Onstott, S. I., W.S. Gregory and S. F. Thode. Removal of chromate f rom cooling tower blowdown by react ion with electrochemical ly generated ferrous hydroxide. Environmental Science and Technology, 7:333-337, 1973.

3. Author unknown. American Metal Market, p. 1. October 1 , 1987.

4. Personal communication. Metropol i tan Recovery Systems, St. Paul, MN. 1988.

5. Amour , M. A., L. M. Browne and G. L. Weir. Hazardous Chemicals - Informat ion and Disposal Guide, 2nd edition. University of Alberta, Edmonton, Alberta, Canada. 1984.

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