Dichromate disposal

Caution Chromates, including potassium and sodium dichromate, are hazardous materials, as are sulfuric and phosphoric acid used in the oxidation of soil organic matter. Great care must be exercised in using these chemicals and in disposing of the waste generated. 

Small quantities of hazardous solid wastes (such as potassium dichromate, lead nitrate, silver nitrate, asbestos, etc.), liquid chemicals (such as chloroform, PCB, methylene chloride, etc.), petrochemicals (such as gasoline. No. 2 fuel oil, etc.), or pure metals (such as mercury, sodium, etc.), which are stored in bottles or cans, however, are not considered to be hazardous household products. Accordingly these nonhousehold hazardous solid wastes, even in small quantities, can only be properly disposed of by licenced or certified environmental professionals. 

Chromites. Salts of general formula MCrC, where M is a monovalent metal. They may be regarded as metachromites derived from hypothetical metachromous acid, HCrC>2, which is known only in solns or in the form of its oxide, C Oj. The most common chromites, NaCiC and KCrOj, can be obtained by the action of chromic oxide, CrjO on Na or K hydroxide (Ref 1, pl97). Although these and other chromites are oxidizers, they do not contain as much oxygen per unit wt as do chromates or dichromates There is no open literature info at our disposal that chlorites have been used in expls, propints, or pyrotechnic compns... 

Disposal. Disposal is best done by reducing the dichromate to the insoluble chromium hydroxide with a sodium thiosulfate solution. The process for neutralizing 100 mL of chromate solution is as follows ... 

Cleaning Up The law states that an unwanted by-product from a reaction is not a waste until the chemist declares it a waste. And once declared a waste, the material cannot be treated further except by a licensed waste treatment facility. So, for example, if all of the dilute dichromate waste from a laboratory were collected together, it could not be reduced chemically or reduced in volume before being carefully packed and trucked away by a hazardous waste disposal company. But if each student, as a part of the experiment, reduces the Cr " to Cr and precipitates it as the hydroxide, the total volume of hazardous waste becomes extremely small and thus can be cheaply disposed of. Throughout this text, procedures based on the best, current practice, are given for the conversion of hazardous by-products to less hazardous ones. 

EXPOSURE ROUTES wind transport from road dust wood treated with copper dichromate leather tanned with chromic sulfate chromate production stainless-steel production chrome plating working in tanning industries chromium waste disposal sites chromium manufacturing and processing plants consumption of food and drinking water inhalation of air... 

Many police forces now use an Alcolmeter instead of the disposable dichromate tubes. The Alcometer is a small instrument with disposable mouthpiece tubes. The subject blows into the instrument and their alcohol level can be read from a digital display. The instrument is an electrochemical cell known as a fuel cell which generates a voltage in proportion to the alcohol vapour concentration in the breath. 

For many years, sulfuric acid—dichromate mixtures wo-e used to clean glassware (a sulfuric acid—peroxy-disulfate solution is now recommended because disposal of chromate is a problem). Confusion about cleaning baths... 

Chemical Toxicity. In chemistry courses students learn a lot about what a chemical can do for them, but they know woefully little about what a chemical can do to them This deficiency in their chemical education is a result of standard and currently recommended academic practices. (For example, almost all new laboratory manuals in general and organic chemistry have eliminated the use of benzene and dichromate because of their carcinogenic status.) For reasons of safety and economy teaching laboratories tend to make use of small amounts of reagents with minimum toxicity, and use low-risk procedures, such as microscale. Students have only a single or at most a few exposures to any one chemical, and learning about a chemical s toxicity is minimal. These procedures often continue into advanced courses, and even research projects. Spills and waste disposal are handled by the instructors. 

A hot chromic-sulfuric acid cleaning solution prepared from potassium dichromate and sulfuric acid provides free oxygen for cleaning but has a tendency to leave residues, and the surface must be rinsed very thoroughly. Disposal of the waste material is also a problem. 

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