Chromic acid disposal

Hexavalent chromium is used in anodizing baths, and in pickling solutions that remove oxide layers from parts. The chromic acid in these solutions eventually enters the waste stream, either through dragout, or when the pickling or anodizing bath is disposed of. Less... 

The fourth system for keeping contamination down is to dilute the bath periodically and add new chromic acid to the remaining bath. This would be giving us a waste disposal problem but the problem would be on a very controlled basis. 

Chromic acid is very corrosive. Any spill should be immediately flushed with water. Phenol is toxic. Also, contact with the solid will cause burns to skin any contact should be thoroughly washed with large quantities of water. Solid phenol should be handled only with a spatula or forceps. Use gloves with these reagents. Dispose of reaction mixtures and excess reagents in proper containers as directed by your instructor. 

The solutions accumulate gradually dissolved material from the plastics and from time to time have to be discarded and replaced disposal presents environmental difficulties and for this reason efforts have been made to find alkaline rather than acidic liquids which are capable of etching satisfactorily but do not contain chromium. At the time of writing, unfortunately, development has not reached the stage at which the process based on chromic acid can be superseded for the entire range of substrates. 

Both chromic acid and hydrofluoric acid disposal are dealt with in Sec. 4.1.9 and Sec. 4.1.10, respectively. 

Disposal. Although HF is an acid, it cannot simply be neutralized and washed down the sink because the fluorine in the acid will attack any aluminum in the plumbing. Thus, HF, like chromic acid, requires special handling. A 5% solution of HF can be safely treated by mixing with a 1 1 ratio of the following solution ... 

This is the exposure of certain plastic surfaces to a solution of reactive chemical compounds. Solutions are oxidizing chemicals, such as sulfuric and chromic acids, or metallic sodium in naphthalene and tetra-hydydrofuran solutions. Such solutions are highly corrosive thus, require special handling and disposal procedures. This treatment causes a chemical surface change, such as oxidation, thereby improving surface... 

Pretreatment is particularly important for structural adhesive joints such as those used in aircraft and motor vehicle construction. Aluminum adhesive surfaces are subjected to chromic acid treatment and an anodizing process, major factors in the overall joining costs. The disposal of used pickling baths is particularly demanding and expensive, especially in view of the CrVl ions resulting from the pickling process. 

SPILL CLEAN-UP ventilate area of leak or spill shovel into suitable dry container and deposit in sealed containers for proper disposal absorb liquid containing chromic acid or chromates in inert materials, such as dry earth, sand or vermiculite,... 

DISPOSAL AND STORAGE METHODS chromic acid and chromates may be disposed of in sealed containers in a secured, sanitary landfill store in a cool, dry location maintain adequate ventilation separate form combustible materials, halogens, sulfides, and metals. 

Some chemical processes require the use of hazardous materials or heavy metals. Oxidations of alcohols into carbonyl compounds or carboxylic acids were frequently performed using either chromic acid or potassium permanganate. However, these two oxidants are derived from heavy metals, which are toxic and hence environmentally hazardous. Safe disposal of salts of these metals thus presents a considerable environmental concern. Fortunately, hypohalites may also be used to oxidize alcohols into carbonyl compounds and carboxylic acids, as exemplified in the procedures in Section 16.2.This oxidation procedure exemplifies green chemistry because the hypohalites are reduced to water and halide ion, which has little environmental impact. 

A. Disposal. Spent chromic acid etchants present a serious disposal problem. Disposal must comply with pollution standards and approved practice. 

Copper etchants do not directly influence the electroless plating process, but are used merely to remove unwanted copper, and should not affect the deposit properties. The costs of waste treatment and disposal have led to disuse of throw-away systems such as chromic—sulfuric acid, ferric chloride, and ammonium persulfate. Newer types of regenerable etchants include cupric chloride, stabilized peroxide, and proprietary ammoniacal etchant baths. 

Oxidative reactions of pyridines are commercially more interesting than reductive ones because catalytic hydrogenation of pyridines is a generally useful method, whereas catalytic oxidation is not. In contrast, anodic oxidation of pyridines is widely applicable and can replace methods that use expensive oxidants such as permanganate salts or chromic oxide. Consider, as an example, oxidation of a methylpyridine to produce 1 kg of the pyr-idinecarboxylic acid this process would consume about 3 worth of potassium permanganate at 100% efficiency and would produce 0.7 kg of byproduct Mn02 for disposal or recycle. The same anodic reaction would consume only 0.30 of electrical power (for oxidation) and would not produce a significant amount of material for disposal. 

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... 

Sometimes, the final dip is a dilute solution of chronaic (30-45 g/Uter 4-6 oz/ gal) or chromic-phosphoric add, which serves to prevent rusting of the surface before the prime coat is applied. Use of chromates is less popular than formerly because their toxicity places restrictions on disposal of spent solutions. Hexava-lent chromium (Cr +) is a potent human toxin and known cancer-causing agent [7]. A relatively nontoxic pickle for steel consists of hot 3-10% ammoniated dtric acid followed by a dilute alkaline sodium nitrite solution to minimize superfidal rusting before application of paint [8]. 

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. 

---