Chromium compounds, water pollution

In addition to these four main types of UV spectra of natural water, many more can be encountered. For memory, when the flow measurement of river, using dichromate, was formerly authorised, typical spectra of hexavalent chromium were obtained (see Chapter 9). In case of pollution, the UV spectrum shape is obviously dependent on the pollutant nature and concentration. In all cases, if the UV spectrum of natural water is flat and close to zero, the pollution probability is very low. On the contrary, a more or less important UV spectrum is always related to the presence of dissolved compounds or suspended solids. 

Zinc and zinc compounds have generally been considered safe. Zinc additives in coatings have replaced many of the chromium and lead additives (both of which are toxic) that were previously used. Today, however, even zinc additives in coatings are being studied for environmental hazards. In Europe, all substances that contain zinc compounds must be labeled as potential polluters of environmental water. More environmentally safe oiganic compounds have been developed to replace the metallic anticorrosion additives, but these compounds are more expensive to produce. Opportunities abound for chemists to develop needed products that are both environmentally safe and economically viable. 

For more than a century, a number of different aluminum alloys have been commonly used in the aircraft industry These substrates mainly contain several alloying elements, such as copper, chromium, iron, nickel, cobalt, magnesium, manganese, silicon, titanium and zinc. It is known that these metals and alloys can be dissolved as oxides or other compounds in an aqueous medium due to the chemical or electrochemical reactions between their metal surfaces and the environment (solution). The rate of the dissolution from anode to cathode phases at the metal surfaces can be influenced by the electrical conductivity of electrolytic solutions. Thus, anodic and cathodic electron transfer reactions readily exist with bulk electrolytes in water and, hence, produce corrosive products and ions. It is known that pure water has poor electrical conductivity, which in turn lowers the corrosion rate of materials however, natural environmental solutions (e g. sea water, acid rains, emissions or pollutants, chemical products and industrial waste) are highly corrosive and the environment s temperature, humidity, UV light and pressure continuously vary depending on time and the type of process involved. ... 

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