Chromium incorporation solutions

Coprecipitation is a partitioning process whereby toxic heavy metals precipitate from the aqueous phase even if the equilibrium solubility has not been exceeded. This process occurs when heavy metals are incorporated into the structure of silicon, aluminum, and iron oxides when these latter compounds precipitate out of solution. Iron hydroxide collects more toxic heavy metals (chromium, nickel, arsenic, selenium, cadmium, and thorium) during precipitation than aluminum hydroxide.38 Coprecipitation is considered to effectively remove trace amounts of lead and chromium from solution in injected wastes at New Johnsonville, Tennessee.39 Coprecipitation with carbonate minerals may be an important mechanism for dealing with cobalt, lead, zinc, and cadmium. 

The production of corrosion-resistant materials hy alloying is well established, hut the mechanisms are noi lull) understood. It is known, of course, that elements like chromium, mckcl. titanium, and aluminum depend for their corrosion resistance upon a tenacious surface oxide layer (passive film). Alloying elements added for the purpose of passivation must be in solid solution. The potential of ion implantation is promising because restrictions deriving from equilibrium phase diagrams frequently do not applv li e., concentrations of elements beyond tile limits of equilibrium solid solubility might he incorporated). This can lead to heretofore unknown alloyed surfact-s which are very corrosion resistant... 

If the oxidizing agent, Co(NH3)5Cl2+, is furnished with radioactive chlorine, the product, Cr(H 0)5Cl2+, contains active chlorine. However, if the chlorine in Co(NH3)5Cl2+ is inactive but the reaction is carried out qu ekly in the presence of active Cl in solution, essentially none of the active chlorine is incorporated into the chromium complex. 

Type 2 (Fig. 19.3-lc). These carry the diffusing species across ihe membrane by incorporating "carrier or chelating compounds in Ihe membrane. This kind of earner-mediated transport can be illustrated by the separation of varions metal ions, such as cadmium, chromium, copper, and mercury, from their equeous solutions by the use of oil-type liquid membranes containing oil-soluble liquid ion-enchange agents/ 2- 6 These mechenisms have been described in detail elsewhere 2 1 and are not repeatnd here. 

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