Chromium surface treatment toxicity

The process can be used to immobilize heavy metals such as Cd, Zn, Cu, Pb, Ni and Co. Cr(VI) can be reduced by some metal-reducing bacteria to the less toxic and less soluble form Cr(III). Arsenate [As(V)] can be reduced to the more mobile arsenite [As(III)] which precipitates as AS2S3, and is insoluble at low pH. Several laboratory-scale tests (batch and column) are currently available to study the feasibility of this process. However, only a few field tests have been performed to date. Two such tests have been conducted in Belgium, one at a non-ferrous industrial site, where the groundwater was contaminated with Cd, Zn, Ni and Co, and the other which was treated by injection of molasses in order to reduce chromium (VI) to chromium (III). A third demonstration in The Netherlands has been performed at a metal surface treatment site contaminated by Zn. The outcomes of a batch test of a groundwater heavily contaminated by Zn, Cd, Co and Ni are presented in Table 5. The initial sulphate concentration was 506mg/l. With the addition of acetate, a nearly... 

The use of ionic liquids to perform various metal surface treatments allows the replacement of several toxic chemical reagents such as CtOs in the case of chromium plating from aqueous electrolytes and KCN involved in Ag, Cu and Zn electrodepwsition. 

However, the toxicity of hexavalent chromium and the cost of its elimination from surface treatment baths have generated a tendency to replace chromate-based conversion treatments. Several products are presently being evaluated as a replacement for chromates [11] ... 

The toxic properties of chromate have led to the political demand to develop an alternative to chromatizing. One possibility is to treat the surface with hexafluorotitanate or hexafluorozirconate. Then a film containing the metal oxide mixed with titanium dioxide or zirconium dioxide covers the surface. One possible substitute for chromatizing is a treatment with a three valent chromium bath. 

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