Generally effluent from Electroplating Factories contain different types of heavy metals like chromium, nickle, copper etc along with cyanide. To remove such pollutants generally chromium and cyanide contaminated effluents tarted individually and separately and then, two streams are mixed with the common stream.Finally, the common effluent is treated with conventional process. It meas treatment have three separate stages. Is there any technique by which we can reduce the steps or treat the entire effluent in a single stage.
Not suggestible to treat combine effluent of plating industry nor economical / technical viability .
While it is technically viable to treat mixed solutions there are dangers to doing so, ie CN solution can evolve HCN gas at low pH, this can create unacceptable safety issues if not managed.
Given the relatively low volumes of solutions and the simplicity of the current steps it is probably not effective to try a combined treatment step.
Try a treatment with ferrous sulfate (FeSO4 * 7 H2O) it will reduce and precipitate the chromate; if you are lucky the Ni will adsorb on the ferric hydroxide. Do not overdose in order not to lower the pH too much.
Alternatively you may think of having a 2-stage sequence 1. Chromate reduction/precitipation by FeSO4; 2 lime milk addition for metal hydroxide precipitation.
Both seem worth trying to me.
Harald
Thanks Professor Harald Weigand. I our country for tannery- ETP the second option is practiced. Would you please tell me if we maintain pH 2-3 by using H2So4, what should be approximate dose of of FeSo4 in ppm?
Use a 2fold soichiometric amount of FeSO4 * 7 H20 in relation to the molar concentration of Cr(VI). I really suggest, xou experimentally try both pure FeSO4 and FeSO4 plus lime-milk addition to the supernatant
It is not wise a common treatment.
You mus sepparate ien two, alkaline flow from the acid flow.
Alkaline flow: destroy CN- with oxidants.
Acid flow:,add a reductant to to Cr3+v( with a little Fe(III) tro coaglate the preciitate., recover Cr by sedimentation and then mix in proportrion to get a neutral effluent.
It is advisable to keep rinse water contaminated with cyanide unmixed with that contaminated with chromium until waste treatment; cf. (e.g.): Leslie E. Lancy, Chap. 12, "Pollution Control in Plating Operations", in: Herbert F. Lund (Ed.), "Industrial Pollution Control Handbook", McGraw-Hill, New York, 1971, pp. 12-1 to 12-16.
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