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Ask the Expert Question-and-Answer Archive (Wastewater Treatment)

by Mike McGinness, EcoShield Environmental Systems, Inc.
May, 2010

Iron Contamination on Nickel Chloride Solution

Q. I rise pH with Sodium Carbonate in a nickel chloride solution to a pH 5.2 to oxidize Iron using Hydrogen Peroxide as follows:

Nicl + HCL + Fe + NaCO + H2O2

I started with 40 oz/gal nickel concentration and ended with 37 oz/gal.

Can you show me why ended up with low nickel when using Soda ash and when I use Nickel Carbonate to rise pH I have no problem with nickel concentration?

A. Nickel carbonate?

"and when I use Nickel Carbonate to rise pH I have no problem" ???

My first first thought would be the H2O2 is reducing some Ni also (Ni+2 + 2e = Ni), or it may be yielding an equilibrium reaction producing some Ni(OH)2, and the oxidized iron is co-precipitating the reduced nickel or nickel hydroxide. H2O2 is an odd ball, in that it is both a reducing agent and an oxidizing agent, as well as being able to initiate free radical chain reactions, all at the same time!

Also, Isn't Ni(CO3)2 (Nickel Carbonate) highly insoluble in water? I would use NaOH, sodium hydroxide for pH adjustment in your case! But even with NaOH for pH adjustment, the H2O2 may precipitate some nickel anyway.

Sincerely,

Mike McGinness



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