nickel in spent pickling acid 1

[rbunge]

Hi there,
we are successfully runnig a vacuum evaporation plant for spent hydrochloric acids from zinc galvanizing plants in Switzerland. As the liquid evaporates we are able recover a high quality FeCl2 as crystallized product. Only after ZnCl2 also begins to precipitate, the residual concentrate must be disposed off. The problem: if the acid contains Ni, NiCl2 precipitate will contaminate our FeCl2. How can we suppress the formation of NiCl2? What happens if I just add some diacetyldioxim? Now, if that is too easy for you: how about Pb - how can I suppress the formation of PbCl2? Your suggestions are much appreciated, Rainer
rbunge@hsr.ch

 

[aspearin1]

I have only a little plating experience, so forgive me if I'm in left field on this. Is your pickling bath of somewhat similar composition as your plating bath? I believe I remember this being the case. If this is so, then would it be possible to place an anode temporarily in solution and plate out the nickel on some regular basis?

Aaron Spearin, EIT
ChemE, M.E.
"The only constant in life is change." -Dan Andia; 1999, Chemical Engineering Progress

 

[rbunge]

Aaron,
Unfortunately, the plant produces off site and is fed with acids from various sources. We therefore need to accept the spent acid as it is delivered and we have no influence on the upstream processes. Eletrowinnig may be one way to process spent acids but our plant uses an evaporator which cannot easily be refitted with electrodes or the like. for further calification: the crystallized FeCL2 is periodically centrifuged off the residual liquor (thickened through the continuous evaporation)and then new waste acid is added. This process runs through as many cycles as possible until the concentraton of Zn or Ni or Pb has exceeded the solubility product of the respective chloride and thus begins to contaminate the FeCl2 product.
Rainer

 

[kenvlach]

Hi rbunge,
I think that you have the correct idea in using a chelating agent such as diacetyldioxim. Use a chelant solution to wash the FeCl₂ slurry, then flow the used chelant through a strong cation column to recover the chelant solution. Regenerate the cation column with HCL solution, then either try electrowinning or neutralize and precipitate the metals as hydroxides to send to a smelter.

I am not familiar with diacetyldioxim, but suggest you look in Lange’s Handbook of Chemistry, 14th Edn., Table 8.12 Cumulative Formation Constants for Metal Complexes with Inorganic Ligands and Table 8.13 [same, for Organic Ligands]. Of the inorganic chelants, ammonia has some preference for Cd, Co, Cu, Hg, Ni, Pb, Ag and Zn relative to Fe. Use as ammonium chloride solution.

Of the organic chelants, Benzoylacetone (75% dioxane), 1-Nitroso-2-naphthol (75% dioxane), and Pyrocatechol-3,5-disulfonate (Pyrocatchetol Violet) look capable of removing Ni, Pb and Zn from an Fe-containing slurry. Triethanolamine can remove Ni and Zn.

The mining engineers, Extraction & production engineering Forum, forum437, and the professional site

http://www.smenet.org/,

may have useful information regarding chelants used in ore benefication, Leaching, Solvent Extraction, etc.

This article is slightly related to your process: “Recovery of the Metals from Pickling Liquors of Stainless Steel by Precipitation Methods”

http://db1.wdc-jp.com/isij/pdf/200107/is410801.pdf

Note in Figure 5 and text indicate that use of NH₄OH kept 99.5% of Ni in solution, while Fe was precipitated (a well-known qualitative analysis method).

Hope this helps. Let us know of your progress and results.
Ken

 

[rbunge]

Ken,
wow - that sounds like very useful advice. I will need some time to follow up on this one but I'll let you know eventually how it all worked out. If that approach works, our customer will be very pleased ... and I'll score big with my boss ;->
Rainer

 

[dirkbouma]

Hi Ken,
The references to compounds containing 75% dioxane should include a disclaimer on the environmental aspects... it is characterized by USEPA as a Class II B potential carcinogen, and the regulatory picture is firming up with respect to its use, treatment and disposal in the U.S. The largest groundwater treatment system east of the Mississippi is treating dioxane to remove it from drinking water, at significant cost to Ann Arbor. Overall, the compound has fallen out of favour in the states, and its use in industry is on the decline.
Dirk