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topic 0808

Wastewater treatment for tin plating


Q. I have a problem to treat waste water from tin plating.
My plating process is dip type plating in a batch reactor (at 80°C.) using aluminium stannate & Potassium stannate.

I have treated that waste water with FeCl3 on base conditions (pH>7) but the result was not satisfactory. Now I have a trial to solve that problem by add K2CO3 to give carbonate condition and base conditions not been change.

Please could someone help me to solve my problem? Thank you very much.

Ari Sutrisno


A. Are you running a continuous flow or batch treating? You might try ferric sulphate. With a 60 GPM system using matte acid tin it works quite well. Neutralization is done with NaOH. You might consider switching to matte acid tin, it is easy to maintain, and gives an excellent deposition rate.

Phil Pace
- Tulsa, Oklahoma


A. Hi Ari. When using iron-based coagulants/co-precipitants, I believe that you should add them while the effluent is still quite acidic; then, when you neutralize, some of the iron stays in solution driving out the other metals.

But what I missing in this discussion is the entire idea of wastewater treatment for tin. When/where is tin regulated that iron is not? That sounds very strange.

I can only recall a very few instances where there were limits on tin, but in each of those cases ferric/ferrous chloride/sulphate could not be used because there were limitations on iron in the effluent as well.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


Q. Thank you Mr. Pace And Mr. Mooney.

I have waste water treatment in batch reactor. For using FeSO4/FeCl3, I have a problem on regulations. As Mr Mooney said, there are limits on Fe, so if we use FeSO4 I will have a problem to control over-added FeSO4.

Ari Sutrisno


A. As I mentioned, I have very little experience in tin removal from wastewater because it is so very rarely regulated. I mean, goodness, we plate cans with tin to render them safe, we tin our cooking surfaces to protect us. We deliberately tin plate food surfaces to make them safe.

I have found that the combination of a proprietary organo-metallic precipitant and DTC is extremely effective in the removal of metals, but I hate to even mention it, let alone actually use it to remove tin, as it seems the cure is much worse than the illness.

Look at the tragedy of the White River fish kill which was caused by excessive use of DTC. Pollutants from the plating shop didn't kill the fish, a chemical that the plating shop was forced by the regulators to add to their effluent caused the massive fish kill. If regulators are forcing you to use a horrible toxin like DTC to remove harmless tin, I despair for our future :-(

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. In my area neither tin or iron is regulated. My system runs approximately 60 gpm continuous flow. Tin plating is our main job. Ferric ions are excellent at removing heavy metals. I believe the reaction involves oxygen with a final product of iron and the other heavy metal bonded together. Ferric sulphate is added with a metering pump at the farthest point from the collection tanks. This allows additional time for reaction with the wastewater before neutralization. I cannot say that it will work with stannate baths, but it leaves our water cleaner than it comes in.

Phil Pace
- Tulsa, Oklahoma

June 22, 2012

Q. I have an industry of phosphate & tin plating with the following effluent characteristics. Can you please suggest the treatment scheme for the effluent?

1 pH 8.18 10-12 2 TSS mg/l 248 146 3 TDS mg/l 1322 3500 4 CHLORIDES AS CL mg/l 609 5 SULPHATES as SO4 mg/l 5 6 OIL and GREASE mg/l 3.3 0.4 7 DISSOLVED PHOSPHATE AS PO4(mg/l) 36.34 8 IRON mg/l 2.6 2.29 9 COD 24 356 10 ZINC mg/l 0.07 0.27 11 NICKEL mg/l 0.13 13.75 12 AMMONICAL NITROGEN mg/l 0.41 13 CHROMIUM TOTAL mg/l 0.33 14 COPPER mg/l 2.65 15 FLUORIDE mg/l 13.37 16 LEAD mg/l 23.4 17 BOD 10.4

- Delhi, India

First of two simultaneous responses -- June 25, 2012

A. Your problems appear to be lead and nickel, not tin. For those contaminants, I'd suggest you raise the pH to about 8, add a bunch of sodium carbonate to bring the pH to 10, then add floc and see how you do. It might be necessary to add some sodium sulfide or DTC to bring the metals down to appropriate levels.

If you are only trying to remove tin, then, add some hydrogen peroxide, and don't raise the pH at all. Sn should drop as "metastannic acid", that white sludgy crap so familiar to tin platers.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

Second of two simultaneous responses -- June 26, 2012

A. The recommended treatment will depend somewhat upon your discharge limits. Hydroxide precipitation at a pH of 9-9.5, followed by flocculation, clarification, and a final polishing filter should meet normal limits, but, if you have an exceptionally low limit for lead, copper or nickel, etc., then a different approach may be required.

Lyle Kirman
consultant - Cleveland, Ohio

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