Metal finishing Q&As since 1989

-----

Treatment for conc. electroless Ni waste

I am a engineer at WWTP. I had some problem on the concentrated electroless Ni plating waste. The concentration of the incoming Ni waste is >5000 ppm at around 2000 US gal per day. Currently, we use the Electrowinning system to treat the conc. Ni waste. The pH for the incoming waste is around 4.5. So, we need to dosing NH3 to the Ni waste to bring the pH up to 8.5 - 9.0 to increase the efficiency of the electrowinning system.

My problem now is the Ni waste always change to black color at the first and second reacting bath. May I know why this things happen?

Is there has a better and easier way to treat the concentrated electroless Ni waste, like using hydroxide precipitation or other more advanced technique?

Thank you.

David Thang
Enersave Engineering Systems - Penang, Malaysia
2005

---

Your problem with blackening probably has to do with the oxidation state of the Ni, or a complex forming in the bath. There are better ways to deal with small amounts of highly concentrated wastewater. From what you've said I'm thinking a simple Hydroxide precipitation system would take care of the problems and save lots of operator time and effort in the process, not to mention energy costs.

Jeff Watson
- Pearland, Texas
2005

---

There are many ways to treat electroless nickel plating wastes. Most people do not try to electrowin it because the efficiency is low and it is difficult to achieve a low enough concentration of nickel to discharge without further treatment.

Many people use chemical precipitation with DTC or another chelate breaker, and some people just add more reducing agent and let it plate out on steel wool [affil link on Amazon]. Sodium borohydride has also been used to produce a nickel powder. Unfortunately, none of these, except the chemical treatment with chelate breakers results in low enough concentrations of nickel to discharge without further treatment.

Lyle Kirman
consultant - Cleveland Heights, Ohio
2005

---

There are a new other solution without any chemicals for Ni remuval. The ECP (Electro-Catalytic Precipitation) will be your solution.

This method remove the metals from solutions, without chemicals, not depend on concentration, not depend on pH level. The oxidation of the metals and chemicals in the solution will do solids oxides and minerals possible to be easily filtered by media filtration or bag filters, or DE filters, depending on the final requirements of the water. The final quality of the water can be almost distilled water, then most cases it can be reused to the process if the client require this.

To offer you a solution, you may give us the detailed wastewater analysis, flow rate and final quality EPA requirements.

Regards

Damian Dinu
SC INGO PROD SRL - Constanta, Romania
2005