It may be surprising to know that the indium plating bath solution has a potential monetary value. Its value is derived from the indium metal still in solution. The plating solution, as supplied from the manufacturer, has approximately 30 grams of dissolved indium metal per liter. And, with normal plating bath use, the indium content of the bath can rise to twice the original amount (~60 grams per liter). So, in the example case of a 5 gallon tank, one could possibly have 1,200 grams of dissolved indium metal.
So.... How does one extract this hidden wealth?
The indium sulfamate plating solution has a low pH (acidic). This is needed to keep the indium in solution. If the pH of the bath rises, the indium will precipitate out in the form of indium hydroxide. Indium hydroxide is not soluble (in water). The bath will turn a milky white as the indium hydroxide is formed.
One can force the indium to precipitate out by adding NaOH (sodium hydroxide) to the bath to raise the pH. Raising the pH to 7 (neutral) is recommended because it will make disposal of the rest of the bath easier and safer. In a static bath (no stirring or agitation) the indium hydroxide will eventaully settle out to the bottom of
the tank. The solution on the top can be siphoned off. And then the indium hydroxide can be dried - leaving a white powder.The indium hydroxide powder can then be shipped to an indium reclaimer. The reclaimer will convert the indium hydroxide back into indium metal which has market value. The value of indium metal can be tracked through such entities as the Metal Bulletin.
Note: Please consult local environmental regulations to insure proper disposal of the indium sulfamate plating solution.
Contact me with any questions.
Eric Bastow