more on no toxic wastes -- Pd plating solutions
An example of how we avoid toxic wastes is how we deal with left overs from our electroless palladium-plating operation. Palladium is rather valuable, about $250/oz currently, but the ordinary left-overs from plating contain hardly any palldium and contain a lot of other nasty stuff. Palladium plating is done in our shop from a solution that contains ammonia, hydrazine, and less than 1/2% Pd, by weight. Thus a quart of fresh solution has barely 1/6 oz of Pd, about $30 worth. After coating, we're down to about $3 worth, and no-one will treat the quart of solution to recover only $3 of Pd, so we enhance it. We only generate a few ounces of left-over electroless plating solution per week, and when we generate it, we put it in a beaker filled with a few grams of left-over Pd, an a few milligrams of PdNO3; you'll see hwere we get the PdNO3 from in a little bit. Generally there is still some reactivity to the solution, and it gets higher when inhanced by the PdNO3 that dissolves and enters solution. In the reaction the follows, most of the palladium is deposited over the next few days, and in the process we react away most of the toxic, carsinogenic reducing agent (hydrozine). We let the rest of the hydrazine and most of the water evaporate and go out the hood. When the liquid is gone, or mostly gone, we have gotten rid of the toxic stuff, but we've formed, along with the Pd a bunch of carbonates. We now wash the contents of the beaker with water, and pour the water and some carbonates down the sink. These carbonates and the wash water are wastes, to be sure, but they are not classified as toxic waste (I wouldn't want to drink it). We get rid of the carbonates by washing with left-over nitric acid that was used to clean Pd from our glassware. In the end we are lft with PdNO3 and other nitrates in the beaker with the Pd.
Over time the value of the Pd in the beaker increases. It's now worth $100, perhaps. Not enough to make us rich, but enough to be sold, and the process gets rid of toxic wastes, so that we don't have to report them and deal with them as such. Pretty cool.