When we treat the waste we use several methods to remove metals from solution, the goal is to end up with a solution and metal powders, the solution will still be a salt solution but with the dangerous metals removed. where these metals are less harmful to us or our environment.
Some metals are replaced from the solution as elemental metal powders when we use the cementation process.
Example cementing values from solution using a copper buss bar, where copper goes into solution and the more noble metals cement out of solution as elemental metal powders that can be separated from the waste solution.
We use iron metal to replace copper and any of the metals less reactive than iron these can include bismuth, antimony, lead, tin, nickel, cobalt, and cadmium.These metals can also cement in elemental form.
Now left with an iron solution which can also contain many other reactive metals in solution. we can remove more of the metals.
we can precipitate many out as sulfides or us pH to precipitate many of them out as oxides or hydroxides (carbonates...).
Above iron, we have several metals which it is possible to have in solution with our iron, such as chromium, zinc, manganese, titanium, aluminum, beryllium, magnesium, calcium, strontium, radium, barium, lithium, sodium, potassium, rubidium, francium cesium.
Many of these metals form hydroxides and can be removed from solution by manipulating the pH of the solution to precipitate them as oxides or hydroxides.
Using a basic solution we can precipitate most of these metals from solution as hydroxides (bring pH up to about 10 or 11).
then we can bring the solution back to neutral with a small addition of acid (which will precipitate more of these metals). basically leaving us with a fairly safe solution of salt water sodium or potassium chloride, sulfate....
See dealing with waste in the safety section.
