Incinerate and process as you wrote. But instead of pouring bars, you pour molds and put them into electro. One for coper, one for silver and one for gold.
That sounds familiar. Did you get this from a certain, very misleading, oversimplified, youtube video? If it's the one I am thinking of, they didn't tell you that, for each of these 3 metals, the residues were treated and re-melted and put through cells using different electrolytes. Pretty standard stuff for about 100-150 years although much more involved than that video indicates. In general: Copper sulfate cell - Thum or Moebius silver cell - Wohlwill gold cell.
One more question. How do they process metals after incineration to achieve 98% purity? With separator?
Most all of the refiner's bars and pulps go to a primary copper smelter/refiner, usually in Europe. They remelt and assay the bars very completely. This assay is what is used to settle with the customer and it also tells them what, if any, pre-treatment is needed. The bars are then blended in with the smelter's normal flow of material from the ore they are processing. Even though the makeup of the bars is somewhat different than the copper from the ore, it creates little problems since the refiner's bars are a drop-in-the-bucket, weight-wise, compared to the the amount of impure copper (from ore) they are blending it with. There are some problem metals that probably must first be removed or at least considered, like nickel. That's why you're penalized for it. I don't know exactly how they process the pulps (which always contain PMs), but it surely involves flux melting.
I only know of one instance in the US where a refiner processed refiner's bars. They used weak sulfuric electrolytically, using a commercial anodic membrane to separate the anode and cathode compartments, thus preventing the dissolved metal from depositing on the cathode. The result was a copper (and other base metal) sulfate solution and a solid residue containing the gold, silver, lead sulfate, etc. The PMs were treated conventionally and the copper, etc., was cemented from the solution using scrap iron. There are a lot more details to this, depending on the metals involved and their amounts, but that is the general idea.
I might mention that, in more recent years, grinding and mechanical separation is slowly replacing the incineration method of electronic scrap. Much greener. The main innovator in this is ECS in California. They use such things as magnetic separation, eddy-current, flotation, etc., to separate all the different fractions, most of which have value.
