The last and possibly the most popular type of scrap (for this forum) to send out to a refiner is e-scrap. From what I've read on this forum a-lot of our members get this scrap and cherry pick the good stuff for refining or do some sort of preparation so they can recover the metals from the higher yield components themselves. This will always leave some kind of lower yield material that is ripe for sending out, providing you can get paid fairly for what's in there. Again the only way to tell what is in there is to sample the material and the sample has to be representative. This material is generally stream sampled. What that means is they chop, shred, grind or pulverize the material into uniform sized chunks so they can draw off a proportional sized sample. A stream sampler will sample shredded paper as well as it will sample lead shot, and therein lies its weakness. It is up to you, the generator of the material, to separate the material into grades of like density scrap. This is a bit of subjective sorting here but let me explain. The material which has been processed into like sized pieces is moved along a conveyor and dropped into a chute as a steady stream of parts, the machine is programmed for say a 25% sample, by switching some diverting arms the sample streaming down the chute is diverted into different lines, one line goes to the 75% accumulating pile, and the other to the 25% pile. It is amazing to watch and I have watched it and weighed the fractions coming off and it's pretty dang close to right on. This procedure will then be repeated on the 25% fraction to produce a fraction which is 6 1/4% of the original and so on. They continue until you have a representative, manageable sample of the entire lot. This sample is either incinerated, crushed, sifted, and the oversize melted with copper, or it's melted directly with copper. The benefit is the smaller sample is produced into an assayable sample while you watch.
Now for the glitch...... :twisted: ........if the material is a mixture of say steel relay headers with gold pins, and depopulated PC boards, the sampling will not be so great. The heavier steel headers fall faster than the light circuits so the stream isn't as dense consistently. Now if you have enough headers to run separately, and enough boards to run separately, the densities will be similar and the sampling is very good. The refiner doesn't know if a bad density mix will work in his favor or in your favor so he isn't too anxious for sampling of poorly sorted materials either. So the sorting is the job of the collector, you, before you ship for stream sampling.
The material which you have pre sorted is received at the refiner where they will decide if it will be best to granulate, shred, ball or hammermill this material before stream sampling. Whatever they decide, you will be part of the decision, and with your nod the material will go through the tortuous process. You will know your start weight and verify the finish weight. From looking at the parts they will also let you know if it will need incineration (likely if it was PC boards) or straight melting. Now it's off to the stream sampling machine. I've brought in 20, 55 gallon drums of plated connector scrap and had it reduced to 3, 5 gallon pails. Now you get to do eenie meeney miney mo and pick one for processing. The other two are sealed up in case another sample is needed.
If the material has to be incinerated, you will end up with a powdered sweep portion which is sampled for assay just as described for sweeps processing, the only difference is the rather large metallics fraction. Actually they mix magnetics and metallics together for a melt with copper.
You will witness the melt and just as before with meltables come away with samples and a sealed umpire. If the job didn't have to be incinerated, it goes directly to the melt room.
In both cases you have come away with samples which you witnessed and are reasonably sure represent your material.
This last type of processing is only done by rather large refiners and if they will not let you witness everything, say thank you and find another refiner who will. If you do enough of this type of recovery, and keep records about different materials you will generate enough data to feel confident that you are getting your just return. Just don't get confident enough to let them process it without you there.
There are others on this forum who have witnessed materials as I have and I invite all comments concerning what I have said or more importantly about what I may have missed.