OK smelting it is.
First let me say that the majority of medium to the small side of large refiners today are running circuit boards today by smelting and refining the copper. The more time you can put into segregating and separating the material the better the payoff. That is why this is done in countries where labor is cheap. Having 15 or 20 sorters picking through the boards and cutting off components is effective at producing a feedstock which lends itself to electrolytic copper refining to concentrate the PM's in slimes. Poor sorting results in smelting lower grades of copper with metals like lead which are a nuisance metal in the copper refining process and they are a reason copper smelters will charge you extra when these metals are in the mix.
So assuming we all have the sorting process down pat, we end up with boards and components which we need to burn. The ideal scenario is controlled pyrolysis, followed by incineration, and then either sifting or smelting. If we go the smelting route generally circuit boards need copper added to get up to about 15% metal weight for the best collection.
When smelting the ideal system involves melting in a rotary kiln. These are pricey and not very versatile.
So let's start out with me showing you a photo of a small tilting pour gas furnace, this is a center pivot furnace and this is about as small as they get.
The center pivot refers to the pivot points on the tripod stand which means the unit pivots from the center when pouring. These are the least expensive units to produce and they are challenging to pour bars with. As you tip the furnace more and more when pouring, the spout where the metal comes out moves closer to the furnace center line. At full tilt, you are under the furnace. So you have to move your mold to catch all of the pour. To define the challenge a little better, if you have a furnace 24" in diameter, the pour spout moves in an arc which will drop 12" down and 12" towards the centerline of the furnace. A hydraulic melt table will make this do-able but it has to be moved in and down as the pour proceeds. It's a skill you acquire with practice, or maybe spills and practice.
The alternative is a nose pour furnace which has the pivot point from the stand on the outside edge in a line tangent to the outside diameter of the furnace body. This results in less travel of the pour point when pouring bars.
this is a catalog cut from a Baker gas nose tilt furnace.
So you might ask, why not a lift and pour crucible? My answer is capacity. I tend to work on bigger stuff so i think along those lines. Plus for a lot of members here on GRF who work alone, lifting and pouring a large crucible is a 2 man proposition. A tilting pour is a one man show.
You could build a furnace into the ground. Just like the refiner in Thailand from this thread posted by Gaurav.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=38&t=23609
To pour from this furnace they need to lift the crucible out and pour it. Generally a crucible is lifted with a pair of these tongs.
These can lift 2 ways, one by having one man on each end, and the other by using a hoist on the ring in the center, the hoist pulls up and the tongs cradle the crucible from the sides tapering to the bottom so it doesn't slip. Then to pour it has to be transferred to a pouring cradle.
That is why I like a tilt pour setup.
The unit I am working on for my client in Mexico is a hybrid of 3 different pieces of equipment. It has a nose tilt crucible furnace which is poured by tilting the furnace with a hoist pulling on a cable attached to the lower half of the furnace 180 degrees opposite the pour spout. Pretty basic.
Then there are different lids. The regular melting furnace lid, the limit the oxygen and deflect the smoke into the afterburner lid, and the actual afterburner.
Now here is a catch. These lids are refractory and quite heavy so you will need an overhead lift. I prefer this type of crane but an overhead I beam would do as well. In a smelting shop an overhead hoist is a blessing. When you shot metal into water, you need a good quantity of water and you don't want to change it often. (climate change, drought, California is a desert, you know the drill) So the shot tank has a rigid metal liner on chains that fits the bottom of the tank and after you pour, you hoist out the liner and all of your nice shot comes with it.
This is the style of hoist crane I prefer;
I made this furnace representation in Paint on my laptop so some of this makes sense. The red is obviously the flame. The bottom flame heats the crucible and its contents. There is no crucible shown in the sketch. I prefer nose pour crucibles but it will also take a standard crucible and you can add a launder to direct the molten metal. The top section is an afterburner. When using the unit for pyrolysis, a lid is added over the charge so all of the smoke comes out the center. The afterburner section is just an extended burn chamber with its own flame which I like to run with excess air as the combustion smoke is air starved at this point. This is pretty effective at burning the smoke off from the pyrolysis providing the hole in the top between the top and bottom (also not shown) limits the smoke and uncombusted fume discharge rate.
The rings on top of the top unit have a chain which is picked up by a hoist to remove the afterburner. A gas quick disconnect is helpful here.
So to operate the unit with a batch of unburnt circuitry first the crucible is filled. Then the air restricting lid is placed on top with the hoist, then the afterburner is put in place. The afterburner fires first and when it is hot (glowing is nice) the lower unit is lit. For pyrolysis this is a low heat not full blast but warm enough to get the pyrolysis going. I toyed with the idea of putting a bottom on the afterburner unit to eliminate the need for the lid to control the smoke entering the afterburner. The bottom would obviously have a small hole to emit the smoke. I chose to not do that because I may need the afterburner for mild smoke conditions at some point and no lid would be needed, so for versatility I chose to keep it separate.
When the pyrolysis is done, a # 150 crucible should take about 1 hour, the burners are shut off and the afterburner is removed, the inner lid is removed, and the furnace (bottom) is re-lit. Then the carbon is burned off to complete the pyrolysis/incineration process. I would be putting the afterburner back on for this process until you learn how long to burn to complete pyrolysis, but that's me, I've inhaled enough crap in my life already.
The furnace can now be either emptied out to sift and flux the powders or flux can be added to the charge in place. A second lid for melting is placed on top of the furnace, it too is placed with the hoist. I added a pin at the rear opposite the pour spout so the lid doesn't slip off while pouring. The pin slides into an oversized sleeve on the furnace so it is easy to place the lid on. For the smelting part of the cycle, copper is added to get the metallic fraction over 15% and I like to rock the furnace. Remember it pivots, so getting the molten pool swirling by slow rocking using the tilt hoist will aid in collection. The molten charge is periodically slagged off by pouring into a slag mold. Large slag molds are sold by Legend and they attach to a buggy so you can roll them around.
After the furnace has melted all of the flux/sweeps charge, the majority of the slag is poured off until the metal starts to flow into a sample ladle then the charge is shot into water to make grain.
The copper based grain is cast into anodes. The furnace is too large to make the high surface area thin anodes needed for the copper cells so that is why grain is cast. It is easily weighed out and cast into individual anodes.
So that is smelting, we do need to cover fluxes and a few details but this is the hardware, the rest is chemistry.
The actual furnace I just described is currently being cast, the 1/4 scale model worked very well, It takes a # 40 crucible. They plan on using the little guy as well as the one being built. The first unit was built by the maintenance crew at the shop from some rather crude drawings I had made, they completely understood the concept (not from my Spanish, from the boss's translation!) and went with it. The bigger unit is more of the same. So for a moderately handy person, this is definitely within reach.
