CaseyJones,
Edit again: I am all mixed up after re-reading your original post. (while writing this my mind shifted from, you were cementing from a nitric solution then I realized Gold from chloride solution) the info I gave here I will not revise much as it will give you ideas, it will help to deal with base metals and put your values in state you can refine them (sounds like your main value is gold, and so much of this will not apply)
Here is something to consider and how I might deal with this (note this is written as a general procedure not necessarily your case or process.
Keep in mind your doing cementation from nitric solution so your powders would not normally contain gold, this step for gold was added as if gold was involved.
But you could expect silver (some lead and tin) and palladium (or PGM depending on source and conditions) from a nitric solution (with chlorides as we suspect here if your gold dissolved in Aqua regia and you cemented these on copper) so this procedure is with the thinking gold is involved)
(Before carrying out the full procedure putting some powder in test tube and dissolving it in HCL/bleach, heating to drive off excess chlorine taking a drop and test with stannous chloride will tell you what part of this procedure you may need or need to eliminate)
A spot plate test would be a better choice, this way you can test for each of these metals in solution, even the PGM's if involved. This post is so long I will not go into detail (searching Harold's posts and spot plate along with Hoke's book will give you more info into this valuable tool.
Copper is low in the reactivity series of metals; study of this will help your understanding of what may be happening. (With metals displacing another in solution).
Most all metals below copper (all that you should be dealing with) are valuable.
(your main value gold, and copper contaminate some lead and tin)
Most of this cemented materials may be valuable, there can also be another reaction happening in this mix that is leaving some invaluable metals also, like lead or tin (tin if chloride was involved), we can deal with this later, just keep the cementation on copper going until after brushing off the powder that clings to copper, and copper gives no more reaction (cementation or nothing more clings to it, and copper stays clean in solution, solution should also change blue from copper nitrate)(here you are cementing from aqua regia solution so solution would stay green), (gold will plate easily to copper from this chloride solution so keeping the copper buss bar for other processes later wash rinse and dry with heat and bag for storage when process complete), stir and brush off copper buss bar into solution), (stirring with the copper buss bar every once in a while help to get solution that may not come into contact with copper to gain electron to the metal ion dissolved in solution (some heat can also speed or help with mixing of solutions) this is a contact process.
After cementation is complete, and all powders are well settled I would decant solution (I use a tool similar to turkey baster suction bulb (you could use small diameter hose and a suction bulb to start siphon or fill hose held in a U position with water then hold thumb over one end of hose and insert open end of hose into liquid, hold thumb end of hose lower to another container and let thumb odd hose, you could also slowly hand pour off top portion of liquid into another container not disturbing powders in bottom, leaving a small amount of liquid and get that with a rinse wash, basically decant (remove liquid from powders).
(I filter my copper nitrate solutions and put them in a clean jug to reuse in other processes), (this copper loaded, spent aqua regia solution should treat for wastes, and make safe for disposal).
Give these powders several boiling hot water washes, letting powders settle in hot water (I usually do this in one container (the more you can leave powder in one vessel the less loss of values), wash until clear (colors of solutions are clues to the metals you may be removing).
Now what to do with these powders? (Spot plate tests will also help you decide) Well I suspect they had solder from the boards, so I would treat them as such.
Prepare for incineration:
I would wash them into my white corning ware dish (or amber or violet vision ware skillet) Rinsing jar with my squirt bottle into dish, add water, low heat, adding sodium hydroxide with stirring untill pH test neutral with pH meter or test strips (wash salts with several hot water rinses letting powders settle before decanting solution (chloride salts will form NaCl (table salts) with the caustic), this dish on my hotplate, my hotplate is the type with solid cast iron plate with heating element under the plate (this is the only kind I would set the dish on directly, if it was the kind with a coil heating element I would put a piece of steel plate between dish and coil, or heavy screen wire, or asbestos sheet (we do not want to break dish from hot spots), turning hot plate on low, till powders dry, a lid can also help if it decides to pop or splash bubbling, leaving gap in lid and dish for gases to escape easily, once powders are almost dry or just barely dry then I crush them to powder, I use a large piece of Pyrex glass (old boiler sight glass), your tool could be a piece of stainless nonmagnetic steel, after powder again I raise heat, raising a little at a time, until full heat (we do not want to break this dish by raising the heat to fast too quick thermally shocking it ), (sometimes these powders will become liquid again fusing of salts at higher temperature, after salts (acidic gases vapor off and dry again ) they may need re-crushing), once all gases cease from acids and carbon-ous materials burning off, I will get my propane torch on low and heat the powders keeping flame back until good and hot so as not to blow out powders (I work outdoors with wind blowing fumes from me or fan at behind me on calm days, a fume hood is the best choice here) (Note you could use stainless steel pan on coal fire or some other method, (with acids or strong bases, or chlorides I prefer the cassarol dish)(I am just telling you how I do it), you will sometimes see more smoke of acidic fumes or carbon materials as the powders start getting red hot, stirring the powders(every once in a while with stainless tool) as you heat them red hot to expose all these red hot powders to air will oxidize the base metals, we want to keep these powders red hot for a while for reaction to complete, but we do not want to melt them.
Now that we have them incinerated, we will let cool, turning down the heat, after cooled I will squirt with wash water bottle on fine mist so as not to splash out powder, wetting them and washing down sides of container, then (for the tin oxides) cover with some HCL and slowly raise heat to boil, once boil again spray side down with mist spray bottle, then dilute acid with water, lower heat to under a boil cover let powders settle till solution clear, then I decant liquid into a jar (with my suction tool), add more rinse water and wash these powders till my water washes come clear (note in the jar you are decanting to after cooling you may see whit lead salts form) (I also reuse this dirty HCl solutions in processes later like removing base metals)(I also save my lead powder in a jar)(you can decide if you wish to save or treat for waste disposal),
Now we have cleaned up our powders tin oxide, copper I chloride with HCl and lead chloride with hot water washes.
So lets say we have silver and gold in these powders.
(if only silver, and almost no gold I would re-incinerate and go to nitric acid)
(Depending on what metals (and how much) are involved and our spot tests show tells us where to go and what to do next).
If just a little silver we can get that silver chloride with ammonium hydroxide, so cover with NH4OH ammonium solution add some water and heat on low (CAUTION HERE we do not want to let this dry never, keep watch on this part till done do not walk away or leave this process unfinished, this step is where we can make an unwanted substance), after silver chloride dissolves into an Amine solution of silver, we will decant this to clean jar, (KEEPING POWDERS WET) and rinse powders several washes with water decanting washes to this jar, (we want powders settled before we do decantation of solutions we are trying to just remove what dissolves not the fine powders), after last water rinse of powders add some HCl to these wet powders (powders are now safe) (to the jar of dissolved silver solution add HCl till ph neutral, this will precipitate silver as chloride (making our solution safe) let silver settle (decant the ammonium chloride solution from silver) (I save this solution and concentrate it to salts later making ammonium chloride salts for other processes).
Now back to our dish with these powders covered in HCl I will add some water and wash pot side with spray bottle, and then add some bleach (sodium hypo chlorite) after some heating may add more bleach, or acid or water (to keep salts from forming), to dissolve gold powders, once dissolved little more heat to drive off excess chlorine, then cool, now we can let sit overnight covered decant salts formed (NaCl, NaCLO3, AgCl, Etc.) and filter (depending on what was involved would determine what to do with filters) and use our precipitant of choice to precipitate the gold, wash gold per Harold’s instruction, depending on color we may refine it again. (2nd refine-ing is easy and will improve your gold in second refining).
(Remaining solution if had other PGM can be tested and if positive selective precipitants used to recover them).
This is not the only way you could do this but just how I may attack it, It is easier for me to do the things I need to than it is to write about them so I hope I did not leave something out.
Edit: some to help clarify a confusing post.
Edit again after more thought:
Put powder into solution, to test in spot plate, using precipitation tests, moving remaining solutions to new spot and another precipitation test.
Also if there are just traces of valuable metals, to the stockpot they go no need to chase tiny portions around the lab. (This is hard to give a plan without being the one doing the process and knowing what may be in solution or making the tests).
. I moved on to the test batch and left it over night. It looked quite good by morning. I thought I would finish off by heating the nitric + fingers to ensure the base metals were fully removed and the gold was free. This is where things deteriorate. The boards all melted together in to toffee and the gold all disappeared into the solution 
