Aurthur can you let as much as possible settle, and filter solution?, some thick solutions will settle better if acidity lowered, some seem to settle better diluted, a funnel filter and a wad of fiberglass insulation in neck can prefilter course stuff, How I may treat a solution may depend on its character, if tin is not too much boiling and concentrated acid may help to dissolve the tin better, and help, or sometime cementing with copper and good boil to drive off some water concentrating the acid and then redilut after cool, , I really do not know specifics of your situation, if alot of solder letting sit decanting liquid, and if I have a thick gel solution, that is imposible to filter, (sometimes I will add copper bus bar to get the acids to add some copper to solution, and help to reduce gold), I will concentrate it to thick syrup remove to cool and let crystalize, then I will move this to a brown glass type skillet and raise heat slowly first the crystal salts will turn back to syrup, and bubble off the gasses from my acids, as this slows or stops, I raise the temperature again, untill the powder at high heat is dry, then I will introduce the torch flame, crushing and stirring till I have fine powders all red hot and no gas is released, this roasting in air oxidizes the tin and base metals,
now depending on how much solder to gold I thought I had will usually depend on how I would go from here, (others may go with dilute nitric ), I would go for a Hcl solution full strength, just enough to cover roasted powders, stir well let sit, later I would dilute stir let sit, decanting later, now I would have a chloride powders, alot of the tin would have been in solution I decanted, I would still think maybe some tin in powder, gold, silver, lead, as chlorides of lead and silver are insoluble in water, and my gold should not dissolve in HCL without oxidizers, Now I would seperate as much lead as possible, lead chloride is slightly soluble in boiling hot water, silver and gold will not be soluble, (here I use the same water, boiling hot keep hot while alowing solution to settle, decant portion of hot lead chloride to another jar to cool and crystalize, one this drops its lead I put that same water back into boiling vessel to collect more lead chloride),
once most of lead and tin are gone, I will let settle decant, a wash or two depending on looks of liquids, settle decant and re-incenerate powders, then treat with dilute nitric and so on.
