the way i do it is get base metals with acid peroxide, and fish tank bubbler.this will leave gold flakes if let run till done,
the acid peroxide will attack the small amount of solder although slow and when I let my solutin sit for long periods will collect the solder as gray powder,it being only slightly soluble as a chloride in the acidic solution,
if processor has a large heat sink soldered on, I desolder them with torch
the processor can be put in AP till pins fall off and they almost float, as only shells of gold left, then removed and then crushed to powder to get the gold inside,
or you can also process in nitric to rid base metals, then Aqua Regia or Hcl/ bleach,
the base metals in your aqua regia or HCl Bleach is just asking for trouble.
I cant tell from picture but are the traces on the board gold plated?