i was researching gold refining last year. i read that you could substitute peroxide for nitric acid. i was planning to use this process but after more research i decided to avoid the pitfalls so i sold most of my e-scrap.
imo it isn't worth your time or your health to process a few boards. however if you can easily obtain tons of e-scrap for little cost then i might spend my time learning, starting with safety and disposal.