Copper will cement anything more noble - gold, silver, PGMs, mercury etc... Putting the copper into the PM loaded AR will cause all precious metals to drop on it. After the nitric acid will deplete from the solution of course.
It is very advantageous to also know the theory behind. Because if you encounter any problems along the way, you will be more able to solve them by yourself.
And I does not believe kilo of urea cost 20 USD in Hungary. Fertilizer grade could be purchased for few euros for 5kg bag in gardening stores. By the way, don´t use urea. Use sulfamic acid instead. Or if you cannot source any sulfamic, stick with copper precipitation.
Learn how to do things how they should be done. There are hardly any shortcuts in this business. And also, never pre-mix AR. Dose nitric acid incrementaly. You save precious nitric by doing so, and also it is much easier to process afterwards regarding excess nitric removal using sulfamic. Adding bases does nothing to the nitric or nitric residues.