You can do a couple of things to get rid of the free nitric acid, add gold and heat to use up the free nitric acid (Harold's trick), or use sulfamic acid, or the evaporation, or a combination of these.
I personally do not like Urea, and if you do suspect platinum using Urea could complicate its recovery.
You should be able to determine if you have gold or platinum with your spot plate tests, after De-NOxing the solution to be tested (you can use sulfamic acid to remove nitric from a small sample to be tested), (sometimes if the solution to be tested has a couple of metals that react to change color of the solution being tested it can be hard to tell, by using a spot plate you can test with a copperas crystal (ferrous sulfate), the gold if in solution will precipitate as brown ring around the copperas crystal, (this precipitates gold from the solution in this test, leaving the solution in this test barren of gold), then we can move the gold barren solution from this test to another well in the spot plate and test it with stannous chloride for platinum.
I thought you just had gold in solution, I did not know you were working with a Dore bar, how does your solution filter?
The solution does look dark, like there are other metals in solution, in the one picture I do see a dark yellow that does resemble gold in solution, but iron can also can look like gold in solution. It also looks concentrated, it is hard to tell what is in solution by just looking at it, that is where our testing helps us see what we really have.
Testing will be important, you need to learn to do it properly, otherwise you would still just be guessing.
The solution looks fairly concentrated, that is good for De-NOxing the solution.
But you will want to dilute and let it sit overnight (for silver or lead to settle),(a little sulfuric acid or sulfamic will help if lead is in solution), and filter before trying to precipitate your gold.
