I know this is an old post. When you use urea to neutralize nitric acid, it doesn't really neutralize it all. It converts some to byproducts like urea nitrate. Urea nitrate, when dry, is very unstable and can explode with little pressure. In it's pure form, it is a high explosive. Certain things that you can do will liberate the nitric acid from the nitrated byproducts. So there is the possibility that the gold simply redissolved back into solution. Ferrous sulfate pentahydrate is a blue color and contains extra water in the crystal. Ferrous sulfate heptahydrate is a aquamarine crystal that slowly oxidizes to a tan to brown color. Anhydrous ferrous sulfate is a white powder. Iron oxide is red and that is staining the white powder. When you mix your dry ferrous sulfate crystals, add a small amount of concentrated sulfuric acid. It will instantly dissolve the off color "rust" and make an aquamarine color. Adding HCl to discolored will not add any benefits to the process. Adding sulfuric acid will redissolve the oxide and recreate useful copperas. Below are two photos. One is anhydrous ferrous sulfate (white -off white) and ferrous sulfate heptahydrate (aquamarine crystals).im hoping someone can help me with a simil;ar problem . i had some solution from when i did 2 kilos of mixed ic chips. the solution was a dark mess which i couldnt do anything with , so i dropped what i hope was gold by using copper.
then i put the black silt into AR . i was extremely delighted when my AR turned a lovely dark orange and when tested with stannous , it immidiately gave a solid black result, i thought wow it must be really concentrated with gold. i have had issues precipitating for years tho , its the final stage of gold recovery that i always have problems with . so i plled out my tiny 250 ml beakers to try several different attempts at dropping gold.
in one beaker i put distilled water on heat and added iron sulfate . i left it on heat for about 10 minutes to try and disolve the powder , once disolved i put hcl to make it go green as id seen on videos . also hokes book talks about adding hcl to iron sulfate.when i poured the iron sulfate solution into the sample of AR , it turned brown and hasnt changed , nothing dropped.
in a second beaker i put AR to almost the top and added smb powder. i kept getting what i thought was either red or brown bubbles . as id never heard of red bubbles , i assumed it must be gold dropping then redisolving. which puzzles me as i had used urea untill no more reaction and there was even a little bit that wouldnt disolve . so i thought how could there possibly be any free nitric.
in a third beaker i put a small amount of AR then added smb which was disolved in water first and warmed up to help disolve . once i added it to the solution it went deep red.
im totally lost , i have no idea why or how it can turn red.
i still have half a coffee pot of the AR , which by the way turned light green after i diluted it to twice its volume and added urea.
what should i do with the remaining solution ?
i would really appreciate your help guys
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