Will adding sodium carbonate to gold-containing aqua regia produce too much sponge gold? If so, how to withdraw money? Please don't Baidu, Ctrl V

For gold-containing aqua regia, neutralize it with sodium carbonate or sodium hydroxide to pHgt; 2, and the aqua regia will become ineffective. The advantage of sodium carbonate is that it is cheap, but a large amount of carbon dioxide is produced during acidic neutralization, and the gold-containing solution may splash out and cause losses. If the processing volume is small, neutralizing with sodium hydroxide is gentler (I used to help others purify crude When gold is used, sodium hydroxide is used). Do not adjust the pH value to alkaline, because it may contain copper, lead and other ions (including trace amounts of silver chloride ions). After it becomes neutral, hydroxide precipitation will begin to form. If you filter and wash it, it will cause the loss of gold liquid. I used to control the pH of deposits at 2-4, and add reducing agents (zinc powder, oxalic acid, ferrous sulfate, sodium bisulfite, glucose, formaldehyde, etc.). If the soluble ones such as oxalic acid and sulfite are added, When gold precipitates from the solution, it is very fine. Pay attention to washing and filtering to prevent loss. If zinc powder is used, sponge gold is precipitated, which is more convenient to operate. However, there are some small technical steps to dissolve the zinc and purify it. Be careful, otherwise it will cause a small amount of gold to be dissolved and lost during post-processing), and the gold will be restored quickly.

The restored gold is brown. If the concentration is very low, you insert a piece of zinc or tin. After a while, purple will appear on the surface, which is also the color of gold. If it does not appear for 10 minutes, If purple appears, then there is no gold in the solution (I used to use this method to judge the end point), and it will become golden after smelting at high temperature.

The restored sponge gold should be decanted and washed (I don’t use filtration. What should I do if the powdered gold remains on the filter paper or filter cloth? It’s troublesome). In particular, it must be washed until there is no chloride ion. This is very important. It is very important (because the sponge gold needs to be treated with dilute acid later). Dissolve and remove copper, lead and other impurities, dry and smelt at high temperature to produce the product.

High temperature smelting: soda ash, salt and borax. There are also some technical essentials to this (especially the "heat" of the removal, I made a joke the first time I separated the gold slag particles), which I won't go into in detail here.

It is easy to withdraw gold, but you must ensure that the deposit is not lost and the purity is above 99.9. This is not something that most chemistry teachers (including university teachers) can make clear. People without practice can only talk about general principles. As for feasible process and technical conditions, many things cannot be found in books and must be summarized in practice.