variable,
That was so many questions at once I do not think I could answer them all, if you have many questions you should spend more time studying and doing small experiments.
I will not try to answer the questions, but I will try to get you to see something I see.
HCl will not dissolve gold; gold is far below hydrogen in the reactivity series of metals, HCl in not a strong enough oxidizer to dissolve gold. Nitric acid can oxidize gold, or chlorine gas can oxidize gold (pry away an electron from gold’s atom).
Sodium hypochlorite (Bleach) is an alkali solution; the sodium hydroxide NaOH involved in the bleach keeps it caustic enough to keep the chlorine in the solution of water.
When you mix the HCl acid with the Alkali Bleach you form chlorine gas which can oxidize gold in solution, but we also lower the acidity of our acid with every addition of bleach forming salt out of our acid (HCl + NaOH --> NaCl + H2O), also the chlorine is a gas that wants to bubble out of solution, so we can here where too much bleach at once can destroy our HCl, and make table salt, and waste chlorine as gas, also the lower the acidity the easier the chlorine would stay in solution, temperature also plays a major role in how the chlorine stays in solution.
So when we have gold fine powder or foils (this method has a very hard time trying to dissolve solid bigger pieces of metal), the gold in the HCl is oxidized by the chlorine gas (formed from the acid and bleach), this chlorine take’s electrons from the gold atoms, the gold becomes an ion (Cation), this gold Cation joins with three chloride (Anions) to form a soluble salt or compound of gold chloride, or dissolved gold in solution.
Now we already discussed loss of chlorine gas through gassing out of solution, and of our acid being neutralized, by the alkali solution, so we need to be aware we need free HCl acid in solution, and just enough chlorine gas to do the job, we can add a little more bleach a little at a time to keep the reaction going.
I believe far too often when we begin learning, recovery and refining, that a newbie’s we tend to way over use acids and solutions, we are impatient, and want to see something happen now, or we do not give it time to react, and do not know how much to add or what the reaction would even look like, much of our solutions or acids and reagents are wasted, and we create other problems for ourselves by using too much.
I would add the gold to the acid, and add the sodium hypochlorite just a little at a time, (personally, I prefer a warm solution), give it time, the reaction may not be very visible maybe only a few tiny bubbles.
Points to consider we want our solution acidic (bleach raises pH), so we must have enough acid to keep it acidic, also adding too much bleach to fast just gasses off most of the chlorine before it has time to react with the gold (also making salt out of our acid), to high of a temperature will also gas off our chlorine faster, but also too low of a temperature take so much longer for the reaction to occur and dissolve our gold, overuse of bleach can leave oxidizer in our solution when we go to precipitate the gold, I believe many times members have also used so much sodium hypochlorite the may have also raised the pH very close to neutral (mainly just dissolved salts, not much free HCl acid to help drive off chlorine), in this case they may have to evaporate the solution much farther than they normally would have to (until the acid concentrates enough to drive off the chlorine in this solution), at this point they may have salts forming from the solution becoming so saturated with salt, a little acid may help in this case.
Now so not only will gold use up your acid in the reaction but the NaClO can also use the acid up, it would be interesting to know what the pH of some of these guys solutions are, that are having trouble with too much chlorine left in solution before they precipitate (my guess is they may have no free HCl and they may not have a very acid solution left to drive off chlorine easily.
When I use HCl/NaClO I do not follow a certain ratio, but if I did I would look at what was recommended, and use that as a guide only, I would still have plenty of HCl and add the bleach on a small proportion at a time, (using the ratio as a guide to help to understand when I may be adding more than needed), but also I am not suggesting others do it this way.
That was so many questions at once I do not think I could answer them all, if you have many questions you should spend more time studying and doing small experiments.
I will not try to answer the questions, but I will try to get you to see something I see.
HCl will not dissolve gold; gold is far below hydrogen in the reactivity series of metals, HCl in not a strong enough oxidizer to dissolve gold. Nitric acid can oxidize gold, or chlorine gas can oxidize gold (pry away an electron from gold’s atom).
Sodium hypochlorite (Bleach) is an alkali solution; the sodium hydroxide NaOH involved in the bleach keeps it caustic enough to keep the chlorine in the solution of water.
When you mix the HCl acid with the Alkali Bleach you form chlorine gas which can oxidize gold in solution, but we also lower the acidity of our acid with every addition of bleach forming salt out of our acid (HCl + NaOH --> NaCl + H2O), also the chlorine is a gas that wants to bubble out of solution, so we can here where too much bleach at once can destroy our HCl, and make table salt, and waste chlorine as gas, also the lower the acidity the easier the chlorine would stay in solution, temperature also plays a major role in how the chlorine stays in solution.
So when we have gold fine powder or foils (this method has a very hard time trying to dissolve solid bigger pieces of metal), the gold in the HCl is oxidized by the chlorine gas (formed from the acid and bleach), this chlorine take’s electrons from the gold atoms, the gold becomes an ion (Cation), this gold Cation joins with three chloride (Anions) to form a soluble salt or compound of gold chloride, or dissolved gold in solution.
Now we already discussed loss of chlorine gas through gassing out of solution, and of our acid being neutralized, by the alkali solution, so we need to be aware we need free HCl acid in solution, and just enough chlorine gas to do the job, we can add a little more bleach a little at a time to keep the reaction going.
I believe far too often when we begin learning, recovery and refining, that a newbie’s we tend to way over use acids and solutions, we are impatient, and want to see something happen now, or we do not give it time to react, and do not know how much to add or what the reaction would even look like, much of our solutions or acids and reagents are wasted, and we create other problems for ourselves by using too much.
I would add the gold to the acid, and add the sodium hypochlorite just a little at a time, (personally, I prefer a warm solution), give it time, the reaction may not be very visible maybe only a few tiny bubbles.
Points to consider we want our solution acidic (bleach raises pH), so we must have enough acid to keep it acidic, also adding too much bleach to fast just gasses off most of the chlorine before it has time to react with the gold (also making salt out of our acid), to high of a temperature will also gas off our chlorine faster, but also too low of a temperature take so much longer for the reaction to occur and dissolve our gold, overuse of bleach can leave oxidizer in our solution when we go to precipitate the gold, I believe many times members have also used so much sodium hypochlorite the may have also raised the pH very close to neutral (mainly just dissolved salts, not much free HCl acid to help drive off chlorine), in this case they may have to evaporate the solution much farther than they normally would have to (until the acid concentrates enough to drive off the chlorine in this solution), at this point they may have salts forming from the solution becoming so saturated with salt, a little acid may help in this case.
Now so not only will gold use up your acid in the reaction but the NaClO can also use the acid up, it would be interesting to know what the pH of some of these guys solutions are, that are having trouble with too much chlorine left in solution before they precipitate (my guess is they may have no free HCl and they may not have a very acid solution left to drive off chlorine easily.
When I use HCl/NaClO I do not follow a certain ratio, but if I did I would look at what was recommended, and use that as a guide only, I would still have plenty of HCl and add the bleach on a small proportion at a time, (using the ratio as a guide to help to understand when I may be adding more than needed), but also I am not suggesting others do it this way.
