Help a Noob... Unwanted white crystals after Precipitation
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goldgee35,
The question and the picture give us very little to go on to help answer your question.
Have you tested the yellow solution for gold?
What is the yellow solution in your picture? What have you done up to this point to create the yellow solution? What is the solution with the white salts?
The more information or clues provided with your question, the easier it is to give answers to a puzzle?
White salts can form from several different ions in solution, Cations like sodium, potassium, lead, silver, and copper salts are common, along with Anions in solution such as chloride or sulfates...
Sodium chloride is soluble in cool water.
Lead chloride dissolves readily in almost boiling hot water, upon cooling most of the lead salt will precipitate back out of solution, as cold water will hold only a small portion of the lead salts, thus the decanted water can be reused to dissolve more lead chloride when reheated to dissolve more of the white salts...
Silver chloride is insoluble in cold or hot water when water rinsed free acids, the surface outer shell of the white salt will darken in light, the light converting its shell to silver metal.
There are methods to dissolve the silver chloride and to verify silver Cations, or chloride Anions...
The white insoluble salts can be from other salts, especially if using more reagents than that which is soluble in solution, like overuse of urea, SMB...most of these are also water soluble.
Basically, the white salts form the chemical reactions, knowing what you have added or done chemically will give more clues to what they are.
The question and the picture give us very little to go on to help answer your question.
Have you tested the yellow solution for gold?
What is the yellow solution in your picture? What have you done up to this point to create the yellow solution? What is the solution with the white salts?
The more information or clues provided with your question, the easier it is to give answers to a puzzle?
White salts can form from several different ions in solution, Cations like sodium, potassium, lead, silver, and copper salts are common, along with Anions in solution such as chloride or sulfates...
Sodium chloride is soluble in cool water.
Lead chloride dissolves readily in almost boiling hot water, upon cooling most of the lead salt will precipitate back out of solution, as cold water will hold only a small portion of the lead salts, thus the decanted water can be reused to dissolve more lead chloride when reheated to dissolve more of the white salts...
Silver chloride is insoluble in cold or hot water when water rinsed free acids, the surface outer shell of the white salt will darken in light, the light converting its shell to silver metal.
There are methods to dissolve the silver chloride and to verify silver Cations, or chloride Anions...
The white insoluble salts can be from other salts, especially if using more reagents than that which is soluble in solution, like overuse of urea, SMB...most of these are also water soluble.
Basically, the white salts form the chemical reactions, knowing what you have added or done chemically will give more clues to what they are.
Jovane,
In the discussion above the white salts could because the gold was reduced with a reducing agent.
In other cases, we can have white salts with no reduced gold.
In the discussion above the white salts could because the gold was reduced with a reducing agent.
In other cases, we can have white salts with no reduced gold.
Jovane,
In your question, you are not dealing with a normal situation where gold is reduced with these base metal salts.
In that case my suggestion is to wash out as much of the salt as possible and put the remains back into solution with HCL and your choice of oxidizer (nitric, H2O2, NaClO)...
Let us assume we have made aqua regia, we mix one mole of nitric acid and 3 moles of hydrochloric acid.
HNO3 + 3HCl --> NOCl + Cl2 + 2H20
As soon as these acids mix they begin to decompose to volatile gases and water (nitrosyl chloride and chlorine gas and water). this decomposition begins even without metals, aqua regia does not have much of a shelf life because of this decomposition (storing in a sealed container could cause it to explode from the pressure of gases)...
Ok so we see that mixing aqua regia pre-hand is a bad idea, actually using an excess of HCl with small additions of HNO3 with heat to assist in driving the reaction is much more conservative and can ensure we consume all free nitric in the reaction...
Ok now say we have a solution of dissolved metals (mostly all gold as we were very careful to eliminate as much base metal from our gold before refining) we have some (very small amounts of) silver, copper, iron, tin. lead... in solution.
Our gold is in solution as a salt (ion), along with these other base metal salts (ions)in the acidic solution.
Say we have just a little excess nitric acid involved, we used just a little more than we should have, we will need to remove this oxidizer from solution, we have several methods available to do this.
Urea is not one I would use.
Triple evaporation process with small HCl addition between each of the evaporations.
Evaporation process with sulfuric.
Adding a button of gold.
Sulfamic acid.
In this case, let us use evaporations, and sulfamic acid to deNOx the solution.
As we heat and concentrate the solution the volatile acids decompose as a mixture of water and acidic fume vapor off as gases, and any remaining free acids in the solution will begin to concentrate as water is driven off, then free Nitic will vapor off as NOx gas, then free HCl which has a lower volatility, base metal salts can form nitrates and chlorides, as we vapor of the gases we get the solution to a thick solution we add just a little HCl the acid which can make a red cloud of NOx gas upon addition as the copper or other base metal nitrates are acidified (by HCl) and remake free nitric in the solution and decompose to a red cloud. With much less volume than we began with originally, we can evaporate a second or third time in much less time.
Then we have sulfamic acid (although evaporation as above to a syrup is not needed, it can be used in combination with sulfamic acid).
Sulfamic acid will DeNOx the solution, the byproduct formed is sulfuric acid, which is beneficial to helping remove lead.
Ok so we have removed the oxidizer from solution, we can dilute the solution and let it settle overnight.
We will have some insoluble salts in the solution these are normally white salts. silver chloride (light and fluffy) lead sulfate (needle-like) and other insoluble salts say silica...
Now we carefully decant and filter the solution which still contains our gold and the remaining base metals in solution.
Note in this case we have removed almost all of the lead and silver salts.
Now we can use a reducing agent like ferrous sulfate or sodium metabisulfite to precipitate the gold.
With minimum base metals in the solution, we can expect fairly pure gold as a tan or light brown powder, with a solution saturated with base metals we will get a black powder or impure gold and base metals like copper...
Here we can give the gold powders good washing procedure and refine it again for higher purity.
As stated earlier some salts are water soluble, and we can separate lead and silver salts by using this and the facts of solubility of these salts in water and the temperature of the water involved.
Sodium chloride is soluble in cool water.
copper I chloride will dissolve in HCl.
Lead chloride dissolves readily in almost boiling hot water, upon cooling most of the lead salt will precipitate back out of solution, as cold water will hold only a small portion of the lead salts, thus the decanted water can be reused to dissolve more lead chloride when reheated to dissolve more of the white salts...
Silver chloride is insoluble in cold or hot water when water rinsed free acids, the surface outer shell of the white salt will darken in light, the light converting its shell to silver metal.
There are methods to dissolve the silver chloride and to verify silver Cations, or chloride Anions...
lead sulfate is insoluble in water.
In your question, you are not dealing with a normal situation where gold is reduced with these base metal salts.
In that case my suggestion is to wash out as much of the salt as possible and put the remains back into solution with HCL and your choice of oxidizer (nitric, H2O2, NaClO)...
Let us assume we have made aqua regia, we mix one mole of nitric acid and 3 moles of hydrochloric acid.
HNO3 + 3HCl --> NOCl + Cl2 + 2H20
As soon as these acids mix they begin to decompose to volatile gases and water (nitrosyl chloride and chlorine gas and water). this decomposition begins even without metals, aqua regia does not have much of a shelf life because of this decomposition (storing in a sealed container could cause it to explode from the pressure of gases)...
Ok so we see that mixing aqua regia pre-hand is a bad idea, actually using an excess of HCl with small additions of HNO3 with heat to assist in driving the reaction is much more conservative and can ensure we consume all free nitric in the reaction...
Ok now say we have a solution of dissolved metals (mostly all gold as we were very careful to eliminate as much base metal from our gold before refining) we have some (very small amounts of) silver, copper, iron, tin. lead... in solution.
Our gold is in solution as a salt (ion), along with these other base metal salts (ions)in the acidic solution.
Say we have just a little excess nitric acid involved, we used just a little more than we should have, we will need to remove this oxidizer from solution, we have several methods available to do this.
Urea is not one I would use.
Triple evaporation process with small HCl addition between each of the evaporations.
Evaporation process with sulfuric.
Adding a button of gold.
Sulfamic acid.
In this case, let us use evaporations, and sulfamic acid to deNOx the solution.
As we heat and concentrate the solution the volatile acids decompose as a mixture of water and acidic fume vapor off as gases, and any remaining free acids in the solution will begin to concentrate as water is driven off, then free Nitic will vapor off as NOx gas, then free HCl which has a lower volatility, base metal salts can form nitrates and chlorides, as we vapor of the gases we get the solution to a thick solution we add just a little HCl the acid which can make a red cloud of NOx gas upon addition as the copper or other base metal nitrates are acidified (by HCl) and remake free nitric in the solution and decompose to a red cloud. With much less volume than we began with originally, we can evaporate a second or third time in much less time.
Then we have sulfamic acid (although evaporation as above to a syrup is not needed, it can be used in combination with sulfamic acid).
Sulfamic acid will DeNOx the solution, the byproduct formed is sulfuric acid, which is beneficial to helping remove lead.
Ok so we have removed the oxidizer from solution, we can dilute the solution and let it settle overnight.
We will have some insoluble salts in the solution these are normally white salts. silver chloride (light and fluffy) lead sulfate (needle-like) and other insoluble salts say silica...
Now we carefully decant and filter the solution which still contains our gold and the remaining base metals in solution.
Note in this case we have removed almost all of the lead and silver salts.
Now we can use a reducing agent like ferrous sulfate or sodium metabisulfite to precipitate the gold.
With minimum base metals in the solution, we can expect fairly pure gold as a tan or light brown powder, with a solution saturated with base metals we will get a black powder or impure gold and base metals like copper...
Here we can give the gold powders good washing procedure and refine it again for higher purity.
As stated earlier some salts are water soluble, and we can separate lead and silver salts by using this and the facts of solubility of these salts in water and the temperature of the water involved.
Sodium chloride is soluble in cool water.
copper I chloride will dissolve in HCl.
Lead chloride dissolves readily in almost boiling hot water, upon cooling most of the lead salt will precipitate back out of solution, as cold water will hold only a small portion of the lead salts, thus the decanted water can be reused to dissolve more lead chloride when reheated to dissolve more of the white salts...
Silver chloride is insoluble in cold or hot water when water rinsed free acids, the surface outer shell of the white salt will darken in light, the light converting its shell to silver metal.
There are methods to dissolve the silver chloride and to verify silver Cations, or chloride Anions...
lead sulfate is insoluble in water.
Geo
Well-known member
Have you tested the solution with stannous chloride? Did you test before trying to drop the gold? Did you test after trying to drop the gold? If not before, how do you know you have gold in solution? If not after, how do you know you removed the gold from solution? Two very simple things that could have answered this question before it was a question. Test the solution and let us know the results. Show a pic if you can.
