mikeinkaty wrote:
Thought I'd take this to a PM.
I guess one critical question is - What is the best strength of Nitric Acid to use for inquartation?
Based on your last paragraph in the previous message, I increased the H20 amount by 20%. This would get the concentration close to 35%. But, is 35% the ideal concentration?
I added a drop-down list for Acid % that restricts it to one of these values - 35%, 40%, 45%, 50%, 55%, 60%, 65%, 68%, 70%.
Given this finite number of values allowed, how much H20 and acid should be added per gram of BM to get the desired reaction for typical karat scrap? I could just put that in a table then just multiply by the wt of BM. The table would have 2 columns - ml h2o per gram, ml hno3 per gram, and 9 rows.
Mike
Mike,
Have you ever actually done this?
There are no absolutes in this. The nitric is what actually dissolves the silver. The only purposes of the water are: (1) To speed up the dissolving. Nitric alone will dissolve silver but it is quite slow. The addition of water makes it go much faster. (2) When dissolving, the solution gets hot. If nitric were used alone and was used until it could hold no more silver or copper (called saturation), silver nitrate and copper nitrate would crystallize when the solution cools. This is undesirable. The addition of water prevents this, if enough water is used. Distilled water must be used. Tap water contains chlorine and this will precipitate some of the silver as silver chloride. This is also undesirable.
Any combination of nitric and water will dissolve silver. The common mix is to use equal volumes of water and 68% or 70% nitric - called 50/50 nitric on the forum. This is about the right amount of water to both prevent crystallization and to maximize the speed. I would base the other strengths on this.
Do you understand the mathematical concepts of the specific gravity (SG) vs the strength? In the handymath.com link I gave you, you can see that, at 20C, the SG of 70% nitric is 1.4134. One ml of 70% weighs 1.4134 grams. However, this is only 70% nitric by weight. Therefore, one ml of 70% would contain 1.4134 X .70 = .989 grams of nitric acid (HNO3). The remaining 1.4134 - .989 = .4244 grams of water. Since 1 ml of water weighs 1g, 1 ml of 70% is made up of .4244ml of water and 1 - .4244 = .5756ml of 100% nitric. This has nothing to do with the amount of water needed to make up a 50/50 solution. I just added this to help you understand what nitric actually is composed of.
Note: For accuracy, each nitric percentage in your drop down list will have to be computed separately, due to the non-linearity of the strengths. You asked if 35% was ideal. No, because 70% diluted 50/50 is not 35%. It calculates out to 41%, using the method given in the paragraph above. Like I said, it's not linear.
Here's a problem. Read my posts on this thread.
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=53&t=16374
In it, you will find the equation for dissolving silver with nitric:
2HNO3 + Ag = AgNO3 + NO2 + H2O
Note that, on the left side of the equation, it takes 2 molecules of nitric to dissolve 1 molecule of silver. However, on the right side, the ratio of Ag to the NO3 is one to one. The second N in the nitric on the left comes off as NO2 on the right. In other words, half of the nitric is wasted, as far as dissolving silver is concerned.
If you assume the use of common commercial 68% nitric, it takes 1.22ml to dissolve 1 gram of silver. However, this figure assumes an open top dissolving container where all of the NO2 produced in the equation goes off in the air and is lost. If you were able to collect all of the NO2 in a condenser and return it to the solution (called refluxing), it would combine with water to produce more HNO3 and you might be able to reduce the nitric usage to half or, 0.61ml/g of silver. There are other ways of refluxing that are mentioned in the thread link I gave above. In some cases, people are doing things to improve the efficiency that they're not even aware of. Were I you, in your calculator, I would use the 1.22ml/g figure, based on 68%, and make the following disclaimer:
"The nitric figures given are accurate assuming the dissolving is done in an open-top container, where all the gases given off are lost. With perfect refluxing of these gases, the nitric usage could be only one-half of these figures. In practice, the nitric usage might be somewhere in between these two extremes."
For copper, nickel, and zinc, which are the most common base metals in karat golds, it takes about 3.4 times as much nitric as with silver or, 4.15ml/g of 68% in an open container.
In the literature, you'll find that some people inquart with copper instead of silver. This works fine but it takes 3.4 times more nitric. Since the members of the forum buy nitric in small quantities, it is extremely expensive. Their average cost is probably $75 to $100 per gallon, whereas, in 55 gallon drum quantities, it's only $3 - $4/gallon, excluding the $750 returnable drum deposit. Using copper, therefore, is undesirable for most people. Also, with copper, you end up with 3.4 times more waste to deal with. The silver is much more expensive than copper to start with but it can be used over and over.
Chris