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lab tests for gold concentration (3 replies and 7 comments)
Not sure I get your questions, but you cannot get the amount of gold concentration through CN titration using silver nitrate method. However, CN titration will help predict the amount of free CN. I am not sure of the standard calculation but the formula I used was:
0.005*amount Silver Nitrate*1000/Amount of Gold Cyanide solution.
My advice is for you to send your gold solution, carbon samples, residues (tails) to the lab to get actual numbers. What type of Gold ore are you working with?
For determination of cyanide I find the best method is to make 50-100ml of cyanide standard solution made up with precision, add a little caustic (KOH or NaOH) to preserve and keep in a tightly sealed plastic bottle. This was there is no need to worry about the precision of making your silver nitrate each time. You can check it with your standard and create your own normalizing factor in the equation and just label the silver nitrate bottle with it each time. Also, I suggest before weighing in your sample of unknown cyanide prepare the sample jar with ~20ml of water and a few drops of saturated potassium iodide (KI) solution. The later will enhance the sharpness of your end point. Also start with a drop of cyanide to see past the end point then slowly titrate back to the end point to start exactly where your will finish after weighing your sample and titrating.
Mohammed, all one needs is a battery powered pocket scale that is accurate to at least 0.01g and a dropper and the silver nitrate, which can be made by dissolving silver in 10-30% nitric acid (other acids will form precip). The KI is not necessary.
Dropper method: Add a couple of mls of water to light plastic cup markered "Poison!!!" Touch a drop of cyanide solution to the wall and swirl. Rinse dropper and add drops of standardized silver nitrate (or the silver nitrate that you wish to standardize, if not already done) until the precipitate that forms will not completely re-dissolve. Without KI this may take a little while. Weigh the cup. Add your unknown sample (or your known weighed and diluted cyanide solution for standardizing your silver nitrate). Weigh again. Rinse dropper and add drops of silver nitrate until the precipitate from the drops does not redissolve, exactly like the start. Weigh the cup again. The net weight of your silver nitrate times your factor (from doing the test on known cyanide) and dividing by the net weight of your sample gives you the concentration of cyanide.
Details: the amount of sample to weigh should be only enough that you get and accurate weight. For example, if your scale is accurate to 0.01g all you need is 1ml of sample to get 95% accuracy. Your silver nitrate standard should be made to theoretically react completely with your expected sample range such that it is 10 times less concentrated than your expected sample range. This means you could expect to add 10g of silver nitrate solution for every gram of sample. This keeps all the weights in range of you pocket scale and also allows accurate technique. To further know the accuracy of your test you can repeat it several times using the last end point weight as your knew starting tare weight, ready for weighing in the next sample.
One way to check for gold in cyanide is to oxidize the gold (I) AuCN2- ion to gold (III) AuCN4- ion and then spot test with dimethylaminobenzylidene rhodanine. https://en.wikipedia.org/wiki/Rhodanine
Google books keywords: "rhodanine spot testing for gold Feigl" and on page 240 Feigl outlines the method. I have found that a couple of drops of alcohol dissolved rhodanine in a test tube will show color change with two drops of 10ppm gold(III) cyanide. The test will not work for gold(I) cyanide. False positives are produced by silver cyanide, cuprous ion [Cu(I)], mercury and palladium. Silver cyanide will drop by lowering PH 2) and palladium with dimethylglyoxime.
The last sentence should read: Silver cyanide will drop by lowering PH below 4 and letting settle. Cu(I) can be sequestered with EDTA at any PH greater than 2 and palladium dropped with dimethylglyoxime.
Hello,
If you are asking about how to compute your cyanide concentration using silver nitrate, here how do i doing it in mine. First of all we dont know what is the concentration of our silver nitrate.
I get a 1L of water and adjust the pH to 10 just to be safe. Then Add 4grams of NaCN. Meaning the concentration of your cyanide solution is 0.4%
Here is my formula grams of NaCN/ volume of H2O in mL then times 100.
Now get a 10mL of your cyanide solution 0.4%
add 5 drops of KI
then slowly titrate it using your unknow silver nitrate solution.
stop your titration once solution turn to milky color.
Check how many mL of silver nitrate it consume.
Now you know already and you can compare it.
if you consume 2.5ml silver nitrate so meaning = to 0.4% your self to do the analyzation.
hi
we are starting new gold mine in Egypt on small scale , using vat leaching
we don't have atomic adsorption device to calculate the gold concentration in ppm
my question is about manual methods of determination of gold concentration in cyanide solution ,on carbon in the column and in tail solution
for cyanide i know that titration against silver nitrate but i don't have the equations
can any one help me with that ?