David1205754 - 19-7-2007 at 19:21
Could anyone tell me the difference between free cyanide and complexed cyanide? What is the total cyanide and amenable cyanide?
dedalus - 20-7-2007 at 04:12
"Free" cyanide is a rather unscientific term that generally means cyanide that shows up in a silver nitrate titration.
Total cyanide is determined by doing a cyanide "distillation." The sample is boiled with sulfuric acid, the water vapor recondensed, while a stream of
air is drawn through the boiler. This air is passed through a sparger containing NaOH solution. Any cyanide present is turned into hydrogen cyanide,
which dissolves in the sparger fluid, becoming sodium cyanide. This fluid is analyzed for cyanide at the end of a one hour reflux period by titration
or colorimetry.
Amenable cyanide, or cyanide amenable to chlorination, is the cyanide that is destroyed by chlorination with calcium hypochlorite at pH 11, where the
free chlorine residual is maintained for 1 hour. Included are salts of all the alkali and alkaline earth metals, plus those with zinc, cadmium, and
copper. Not included: cyanide complexes with nickel, iron, cobalt, and gold.
Why, do you have some? Removing non-amenable cyanide from wastewater is a specialty of mine. I have a process for treating really strong cyanide
wastes, take a look at
http://www.dedalusenviro.com/cyanide2.html
if you're interested.
[Edited on 20-7-2007 by dedalus]
David1205754 - 22-7-2007 at 21:40
Thnaks for your explanation.
one further question regarding the free cyanide and reactive cyanide. How could I detect it by qualitative and quantitative way?
dedalus - 22-8-2007 at 03:25
Not sure how involved you want to get.
Macro method, good down to about 50 mg/l, in distillates or pure "free" cyanide solutions, is silver nitrate titration, 0.0192 N, using N,N
dimethylbenzalrhodanine indicator. Similar, though less sensitive, is the 19th centrury vintage Liebig method - most frequently used for plating
baths. This is titration with a 0.1 N AgNO3 solution, using potassium or sodium iodide as indicator. The yellowish turbidity of precipitated AgI is
the endpoint.
For trace level, there are Hach "Cyaniver" 3, 4, and 5 reagent pillows. You can also, if you want to get that involved, make pyridine/barbituric acid
reagent, phosphate buffer, and Chloramine 'T', and do it the way I used to, when I worked for a certified laboratory.
The "real" way to do it - the distillation is required. There are all kinds of half-assed spot tests using ferrous sulfate, or ferric
chloride, and looking for Prussian Blue formation. These have their place, but there are many interferences and they are not at all reliable.
Ozone - 22-8-2007 at 19:11
This should help.
Cheers,
O3
Attachment: EPA 335.4.pdf (198kB)
This file has been downloaded 926 times
Ozone - 22-8-2007 at 19:13
The method for ammenable CN is attached.
O3
Attachment: EPA 335.1.pdf (16kB)
This file has been downloaded 822 times
David1205 - 7-10-2007 at 21:39
Dear All,
How about the "reactive cyanide"? Could we use the same analytical method to test? or different way to define?Thanks!!!