Sampling & Analysis

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• 0510010107
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Description

Analytical Procedures
A quality laboratory with necessary technician experience can achieve good results with many different methods. The modified automated SFAA method using the McLeod microstill may be the method of choice for the most advanced laboratories, however global uniformity, availability and cost factors indicate that the analytical methods listed as "Primary" in the following table as are suggested.
TABLE OF PRIMARY AND ALTERNATE ANALYTICAL METHODS

Analyte	Method	Comments
Free Cyanide	AgNO3 titration	Preferred method For process solutions primarily above 1 mg/l LQL1: 1 mg/l HCN(aq), CN-, Zn(CN)x, parts of Cu(CN)4
	AgNO3 titration with potentiometric endpoint determination	Alternate method Precise method of endpoint determination Measures same species as primary method
	Micro diffusion of HCN from static sample into NaOH [ASTM D4282]	Alternate Method Close to "free cyanide"
	Ion Selective Electrode	Alternate Method Close to "free cyanide"
	Direct colorimetry	Alternate Method HCN(aq), CN-, Zn(CN)x, parts of Cu(CN)4 + ?
	Amperometric determination	Alternate Method Measures same species as primary method
WAD Cyanide	Manual distillation pH 4.5 + potentiometric or colorimetric finish [ISO/DIS 6703/2, DIN 38405 Part 13.2: 1981-02]	Preferred method LQL1: 0.05 mg/l HCN(aq), CN-, Zn/Cd/Cu/Ni/Ag(CN)x Better results than ASTM method in presence of high copper concentration
	Amenable to chlorination (CN Total - non-chlorinatable part) [ASTM D2036-B, US-EPA 9010]	Alternate Method Measures same species as primary method
	SFIA in-line micro-distillation pH 4.5 + colorimetric finish [ASTM D4374]	Alternate Method Measures same species as primary method
	FIA In-line ligand exchange + amperometric finish [US-EPA OIA-1677]	Alternate Method Measures same species as primary method
	Picric Acid, Colorimetric determination	Alternate Method Measures same species as primary method
Total Cyanide	Manual batch distillation + titration/potentiometric or colorimetric finish [ISO/DIS 6703/1, DIN 38405 Part 13.1: 1981-02]	Preferred method LQL2: 0.10 mg/l HCN(aq), CN-, Zn/Cd/Cu/Ni/Ag/Fe(CN)x, parts of Au/Co/Pt/Pd(CN)x
	SFIA, in-line UV irradiation, micro-distillation + colorimetric finish [ASTM D4374]	Alternate Method Measures same species as primary method

1 LQL, Lower Quantitation Level, is defined as about 3 times Detection Level or 10 times the Standard Deviation at near blank level.
For these primary methods, the table also provides a Lower Quantification Level representing the concentration that all laboratories should be able to reliably determine. Laboratories with a proven record of working with alternative methods, such as those based on automated standard methods, should be encouraged to continue with those methods but should establish cross-references for each site by applying the suggested methods.
To insure that the mine receives quality analytical service, the chosen laboratory must:
Have experienced staff perform the analyses.
Be certified by the respective national accreditation body for all analytical methods.
Have sound quality control procedures in place.
Be able to prove the quality of their data by participation in proficiency tests.
Trained analysts and supervisory staff with an expertise in cyanide chemistry methods are critical to consistent and reliable results, as they are aware of the potential interferences inherent in each method. The preferred methods for analytical determination of the different types of cyanide are briefly summarized below:
Free Cyanide
The preferred method for the analytical determination of free cyanide is silver nitrate titration. Silver ions are added to the solution to complex the free cyanide ions. When all free cyanide is consumed as silver cyanide complex, the excess silver ions indicate the endpoint of the titration. The analytical equipment used for the titration is rather simple. To accurately determine the cyanide concentration, a normalized silver nitrate solution is dosed with a manual or automatic burette, which should be capable of measuring volumes to an accuracy of better than 0.005 ml.
Several techniques can be used for the endpoint determination. The easiest possibility is to use an indicator such as potassium iodide or rhodanine that changes color upon appearance of free silver ions. It is important that the first color change is used as endpoint indication because the silver ions tend to liberate cyanide ions from other complexes, which leads to a disappearance of the color. The potentiometric endpoint detection is a more accurate way to determine the endpoint as a more easily identified peak signal is produced.
Weak Acid Dissociable Cyanide
The preferred analytical method to determine weak acid dissociable cyanide is the distillation method according to ASTM or ISO/DIS. These methods create chemical conditions which allow the CN_WAD to be liberated as dissolved hydrogen cyanide gas which is then carried in an air stream to a caustic soda absorption where the CN_WAD appears as CN_F. As the hydrogen cyanide is adsorbed in a much smaller volume than the original sample solution, the CN_F concentration to be analyzed is typically at least 10 times higher than the original CN_WAD concentration in the sample solution. The CN_F concentration in the distillation product sample is then determined using silver nitrate titration as described above. The methods according to ASTM and ISO/DIS are similar. However, the results from ISO/DIS method are more accurate than those from the ASTM method for samples containing a high concentration of copper cyanide.
Total Cyanide
The preferred analytical method to determine total cyanide is the distillation method according to ASTM or ISO/DIS. The applied method is in principle very similar to the distillation method described for weak acid dissociable cyanide. However, strongly acidic conditions and elevated temperatures are required to liberate the cyanide ion from the stable cyanide complexes such as ferri- and ferrocyanides.
References
Complete descriptions of these analytical procedures can be found in the following references:
DIN 38405-13: 1981-02, German Standard Methods for the Analysis of Water, Waste Water and Sludge -Anions (Group D) -Determination of Cyanides (D13), German Standards (DIN Normen, Beuth Verlag GmbH, Burggrafenstr. 6, 10787 Berlin/Germany).
South African Water Quality Guidelines, Volumes 1-7, Department of Water Affairs and Forestry, 1996.
Standard Methods For The Examination Of Waters and Wastewater, APHA-AWWA-WEF, 20th Edition, Washington DC, 1998.
Water Quality - Determination of Cyanide -Part 1: Determination of Total Cyanide ISO/DIS 6703/1, International Organization of Standardization.
Water Quality -Determination of Cyanide -Part 2: Determination of Easy Liberated Cyanide ISO/DIS 6703/2, International Organization of Standardization.
USEPA "Methods and Guidance for Analysis of Water", United States Environmental Protection Agency (USEPA), June 1999.