January 19, 2010 

Mr. Kevin Lewis 

Air Sciences 

Re: Barrick Goldstrike Hydrogen Cyanide (HCN) Results 

Dear Mr. Lewis: 

The purpose of this letter is to comment on the validity of the HCN testing results provided by 

Method 320 and CTM-033 from the recent emissions testing at the Barrick Goldstrike facility on 

the exhaust stack of the Electrowinning unit. Method 320 uses a Fourier Transform Infrared 

(FTIR) spectrometer to provide on-site, real-time HCN concentration data. CTM-033 collects 

HCN in a basic solution for subsequent off-site ion analysis. 

As you are aware, the Electrowinning stack (along with several other sources) was tested for 

HCN in September 2009 using FTIR. Because the FTIR results from the Electrowinning stack 

were higher than expected (based on results from similar sources), in November the 

Electrowinning stack was re-tested for HCN using CTM-033. The results of the November testing 

were significantly lower than the September results, and the question of which data set is correct 

is of interest. 

Method 320 is known to be susceptible to interference from other gaseous species that absorb 

infrared light. The degree of interference is a function of the concentrations of interfering species

and the absorbance overlap between the interferents and the target analyte. In the current case, 

known and detected interfering species consisted of water vapor (H2O), ammonia (NH3) and 

carbon dioxide (CO2). The FTIR instrument attempts to correct the target analyte concentration 

for known interfering species. The instrument then determines the influence of the interferents by 

calculating an SEC (standard error calculation). This SEC value is statistically determined by the 

FTIR instrument, and is calculated for each stack matrix. A conservative rule of thumb with FTIR 

data is to use two times the SEC as an estimated uncertainty on results. If this approach is used 

on the Goldstrike data, the results demonstrate very large relative uncertainties on the HCN 

measurements, and consequently low confidence in the FTIR results as shown below. 

Barrick Goldstrike FTIR Data

 HCN (ppm) CO2 (ppm) NH3 (ppm) H2O (ppm) (1)

Electrowinning 6 +/- 7 109 +/- 9 190 +/- 5 25,000 

1 – H2O data taken from subsequent integrated measurements – FTIR data are used for 

spectral subtraction, but do not provide quantitative results. 

The figures on the following pages provide various FTIR spectra, including stack gas 

measurements and various standards. The sample spectra are provided to show the differences 

between species with very clear identification (CO2, NH3 and H2O) and less conclusive 

identification (HCN). 
Stack Matrix EW (red - bottom) Stacked under CO2 Standard (pink - top) 

Close-up of Stack Matrix (red - top) Overlaid with CO2 Standard (pink - bottom). 

For carbon dioxide, elements of the reference spectrum are easily observed in the stack matrix, 

including a close-up view of the region used to quantify the stack levels. 
Stack Matrix EW (red - top) Stacked over NH3 Standard (blue - bottom) 

Close-up of Stack Matrix (red - top) Overlaid with NH3 Standard (blue - bottom) 

Similarly for ammonia, elements of the reference spectrum are easily observed in the stack 

matrix, including a close-up view of the region used to quantify the stack levels. 
Stack Matrix (red - top) Stacked over H2O Standard (pink - bottom) 

Close-up Stack Matrix (red – shorter middle peaks) and H2O 

Standard (blue – taller middle peaks) 

As with carbon dioxide and ammonia, elements of the water reference spectrum are easily 

observed in the stack matrix, including a close-up view. 
Stack Matrix EW (red - top) and HCN Standard (blue - bottom) 

Close-up of Stack Matrix (red - top) Overlaid with HCN Standard (blue - bottom) 
Extreme Close-up of Stack Matrix (red – top) Over HCN Standard (blue - bottom) 

The final three spectra show the FTIR stack data used to estimate HCN levels. The zoomed in 

figure shows the lack of obvious agreement between the stack data and standard. While there 

are clearly common peaks in the stack data and reference standard, there are obvious nearby 

peaks in the stack spectra indicating some other unidentified species with IR absorption in the 

same region that is used to quantify the HCN. This uncertain agreement is reflected in the high 

SEC for the HCN FTIR data. 

As with Method 320, and any measurement method, CTM-033 is also subject to potential 

interferences. The interferences provided in CTM-033 consist of acid gases which would reduce 

the impinger pH, sulfides, oxidizing agents, and blank contamination. The absence of acid gases 

was confirmed by checking the impinger pH after each test run. No sulfides or oxidizing species 

are suspected, and the reagent and train blanks showed non-detected cyanide for all samples. 

So interferences with the CTM-033 results are not expected. 

Because of the demonstrated interference issues with the Method 320 data, and the apparent 

lack of similar concerns with the CTM-033 data, it is believed that the FTIR results are subject to 

substantially higher uncertainty than the CTM-033 data. Consequently, the CTM 033 data are 

believed to be the more representative results, effectively invalidating dissimilar FTIR results. 

Based on this analysis, APT has prepared a final report for the CTM 033 Electrowinning test data 

only, which has already been delivered to Barrick Goldstrike. The summary sheets for the 

Method 320 data are attached. 

Respectfully, 

Paul Ottenstein 

Technical Director