From:       "Barbanell, Melissa (Salt Lake City)" <mbarbanell@barrick.com>                 

                                                                                             

  To:         Chuck French/RTP/USEPA/US@EPA                                                  

                                                                                             

  Date:       02/24/2010 08:40 PM                                                            

                                                                                             

  Subject:    CEMs White Paper                                                               

                                                                                             

Chuck,

Attached you will find a copy of the memorandum we promised addressing continuous

emissions monitors.  We are having a call first thing tomorrow morning to discuss

the status of the HCN report and I will be happy to follow up with you on that

issue after that call concludes.

I will plan to call you around noon EST tomorrow.

Thanks,

Melissa(See attached file: cems white paper (6).pdf)
4811-4910-3877.3 1

CONTINUOUS EMISSION MONITORS ARE NOT FEASIBLE OR NECESSARY FOR 

GOLD MINING ROASTERS

Compliance with MACT standards under the gold mining NESHAP can be demonstrated 

reliably and efficiently without the feasibility and reliability concerns associated with continuous 

emission monitors (CEMs) for mercury emissions. As discussed below, it is not feasible to 

install CEMs technology for mercury emissions generally, and especially not in the unique 

emission conditions present in roasters used in the gold mining industry. Moreover, established 

parametric testing methods currently employed at these sources are proven and reliable methods 

to confirm that mercury emissions controls are functioning properly and consistently.

I. MERCURY CEMS TECHNOLOGY IS NOT FEASIBLE FOR GOLD MINING 

ROASTERS

Despite several years of sustained efforts to develop mercury CEMs technology for large 

source categories such as coal-fired electric generating units, this technology must continue to 

improve before it can be reliably used for demonstrating continuous compliance with mercury 

emission standards. The feasibility of applying mercury CEMs technology to gold mining 

roasters is even farther down the road. Most of the challenges to continuously measuring 

mercury from point sources (stacks) fall into one of three general categories: (1) mercury CEMs 

calibration; (2) sample transport; and (3) system operability and reliability. The unique 

characteristics of roasters used in the gold mining industry and the fact that mercury CEMs have 

not been designed to meet these specific characteristics further complicate the resolution of each 

of these types of challenges.

A. Mercury CEMs Calibration

A principal concern of applying mercury CEMs to gold mining roasters is the 

unavailability of a means to calibrate the CEMs for this application, resulting in data of limited 

and suspect value. Continuous monitoring of mercury, even from a best-controlled gold mining 

roaster presents a twofold calibration challenge for existing mercury CEMs technology. First, all 

vendors would have to modify their existing head-space calibrator units. An important 

component of a mercury CEMs is the mercury calibrator (or gas generator) unit. In simplest 

terms, mercury calibrators are head-space devices that work on the principal that mercury vapor 

has well defined pressure and temperature characteristics. Thus, passing a known volume of

carrier gas over a pool of liquid mercury at a carefully controlled temperature and pressure 

produces a known mercury concentration, typically expressed in the units of micrograms of

mercury per cubic meter of carrier gas (μg/m3). Existing calibrator designs are simply not 

capable of generating mercury concentrations high enough to provide meaningful upscale 

calibration points that correspond to gold mining source characteristics. 

Second, and much more problematic, is the unavailability of National Institute of 

Standards and Technology (NIST) traceable calibration gas. NIST certifies methods and gases 

used for calibrating monitors, an important and necessary procedure for ensuring that measured 

data is accurate and reliable. As EPA acknowledged at our meeting on February 17, NIST 

traceable mercury gases and methods for generating such gases are not currently available and 
4811-4910-3877.3 2

are not expected to be available within the time frame that EPA anticipates promulgating a final 

MACT standard for the gold mining industry. 

B. Sample Transport

Current designs of mercury CEMs for coal-fired electric generating units require hightemperature umbilical lines to transport the sample from the stack to the analyzer. The mercury 

sample transport lines must be maintained at a higher temperature than conventional (i.e., 

SO2/NOX/CO2) sample lines because mercury is a “sticky” molecule, especially the oxidized 

form (e.g., HgCl2). As these systems have been installed on coal-fired electric generating units, 

an inordinate number of umbilical failures appear to be occurring. The umbilical failures 

represent another challenge to having CEMs function consistently for the continuous monitoring 

of mercury from industrial sources.

C. System Operability and Reliability

Mercury CEMs are much more complex systems than are conventional SO2/NOX/CO2

monitoring systems. Mercury CEMs must contain some type of converter for reducing oxidized 

Hg (Hg+2) to elemental Hg (Hg0). This is because only Hg0can be “seen” or detected by either 

atomic absorption or atomic fluorescence. In the early stages of mercury CEMs

commercialization (circa 1997 – 2003), the prevalent technique for mercury conversion used 

chemical processes. This approach was doomed to failure as various flue gas constituents 

quickly proved to be poisonous to the chemical catalysts. Most mercury CEMs suppliers have 

changed to a thermal catalytic process for mercury conversion, and this approach has proven to 

be generally satisfactory. Premature catalytic failures periodically occur in these units; however, 

and this often results in periods of missing data of several days. 

In initial phases of implementing this technology by the electric utility industry, users 

have reported mercury CEMs to be unavailable as much as 30 to 40 percent of the unit operating 

time. Based on the complexities of applying this technology to a new source category such as 

gold mining roasters which have gas stream differences from electric utility generating units 

(where mercury CEMs remain problematic), the amount of downtime to be expected from these 

systems would likely be even higher. These breakdown events, combined with the other types of 

failures discussed herein, result in data availability that is substantially inferior to parametric 

monitoring and therefore cannot justify the significant cost and resource investment necessary to 

install, operate and maintain these devices.

D. Mercury CEMs Face Prohibitive Uncertainties Associated with Cost, 

Reliability and Accuracy

In summary, there are no viable prospects for a successful implementation of mercury 

CEMs at gold mining roasters at the present or any time in the near future. After years of

development for coal-fired electric generating units, a much larger market for CEMs technology

than gold mining roasters, significant progress still needs to be made before CEMs will work 

reliably for that source category. Based on the complexities associated with adapting that 

technology to effectively monitor mercury emissions from unique sources such as roasters, 

availability of mercury CEMs is even farther off for the gold mining source categories, 

especially when the very small number of roasting units nationwide is considered (a total of six 
4811-4910-3877.3 3

units, emitting through only four stacks, and little likelihood that any more units will be 

constructed).

As noted above, the challenges facing mercury CEMs are not just based on cost and 

reliability, but also include undeveloped calibration standards. Even assuming the devices were 

online and operating, without adequate calibration methods and protocols, there is no assurance 

that the results obtained from mercury CEMs would be accurate and representative of actual 

stack emissions. Thus, even if the mercury CEMs were used only to provide assurances that 

emission controls were functioning properly, and were not used to determine compliance with 

the NESHAP, such data would not be verifiable without proper calibration of the equipment. 

This problem could result in both false alarms that emission controls are not working, when in 

fact they are, and vice versa. To rely on CEMs for the limited purpose of verifying proper 

emission control operation ignores the very real concern that is presented by continuous data 

reports of mercury emissions to the atmosphere that are not accurate, reliable or credible. 

Further, we are concerned that, notwithstanding EPA’s representations that it does not intend to 

utilize the CEMs data for direct compliance purposes, the uncertifiable data that results from the 

monitoring might nonetheless be offered as “credible evidence” to assert a violation. This is 

particularly troubling where, in Nevada, there are separate mercury limits established pursuant to 

state law.

II. PARAMETRIC MONITORING IS AN ACCURATE AND COST EFFECTIVE 

ALTERNATIVE FOR DEMONSTRATING COMPLIANCE

Fortunately, the lack of feasible CEMs technology for mercury emissions at gold mining 

operations is offset by the availability of established, comprehensive parametric monitoring 

programs that can be used to confirm that emission controls are functioning properly. Two 

examples of successful parametric monitoring programs for demonstrating compliance at ore 

roasting facilities are discussed in the following sections.

A. The Goldstrike Roaster

1. The Goldstrike Roaster is Able to Demonstrate Compliance with 

Mercury Emission Limitations By Use of Parametric Monitoring

The Goldstrike Mine operates a roaster facility which consists of two roasters that share a 

common off-gas cleaning system and a common quenching, neutralization and leaching circuit. 

The roasting process oxidizes the carbon and sulfide compounds in the ore to facilitate gold 

recovery. Oxygen, supplied by the oxygen plant, is added to each of the roasters to create an 

oxidizing environment. Each of the roasters is a two stage, fluidized bed roaster that is permitted 

to process up to 500 tons per hour. The first stage bed of the roasters operates at about 1030°F 

and the second stage bed operates at about 980°F. The roasters were designed to operate 

autogenously and ore is blended for the optimum fuel value of sulfides and carbonates. Coal and 

fuel oil can be added to the roaster to provide additional fuel value for roasting. Due to the high 

temperatures at which the roasters operate, the naturally-occurring mercury found in the ore is 

vaporized into gaseous, elemental mercury. After roasting, the ore is quenched, neutralized with 

slaked lime and pumped to the carbon in leach (CIL) circuit. See figure 1 below. The exhaust 

from each roaster is cycloned, then treated in the off-gas cleaning system before being released 

to the atmosphere.
4811-4910-3877.3 4

Figure 1 – Roaster Ore Circuit

The off-gas cleaning system on the roaster consists of two gas quenchers, two venturi wet 

scrubbers, two condensers, two mist eliminators, a wet electrostatic precipitator (WESP), a 

Boliden Norzinc mercury scrubber, an SO2 scrubber, a CO thermal oxidizer and a NOX selective 

catalytic reduction (SCR) system. Figure 2 shows the roaster off-gas system. Each roaster has 

its own gas quencher, venturi wet scrubber, condenser and mist eliminator. The WESP, mercury 

scrubber, SO2 scrubber, CO oxidizer and NOX SCR are common to both roasters.

Figure 2 – Roaster Off-Gas System

DUST

SCRUBBERS (2)

OFF-GAS 

FROM

ROASTERS

GAS

QUENCHERS (2)

CONDENSERS (2)

SO2

SCRUBBER

WET ESP

MERCURY

SCRUBBER

CYCLONES

MERCURY

TAP

COOLING

TOWER

CHILLED

WATER

TANK

CONDENSATE

COLLECTION

TANK

MIST

ELIMINATORS (2)

WET ESP

DRAIN TANK

CALOMEL

AND REAGENT

REAGENT

REAGENT

MIST

ELIMINATOR

BOOSTER 

FANS (2)

CO THERMAL 

REDUCTION

SCR NOx

REDUCTION

TO

ATMOSPHERE

SCRUBBER

FAN

CARBONIN-LEACH

TANKS

DRY GRINDING 

CIRCUIT

FROM 

CRUSHING

CIRCUIT

NEUTRALIZATION

TANKS

CALCINE

QUENCH

TANKS

ROASTER
4811-4910-3877.3 5

a. Mercury Removal

Mercury vaporized during the roasting process is captured in the roaster off-gas system 

by both physical (condensation) and chemical (scrubbing) processes. Physical capture of 

mercury is achieved by lowering the temperature of the gas stream to less than 90°F at the 

condenser outlet. The gas quenchers, venturi scrubbers and condensers are all cooling processes 

in the gas stream. As the temperature of the gas decreases, the concentration of mercury in the 

gas phase decreases and mercury condenses out of the gas stream. The elemental mercury is 

collected and poured into mercury flasks.

The chemical removal process for mercury is completed in the Boliden-Norzinc scrubber. 

The scrubber uses a mercuric chloride solution to scrub mercury from the gas stream, forming a 

mercurous chloride, or calomel, precipitate. The calomel is collected and poured into drums for 

subsequent recovery of the mercury.

b. Monitoring and Mercury Removal Effectiveness

Goldstrike monitors a number of parameters within the off-gas system to ensure that all 

mercury controls are operating and functioning within manufacturers’ specified ranges. The 

monitored parameters indicate how well the system is operating. Each of the parameters and 

specified operating ranges listed in this section are currently monitored and recorded and are 

already required by Goldstrike’s Phase I Nevada Mercury Control Program (NMCP) permit. 

The currently monitored parameters that affect mercury are listed below:

● Water flow rate to gas quenchers

● Venturi scrubbers’ differential pressure

● Venturi scrubbers’ water flow rate

● Gas stream temperature at condenser outlets

● Mercury scrubber inlet gas temperature

● Mercury scrubber head pressure

● Mercury scrubber mercuric chloride (HgCl2) concentration 

The water flow rate to the gas quencher, the venturi scrubber differential pressure and 

water flow rate, and the condenser outlet temperature are monitored continuously. The water 

flow rate to each of the gas quenchers averages approximately 375 to 400 gallons per minute, 

and must be maintained above 60 gallons per minute. The differential pressure for each of the 

venturi scrubbers is required to be maintained above 35 inches of H2O and the water flow rate is 

kept above 300 gallons per minute. The condenser gas stream outlet temperature must be 

maintained below 90°F. The venturi scrubbers remove particulate mercury and aid in gas stream 

cooling and the quenchers and condensers further cool the gas stream to aid in mercury 

condensation. The continuous monitoring of these devices shows that they are operating within 

specified ranges, and providing maximum scrubbing, cooling and mercury condensation. These 

parameters are the same as operating ranges during stack testing, ensuring that the system is 

operating in the same manner as during annual testing. If any of these parameters fall outside the 

specified ranges, ore feed to the roasters is suspended until the situation is corrected. 

After physical condensation of mercury, a chemical scrubbing process takes place. The 

gas stream enters the Boliden Norzinc scrubber. The scrubber is a packed column that 
4811-4910-3877.3 6

continuously circulates a mercuric chloride solution which reacts with the elemental mercury in 

the gas stream. The mercuric chloride reacts with elemental mercury to form mercurous chloride 

(calomel). The important parameters for efficient operation of the mercury scrubber are the 

mercuric chloride concentration in the effluent solution, the inlet gas stream temperature and the 

head pressure of the scrubber. The gas inlet temperature is monitored continuously and 

maintained below 134°F to ensure that the scrubber is operating at the optimum temperature. 

The solution exiting the scrubber is tested twice daily for mercuric chloride concentration to 

ensure that the mercury scrubber has enough mercuric chloride in the feed solution to efficiently 

scrub the mercury from the gas stream. The mercuric chloride solution must be above 1.0 

gram/Liter. In addition, the mercury scrubber head pressure, which is an indication of scrubber 

solution flow rate, is monitored continuously and must be maintained between 1.0 and 9.0 psi. 

Monitoring these parameters ensures that the mercury scrubber is operating efficiently. These 

parameters are within operating ranges during stack testing and ensure that the scrubber is 

operating at the same efficiency as during annual testing.

In summary, the operating parameters that Goldstrike monitors on a regular basis are key 

parameters for measuring the efficiency and operation of the mercury controls in the off-gas 

cleaning system. Operating each of these units within the optimum ranges ensures that mercury 

emissions are being effectively controlled. Because these parameters are monitored regularly 

and controlled to certain specifications consistent with annual testing conditions, the operation of 

the system is known to be reliable and consistent. The annual testing values are representative of 

day to day operations, as shown by the records of the monitored parameters. Though installing a 

CEMs for mercury would provide additional data (albeit of questionable accuracy and 

reliability), additional monitoring is not necessary because the currently monitored parameters 

provide daily reassurance that the system is operating properly.

2. Periodic Testing of Mercury Emissions Using Method 30B would—if 

Necessary—Provide a Superior Basis for Monitoring Mercury 

Emissions than would CEMs.

As discussed in the preceding section, robust parametric monitoring is currently being 

conducted for the Goldstrike roaster providing a sound basis for ensuring continuous mercury 

removal and control performance. This periodic monitoring is established, reliable and proven. 

For the reasons noted above, mercury CEMs are unproven for application to gold mining roasters 

and are, in fact, unavailable from a regulatory/compliance perspective in that there is simply no 

means currently available to conduct calibration checks, rendering the data immediately suspect 

and unreliable. Data generated from the use of CEMs would raise more questions than it would 

provide useful information.

Notwithstanding the foregoing, to the extent that EPA maintains that something more 

than the parametric monitoring described above and annual stack testing is necessary for the 

Goldstrike roaster, a much superior option to CEMs would be quarterly testing using Method 

30B. Method 30B does not suffer from the same infirmities identified for CEMs; it will produce 

a reliable estimate of emissions using EPA-approved methods. We hasten to add that we do not 

believe that such testing is necessary; however, quarterly Method 30B testing would clearly be a 

better alternative than mercury CEMs.
4811-4910-3877.3 7

B. The Newmont Gold Quarry Roaster Ensures Proper Mercury Control 

Operation with Parametric Monitoring

Newmont’s Refractory Ore Treatment Plant (ROTP) also consists of two identical 

roasting trains with a unique series of air pollution control devices. After the roasting process, 

the effluent gas streams pass through Waste Heat Boilers, Hot Gas Electrostatic Precipitators, 

and then merge and pass through the following series of Gas Cleaning/Cooling controls: (1) a 

Wash Tower (cooling sprays); (2) Heat Exchangers (two star coolers); (3) Wet Electrostatic 

Precipitators (two units); (4) a Fluorine Removal Tower; and (5) a Boliden/Norzinc Mercury 

Removal Tower (calomel scrubber).

Gas stream temperatures are monitored continuously to ensure the proper cooling 

operation of the Spray Tower and Heat Exchangers. Voltages of the Wet ESPs are monitored on 

a continuous basis to ensure proper operation of these control devices. The feed to the roaster is 

shut off if both of these devices are not in proper operation. The mercuric ion concentration of 

the calomel scrubber solution is monitored on a daily basis to ensure proper operation of the 

Mercury Removal Tower. Based on the NMCP Phase 1 permit the monthly average must be 

maintained between 2.0 and 4.0 g/L. In addition, Newmont’s Phase 2 application proposed to (i) 

maintain the chloride ion concentration between 2.0 and 5.0 g/L; (ii) maintain the tower level at

20% to 65% of capacity; and (iii) bleed calomel from the tower each shift as needed for 

chlorination and electrowinning. Monitoring these parameters ensures that the control 

equipment is operating properly and consistently with the operation that was measured for the 

mercury emission test, ensuring ongoing stack emissions within the range of the annual test 

results.

The gas stream is further dried and sent to the acid plant, where SO2 is converted to 

sulfuric acid. This product acid is sampled on a daily basis for mercury concentration. While 

this mercury is actually removed from the gas stream and not emitted to the atmosphere, it is 

indicative of the amount of mercury that makes it past the Mercury Removal Tower and is 

another reliable daily indicator of whether the upstream mercury controls are properly operating. 

Newmont’s goal is to maintain a concentration of ≤ 1 mg/L Hg in the sulfuric acid and this level 

Roaster

Calcine

Calcine Cooler

Waste Heat Boiler Hot Electrostatic Precipitator

Gas Cleaning

cooling

wet ESP (2)

fluorine removal

Boliden-Norzinc Mercury Removal

Acid Plant

drying tower

SO2 converter

two stage adsorption

SO2 stripping tower

RTO –

CO conversion

Quench Tank

Ducon

Scrubber

Quench Water

Atmosphere

Slurry to CIL

Atmosphere

Preheated

Ore

SO2

SO2

Recirc CO

Burner

Recirc to roaster

Oxygen

Burner

Combustion Gas

to atmosphere H2O2 Scrubber

94% Sulfuric Acid

Hg, Fe, SO2
4811-4910-3877.3 8

is contained in Gold Quarry’s NMCP Phase I permit. If sample results indicate higher 

concentrations, corrective actions are taken to ensure the proper operation of the calomel

scrubber and any upstream devices, and to ensure that the operation of such controls is optimized 

to reduce mercury emissions. In addition to ensuring proper operation of the control equipment 

and compliance with its permit requirements, Newmont has an independent business reason to 

monitor mercury from the acid and maintain mercury levels at or below the 1 mg/L target – its 

sales contracts with purchasers of the acid specify that the acid will contain no more than 1 mg/L 

of mercury.

After the acid plant, approximately 50% of the gas stream is recycled back to the roasting 

process. The remaining gas stream passes through another Peroxide Scrubber and a 

Regenerative Thermal Oxidizer (RTO) prior to exiting the exhaust stack. Due to the numerous 

and diverse controls and their interdependency and critical interactions, along with the diligent 

continuous and rigorous monitoring that already occurs, it does not appear that an additional 

CEMs for mercury would improve the operation of these controls. Nor is it likely that mercury 

emissions would be significantly improved, given the testing history of this exhaust stack that 

consistently shows less than 5 lbs of mercury emissions per year. An additional concern would 

be the reliability of mercury CEMs in this exhaust gas stream which is heated up to 1600 deg F 

prior to discharge from the RTO. It is also quite likely that design modifications would be 

required to CEMs that are currently used in other industries to account for the unique chemical 

composition of this gas stream.

C. Jerritt Canyon Roaster Periodic Monitoring

We understand that NDEP is providing information relevant to monitoring conducted for 

the Jerritt Canyon roaster.