
September 3, 2019
SUBJECT: 	Trip report for site visit to U.S. Steel  -  Minntac, Mountain Iron, MN, October 10, 2018
FROM:	Michael Laney, RTI International
TO:		David Putney, U.S. Environmental Protection Agency (EPA)
       BACKGROUND
As part of the risk and technology review (RTR) project for the national emission standards for hazardous air pollutants (NESHAP) for taconite iron ore processing, site visits were conducted to three taconite iron ore processing facilities located along the Mesabi Range in Minnesota. This trip report summarizes the October 10, 2018 visit to the U.S. Steel  -  Minntac mine and processing facility in Mountain Iron, MN.
       PARTICIPANTS
U.S. Steel
Chrissy Bartovich, Director Environmental, Minnesota Ore
Stephani Campbell, Environmental, Minnesota Ore
Jim Chacich, Mine Operations Coordinator, Minnesota Ore
Chris Hardin, Environmental, Headquarters, Pittsburgh
Brett Tunno, Environmental Engineer, Headquarters, Pittsburgh
Tishie Woodwell, Environmental, Headquarters, Pittsburgh
U.S. EPA
David Putney, Office of Air Quality Planning and Standards
RTI International
Michael Laney
       SUMMARY
 Preliminary Discussions
Prior to touring the facility, participants met to discuss the agenda for the day.
David Putney, EPA, provided background information on the RTR project, specific information needs for the RTR project, and responded to questions from U.S. Steel representatives. Topics discussed included the following:
RTR project schedule. The estimated RTR proposal date is April 2019 with promulgation of the final rule in June 2020.
Mercury concentration in raw ore. David Putney explained the process that would be used for setting emission limits for mercury if the EPA decides to propose numerical MACT standards for mercury emissions. He explained that, in addition to emissions data, information on the variability of mercury concentrations in raw ore could be important information for EPA to consider in developing emission standards that accurately reflect variability in mercury emissions. He noted that there is precedence for using information on mercury variability in raw ore to set emission standards. He requested that U.S. Steel provide the EPA with any such mercury data they may have, or can get, to assist EPA in the event they propose mercury emission standards for the industry.
According to U.S. Steel, core samples have not measured mercury concentrations and that may not even be possible.
Minnesota Pollution Control Agency (MPCA) mercury initiative. U.S. Steel representatives stated that they are currently evaluating control options for meeting the 72 percent reduction in mercury emissions that will be required by MPCA. They stated that the inherently low mercury concentrations make the evaluation of control options more difficult. U.S. Steel's proposal for meeting the required reduction is due to the MPCA by December 30, 2018. The MPCA has scheduled implementation of the mercury reductions for January 2025.
Burden reduction. David Putney explained the EPA is interested in industry's experience with any requirements of the current rule that they consider to be burdensome that could be revised to be less burdensome while not comprising environmental protection.
U.S. Steel stated that they did not see a reason for the rule requirement that Method 5 test runs had to be at least 2-hour runs. They stated that with the 2-hour requirement plus the time needed between test runs, a Method 5 test took from 10 to 12 hours to complete and was costly and adds safety concerns. They felt that a 1-hour test run was adequate and would meet the criteria, such as required sample volume, of Method 5.
Technology Review. David Putney explained the technology review aspects of the RTR project and requested information regarding the development of any new controls or processes in the taconite industry that have become available that could reduce emissions.
U.S. Steel stated that they have not developed any new controls or processes in their taconite iron ore processing facilities and were not aware of any such developments in the industry sector.
 Site Tour
Mine Operation. Mine operations are located proximate to the taconite processing facility. At the Minntac site, there are two pits being mined: the West pit and the East pit, which is the smaller of the two pits. The total length of the two pits is about 9 miles with the widest point being 2 miles.
Silica and iron content varies across the mine. Materials from different mine locations are blended to attain the optimum blend.
Mine operations involve blasting, loading large boulders from the blasting into trucks, which deliver the boulders to the primary crusher where they are reduced to about football size. Additional crushing steps further reduce the ore size until it is ready to enter the concentration phase.
The following information was provided on the mine and other related operations:
Blasting is done about three times per week. Meteorological conditions, such as wind direction and cloud ceiling, are evaluated to select blasting times. It takes about 3 weeks to set up a blasting pattern.
Electric and diesel CAT shovels with 40-yard buckets are used to load blasted material into 240-ton trucks. Both diesel and electric drive trucks are used.
Tailings from the mine operation and taconite processing are returned to the mine where they are used for roadways and to backfill and reclaim inactive parts of the mine or sent to the tailings basin for deposition. Reclaimed portions of the mine are vegetated to reduce runoff and erosion.
Water trucks wet mine roads for fugitive dust control.
Processing. Finely crushed ore is conveyed to storage bins at the concentrator building. These bins supply the material for the concentration processes. Wet scrubbers control dust at the transfer of the ore from the ore storage bins to the conveyor into the initial concentrator process. All processing in the concentrating building is wet and any emissions are minimal. The wet ore is fed to rod mills and then ball mills to further reduce the size of the ore. In subsequent steps, the slurry of fine particles goes through magnetic separation steps where the iron containing particles are separated from waste materials. The concentrated iron particles go through additional grinding and separation steps before entering the agglomeration process.
In the agglomeration phase, the iron-containing material is removed from the slurry by a series of vacuum disks filters which pull the particles onto filters. The iron-rich material is dewatered and then released onto a conveyor. Bentonite is added to aid in the agglomeration phase. Other agents, such as limestone and dolomite fluxes are also added at this point. The material is then fed into a balling drum where it is converted into unfired ("green") pellets.
From agglomeration, the green pellets are conveyed to a grate kiln indurating furnace. The pellets travel on a steel grate through gradually hotter temperature zones in order to first dry the pellets before entering the hottest part of the furnace. In the grate kiln furnace, the pellets next enter a rotary kiln and are discharged through a cooler. The heated exhaust from the cooler is recirculated to the furnace. Because of the moisture content of furnace exhaust gases, wet scrubbers are used for the control of PM.
Finished ("fired") pellets are stockpiled and then transported by train to Great Lakes ports for ship transport to steel-making facilities.
Process conditions and control device parameters are monitored from a control room.
 Wrap Up
David Putney described changes to the NESHAP that are being planned beyond any that might be made as a result of the RTR. Among the revisions currently planned are the following:
Once in always in. This refers to a provision of the rule (i.e., 40 CFR 63.9581), and has been EPA policy, whereby if a source was subject to the rule as a result of being a major source for purposes of title III of the CAA (greater than 10 tons of a single HAP or 25 tons of all HAP combined), it would always be subject to the rule, even if they reduce their HAP emissions to less than major source status. As a result of a change in EPA policy, this provision in the NESHAP will be modified.
Startup, shutdown, and malfunction (SSM). As a result of a court ruling, the exemption from the emission standards during periods of SSM will be removed. Sources will be subject to an emissions standard, but it may be a work practice standard if it is not possible to demonstrate compliance with the emission limits.
Electronic Reporting. Compliance test results will be required to be submitted to EPA through EPA's electronic reporting tool (ERT).
Following up on earlier discussions regarding mercury concentrations of taconite ore, parts of the rule that U.S. Steel considered particularly burdensome, and developments in processes, controls, and work practices (as part of the technology review), David Putney requested that any information - or input - that U.S. Steel could provide on these and other topics be provided by the middle of November 2018.
