MEMORANDUM

TO: J. Baggenstos, M. Long

FROM: Jon R. Maki

Copy: R. Aaseng, B. Bond

DATE: November 1, 2007

SUBJ: Sulfur Sources at Minorca and Analysis

Background. This document addresses sources of sulfur for information regarding sulfur 

emission limits at the ArcelorMittal Minorca Mine. 

ORE. The majority of sulfur dioxide (SO2) emissions originate from the ore during pellet 

heating and oxidation. Emissions are proportional to pellet production and are typically 

calculated on a lb/ton pellet basis. Since Mittal uses natural gas for fuel, SO2 emissions from 

fuel combustion is negligible. (Ref. Barr – Oct 07).

Generally, the slaty ore has more sulfur than cherty ores. Therefore, if we are mining near 

the contact layer, we could experience an increase in sulfur in the ore. 

UC-2 is the highest in sulfur in the cherty ores. It has 3 horizontal, interbedded quartz / 

chlorite bands that contain sulfur. In the ore, pyrite and marcasite are the two iron sulfide 

minerals that are a source of sulfur. (Ref – J. Arola E-mail, Oct 29, 2007) 

In discussions with United Taconite’s Geologist, they found more sulfur in the slate as well 

but the lower cherty ores had more sulfur than the upper cherty ores (.04 vs .015 to .03%) 

Therefore, if our future plan is to increase the amount of lower cherty in the blend, we may 

see an increase in sulfur content.

Fluxstone. The limestone/dolomite added to make fluxed pellets is also a source of sulfur 

(see below). However, a benefit of the flux stone is that the limestone/dolomite dust raises 

the pH of the scrubber water. This improves the sulfur dioxide scrubbing efficiency. 

O-N has exhausted their pit for supplying flux stone to Minorca. At this time, no input about 

future sulfur concentrations was provided.

Request # 7

Document 7-4
% S in Fluxstone per Shipping Vessel (Ref. O-N Minerals)

Water chemistry. The chart on the next page shows the increase of sulfur in our process 

water and supply water (Ref. NTS). Most of the S in the process water will remain in the 

greenball, but some will contribute to emissions. DNR states that the higher S content in the 

process water will actually improve the scrubber’s efficiency at removing SO2. (Ref. J. 

Engesser – Oct 07).

Scrubber Efficiency.

For Minorca’s recirculating scrubber, the pH of scrubber blowdown water is the best indicator 

that the scrubber is removing sulfur dioxide. As the pH of the recirculated scrubber water 

decreases, the amount of SO2 removed from the induration waste gas will decrease. 

Recirculating scrubbers that maintain scrubber water pH > 6 should be removing the 

maximum amount of SO2 for that particular scrubber design. 5 of 6 scrubber water samples 

taken at Minorca during 2004 - 2006 had pH values that ranged from 6.47 to 7.51 indicating 

that SO2 scrubbing was maximized. . (Ref. J. Engesser – Oct 07).

Minorca should be removing between 50-75% of the SO2 during fluxed pellet production 

when the pH in the recirculating scrubber water is greater than 6. (Ref. J. Engesser – Oct 

07).

y = 2E-06x - 0.058

R

2

 = 0.1549

0.010

0.015

0.020

0.025

0.030

0.035

0.040

M-00 N-00 M-01 N-01 M-02 N-02 M-03 N-03 M-04 N-04 M-05 N-05 M-06 N-06 M-07 % S in Minorca Fluxstone
Process Water Sulfate

40

50

60

70

80

90

100

110

198719891991199319951997199920032005

Sulfate (mg/l)

Process

Enterprise

Reclaim

Plant Site

In the future, when we conduct stack tests and we are measuring SO2, we should include the 

pH of the scrubber water as part of the study.

Sulfur Analysis – Ore/Plant. At this time, Minorca does not measure the amount of sulfur 

in the ore, RMF, acid concentrate, flux concentrate, green balls or pellets. However, using 

the XRF on the acid concentrate and flotation concentrate would be a good indicator of sulfur 

variation due to ore change.

Samples have been collected to be sent out to various laboratories to develop calibration 

standards for the XRF unit. Also, to reduce the error due to ore mineralogy, using a fused 

puck vs a pressed puck for the XRF is recommended. Training may also be required to 

calibrate the XRF.