TASK 8: MINING PIT WALL STABILIZATION Clarkson University Remediation Engineers C.U.R.E Presented By: Debra Ackerman Jason Ammerman Charles Bennett Wendy Casazza Jennifer Caufield Michael Collier Kim Davey Rockell Davis Kodi Duprey Jeremiah Johnson Patricia McTigue Melissa Smith Spring 2001
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TASK 8: MINING PIT WALL STABILIZATION
Clarkson University Remediation Engineers C.U.R.E
Presented By:
Debra Ackerman Jason Ammerman Charles Bennett Wendy Casazza
Jennifer Caufield Michael Collier
Kim Davey Rockell Davis Kodi Duprey
Jeremiah Johnson Patricia McTigue
Melissa Smith
Spring 2001
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TABLE OF CONTENTS EXECUTIVE SUMMARY………………………………………………………………3 1.0 PROBLEM BACKGROUND…………………………………………………...5 2.0 FULL-SCALE PROCESS DESCRIPTION………………………….…….….6
4.0 ECONOMIC ASSESSMENT AND BUSINESS PLAN………………………13 5.0 LEGAL AND REGULATORY CONSIDERATIONS……………………….16 6.0 HEALTH AND SAFETY CONSIDERATIONS……………………………...17 7.0 CONCLUSIONS……………………………………………………….………..20 8.0 ACKNOWLEDGEMENT……………………………………………………...20 9.0 REFERENCES………………………………………………………………….21 10.0 AUDITS…………………………………………………………………………22
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EXECUTIVE SUMMARY This report summarizes the remediation process proposed by Clarkson University Remediation
Engineers (C.U.R.E.) that will reduce the generation of acid mine drainage (AMD) from 75 acres of
exposed open pit mine high walls at one mine in New Mexico. To date, no preventative measures have
been taken to reduce the AMD, and as a result leaching can occur for hundreds of years. C.U.R.E. has
developed an innovative solution to reduce AMD by utilizing waste streams from nearby facilities to create
a mixture that will be applied to the highwalls and benches of the mine.
The desired mixture would neutralize the acidic conditions, scavenge oxygen to inhibit
microorganisms such as Thiobacillus and Leptospirillum ferrooxidans that catalyze the leaching process,
and resist weathering. In addition, the material can be affectively applied and set on the highwalls. The
waste product search and testing lead to a mixture composed of cement kiln dust from a cement kiln
operation for neutralization and weathering resistance, fly ash from coal combustion for neutralization and
some cementious properties, calcium carbonate (CaCO3), a sugar beet manufacturer by-product, for
neutralization, and municipal wastewater sludge for oxygen scavenging and desired consistency of the
application material. Leaching tests were performed using samples of the ore with the aforementioned
waste products to determine the critical metals concentrations. Of specific concern were iron, copper, zinc,
lead, and arsenic. In each test, the amount of metals that leached from the ore was significantly reduced to
below EPA and New Mexico ground water standards. Different weight percents of solids were mixed to
determine the best material properties for application, cracking and weathering, resulting in a mixture of
50% solids by weight: equal amounts of cement kiln dust fly ash, and CaCO3.
The application of the mixture utilizes some of the latest technologies in the construction and
concrete industries. A concrete batch plant will be built at the top of the pit for mixing the material that
will be transported to the bottom via cement mixer trucks. A crane will be placed at the top of the pit a safe
distance from the edge and a pipe layer machine will be at the bottom of the pit. A cable attached to the
crane by a pulley system will span the 1000 feet between them, with the pulley allowing for tension
adjustment. A Shotcrete pump capable of pumping the vertical and horizontal distance will be at the bottom
of the pit. A hose pumping the mixture will carry it to a robotic application arm that will travel up the
distance of the cable spraying a width of five feet. The adjustable robotic arm will hang down vertically
from the cable to ensure an application distance within the desired range. The arm will also contain a video
monitoring system with distance gauge that will be used by the technician to control the robotic arm and by
a Process Control Engineer to check for even coverage. The heavy construction equipment will then move
along the wall to repeat the process until the entire wall has been coated. The application process will take
approximately 11 months.
The overall time period required for completion of the project, excluding continued monitoring for
the design life of the project, is 13 months. During the first two months, set up of a batch plant operation
and mobilization of the necessary equipment will take place, followed by the 11 months of application and
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one month of cleanup after completion of the application. The total present value cost of the project is
$5,541,000.
The health and safety of all personnel was a requirement for the final remediation process and will
remain the primary concern throughout the project. To address the health and safety concerns an Industrial
Hygiene consultant will be hired to conduct initial airborne dust concentration testing, heat stress and noise
levels of the operation. Periodic monitoring will be conducted thereafter as needed. The batch plant
operator will monitor the quality of the waste materials received. The application method previously
described allows all workers to remain a safe distance from the application of the material and the open pit
mine high walls. Personal protection equipment will be worn by the workers with the greatest risk of
contact with the material. Emergency eyewash and shower stations will be located at the top and bottom of
the pit. Occupational Safety and Health Administration (OSHA) guidelines will be followed at all times.
A Public Involvement Plan will be in place to inform the community of the remediation process.
An initial public hearing will allow citizens to voice their questions and concerns regarding the project.
Community relations personnel will be hired through the duration of the entire project to provide
information and address questions and will continue through the design life of the project. All legal and
regulatory standards will be met concerning levels of certain metals and toxins in the soil and water in
surrounding areas.
The following report provides a detailed description of the overall process including selection of
waste materials and application technique, bench-scale experiments, economic assessment and business
plan, as well as legal and regulatory considerations and health and safety aspects. C.U.R.E. can assure that
the remediation process described will reduce acid mine drainage from the site in a safe and cost effective
manner, while helping to recycle waste products generated by nearby industries during its year of
construction.
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1.0 PROBLEM BACKGROUND Site Background and Problem Overview An open pit copper mine nearing the end of its
productive life will leave approximately 75 acres of mineralized rock exposed to weathering. If left
untreated, a considerable amount of acid mine drainage (AMD) would be produced for hundreds of years.
This would be quite detrimental to the environment, so remediation options have to be considered. For a
remediation technique to be practical, it must be both effective and economical. Therefore, waste products
from nearby industries were examined for their potential usefulness to mitigate the production of AMD.
From that examination, it was determined that a combination of cement kiln dust, calcium carbonate from a
sugar beet processing factory, wastewater sludge, and fly ash would reduce the amount of acid mine
drainage produced and resist weathering while still being economically feasible.
Copper mining sites as described in the WERC “Design Considerations” could not be found near
Las Cruces, New Mexico. However, a similar site was found in Silver City, New Mexico and it was that
mine that was used as a basis for this study. The average total vertical relief of this site is five hundred and
fifty feet, with side slopes of 0.5 horizontal to 1.0 vertical. Each bench of the high wall is approximately
fifteen feet wide and is present every twenty vertical feet. The industries that produce the waste products
that will be utilized for the remediation are assumed to be within one hundred miles of Silver City, NM.
Acid Mine Drainage Acid mine drainage (AMD) is a serious problem in areas that have a
history of large-scale mining (especially coal, copper and hard rock mining).1 The geochemical oxidation
of exposed sulfides on the open pit mine high walls and benches generates sulfuric acid by reacting with
oxygen and water (Eq.1). The major types of bacteria involved in this step of AMD formation are the
Thiobacillus and Leptospirillum (T. and L.) ferrooxidans.2 Oxidation of FeS2 is normally a slow process,
producing ferric ions and hydrogen ions. With the inclusion of T. and L. ferrooxidans, the rate that these
ions leach out of the ore is dramatically increased.
2FeS2 + 7 O2 + 2 H2O ! 2 Fe2+(aq) + 4 SO4
2- + 4H+(aq) (1)
Fe2+ ions are oxidized to form Fe3+ ions:
4Fe2+(aq) + O2(g) + 4H+
(aq) ! 4Fe3+(aq) + 2H2O(l) (2)
These Fe3+ ions now hydrolyze in water to form iron hydroxide. This process releases even more hydrogen
ions into the aquatic or semi-aquatic environment and continues to reduce the pH. (Eq.3)
4Fe3+(aq) + 12 H2O(l) ! 4Fe(OH)3(s) + 12H+
(aq) (3)
Cracks in the high wall sections of the mining pit provide channels for infiltration where the acid
production occurs. This acidic water containing heavy metals that have leached out can contaminate
groundwater and surface water, poses a threat to the environment, as well as the health of those who utilize
this water.
2.0 FULL SCALE PROCESS DESCRIPTION The process that C.U.R.E developed uses a range of chemically reactive waste products from the
surrounding industries to mitigate AMD. The material, in the form of a slurry, is applied to the steep walls
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using state-of-the-art technology developed for the cement industry. A robotic arm, which is suspended on
one cable spanning the entire wall and remotely controlled, will be used to spray the slurry to the steep pit
wall. The applied material will protect the wall from further generation of AMD and withstand weathering.
Material Selection In order to stabilize the mine pit walls several material properties of the
remediation agents were evaluated. These include the ability to reduce the pH of the environment, to resist
weathering, to limit oxygen, and to adhere to the walls. The C.U.R.E. design team evaluated several
possible area industries for their likelihood to produce co-products that might be used in such a manner to
develop the most economical solution to the design problem. Several materials had potential, and were
chemically and physically analyzed in a laboratory setting. Inductively Coupled Plasma spectrophotometer
tests were conducted on leachate ore, which had been stabilized with fly ash, calcium carbonate (CaCO3),
calcium oxide (CaO), municipal wastewater sludge, and the combination of sludge with CaO and CaCO3.
These tests are further described in Section 3.0. Table 2.1 gives initial qualitative observations regarding
the investigated products.
Table 2.1 Qualitative Materials Analysis
Material Available Quantity Beneficial Traits Negative Traits Municipal 10,000,000 Gal/yr -Inexpensive water source -Variability of solids content
Paper Pulp8 20,000 Tons/Yr -Reduces cracking of material -Poor adhesion to wall -Causes plug in pumping equipment -Decreases sludge BOD -Not homogeneous
All of these materials are to be used in the application mixture, except for the paper pulp. While
paper pulp at low concentrations appears to be beneficial to reduce cracking, it reduced the oxygen uptake
rate of the organic mixture, when combined with the wastewater sludge. At higher concentrations the
mixture was heterogeneous and caused poor adhesion to the walls.
Application Technology Selection. Several application methods were investigated during the
development of the full-scale process and are summarized in Table 2.2. Grading the entire slope, by taking
soil away from the top of the face and placing that soil at the bottom, would make application of the
remediation material easy as well as reduce runoff velocity. However, this would be a long and expensive
process and the problem statement clearly requires that the material needed to be applied to the steep walls.
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Also, since rubble has accumulated on each bench it has been deemed unsafe to operate heavy machinery
on them. For this reason any solution that required machinery on the benches was ruled out due to safety
concerns.
The two most feasible alternatives were manual application and the cable system of application
(Table 2.2). Manual application would require workers to gain close access to benches and the walls. This
was a cause for concern due to safety reasons. The manual system also would require a long duration for
process completion and therefore C.U.R.E. chose the cable system for the application process.
<http://www.mines.edu/fs_home/jhoran/ch126/thiobaci.html> 3. Jojola, Mickey. Personal Communications, 2-15-01 4. Poo, Richard, Personal Communication on sludge quantity. Potsdam Municipal Wastewater Plant,
Potsdam, NY, 2-19-01 5. Crawford, Dan, Personal Communication on fly ash. Combustion Products Management, Bridgeport,
West Virginia. 2-14-01. 6. WWW Draft Risk Assessment for Cement Kiln Dust Used as an Agricultural Soil Amendment. Kiln
Dust Quantity, Management, and Cost. 2-2-01 <http://epa.gov/epaoswer/other/ckd/cld/cld[0103.pdf> 7. Holly Sugar Corporation. Fm2856 Rd., Hereford, TX. Personal Communication, 1-17-01. 8. Geary, Robert. Personal Communications about paper manufacturing. Felix Schoeller Technical
Papers. Pulaski, NY. 2-12-01. 9. WWW, Robotic Arm Information. Shotcrete Technologies, Idaho Springs, CO. 2-23-01.
<http://www.adbri.com.au> 12. Rawlings, D. E. et al, “Dominant iron-oxidizing bacteria, Microbiology,” Volume 145, Number 5-13. 13. Cotton, Albert, Basic Inorganic Chemistry, 3rd Edition. John Wiley and Sons, New York. 1994 14. WWW EPA Office of Water, 2-28-01.
<http://www.epa.gov/OGWDW/methods/indchem.html#3120_B> 15. R.S. Means Co. Heavy Construction Cost Data. 12th Edition. 1998. 16. WWW Used Mixer Trucks and Batch Plants, Construction Equipment Parts, Inc. 2-28-01.
<http://www.cepimixers.com/usedequip_bp.htm> 17. WWW Sampling and Analysis Guide. Galson Laboratories, East Syracuse, NY.
<http://www.epa.gov/epacfi-40/chapt-I.info/> 22. WWW New Mexico Environmental Department, Regulations and Permitting. 2-17-01.
<http://www.nmenv.state.nm.us/regs_idx.html> 23. Philip, Mark. Personal communications on permits. 2-8-01. 24. Von, Dennis. Personal communications on permits. 2-14-01. 25. WWW Material Safety Data Sheet of Calcium Carbonate. Mallinckrodt Baker Inc. 2-10-01.
<http://www.jtbaker.com/msds/m0884.htm> 26. WWW Material Safety Data Sheet of Cement Kiln Dust. Riverton Corp, Riverton, VA. 2-10-01.
<http:// msds.pdc.cornell.edu/msds/siri/msds/h/q127/q339.html> 27. WWW Material Safety Data Sheet of Coal Fly Ash. Arizona Public Services Corp. Joseph City, AZ.
2-10-01. <http://msds.pdc.cornell.edu/msds/siri/msds/h/q133/q155.html> 28. WWW Material Safety Data Sheet of M8 Paper. Anachemia Chemicals Inc, Rouses Point, NY.
2/10/01. <http:// msds.pdc.cornell.edu/msds/siri/msds/h/q190/q328.html> 29. Rossner, Alan. Personal communications on health and safety. 3-02-01.