Recommended Methodology and Processes for Mine Water … · Recommended Methodology and Processes...

9/25/2013

Apex Engineering, PLLC

Mark Reinsel, Ph.D., P.E. 1

Short Course: Water Management for Mining

Recommended Methodology and Processes for Mine Water Treatment

November 4, 2008

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Mark Reinsel, Ph.D., P.E.

Presentation Outline

Steps in Selecting a Treatment Process

Potential Treatment Technologies

Mine Water Applications

Specific Contaminants

Recommendations

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Steps in Selecting a Process

Explore/confirm design criteria

Review potential treatment technologies

Develop process flow sheet

Develop budgetary capital and operating

costs

Perform bench and/or pilot tests

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Design Criteria

1. Flow

Maximum (design capacity)

Average (for determining operating costs)

2. Influent concentrations

Are they already known?

How well can they be estimated/modeled?

3. Effluent concentrations

Are permit limits already established?

If not, can they be estimated?

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Potential Treatment Technologies

Physical

Chemical

Biological

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Physical Treatment Technologies

Clarification

Filtration

Membranes

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Clarification

Multiple processes to remove particles in

suspension:

Coagulation/flocculation

Settling

May use sludge recycle

Will not remove dissolved contaminants

Need a disposal site for sludge

Clarifier at Kensington Mine

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Rapid mix tank at Kensington Mine

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Clarifier centerwell at Central Treatment Plant (Kellogg, ID)

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Clarifier overflow at Central Treatment Plant (Kellogg, ID)

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Filtration

Bag filters

Cartridge filters

Sand filters

Multimedia filters

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Multimedia Filters

Coarse but light on top, fine but heavy on

the bottom

Typically anthracite, sand and garnet

Automated operation

Downflow operation, upflow backwash

Backwash via DP, timer or manually

Typical Multimedia Filter

No. 1 Anthracite Coal

Flint Sand

Fine Garnet

Support Gravel

1000-gpm multimedia system at Lucky Friday Mine (Mullan, ID)

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Membrane Processes

Microfiltration (MF)

Ultrafiltration (UF)

Nanofiltration (NF)

Reverse osmosis (RO)

Electrodialysis/electrodialysis reversal

(EDR)

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Microfiltration

Most common membrane process

Provides “sterile filtration”

Pore sizes are 0.05 to 3 microns

Removes most suspended solids but no

dissolved contaminants

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Ultrafiltration

Removes colloidal particles, polymers and

bio-molecules

Pore sizes are 0.003 to 0.1 micron

Pressure of 30-150 psi

Also does not remove dissolved

contaminants

500-gpm UF system at Montanore Mine (Libby, MT)

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Nanofiltration

Pore sizes are 0.001 to 0.006 microns

Feed pressure may be up to 200 psi

Removes solids, bacteria, high-MW

contaminants, and divalent or larger ions

(e.g., sulfate)

Will not remove monovalent ions (e.g.,

nitrate)

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Reverse Osmosis

Pore sizes are 0.0001 to 0.001 microns

Feed pressure may be up to 1000 psi

Removes solids, bacteria, viruses and

dissolved solids

Removes (“rejects”) 95-99% of inorganic

salts and charged organics

Higher-valence ions are better-rejected

Reverse Osmosis

Pure Water

Sal

t S

olu

tion

Pressure

Semipermeable Membrane

Salt Rejection

H2O

Cl

Na

Spiral Cartridge Configuration

CONCENTRATE

PRESSURE VESSEL BRINE

SEAL

COUPLING

FEED FLOW

PERMEATE PERMEATE

COLLECTION

TUBE

Schematic Cross-Section of Thin Film

Composite R.O. Membrane

Polyamide

Polysulfone

Ultrathin Barrier Layer

0.2 micron

40 micron

120 micron Reinforcing Fabric

Microporous

Polysulfone

RO Disadvantages

Produces high-volume, continuous waste stream

Can be energy-intensive

Removal of monovalent ions such as nitrate may

be limited

Will not remove dissolved gases (e.g., ammonia)

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Chemical Treatment

Technologies

Hydroxide precipitation

Sulfide precipitation

Oxidation/reduction

Ion exchange

Natural zeolites

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Hydroxide Precipitation

Typically use lime to increase pH

Can be hydrated lime or pebble lime (slaker)

Can also use caustic soda (liquid), soda ash or

magnesium hydroxide

pH target depends upon contaminants of

concern

Co-precipitation can increase removal

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Central Treatment Plant in Kellogg, Idaho

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Aeration Basin at Central Treatment Plant

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Sulfide Precipitation

Typically used as “polishing” step for low metals

concentrations

Will achieve lower levels than hydroxide ppt.

Can use sodium sulfide or hydrosulfide (NaHS)

Need little reagent and low retention time

Perform at neutral-to-alkaline pH to avoid H2S

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Oxidation/Reduction

May be required to transform contaminants into

less-soluble form

Arsenic: Add oxidizing agents such as chlorine,

hydrogen peroxide, ozone, permanganate

Chromium, selenium: Add reducing agents such

as sodium bisulfite or metabisulfite

Reaction is quite rapid

Will add TDS

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Ion Exchange (IX)

Specific resins available for dissolved metals,

arsenic, nitrate

Sodium and chloride are exchanged for

contaminants removed

Several resin manufacturers available

Resin is expensive but can be regenerated (on-

site or off-site)

Waste stream is typically much less than RO

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WATER SOFTENER

RESIN IN THE Ca+2 FORM

RESIN IN THE Mg+2 FORM

RESIN IN THE Na+ FORM

WATER W/ CaCl2, NaHCO3,

MgSO4

WATER W/ NaCl, NaHCO3,

Na2SO4

Typical Ion Exchange Resin

Capacities

Weak Acid Cation - 45-60 kgr/ft3

Strong Acid Cation - 12-30 kgr/ft3

Weak Base Anion - 19-28 kgr/ft3

Strong Base Anion I - 10-18 kgr/ft3

Strong Base Anion II - 18-22 kgr/ft3

IX vessels at Buckhorn Mountain

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Loading IX media

at Buckhorn Mountain

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IX Regeneration

Regenerate with acid, base and/or salt,

depending on the resin

Frequency depends upon contaminants,

feed water quality and discharge limits

Use co-current or countercurrent

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Natural Zeolites

Can be used for ammonia removal

Also have a high selectivity for thallium

Much less expensive than IX resin

Regenerate with salt

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Biological Treatment

Can be used for the following contaminants:

Organics

Ammonia

Nitrate

Selenium

Sulfate

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Biological Treatment Technologies

Attached growth systems

Suspended growth systems

Membrane bioreactors

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Attached Growth Systems

Bacteria are attached to a surface or media

Biofilm provides a very robust process

Very resilient to changes in flow, pH,

concentrations, etc.

Best choice for high concentrations

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Suspended Growth Systems

Commonly used in municipal treatment

systems (activated sludge)

Often used for nutrient removal (N and P)

Nitrification and denitrification

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Membrane Bioreactors

Combine suspended growth biological

treatment with MF or UF

Membrane replaces clarifier and/or

multimedia filters

High biomass concentration/small footprint

Becoming more popular

Biological treatment system at Key Mine (Republic, WA)

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Biological nitrate removal system at Stillwater Mine (Nye, MT)

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0

5

10

15

20

25

30

35

10/10/06 1/18/07 4/28/07 8/6/07 11/14/07 2/22/08 6/1/08 9/9/08

mg

/l

Date

Nitrate levels at the Key bio-treatment system

NO3- in NO3- out

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0

200

400

600

800

1000

1200

10-Oct-06 18-Jan-07 28-Apr-07 6-Aug-07 14-Nov-07 22-Feb-08 1-Jun-08 9-Sep-08

mg

/l

Date

Sulfate levels at the Key bio-treatment system

SO4 in

SO4 out

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Typical Contaminants of Concern in Mining Waters

Suspended metals

Dissolved metals

Nitrate

Ammonia

Arsenic

Sulfate

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Flow Sheet and Costs

Could develop for more than one option

Capital costs

Operating costs

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Bench/Pilot Testing

Will determine whether selected technology

can meet discharge limits

Can provide valuable information for full-

scale capital and operating costs

May be required by agencies

Bench testing is simpler, shorter and less

expensive than pilot testing

Jar tests or column tests?

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Possible Jar Tests

Chemical precipitation

Coagulation/flocculation

IX

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Possible Column Tests

Leach testing for nitrate/ammonia

IX

Biological

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Recommendations Dissolved metals

Hydroxide ppt. or sulfide ppt. or IX

Nitrate

Denitrification (attached growth) in almost all cases

Ammonia

Nitrification or zeolites or breakpoint chlorination

Arsenic

Iron addition/filtration or iron adsorption or IX

Sulfate

Biological (attached growth) or NF

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Questions

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