Roger J. Hornberger, Keith B.C. Brady, Barry E. ScheetzWilliam B. White and Stephen C. Parsons

Objectives

1.Standardize procedures2.Improve method

a. CO2-enriched airb.Quantify particle size

effects3.Flexibility in method4.Improved interpretations

Sought a Varietyof Rocks to Leach

Roger

Keith

Steve

Barry

Will

Rt. 66 Brush Creek Shale Site

Valentine Limestone

Drill rig

Wadesville Anthracite Mine,Schuylkill County, PA

Tracy Lynn Mine%S 0.91NP 133

%S 0.01NP 270

%S 0.00NP 930

%S ~7NP 0.0

Standardization

Air CO2

ImprovementIncrease Pco2

~75 mg/L

10%

0

50

100

150

200

250

300

350

400

0 1 2 3 4 5 7 9 11 13 15Week

Alk

alin

ity (m

g/L

as C

aCO

3)

Air OnlyAir CO2 Mix

Results from 2002: CO2 Mix, Higher Alkalinity

Leaching Column

(Flexibility)

Sample

Air/Gas Vent

Sieves

Sieve Sizemm

Percent of Total Weight

9.52 04.76 402.00 251.19 100.50 100.25 5

<0.25 10

Particle SizeDistribution &Surface Area

1

2

0

2

4

6

8

10

12

14

Sur

face

Are

a (m

2 /g)

13.99

1.001.45

2.66

Before LeachingAfter Leaching

BC Shale Wadesville SS Coal Refuse Bald Eagle SS

12.48

1.080.65

Surface AreaSurface Area6 m2

48 m2

Particle Size

Shape

1 m

Partial Pressure CO2

Interpretations

0 10 20 30 40 50 60 70 80 90 100Days

250

300

350

400

450

500

550

Alkalinity

(mg/

L CaC

O3)

Mean: Constant CO2 FlowMean: CO2 Saturated WaterHigh & Low ValuesHigh & Low Values

Carbonate Dissolution & Alkalinity Generation

0 10 20 30 40 50 60 70 80 90 100Days

0

400

800

1200

1600

Sul

fate

(mg/

L)

Mean: Constant CO2 FlowMean: Saturated CO2 WaterHigh & LowHigh & LowConstant CO2 Flow, No Fines

Pyrite Oxidation &Sulfate Production

Brush Creek Shale

Cumulative Load (Mass) of CaCO3 & Sulfur(or How much weathered each week?)

1. Calculated Mass of Sulfur and CaCO3 in Columnusing total percent sulfur (%S) and neutralization potential (NP)

2. Determined amount of sulfur weathered from: sulfate x volume of leachate*

3. Determined amount of CaCO3 weathered from: (HCO3 + alkalinity neutralized) x volume of

leachate. Alkalinity neutralized calculated from SO4

*

* For this to work must be undersaturated w/ respect to gypsum

Gypsum Oversaturated

Gypsum Undersaturated

Calcite Oversaturated Effects of Solubilityon Interpretations

Brush Creek Shale

Determine Saturation Indices

y = 1.1157x + 0.449R2 = 0.9967

y = 0.881x + 0.8051R2 = 0.9977

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 1 2 3 4

leaching time [weeks^0.5]

Perc

enta

ge S

leac

hed

FtKNS += 2/1

Brush Creek Pyrite OxidationDiffusion Reaction

0 10 20 30 40 50 60 70 80 90 100Days

0

1

2

3

4

5C

umul

ative

% C

aCO

3 or

S W

eath

ered

Per

Wee

kM1 CaCO3 (CO2 Bubbling)

M1 Sulfur (CO2 Bubbling)

M2 CaCO3 (CO2 Bubbling)

M2 Sulfur (CO2 Bubbling)

M8 CaCO3 (Sat H2O)M8 Sulfur (Sat H2O)M9 CaCO3 (Sat H2O)M9 Sulfur (Sat H2O)

Years

0

4

8

12

16

20

Cum

ulat

ive

% C

aCO

3 or

S W

eath

ered

Per

Wee

k

0 1 2 3 4 5 6

Sulfur

CaCO3

16-18%

8-10%

Brush Creek ShalePredicting WaterChemistry into

the Future

Sulfur

CaCO3

HydrothermalPyrite

Pyrite Veins

0.05.0

10.015.020.025.030.035.040.0

0 20 40 60 80 100

leach time [days]

cum

ulat

e pe

rcen

tage

su

lfur r

elea

sed

coal refusesandstone

2.27 mg.m2/day

0.02mg/m2/day

Weathering Rates of Coal Refuse & Hydrothermal Pyrite

Findings

1. The ADTI-WP2 method produces concentrations of acidity, alkalinity, sulfates and metals comparable to mine environment.

2. The laboratory performance show good repeatability for duplicate samples in columns.

3. It is important to normalize the leaching data. Steps include: standardized particle size distribution; surface areas measurements, and surface area to volume ratios.

4. %S leached through time for the different rocks indicate differences in leaching processes. The Brush Creek shale exhibits a square root of time dependence, which suggests a diffusion-controlled process. The coal refuse and the Bald Eagle sandstone conform to a simple linear weathering process.

5. To interpret leaching data solubility controls must be considered.

Findings, continued

Any Questions?