Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

Mine Drainage ManagementReplicating Dump Physiogeochemical Conditions

in Laboratory Columns

Kirstine Malloch, Pavel Petrov, Paul Weber

AusIMM 2018

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

Introduction Use of kinetic tests to

determine reaction rates (eg AMIRA, HCT)

Issues with scaling ACLC Stockton mine site Northern ELF, Cypress pit Understanding waste rock

as part of AMDMP management

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

Cypress NELF Waste Rock

ABA Characteristics Paste pH 3.8 Total S% 1.6 NAG pH 2.5 ANC -4 NAPP 50 (PAF)

Friable mudstone (high surface area)

WRD – smaller particle size – limit oxygen ingress

Framboidal pyrite (higher surface area –more reactive)

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

WRD Variables and ACLCsPyrite + Water + Air (oxygen) =

Sulfuric acid (AMD) + metals

Cypress NELF─ moisture content 12-14 wt%─ Temp ~10 C─ O2 ~21% at surface,

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

IORs and PORs AMD driven by POR

POR = IOR - COR Traditional kinetic tests (AMIRA, HCT) use stoichiometric relationship

between sulfate released (SO4 mg/kg/wk) in leachate to the quantity of pyrite oxidised

OKC ACLC method uses oxygen consumption to derive an IOR (kgO2/m3/sec)

Pyrite

FeS2 + 7/2O2 + H2O ⇒ Fe2+ + 2SO42- + 2H+

Fe2+ + 1/4O2 + H+ ⇒ Fe3+ + 1/2H2O

Fe3+ + 3H2O ⇒ Fe(OH)3(s) + 3H+

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

ACLC set up Oxygen consumption calculated

using ideal gas law:PV = nRT

P = column pressure (kestrel)V = air supplied (air reg & apogee)N = number of O2 moles R = gas constantT = column temperature (kestrel) Measuring oxygen consumption

to calculate an IOR (kgO2/m3/sec)

Collating leachate – compare release of metals at different IORs

Apogee O2 sensor

Air intake and regulator

KestrelColumn temp.

and press.

Sensor internal temp.

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

Wet Up, No Air

Air constantly on for 48 hrs (flood column/pore spaces) then switched off

Indicates reactive material

In a ‘closed’ environment will use up O2 rapidly

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

ACLC 1. Freely Oxidising Conditions

Less than 1%

1-2% 3-4%

Same gas flux, increasing O2 consumption

~2%

Flux increase

pH of BCM (pH ~2) too low to form Fe(OH)3 so Fe3+ remains in solution

FeS2(s) + 14Fe3+(aq) + 8H2O(l) ⇒15Fe2+(aq) + 2SO42- + 16H+

Likely enhanced by bugs (acid-loving bacteria)

Accelerating system, accelerating acid generation

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

ACLC 1. Freely Oxidising Conditions

O2 at outlet─ lowest immediately after air

supply (14:00)─ Highest

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

ACLC 2. Anoxic Conditions 1% O2 gas (99% N2) Operating at low flux Air supply

inadequate – choked system

Increase flux so O2 sensor can detect –IOR increased

Now on low flux of 21% O2 (21% in, ~2% out) – IOR increase order of magnitude

Sensor battery change

Near DL of sensor

1% O2 supply 21% O2 supply

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

AMIRA

Weekly wetting, monthly flushing (high L:S) Heating to 20-30 °C in between wetting cycles Analysing water quality to get sulfate reaction

rate (mg/kg/wk) to calculate an IOR (kgO2/m3/sec)

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

Oxidation Rates (IOR) Comparison

Comparison of IORs from SO4 release (AMIRA, BT leach) rates vs O2 consumption (ACLC)

L>>S

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

Stored vs Release Acidity (Load) Secondary sulfate saltsMelanterite (Fe 2+)FeS2 + 7/2O2 + H2O ⇒ FeSO4 + SO42- + 2H+

FeSO4 + 1/2O2 + 5/2H2O ⇒ Fe(OH)3 + 2H+ + SO42-

Jarosite (Fe 3+)KFe3(SO4)2(OH)6 + 3H2O ⇒ 3Fe(OH)3 + 3H+ + 2SO42- + K

Implications WRD rehandling

Column Deconstruction next stageSecondary salts

Indicators of acid salts:Rinse pH values < 5.5Negative ANC Values

NP drives acidity load (secondary salts) from WRD

Limit O2 ingress reduce IOR reduce acidity load

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

Implications for Waste Management

Model field conditions to understand reaction rates

ABA to characterise waste (PAF, NAF) Into block model for waste rock

scheduling Kinetic testwork – indicates minimise O2

reduces IOR

What effect does reducing IOR have on stored and released acidity loads

Construction of dumps (PAF cells, shorter lifts, compaction between lifts)

Reduce acidity loads, reduce contaminant load requiring treatment

Integrated Mine Waste Management and Closure ServicesSpecialists in Geochemistry and Unsaturated Zone Hydrology

Rainbow of Hope for Children and, Habitat for Humanity Initiative

CRL laboratoriesOKC Perth laboratories –Miguel JeromeBT MiningChristine McLachlanCMER

Slide Number 1IntroductionCypress NELF Waste RockWRD Variables and ACLCsIORs and PORsACLC set upWet Up, No AirACLC 1. Freely Oxidising ConditionsACLC 1. Freely Oxidising ConditionsACLC 2. Anoxic ConditionsAMIRAOxidation Rates (IOR) ComparisonStored vs Release Acidity (Load)Implications for Waste ManagementSlide Number 15