Mine Site Geochemical Modeling Through the Lens
of PHREEQC

Kirk Nordstrom

Hydrogeochemist, U.S. Geological Survey emeritus

Ann Maest

Vice President, Buka Environmental

 
Workshop Need

Although geochemical codes are routinely used throughout the world for investigating mine site characterization and remediation, there is an underappreciation for the knowledge that a code user must bring to bear on the interpretation of output. This workshop addresses this concern by reviewing major water-rock processes at mine sites, the mineralogy and its relation to water chemistry, types of geochemical models, mass balances, and specific examples where these have been applied. The emphasis will be on the conceptual model, how to develop it, test it, understand the limitations, and identifying pitfalls when using a code like PHREEQC.

 
Target Audience

Consultants, regulators, scientists, engineers, academic and government researchers

 
Short Workshop Programme
  1. Morning – Geochemical principles and conceptual models

    1. Major hydrogeochemical processes at mine sites: oxidation/dissolution of pyrite and other sulphides, redox reactions, geochemistry of trace elements, stoichiometry, oxidants and their effects, field vs lab rates, metal sulfide dissolution and effects, mass balances

    2. Neutralization: acid-base titrations; calculating lime/limestone neutralization needs; carbonates vs silicates, clay minerals

    3. Secondary minerals: their underappreciated role in storage and release, soluble vs insoluble phases

    4. Conceptual model development: common missing elements, how to test and improve, examples; development of conceptual models from simulations to bench scale to pilot to full-scale field conditions

    5. Setting up PHREEQC: overview, databases, options; preparation for afternoon session.

  2. Afternoon – Applications: from lab results to predictions

    1. Mass fluxes: field compared to lab, natural background vs mine site
    2. Humidity cell tests: reactions, interpretations, how to use results in models, examples

    3. Acid transport through waste rock pile: the Pinal Creek Case, Arizona, USA

    4. Neutralization example: Norway

    5. Waste rock pile leaching examples: Nevada, Canada.

  3. Optional Extra Half Day - Continuation of applications from previous day

    1. More participant Q&A and participant examples

    2. Open pit examples: Nevada, Alaska

    3. Coal mine drainage: Canada – selenium

    4. Cyanide heap leach drainage over 25 years: Nevada.

 
Example Graphs:

Figure 1. Change in pH with the amount of pyrite oxidized under several product scenarios.
Lines: green=acid ferrous sulfate solution; red=acid ferric sulfate solution (nothing allowed to precipitate); orange=fresh precipitate (ferriydrite) allowed to precipitate; magenta=goethite precipitates; grey=K-jarosite precipitates.

Change in pH with the amount of pyrite oxidized under several product scenarios.
Geochemical processes operating in humidity cell tests for the Pebble Project, Alaska, USA.

Figure 2. Geochemical processes operating in humidity cell tests for the Pebble Project, Alaska, USA.

Date: July, 13-14, 2019

Minimum: 15 delegates,

Maximum: 35 delegates

​Price:

  • Regular €250/€270,

  • Students €170/€200

IMWA2019 Conference

Genkel st. 4, Perm, Russia, 614990

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