Geochemical Engineering

Ded-risking mine waste management by assuring geochemical stability, from planning to closure and beyond

The generation of acid and metalliferous drainage (AMD) and neutral metalliferous drainage (NMD) are issues that affect mining operations worldwide. The short- and long- term environmental and economic liabilities of contaminated mine drainage are estimated to cost the mining sector hundreds of millions of dollars annually.

AMD, NMD, salinity and other water quality impacts are caused by geochemical processes associated with the disturbance of geological materials. When excavated, exposed, dewa- tered or otherwise disturbed, rock and over- burden can become geochemically unstable, breaking down to release metals, acid and salinity, and in some cases leading to a loss of material volume and strength with geotechni- cal consequences. Fortunately, there are many ways to keep materials geochemically stable and so avoid these impacts, and designing for geochemical stability in the first instance can prevent these issues – and their associated costs – from ever arising.

HOW GEOCHEMICAL ENGINEERING CAN HELP

All mining operations include geotechnical engineering as a routine part of mine design and development. But geotechnical engineer- ing only represents half the story. Geochemical engineering addresses many of the critical issues not captured by geotechnical engineer- ing, including:

PotentialforAMD/NMD/salinitygeneration

• Subsidence of stored wastes due to mass loss associated with the dissolution of car-bonates, reactive sulfides and sulfates, etc.

• Ion exchange of clays in liners, clay cores and clay caps due to geochemical processes in waste storage facilities.
• Potential for in-situ management or treatment of contaminated seepage to prevent or mitigate AMD discharge.
• Long-term impacts of accumulation of acid-storing secondary minerals.
• Long-term geochemical and geotechnical stability of closure landform Geochemical stability is therefore as impor- tant as geotechnical stability in assuring the long-term structural competence of mine components and avoiding economic, social and environmental impacts associated with impaired water quality during operations and beyond closure. Integrating geochemical engineering as a routine component of mine planning, operation and closure – as with geo- technical engineering–de-risks the project both environmentally and economically, and provides certainty around future closure sce- narios and costs. It is little wonder that in many jurisdictions, regulators have come to expect good geochemical engineering practices to be incorporated into mine design. This makes geochemical engineering a critical aspect of leading practice for the mining industry.

REAL ADVANTAGES

Assuring geochemical stability through design can greatly assist in avoiding many of the long- term legacy issues now faced by mine sites worldwide. In the past, most mining opera- tions have sought geochemical advice post- design and on an ad hoc basis as issues arise. However, the advantages of integrating geo- chemical engineering into the mine planning, management and closure lifecyle are many:

A significant edge for project approvals
Lower compliance, management and treatment costs
Stronger regulator and community relationship
Smaller environmental bonds
Confidence in long-term closure strategies – de-risking mine closure

Leading practice

Geochemical engineering has typically been applied ad hoc as issues arise. Integrating geochemical engineering into routine mine design, management and closure activities helps to de-risk the project both environmentally and economically.

Integrating geochemical engineering into mine planning and management increases regulator confidence in project compliance and effective closure, facilitat- ing project approval and providing clarity around closure scenarios.

Leading practice sees geochemical engineering established as a routine component of mine planning and management, comparable to geotechnical engineering.