Tool 3 – Integrating biodiversity into operations

The main potential impacts on biodiversity relate to:

• Accidental releases of process chemicals and tailings disposal from hydrometallurgical processing
• Air emissions from pyrometallurgical processes eg roasting and smelting
• Disposal of slag from pyrometallurgical processes
• Low-grade stockpiles seeping into surface and groundwaters

Tailings:

Tailings are the ore waste of mines and arise when mined ores are upgraded to concentrates or final products by physical processes. Risk assessment procedures can be used to identify potential impacts. Tailings management practice must be made on a case-by-case basis and meet the requirements of stakeholders and regulatory agencies.

Tailing impacts –

• Creation of initial footprint – site selection has the most profound influence on operational impacts, rehabilitation costs and post-closure liability
• Liquor and mobile metal containments seeping from tailings into waterways
• Accidents

Disposal of tailings –

• Land-based storage is the most commonly used method
• Water-retaining dams and diversions are used in countries where precipitation exceeds evaporation eg in places such as Canada and Norway. They are created around existing waterways to allow tailings to be placed below the water surface. However if a breach occurs, downstream impacts can be extensive
• Submarine tailings disposal (STD) – the aim is to release the tailings below the surface thermocline and euphotic zone, so the tailings form a ‘density current’ that descends to the depths of the ocean. Critics challenge this on environmental grounds
• Riverine disposal – this is an uncommon method using surface waters to dilute and disperse tailings to a managed deposition area where they can be stabilised and rehabilitated. This is used in areas where high rainfall, mountainous terrain and seismic activity rules out other options