Tailings - Composition

Composition

The composition of tailings is directly dependent on the composition of the ore and the process of mineral extraction used on the ore.

Certain types of extraction process, like heap leaching for example, may result in quantities of chemicals used to perform the leaching remaining in the material once leaching has been completed. Older forms of mineral extraction, such as those utilised during the early gold boom years of Australian gold mining, resulted in large heaps of fine tailings being left dotted around the landscape. These tailings dumps would continue to leach residual chemicals into the environment, and if weather conditions allowed it the finer fraction would become windborne, blowing around the townships surrounding the now-dormant mining areas.

Typically, the bulk quantity of a tailings product will be barren rock, crushed and ground to a fine size ranging from coarse sands down to a talcum powder consistency.

Tailings may contain trace quantities of metals found in the host ore, and they may contain substantial amounts of added compounds used in the extraction process. Elements are rarely in elemental form, more often as complex compounds.

Common minerals and elements found in tailings include

  • Arsenic - Found in association with gold ores
  • Barite
  • Calcite
  • Fluorite
  • Radioactive materials - Naturally present in many ores
  • Mercury
  • Sulfur - Forms many sulfide compounds / pyrites
  • Cadmium
  • Hydrocarbons - Introduced by mining and processing equipment (oils & greases)

Common additives found in tailings

  • Cyanide - as both sodium cyanide (NaCN) and hydrogen cyanide (HCN). Leaching agent in extremely dilute quantities which readily volatize upon exposure to sunlight.
  • SEX - Sodium Ethyl Xanthate. Flotation agent.
  • PAX - Potassium Amyl Xanthate. Flotation agent.
  • MIBC - Methyl Isobutyl Carbinol. Frothing agent.
  • Sulfamic acid - Cleaning / descaling agent.
  • Sulfuric acid - Used in large quantities in the PAL process (Pressure Acid Leaching).
  • Activated Carbon - Used in CIP (Carbon In Pulp) and CIL (Carbon In Leach) processes.
  • Calcium - Different compounds, introduced as lime to aid in pH control.

Tailings present a long term cost to the mining industry. If the company leaves or goes bankrupt, the local government can find itself with responsibility for the maintenance and monitoring of tailings dumps essentially forever - this, and other costs of cleanup, can impose liabilities that were estimated at up to 12 billion dollars in the US alone in 2005.

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