Paste Technology / Tailings
Tailings (also known as slimes, tailings pile, tails, leach residue, or slickens) are the materials left over after the process of separating the valuable fraction from the worthless fraction of an ore.
In coal and oil sands projects mining the word ‘tailings’ refers specifically to fine waste suspended in water.
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, such as heap leaching, may result in quantities of the chemicals used to perform the leaching remaining in the material once leaching has been completed. As well, older forms of mineral extraction resulted in large heaps of fine tailings being left dotted around the landscape. These tailings dumps may continue to leach residual chemicals into the environment.
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 minute amounts of added compounds used in the extraction process.
The negative image of mine tailings grows in spite of a sound record of environmental stewardship with mine tailings in the past 20 years.
The 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 (oils and greases introduced by mining and processing equipment)
The common additives found in tailings include:
- 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
