The extraction of minerals is an intensely water-dependent process, requiring vast quantities of the resource at nearly every stage of operation. Modern mining relies on water for core processing, safety, and logistics. The sheer volume required places significant demand on local water sources, making responsible water management a necessary component of global mining practices.
Water in Mineral Processing and Extraction
Water is the primary medium for separating the desired mineral from waste rock, a process known as beneficiation. This separation uses physical and chemical techniques that exploit the different properties of materials in a water-based environment. A common method is froth flotation, which requires water to create a slurry of finely crushed ore.
In froth flotation, chemical reagents are added to the water-ore mixture, causing the valuable mineral particles to become water-repellent, or hydrophobic. Air is then pumped into the mixture, and the hydrophobic mineral particles selectively attach to the bubbles, rising to the surface to be collected as a froth concentrate. This process is highly water-demanding, with metal sulfide flotation often requiring three to seven tons of water for every one ton of ore processed.
Another common technique is leaching, where a water-based solution acts as a solvent to chemically dissolve the target mineral from the ore. For example, in gold or copper mining, a water solution containing a leaching agent is percolated through large heaps of crushed ore to dissolve the metal. The quality of the water used in both flotation and leaching must be carefully managed, as high concentrations of dissolved salts or contaminants in recycled water can negatively impact the chemical reactions and reduce the final recovery of the metal.
Water is frequently used to wash or scrub the raw ore before processing, especially for deposits containing significant amounts of clay. High-pressure water jets and mechanical scrubbers agitate the ore, removing fine particles and clay before the material moves to the next stage. This initial washing step reduces the amount of waste material, or gangue, sent to energy-intensive processing circuits, improving overall efficiency.
Hydraulic Transport of Materials
Moving massive volumes of material across a mine site is often accomplished through hydraulic transport, which involves mixing solids with water to create a pumpable slurry. This method moves material continuously over long distances and varied terrain with less direct labor than traditional truck or rail transport. Efficiency depends on maintaining the correct ratio of water to solids to ensure the mixture can be pumped without clogging pipelines.
Conveying crushed ore to the processing plant is a primary application, allowing a steady flow of material into the grinding and separation circuits. Water is also the carrier for tailings, the most significant waste product of mining. Tailings are the finely ground, rock-like residues left after valuable minerals have been extracted.
Tailings are mixed with process water to form a slurry that is pumped to designated tailings storage facilities (TSFs). Conventional slurry disposal often involves a mixture that is approximately 50% water by volume. Using pipelines is advantageous because it reduces the need for extensive road infrastructure and minimizes noise and dust pollution from surface vehicle transport.
Maintaining Mine Site Operations
Beyond processing and transport, a substantial volume of water is required for general maintenance, safety, and infrastructure. A major operational use is dust suppression, particularly in large open-pit mines where heavy machinery movement generates significant airborne particulates. Water trucks spray roads and stockpiles to prevent fine dust from becoming a health and safety hazard for workers and surrounding communities.
Water is circulated through cooling systems to manage heat generated by heavy machinery, such as haul trucks, excavators, and drilling equipment. These industrial cooling applications prevent overheating and ensure the continuous operation and longevity of the equipment. Water is also used to cool process streams and products throughout the plant.
Other uses include managing the water environment, such as dewatering operations. Mines extending below the natural water table require continuous pumping to remove groundwater inflows and prevent flooding. Finally, water is used for general site sanitation, including washing equipment and providing potable water for workers who often reside or work for extended periods in remote locations.