The mining industry uses a significant amount of water during the process of turning ores into metals. Mining and mineral processing are the typical first two steps in the life cycle of metal production, which are generally followed by smelting and refining stages, all requiring water in the process.
Mines are often located in remote areas where water is scarce, and many mining projects have failed due to a lack of adequate water supplies. Sometimes, the mining industry can be in competition with others for access to water resources, depending on the mine’s location. Permission to access the limited water supply is through allocations, rights, or a variety of different licenses, and changing the amounts can be a difficult process controlled by Government. Other factors such as climate change, requirements for increased production, and a reduction in ore quality exacerbate the problem, and contribute to the importance of recycling available water.
Water can be sourced from many locations for use in the mining industry, including local water authority reticulation systems, purpose built dams, pipelines, rivers, lakes and many types of groundwater sources. Australia’s Bureau of Statistics shows a relatively steady water use, from 592 GL in 1993-1994 to 508GL in 2008-2009, suggesting an improvement in water efficiency and an under-reporting of use (such as water used in tailings dams) to balance against an exponential production growth. Research into Australia’s mining industry water supply in 1997 revealed only 5% of water was supplied through mains infrastructure, with 95% sourced locally from surface and ground water.
Substantial amounts of water is used in the minerals processing industry, and water is the liquid of choice for operational activities which include:
- Transport of ore and waste in slurries/suspension
- Separation of minerals through chemical processes
- Physical separation, such as centrifugal separation
- Cooling systems around power generation
- Suppression of dust for mineral processing, conveyors and roads
Creating potable water can also required to support towns in local areas that have developed to house mining staff. An estimation of water used in metal mining applications when in ore form and metal refining operations is given below1
Typical water usage per unit of metal extracted
|m3/t of metal||m3/t ore|
|Heap acid leaching + SX/EW||38||0.5|
|Nickel||Flash furnace smelting + sherritt gordon refining||79||1.4|
|Pressure acid leaching||376.6||3.5|
|Imperial smelting process||21.7||0.9|
|Zinc||Imperial smelting process||21.2||1.5|
|Iron/Steel||Blast furnace + BOF||11.34||1.8|
|Stainless steel||Electric arc furnace||13.4||2|
|Gold||CIL cyanidation + EW/smelt||252087||0.8|
Tailings are the materials left over after the valuable portion of the ore has been separated, and are usually present in a slurry form, a mixture of fine mineral particles and water. Depending on the ore being mined, tailings can be high in sulphides which can lead to acid mine drainage, be radioactive due to naturally occuring radioactive isotopes such as uranium, be highly alkali, and/or can have other properties which are difficult to treat and an environmental problem when discharged. In a lot of cases, the concentration of metal ions in tailings is too low for recovery to be economical, but where evolving regulations are starting to become stricter, recovering these metals as part of the water treatment process is becoming more attractive.
Acid Mine Drainage
Waste rock from mining operations can contain high quantities of sulphides, which can oxide when exposed to air and form sulphuric acid. As the rock is mixed with water at this stage, the water acidifies and leaches metal ions from the rock into a concentrated waste stream known as Acid Mine Drainage (AMD). This stream can have varying concentrations and composition depending on the rock, but can include arsenic, cobalt, copper, cadmium, lead, silver and zinc. In high concentrations these contaminants can have an impact on the local environment and require treatment before being reused or discharged.
Process water re-circulation is a common practice in the mining industry to reduce tailing storage, water intake and discharge volumes. The amount of times water can be reused before trace contaminant build up negatively impacts the extraction process depends on the process being used and substance being extracted, with research into Canadian mines showing water is recirculated 3-4 times before it becomes unsuitable. Water reused in this way is often not treated before being reused, but has the concentration of contaminants reduced by the addition of non-contaminated intake water. Care must be taken when using recirculated water as higher concentrations of impurities can lead to scaling and corrosion issues.
Mining Water Disposal
Strict mining water discharge regulations exist in most countries in the world, ensuring a limited environmental impact when water is released from the mine site into surface water or ground water. Governments often mandate water discharge volumes to surface and ground water for environmental reasons, to balance the amount of water sourced for the mine. Regulations are constantly evolving, with some countries moving from point source discharge limits to a limit on the discharged location as a whole (e.g. rivers), taking into account not only the discharged water, but any runoff from the site too. These changes may see the rise of large scale water treatment being required on groundwater and surface water close to the mine site.
The cost of treating mining wastewater is significant, as desalination and toxic contaminant removal are usually required. For this reason, large and expensive evaporation ponds are often built to dispose of water, but these have the risk of leakage into soils, aquifers and rivers.
Mine Water Treatment
Many approaches can be used for the treatment of mine waters, with the treatment solution dependent on the mine water contamination. Membrane treatment such as reverse osmosis is a commonly used approach, but can have issues with scaling and fouling from compounds such as metals, sulphates, and carbonates. This often means that pre-treatment is required before membrane treatment can be employed, which might include chlorination to remove bacteria, lime addition to remove metals and supersaturated gypsum, suspended solids removal, pH adjustment to limit scaling, and addition of anti-scalants.
Reverse osmosis is typically used for water with low calcium and sulphate concentrations (100-700mg/L is the general saturation level for RO), and a high volume of brine is usually produced which can have a significant cost to dispose of. A typical single RO pass achieves a clean water recovery of 60-70%, with the remainder expelled into the brine stream. This stream can then either be treated with lime (destroying the anti-scalant and precipitating out the supersaturated salts) or it can be passed through a crystallizer/evaporator to remove excess water, thereby increasing capital and energy expenses.
Our Water Treatment Technologies
Clean TeQ Water can provide solutions to the most challenging mine water treatment problems. Our CIF® (continuous ionic filtration) technology is robust and provides both physical filtration and ionic exchange concurrently, reducing the amount of pre-treatment required. The process results in maximum water recovery with minimum waste, flexibility in output water quality, and resistance to scaling and fouling. Depending on the feed water specification, different combinations of our technologies can be used to reach the desired product water specification. For example, DESALX® technology can be paired with high density sludge (HDS) systems, recycling the gypsum based brine to achieve zero liquid discharge.
|Solution||Clean TeQ Technologies|
|Desalination||DESALX® (2-Stage CIF®)|
HIROX® (High Recovery Reverse Osmosis)
|Nutrient Removal||CIF® (Nutrient Removal)|
BIONEX™ (Nutrient Removal and Treatment)
BIOCLENS™ (Nutrient Treatment)
|Arsenic/Antimony Removal||CIF® (With Iron Impregnated Resin for Selective Removal)|
Granular Activated Carbon (GAC) Techniques
Along with these technologies, our robust EVAPX™ evaporation and crystallisation technology can treat the most difficult streams, acheiving zero liquid disacharge (ZLD). We can also design a flow sheet to meet feed and product water specifications, and use our capabilities in Research and Development to solve niche problems.
Our Metal Recovery Technology
Our CLEAN-IX® continuous ion exchange technology provides highly efficient extraction and purification for a range of valuable strategic metals from slurries and solutions. We are focused on applying our proprietary ion exchange processes for the recovery of metals
from ores and tailings where the conventional routes are economically marginal or pose an environmental burden that is not sustainable. The resin used in the continuous ion exchange process can be selected to directly target metal ions, adsorbing them onto the resin and creating a highly concentrated metal ion stream.
CELAN-IX® covers the complete spectrum of leach systems (both acid and alkaline). Continuous Resin-In-Column (CLX) is used for clarified leach solutions (<4% solids), Continuous Resin-In-Pulp (CRIP) and Resin-in-Leach (CRIL) for slurries (4-50% solids), and Continuous Elution (U-Column) for metal elution and purification.
Find Out More
Contact us to discuss your water treatment needs.