The mining industry requires access to a safe and stable water supply for its operations. However, this becomes increasingly difficult as the connection between mining and water risk grows, including challenges related to water availability and water quality in nearby mining operations.
This problem becomes particularly serious in regions with limited water resources or where mines are located upstream of communities that depend on the same water source for drinking and farming.
The legal frameworks for water use differ in different mining countries, from private water use (Chile) to a hybrid system (USA). The legal framework, laws, and regulations allow the mining industry to use water.
Through water rights, using water from a river or a deep well is allowed in Chile; however, in locations where drought is present due to climate change, the water use can create social tensions between local populations and Mining companies.
In Chile, an approved environmental qualification resolution (RCA) permit and a “Social License” are required to start a mining operation. The latter is a concept of social approval of citizens to extractive mining projects. This concept allows harmony and establishes acceptance of the project by the surrounding communities.
One alternative to achieving harmony with communities is reducing water use through resource optimization and supporting communities through technologies and agreements.
This article will review alternatives for optimizing water use and other water sources.
ALTERNATIVES TO OPTIMIZE WATER USE
1.– Increase solids in conventional tailings thickeners
- Conventional thickeners typically operate between 50% to 55% solids content, so makeup water can vary from 0.6 m3/t to 1.0 m3/t if there is no water recovery from the tank. By discharging tailings with a higher solids content, for example, between 55% to 60% solids, more process water can be recovered, and the water use is optimized, reducing the makeup to 0.5-0.6 m3/t.
- An option to increase the percentage of solids is by adding specific flocculating reagents for each type of tailings (optimal selection), for example, rheological type reagents that increase the % of solids without excessive increase in rheology (shear stress and viscosity), intelligent control of the thickener (process improvement through the use of the continuous Smartdiver thickener bed sensor) and the incorporation of pre-charge pumps or series pumps (pumping optimization) when the tailings need to be disposed of remotely. This process control improves tailings pumping, increasing the solids discharged from the thickener. For example, at Process Minerals Consulting, we have the experience of achieving 15% savings in water with this measure, and our client increased the solids in thickener from 60% to 65%. In addition, it is possible to improve the tailings deposit by maintaining the revenge and avoiding reaching the wall with more diluted tailings.
2.- The thickened Tailings discharge Management in tailing deposits
- Managing and controlling the deposition is essential to reducing water loss in the tailings due to evaporation. Strategically depositing the tailings to minimize the area exposed to evaporation, increasing the supply of process water in tailings deposits. For example, at Process Minerals Consulting, we have experience providing a strategic deposition plan for a client, reducing water loss by up to 30%.
3.- High-density and paste tailings
- With this technology, the thickening is achieved with 65% to 70% solids, so the tailing is a fluid that cannot be segregated by particle size; it is discharged directly into the tank without separating sands and slimes. In this type of deposit, the make-up decreases to 0.5-0.4 m3/t.
- There is no clear water lagoon, although small lagoons can be generated in the tailings with 62%-65% solids, from which the recovered water is returned to the process.
- Additionally, this type of tank has significant environmental advantages: less use of water, greater stability, less dust generation, and minimal infiltration.
4.- Filtration and tailings management
- Implementing filtration technology and managing tailings in piles lowers the water content of the tailings. We have observed in our clients that by implementing this technology, it is possible to obtain 15% to 20% humidity, which allows recovery of 80% of the total process water sent to the tailings and reduces the make-up to 0.25 m3/t.
- These are more stable deposits, requiring less use of water, less use of the required surface area, and less impact on the environment.
USE OF OTHER WATER SOURCES: SEAWATER
Two types of seawater are used in mining: desalinated seawater and un-desalinated or raw seawater.
1.- Desalinated seawater has been used in the large mining industry for several years, such as Minera Escondida, Manto Verde, and MLP. Mining companies mainly use the reverse osmosis (RO) separation process to produce desalinated water from seawater. Despite reducing or eliminating water use in the mining industry, the desalination process uses a high amount of energy, and its impact on the environment in the discharge area of the brine or waste from the RO process must be studied.
2.- Using raw seawater requires that the mining process be adapted to these conditions, using filters, chemical agents, materials, and special corrosion-resistant equipment. In the flotation stage, lime (CaO) must be replaced by MBSNa as a pyrite depressant agent. Therefore, a complete design and adaptation of the mining process are required. An example of this application is in Mina las Luces of the Las Cenizas mining group and Minera Centinela of Antofagasta Minerals, using salt water on a large scale in the Esperanza project.
Salt water use in heap leaching is beneficial; there are even processes in which the salt content is increased. In the SX-EW stage, modifications must be made to eliminate the chlorine present in seawater.
A third option mentioned in the literature is using partially desalinated seawater, which could leave favorable elements for mining processes and be suitable for foam flotation processes, thus increasing mineral recovery.
The use of seawater is regulated, and the collection and discharge standards (brine) must be complied with; to keep environmental commitments (RCA) controlled, discharge water must be sent through offshore outfalls to generate the corresponding dilution.
CONCLUSION
The path towards sustainable mining requires continuous improvement of processes and a commitment to environmental responsibility.
Water use optimization in the mining industry can be achieved through control of solids in the thickeners, strategic management of tailings deposition, high-density and/or paste tailings, and filtration technology.
On the other hand, there is the alternative of redesigning the mining process to use raw seawater or implementing a desalination plant for seawater use in the mining industry.
At Process Minerals Consulting, we have experience optimizing water resources and designing mining plants using seawater. If you want to evaluate your process to optimize water use, contact us at info@processminerals.cl, and we can help you. We invite you to challenge and assess your process.
What strategy would you use to optimize water use in your mining project?
Rodrigo Bernal
rodrigo.bernal@processminerals.cl
