Mining Wastewater Treatment Challenges
Mining wastewater treatment is associated with several challenges due to unique water characteristics, composition of pollutants, and specific activities of the enterprises:
The diverse composition of pollutants in mining wastewater makes the choice of purification methods complicated:
Complex composition of pollutants
Acid mine drainage, AMD
It is pretty standard, especially in coal and specific metal ore mining. A low pH value and high concentrations of dissolved heavy metals characterize AMD (Acid Mine Drainage). It requires particular methods of neutralization and treatment: chemical neutralization, ion exchange, neutralization through reverse osmosis, and dilution.
High concentrations of heavy metals
Mine water often contains significant concentrations of heavy metals: lead, copper, zinc, and others.
Removal of these metals requires efficient and specific technologies, including membrane filtration, ion exchange, chemical reduction, chemical precipitation, adsorption, nano-, ultra-, micro-filtration, coagulation, flotation, and electrocoagulation.
Difficulties in ensuring efficient treatment
Sometimes, for example, when there is no electricity or water infrastructure access, it is challenging to ensure water treatment efficiency. In such cases, energy reserves from independent sources must be provided. For instance, in city networks, if you have a thermal power plant and the water is insufficient, finding ways to reduce fresh water consumption or organize water supply from other sources is necessary.
Long decomposition time
Some pollutants, such as heavy metals, can remain in the environment for a long time. Long-term pollution monitoring and management measures may be required even after mining stops.
Environmental consequences
Contaminated mine water discharge into natural water bodies can cause serious environmental consequences, including contamination of surface and ground waters, damage to ecosystems, and threats to human health.
Necessity to match the standards
Water treatment for mining often requires compliance with strict regulations and water quality standards set by law.
Economic aspects
Development, installation, and maintenance of modern treatment facilities can be expensive. The balance between purification efficiency and economic feasibility is an important consideration.
Basic ways of mining wastewater treatment
Research and innovations
Scientific research leads to the development of more efficient and environmentally friendly mining wastewater treatment methods and the creation of new technologies.
Use of bacteria
Wastewater treatment utilizing microbial fuel cells (MFC) has a unique advantage: the possibility to use microorganisms to generate energy, which is used for disinfection processes and wastewater treatment.
Membrane technology
It is one of the most advanced wastewater treatment technologies available today. Its advantage lies in the method’s high efficiency, simplicity, and environmental friendliness.
Biosorption
It is a physicochemical process that occurs naturally in some types of biomass and binds wastewater pollutants.
In this method, biological materials accumulate heavy metals from wastewater through an indirect metabolic absorption pathway. One of the significant advantages of this method is that it does not require energy. However, the amount of contaminants a solvent can remove depends on the cellular sorbent’s kinetic balance and surface composition, as the contaminants are adsorbed on the cellular structure.
Engineering decisions
Mining water treatment plant is a set of methods and activities.
Engineers develop special treatment systems adapted to the unique wastewater characteristics of a particular mining enterprise. These mine water treatment solutions can include developing complex systems and combining multiple processing methods.
Training
Design companies offer staff training programs to ensure proper use of wastewater treatment and management methods. Training is among the numerous industrial wastewater treatment services such companies offer to their clients.
Cooperation with authorities
Mining companies cooperate with government environmental authorities to ensure compliance with regulations and standards.
Monitoring and analysis
Regular monitoring of wastewater quality makes it possible to quickly respond to changes and take necessary measures to comply with the standards.
Financing and investments
Financing for developing and implementing modern treatment technologies can significantly improve the efficiency and environmental safety of the process.
Cooperation with the public
Cooperation with the public, environmental organizations and local residents can help improve corporate ecological responsibility and increase transparency in wastewater management.
Combining the above approaches helps overcome the challenges associated with wastewater purification in the mining industry and ensures more sustainable and environmentally friendly operation of enterprises.
Check out also our mine waste management guide.
Why is Mining Water Treatment Important?
Mining wastewater treatment is a critical process for minimization of negative environmental impacts. The mining industry includes the extraction of coal, ore, oil, gas, and other minerals. During the extraction and processing of materials, a large amount of wastewater is produced, which contains various contaminants, such as heavy metals and other hazardous chemicals and compounds.
Wastewater treatment in the mining industry requires careful planning and various technologies, depending on the type of activity and nature of pollution. Wastewater treatment maintains the environmental sustainability of the industry.
Mine Water Treatment Process
Mine water, formed during mining activities, gets highly contaminated after contact with minerals, chemicals, and other substances.
The mine wastewater purification process helps minimize the impact of water discharge onto natural water bodies.Specific mine water treatment plant depend on the type of contaminant and mining activity. However, the general mine water treatment process is as follows.
Collection and preliminary treatment
Mine wastewater is collected from various sources, such as open mine pits, tailing ponds, drainage systems, and underworkings. Collected water undergoes primary cleaning to remove large particles and sediments through capturing, precipitation, and sedimentation.
Physical and chemical treatment
After preliminary purification, water undergoes various physical and chemical treatment stages to remove suspended solids and dissolved contaminants. Coagulation and flocculation are standard chemical treatment methods. These methods mean adding chemicals into water to combine smaller particles into larger lumps (flakes) that are easier to settle.
Clarification
Water is allowed to settle, and the flakes, formed during the coagulation-flocculation process, settle to the bottom of the settling tank or clarifier. Clean water is then removed through the overflow.
Filtration
Some purification systems use filters for further removal of suspended solids, which did not precipitate during clarification. Filtration can be performed with the help of sand, activated carbon, or other materials, capturing small particles.
Chemical precipitation
Chemical precipitation includes the addition of some chemicals, which react with dissolved contaminants and form solids (sediments). Then, these sediments can be separated from water by clarification or filtration.
Biologic purification
When mine water contains organic contaminants, biological purification can be applied. It means using microorganisms for biodegradation of organic pollutants. Depending on oxygen presence, aerobic and anaerobic reactors can be used.
Ion exchange and adsorption
Ion-exchange resins or materials are used to remove specific ions or contaminants from water. Ion exchange means the replacement of unwanted ions on resin with safer ions, while adsorption uses materials that absorb pollutants on their surfaces.
Disinfection
If necessary, disinfection processes such as chlorination or UV treatment can be used to neutralize harmful microorganisms present in water.
PH adjustment
If mine water is acidic (acid drainage water), pH adjustment for water neutralization can be required to avoid negative environmental impact.
Wastewater reuse or discharge
After purification, water can be tested for quality and either reused in other mining operations or discharged into local water ponds, provided it meets water quality standards.
It is important to note that mine wastewater purification can be challenging and requires combining these methods, depending on specific water and contaminant characteristics. Besides, mine wastewater treatment must be planned in such a way that it helps minimize long-term environmental impacts.
Mine Water Treatment Technologies
Mine wastewater
These waters can be of two types: mine drainage and domestic water discharge.
Mine drainage waters are ground waters. They usually come from fractured formations to water collectors through open or closed underworkings, where they are regularly or periodically pumped to the surface, depending on their quantity.
The initial composition of mine wastewater depends on soil texture and underground water level. Mine waters are usually highly mineralized, meaning they contain significant dissolved salts.
When mine waters are discharged into a water pond, the water’s physical and chemical composition deteriorates and often causes a change in its color. At the same time, these waters can be reused in the technological process of ore-dressing treatment by washing after their purification.
Wastewaters from ore-washing plants
The amount of these waters is approximately equal to the amount consumed and averages about 7m3/l of washed ore with a deviation from 5 до 8,5 m3. Only a small part of water (up to 12-15%) gets lost for wetting ore and other needs. However, the volume of waste liquid (pulp) remains approximately equal to the volume entering the plant, as water losses are compensated by impurities coming into the wastewater–suspended substances. The quantity of discharged water usually is almost the same.
Large quantities of clay, sand, and waste rocks (tailings) are removed with wastewater.
The chemical composition of iron ore washing waters is ordinarily harmless. They usually do not contain organic and toxic substances. Effluents from manganese ore enrichment have a finer granulometric composition of the sludge. The water supply of ore-washing plants is a closed loop with multiple water reuses, which was previously purified in clarifiers (sludge collectors).
Solid wastes of the ore washing plants are highly abrasive for pipelines and chutes, through which they are transported to the sludge collectors.
Wastewater from iron and manganese ore processing through washing and flotation
Here, we have two types of wastewater: after the first purification stage (washing), only contaminated with suspended impurities and not containing flotation agents. After the second purification stage (flotation), they are contaminated with suspended impurities and flotation reagents. The quantity of wastewater from flotation is less than that from ore washing, and its income is regular.
Reuse of water, previously clarified in sludge collectors, can be obstructed by residual content of suspended matter in the form of clay particles of more than 200 mg/l. Discharge of such wastewater into ponds is unacceptable.
It must be considered that only water with impurities, which do not affect the flotation process, can be used for flotation plants. The content of heavy metal salts in water is unacceptable. Iron and copper oxide hydrates are also not desirable. Water must be free of organic compounds: oils, fats, etc.
Wastewaters from the washing of non-metallic minerals – feldspar, dolomites, fluxing limestones, and quartzites
Their quantity is approximately equal to the amount of water consumed, ranging from 1.5 to 5 m3 per 1 ton of washed raw materials. In this case, water losses for wetting the rock are the same as when washing iron ore, 10-15%. Water discharged is regular.
Clay and sand particles and low-value pieces of enriched material go away with wastewater. This material is less abrasive than the material used in iron ore processing. The discharged pulp contains 1:10 solids (impurities) in relation to water with deviation up to 1:30. The volumetric mass of sludge is, on average, 1.25 t/m3.
Wastewater, after washing non-metallic minerals, usually does not contain toxic substances and can be reused for the exact needs of the circulating water supply system after purification in clarifiers (sludge collectors).
Wastewaters after hydraulic stripping of mines and open pits
In some cases, stripping of ore deposits and the above-mentioned non-metallic minerals, as well as refractory clays, is carried out hydraulically – with the destruction of soft rocks utilizing a water stream and their transporting in a stream of water to the storage place. Clarified wastewater from the destructed rock storage place is reused for the same needes in the circulation system.
Wastewaters from sinter factories
Their quantity is 50–60% of the water consumed or about 0,5-0,6 m3 for 1 t of sinter. These waters come regularly with the same amount. They contain many mechanical impurities – ore, coke, limestone, etc. (up to 30 g/l). At sinter factories, where lime slaking in a fluidized bed is used, a lot of fine, difficult-to-settle suspension is formed in wastewater. This suspension comes from air purification in scrubbers and washing off dust from floors and walls.
After clarification in a clarifier or a particular sedimentation pond, wastewater is reused for the same needs in the circulation system.
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Our Expertise in Wastewater Treatment in the Mining Industry
- Mine water purification with a high concentration of salts through ion exchange filters, followed by disinfection, to overcome freshwater deficiency in a city with a population of 60,000.
- Sludge water concentration in the amount of 67,650 m3/day to reduce water discharge into the sludge ponds.
NEW CONSTRUCTION OF A COMPLEX FOR CONCENTRATION OF TAILINGS AT THE TERRITORY OF THE PROCESS WATER AND SLUDGE MANAGEMENT SHOP, PJSC “NORTHERN MINING AND PROCESSING PLANT”
PROJECT START: 2019
COMPLETION DATE: 2023
EXISTING SITUATION AT THE ENTERPRISE:
Water with concentration process tailings in a volume of 67,650 m3/h with 3% solid content is fed through underground gravity chutes to a pumping station, where sludge pumps pump it into a sludge storage reservoir with a length of 2000 meters, located at the height of more than 52 m. Pumping such a volume requires enormous energy consumption.
PROJECT OBJECTIVE:
To reduce energy consumption for pumping tailings.
To increase the service life of the sludge storage reservoir.
DESCRIPTION OF DECISIONS MADE:
To reduce energy consumption in high-capacity technological processes, it was decided to use tailings concentration technology to decrease the amount of wastewater being pumped into the sludge storage reservoir.
A technology developed for thickening tail pulp ensures its entire processing in radial thickeners utilizing flocculants. After clarification, water from the thickeners is returned to the complex’s circulation system and used for the technological needs of the enterprise. Concentrated tailings are pumped into a tailings pond.
This solution shortens the route for transportation of fresh water for dressing technology.
BRIEF DESCRIPTION OF THE DEVELOPED TECHNOLOGY:
From the ore processing plant, OPP-1 tailing pulp with a solid content of 3.49% comes via gravity slurry chutes to the booster pumping station PS-1. It is planned to replace the pumping equipment in this station with low-pressure pumps. In total, ten pumping units have to be replaced. After that, the pulp is pumped into the tailings distribution chamber (TDC). From TDC tailings, pulp comes into four radial high-performance thickeners, the diameter of each being 60 m.
There, the solid matter is settled onto the bottom under the influence of a flocculant. Next, pulp is fed into the collection sump (tank) of the integrated slurry pumping station (ISPS) through unloading pumps, and then concentrated pulp is pumped into the tailings storage facility.
The final product – concentrated pulp – contains 50-55% solids and has a volume of 1963.86 m3.
Clarified water, drained from the thickeners and has a solid matter of 150 mg/l, flows by gravity into the receiving chamber of the return water supply pumping station (RWSPS), where it is fed for the technological needs of the enterprise utilizing water pumps.
The pay-back period for the enterprise is ten years.
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