In this article the industrial water treatment specialists at WTS consider some of the challenges faced by the mining industry when treating their wastewater for reuse or disposal.
The article explains why the treatment of wastewater from mining operations is important, what the treatment options are, and how the use of physical filtration and chemical techniques can be used to reduce costs, increase the reuse of water resources, and improve environmental performance.
Wastewater treatment in the mining industry
The mining industry consumes a lot of water in its operations. Not just in getting the ores or minerals out of the ground in the first place, but the processing of ore to extract valuable metals also uses considerable quantities of water.
Using water to process metals can lead to a serious build-up of minerals or solids in a mines available water supply, resulting in contaminated wastewater. In nearly all cases, discharging this contaminated wastewater straight into the drains or local water course isn’t an option. It can’t be reused easily either without specialised water treatment.
Dealing with wastewater from mining operations
One of the simplest solutions to the build-up of contaminated water from a mine is perhaps to outsource the problem to a third-party company which will send tankers to remove any sludge or waste water, and process it off-site. However, this is usually fairly costly. Having retention ponds on-site is another possibility, but over time these can become increasingly dirty and hard to manage. By far the best option is to treat the waste water on-site, using specialist filtration techniques, treatment chemicals, or both.
The benefits of using filtration and water treatment chemicals
There are several advantages to choosing filtration or chemical treatments to clean up waste water from mining operations. These include:
- Often far less expensive.
- Possibilities of reusing the water.
- Control over how the water is treated.
- Ability to have a closed-loop system and water recovery.
- Improved environmental performance.
What contaminants are present in mining wastewater?
The sediment present in waste water produced from mining operations will typically depend on the type of rock leaching into the water used for extracting ore. As the water becomes more contaminated with metals and sulphates, its acidity level rises too. This acidic, contaminated wastewater is known in the industry as Acid Mine Drainage or AMD.
Why should you treat the wastewater from mines?
Not dealing effectively with the wastewater created from mining activities can have a huge impact on a mines efficiency and the local environment. Mining water which is often very acidic can lead to groundwater contamination and acid runoff from drainage which can be extremely damaging to the local environment and watercourses.
The fact that many mining processing plants are located in areas where the local water supply is already under stress leads to what fresh water there is becoming increasingly polluted.
From an environmental perspective, the best option is to try to stop the water becoming contaminated in the first place. The main aim of any mining water treatment process is to remove solids, contamination and metals from the water, and stop it from becoming too acidic.
Using pH adjuster chemicals to control excess acidity
One of the first things to consider when treating wastewater from mining operations is to get the pH level back into the correct range. Getting the pH right will help to maintain water quality, and stop the metals from dissolving and becoming suspended in the water.
Raising the pH of the water will cause a chemical reaction to take place, creating insoluble metal particles which are easier to deal with. Chemical pH adjusters will help to lower the acidity of the waste water, aiming for a pH of around 8 before exploring other treatment methods.
Using flocculants and coagulants in the wastewater treatment process
Flocculants and coagulants are speciality chemicals that are used to take the tiny particles of metals and other solid contaminants suspended in the used water and “clump” them together, making it much easier to filter them out. There is an extensive range of wastewater coagulants available which are designed for many different applications, so it’s important to select the best one for your needs.
What other water treatment chemicals can be used in mining?
Specialist coagulants and pH adjusters are the most frequently used chemicals in mining wastewater treatment, but there are other speciality chemicals that can often be applied to great effect. These include corrosion inhibitors, and biocides to control the growth of algae and bacteria. Water softeners may also be useful in hard water areas.
Mining wastewater and sludge dewatering techniques
Treating the sludge created during the mining process is essential. One of the most important parts of this process is to remove any excess water from the sludge to create a solid waste that can be easily managed, transported and disposed of. This process is known as sludge dewatering.
There are various techniques used in sludge dewatering, and selecting the most appropriate one will usually depend on your budget, constraints on available space, the type of mining, local geology and environmental conditions. Some of the most common approaches to sludge dewatering of mining wastewater include:
One of the most commonly used techniques for dealing with sludge dewatering in the mining sector is the use of hydrocyclones. These are specialised pieces of equipment that are very efficient at removing solids from water. Their versatility and efficiency means they are used in many different settings in the mining industry.
Hydrocyclones work using centrifugal force to remove solids from the wastewater. One of the main advantages of this technology is that it has no moving parts, and can process a large quantity of wastewater without the need for lots of floorspace. The downside to using a hydrocyclone is that it can rarely be used in isolation. Another method of wastewater treatment will typically need to be used in conjunction with the hydrocylone, perhaps a high-efficiency filter press.
A belt press is a very popular choice in mining operations. They are quick to set up when compared to other wastewater treatment techniques and don’t need a high initial investment. For these reasons they have become the default choice in situations where the key consideration is keeping costs for dewatering mining sludge as low as possible.
A belt press or filter consists of two moving belts, running between a series of rollers. As the waste water passes over the belts and through the rollers, the solids form into an easily-removed clump of solids called a “cake”.
Although belt filters and presses are easy and cheap to set up initially, they can start to become more expensive to run as they can require more flocculant to operate effectively. Replacing belts can also be expensive, and they may need to be replaced often. Finally, the solid cake which is produced often needs to go through another stage of processing before disposal.
Probably the top-rated method and most efficient way of removing solids from mining wastewater in the UK is the filter press. Pumps push waste slurry through the various chambers which make up the filter press, where plates remove the solids, ensuring the treated water which flows from press can be released back into the system.
Filter presses run efficiently, and have lower operating costs than other wastewater treatment solutions such as a belt press or centrifuge.
In the mining industry, there are both high-pressure and low-pressure filter presses in use. However, the low-pressure version is less widely used as they are relatively inefficient and often more complex to install and then maintain.
Wastewater treatment solutions for the mining industry
Water Treatment Services offer a comprehensive range of innovative water and wastewater management solutions for the mining sector.
Our experts can provide advice and support to help you identify the most appropriate strategies for the identification, investigation and implementation of environmentally sensitive remediation programmes for the treatment of mining related wastewaters.
With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained engineers and wastewater treatment specialists we offer cost effective environmental support solutions across the whole of the UK and internationally.
Contact us today to learn how our mine wastewater solutions can help you reduce costs and improve environmental performance.
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