Water Treatment Solutions for the Mining Industry

1. Background

In recent decades, environmental regulations around the world have become more stringent as awareness of environmental impacts and water scarcity has increased. The international mining industry has responded accordingly.

Water management strategies are at the heart of mine development, operation, and rehabilitation activities and are now being used to minimize the environmental impact of mining operations. From potable water production, cooling equipment, waste separation from precious minerals to dust control, water is encountered in the mining process and therefore poses a risk to the large volume of water demand.

NEWater is concerned about the pollution of the environment and accepts the challenge of sustainable development. We see water treatment applications in the mining industry including potable water treatment at the mine site, process water treatment, product recovery, recycled water treatment systems, residue management, and various other treatment technologies.

Figure 1: Mining Industry

2. Principle of Reverse Osmosis Technology

Reverse osmosis technology is the most widely used and mature technology in membrane separation technology. Its principle is to apply a higher pressure than the natural osmotic pressure to the saline water (such as raw water), so that the osmosis proceeds in the opposite direction, pressing the water molecules in the raw water to the other side of the membrane and turning it into clean water, thus achieving the purpose of removing impurities and salts in water.

The separation characteristics of the reverse osmosis membrane can effectively remove dissolved salts, colloids, organic matter, bacteria, microorganisms, and other impurities from water. So far, membrane separation technology mainly includes reverse osmosis (RO), microporous membrane filtration (MF), ultrafiltration (UF), and electrodialysis (EDI) technology. Among them, RO, UF, and EDI are mainly used in industrial applications.

 

Figure 2: The working principle of NEWater reverse osmosis system

3. The Working Principle of Nanofiltration Technology

Nanofiltration is a pressure-driven membrane separation process between reverse osmosis and ultrafiltration, and the pore size of nanofiltration membranes ranges from a few nanometers or so. Most of the nanofiltration membranes are derived from reverse osmosis membranes, such as CA, CTA membranes, aromatic polyamide composite membranes, and sulfonated polyethersulfone membranes.

Therefore, nanofiltration, also known as low-pressure reverse osmosis, is an emerging field of membrane separation technology, whose separation performance is between reverse osmosis and ultrafiltration, allowing some inorganic salts and certain solvents to pass through the membrane, thus achieving separation.

Due to its excellent retention rate, it has a good removal rate of heavy metals and does not have membrane contamination problems. In addition, the operating cost of NF membrane is lower than that of reverse osmosis technology, and it has a good removal rate of organic small molecules, so it is widely used to treat industrial and chemical wastewater.

 

Figure 3: Working Principle of NEWater Nanofiltration System

4. NEWater Water Treatment Application in the Mining Industry

4.1 Acid mine water drainage

Mine drainage, process water, and stormwater associated with industrial activities are the main types of water generated in mining operations. The two main purposes of treating contaminated mine water are to neutralize acidity and to remove metals. Contaminated mine water is produced when rocks containing sulfides come in contact with water and oxygen.

Sulfide-containing rocks are exposed to water and oxygen, resulting in acidity and high concentrations of metals and sulfates in the water, so mine wastewater is typically acidic. The addition of lime, limestone, or caustic soda is required to raise the pH (chemical precipitation) throughout the water treatment process.

Figure 4: Limestone

NEWater uses a three-stage membrane process. Multiple ultrafiltration and reverse osmosis membrane systems are operated in series to provide up to 97% water recovery. Two CSIR processes, limestone/lime neutralization, and gypsum crystallization are combined for pretreatment, followed by wet sand filters to remove residual manganese. After this treatment step, the water was treated with an ultrafiltration (UF) membrane element to remove microorganisms and suspended solids.

Finally, reverse osmosis (RO) membranes are used for subsequent treatment. Brine highly supersaturated in gypsum salts (dissolved salts removed by RO membranes) is treated with lime to remove the supersaturation. The final cycle was performed three times to improve water recovery, increase solids removal and reduce brine volume.

 

Figure 5: Acid mine water drainage treatment process

The result is a clean water stream with high-quality standards that can be reused in other processes or safely discharged into the environment. Removing sulfates and other dissolved impurities from contaminated water to obtain high-quality produced water that used to be discharged to the environment is now reused in operational processes.

Depending on the desired final water quality, a number of techniques are used to remove dissolved minerals, such as reverse osmosis and other membrane filtration, performing ion exchange, electrodeionization, adsorption media, etc. Thus, the wastewater is fully utilized and provides the operator with a zero liquid discharge solution. From providing consistent quality RO feed water, to greatly reduced plant design size, improved performance, and reduced CAPEX.

 

Figure 6: Mine water treatment

4.2 Coal mine water treatment

With the continuous development of the social economy, the human demand for water resources is increasing. With the rapid development of the coal industry in recent years, a large amount of groundwater is discharged to the surface, and the available freshwater resources for humans are decreasing. How to effectively use the mine gushing water, reduce the surface wastewater discharge, and save the available freshwater, has become a pressing problem in the coal industry.

With its low energy consumption, low operating cost, reasonable structure, small footprint, high water utilization rate, and a high degree of automation, reverse osmosis technology will be more and more widely used in the coal industry.

 

Figure 7: Water treatment in the coal mining industry

In mine water treatment, the treated saline mine water is desalinated by reverse osmosis technology to meet the drinking water standard. Because of the special characteristics of the membrane, the reverse osmosis unit has very strict requirements for the water quality of the feed water. The feed water can have a large number of dissolved salts, but the requirements for colloid, residual chlorine, suspended matter, iron ions, and microbial content in the water cannot be too high.

Mine water quality is generally good, individual areas of hard water, if you want to reuse for drinking water, must be softened desalination treatment. As long as the raw water pretreatment, so that its water quality to achieve the reverse osmosis device feed water quality requirements, you can apply reverse osmosis technology to produce drinking water.

 

Figure 8: Mine water treatment process flow chart

The water quality of the feedwater entering the reverse osmosis unit after pretreatment system is controlled as follows: pH=6~9, p(free chlorine) <O.1 mg/L, turbidity <1.0NTU, SDI(15min)<5, p(Fe)≤0.1 mg.

The necessary anti-corrosion and anti-scaling treatment must be carried out before the reverse osmosis device, that is, pretreatment, which is an important guarantee for the long-term stable operation of the reverse osmosis system. NEWater coal mine water treatment pretreatment equipment selected multi-media filter and activated carbon filter, the material is stainless steel.

The multi-media filter can effectively remove a small amount of sediment and rust contained in the groundwater; activated carbon filter mainly uses activated carbon’s large specific surface area and pore space to adsorb organic matter in the water, while removing organic matter, it can also remove chlorine, lipids, colloidal silica and suspended matter in the water, so that the mine water is deeply treated into drinkable water.

 

Figure 9: NEWater Reverse Osmosis Plant Details

NEWater reverse osmosis units are also equipped with automatic backwash pumps or timed backwash devices. When the reverse osmosis unit runs for a period of time, or when the feed water quality changes, the surface of the reverse osmosis membrane may become scaled or clogged, or contaminated by microorganisms.

At this time, the feed water pressure and concentrated water pressure increase significantly, the pressure difference across the membrane increases, and the water output decreases. An automatic backwash pump or timed backwash device can immediately clean or sterilize the membrane, reduce the loss of membrane and project cost investment, and reduce unnecessary waste.

4.3 Coal mine water treatment

Gold mining and ore processing are economically important activities. However, they are associated with the production of highly polluting wastewater containing high concentrations of heavy metals and low pH values. Gold has been used in many different applications, from raw materials for jewelry manufacturing and currency reserves to more technical applications such as catalyst and nanoparticle production. On the other hand, the environmental hazards associated with gold mining and processing can range from the destruction of natural habitats to the discharge of highly polluting wastewater that can contaminate the environment.

 

Figure 10: Gold mine wastewater treatment

Wastewater from ore processing has a low pH and high concentrations of heavy and quasi-metals such as Cd, Cr, Hg, As, etc., as these elements are typically associated with valuable components in ores and concentrate. Wastewater from gold mining contains high concentrations of sulfate, calcium, and magnesium, and the main contaminants are divalent ions, which are more effectively treated with NF membranes than with RO membranes.

 

Figure 11: NF membrane vs RO membrane

As an effective secondary or tertiary wastewater treatment system, NF is widely used to purify water for industrial, agricultural and/or indirect reuse as drinking water due to its ease of operation, reliability, low energy consumption, and high efficiency, and can retain efficiency compatibility. a feed pH of 5.0 provides greater permeate flux and higher retention efficiency.

 

Figure12:NEWater Nanofiltration System Workflow Diagram

We conclude that the permeate flow rate shows a linear decrease as the permeate recovery increases. In addition, the conductivity increases significantly when the RR is higher than 40%. Therefore, an RR of 40% was selected as the ideal value for this process. NE Water provided a treatment system that operated under optimal conditions, and the cost input of the project provided a high-quality final treated effluent at a cost of approximately $0.81/m3.

5. NEWater Provides Sustainable and Complete Water Treatment Solutions for the Mining Industry

5.1 Solutions we can offer you.

  • Sulfate Removal.
  • Removal of heavy metals.
  • Desalination / Desalinization.
  • Zero Liquid Discharge (ZLD).
  • Wastewater reuse/recycling.

 

Figure 13: Application of NEWater water equipment

5.2 NEWater’s Advantages.

(1) Provide unique water and equipment needs providing engineered and customized solutions.

(2) Turnkey solutions, including design, engineering, manufacturing, and automation.

(3) Use of state-of-the-art water treatment technology for effective water and wastewater reuse.

(4) Team of professional engineers with an average of 15 years of experience to provide optimal online assistance and on-site service and support.

(5) Worldwide operations and assistance with all language capabilities to support local projects.

 

NEWater reverse osmosis membrane separation technology, as a new purification technology with environmentally friendly, no secondary pollution, high treatment efficiency, and good water output, is increasingly used in mining operations. This method is more economical and easy to use, has lower costs, and meets the needs of mining operations. If you have a need for this or related technical advice, just contact our engineers. We can provide you with professional and powerful technical support and equipment support.

 

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