Mining Wastewater Treatment Industry


1. Background of mine wastewater

According to YuXinHuan's industry analysis: Mining activities generate a large amount of wastewater, which is complex in composition and fluctuates greatly in water quality and quantity, containing pollutants such as heavy metals, suspended solids, and mineral processing agents. 

These wastewater sources cause damage to aquatic ecosystems and affect the survival of aquatic organisms; Polluting soil, reducing soil fertility, affecting crop growth, and threatening human health through the food chain; It also changes the acidity and alkalinity of the surrounding water environment, accelerates the dissolution and migration of heavy metals, expands the scope of pollution, and may contaminate downstream drinking water sources, posing a threat to residents' drinking water safety. Therefore, the treatment of mining wastewater and environmental protection are crucial.

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2. Source of mine wastewater


① Mining operation process: underground mining drainage forms mineral containing wastewater, and sulfide reactions cause acidity; The rainwater runoff from open-pit mining increases the concentration of heavy metals and suspended solids in the ore, while blasting operations intensify leaching, both of which produce highly polluted wastewater.

② Mineral beneficiation process: During ore processing, crushing and grinding, water spraying for dust reduction and cooling produces wastewater containing fine particles and dissolved minerals; Flotation dosing discharges complex wastewater containing reagents and heavy metals; Magnetic separation and reselection of water transport can cause impurity pollution, especially in the production of highly suspended wastewater from clay minerals. Each process generates mine wastewater with different characteristics.

③ Ore storage and tailings pond drainage: Ore piles are leached by rainwater to form wastewater containing heavy metals and other components. The wastewater from tailings ponds comes from pore water seepage, rainwater leaching, and internal chemical reactions. If left untreated, it will cause serious pollution to the surrounding soil, water bodies, and ecology.


3. Main components of mine wastewater

Mine wastewater contains heavy metal ions, suspended solids, acidic and alkaline substances, and residual mineral processing agents, which are toxic and affect the ecology. The accumulation of heavy metals poses a threat to human health, suspended solids reduce water transparency, acidic and alkaline substances alter water PH, and chemical residues increase wastewater complexity, all of which require proper treatment to reduce pollution.


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4. Main treatment processes for mine wastewater

Neutralization and sedimentation method: 

Wastewater is added to a neutralization tank with alkali and stirred to adjust the pH to 7-9 to promote heavy metal precipitation. 

① Add Polyaluminum chloride(PAC) as coagulant, which can effectively stabilize the particles in the wastewater and promote the aggregation and precipitation of particles through charge neutralization and bridging.

② Add Polyacrylamide(PAM) as a flocculant, which further enhances the formation and settling of flocs and improves the removal of suspended solids, colloids and some heavy metals.

③ After sedimentation, the supernatant is treated and discharged to meet the standards, while the sediments are treated through a sludge treatment system for eventual burial or heavy metal recovery


Sulfide precipitation method: 

The wastewater is mixed with sulfide precipitant in the reaction tank, and then separated in the sedimentation tank after the reaction. Subsequent treatment of supernatant and treatment of sediment and sludge. It is necessary to strictly control the dosage of precipitant to prevent secondary pollution.

In order to further improve the quality of the effluent, the supernatant can be coagulated-flocculated after precipitation.

Again, the use of Polyaluminum chloride as the coagulant and Polyacrylamideas the flocculant effectively removes residual suspended matter, colloids and heavy metal ions that may not have been fully precipitated. It ensures the stability of effluent water quality and provides guarantee for subsequent treatment or discharge.


Coagulation flocculation method: 

The coagulation flocculation process stabilizes wastewater particles by adding coagulants, aggregates flocs by adding coagulants, and removes suspended solids, some colloids, and heavy metals. The case shows that the combination of polyaluminum chloride and Polyacrylamidecan achieve a suspended solids removal rate of over 90%, improve the effluent quality, and facilitate subsequent deep treatment.



Adsorption method: 

Adsorbents (such as activated carbon) adsorb pollutants from mining wastewater, remove organic flotation agents and heavy metal ions. The case shows that the activated carbon adsorption column can treat wastewater with a removal rate of over 80% for organic chemicals and an improved removal rate for heavy metals, effectively reducing the toxicity of wastewater.

To further improve the treatment efficiency, by adding Polyaluminum chloride and Polyacrylamide, pollutants that may remain in the adsorption process can be removed to ensure stable effluent water quality.


Biological treatment method: 

Microbial treatment of mine wastewater, pH adjustment by acidophilic bacteria, biological adsorption, precipitation and transformation of heavy metals. Eosinophilic bacteria treat acidic wastewater, increase pH, achieve a heavy metal removal rate of 70% -80%, and improve water quality.


5. Case study of coal mine washing wastewater treatment

Problem: 

During a business trip to Yunlian County in Yibin to debug the Lubanshan coal mine in southern Sichuan, the coal washing wastewater has the characteristics of high suspended solids content (mainly coal powder), high turbidity, and large fluctuations in water quality and quantity. In addition, the wastewater also contains a small amount of heavy metal ions and residual flotation agents.

The processing procedure is as follows:

Firstly, the coal washing wastewater is introduced into the regulating tank for the adjustment and balance of water quality and quantity, in order to ensure the stability of the subsequent treatment process.

Then, the wastewater enters the reaction tank and polyaluminum chloride (PAC) is added first. The dosage is adjusted between 30-50mg/L according to the water quality of the wastewater. PAC rapidly hydrolyzes in water to form a large amount of aluminum hydroxy complexes. After adding PAC, stir rapidly (at a speed of about 100-150r/min) for 1-2 minutes to fully mix the agent with the wastewater, followed by medium speed stirring (at a speed of about 40-60r/min) for 10-15 minutes to promote the growth and collision of small flocs.

Next, Polyacrylamide(PAM) is added as a coagulant aid, with a typical dosage of 0.5-1mg/L. After adding PAM, stir slowly (at a speed of about 20-30r/min) for 10-20 minutes to allow the flocculation reaction to fully proceed.

The wastewater after flocculation reaction enters the sedimentation tank for sedimentation and separation, with a sedimentation time of about 2-3 hours. The treated supernatant has clear water quality, and the suspended solids concentration has decreased from the initial 1000-2000mg/L to below 50mg/L. The turbidity has significantly decreased, meeting the standards for circulating water in coal washing plants, and can be reused in coal washing processes.


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Effect: 

The combination of polyaluminum chloride and Polyacrylamidein the treatment of coal mine washing wastewater achieves the recycling of water resources and greatly reduces the use of fresh water. The coal slurry produced by sedimentation is dehydrated through a filter press, and the dehydrated coal slurry can be sold or further processed as low calorific value fuel, reducing solid waste emissions and creating certain economic benefits.‌

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