First, the source, characteristics and harm of mine wastewater
(1) Source of mine wastewater
Mine wastewater mainly comes from mine production. According to the production process, it can be divided into mining operation wastewater and mineral processing wastewater; according to the pH value of wastewater, it can be divided into acidic wastewater and alkaline wastewater.
1. Mine acid wastewater. Most non-ferrous metal mines are symbiotic sulfur or sulfides, such as pyrite, brass ore. Under the combined action of oxidation, weathering, decomposition and water-gas-acid-mineral reaction in the natural world, sulfide minerals form acidic wastewater unique to mines. The degree of damage is related to the acid water production, pH value, metal ion species and valence state, and concentration. The pH value and heavy metal content of some mine wastewater are shown in Table 1.
Table 1 Table of pH and heavy metal content of some mine wastewater 
Mine acid waste water mainly comes from mine water, waste rock heap leaching filtrate, etc. Its environmental pollution can be attributed to acidic wastewater and heavy metal ions.
2. Mine alkaline wastewater. Mine alkaline wastewater is mainly produced in the beneficiation operation. When the ore is subjected to flotation and enrichment, in order to obtain the best separation effect, the pH of the slurry system needs to be adjusted. Generally, non-ferrous metal ore can obtain better floatability under alkaline conditions. For example, when the chalcopyrite pH is 10.5, the floatability is optimal, and the resulting wastewater is generally alkaline. Alkaline wastewater contains different contaminants depending on the chemicals added during the production process.
(II) Characteristics of mine wastewater
The main pollutants in mine wastewater include heavy metals, acids, organic pollutants, oil pollutants, cyanide, fluoride and soluble salts. Heavy metal pollution and acid pollution are the most common in wastewater pollution. The heavy metals in wastewater mainly include lead , zinc , nickel , copper, mercury , chromium , cadmium , cobalt , manganese , titanium , vanadium and antimony .
Characteristics of mine wastewater: large amount of wastewater, long water flow time; scattered drainage points, large changes in water quality and water with seasons and climate; rich in various metal ions such as Fe 2+ , Fe 3+ , Cu 2+ , Zn 2+ , Pb 2+, etc.; have a lower pH value, and the like.
(3) Harm of mine wastewater
The harmfulness of mine wastewater, including damage to the ecological environment and toxicity to organisms, mainly comes from acid pollution and heavy metal pollution. A large amount of acid waste water from mines is discharged into rivers and lakes, which changes the pH of water bodies, inhibits the growth of bacteria and microorganisms, affects the growth of aquatic organisms, and seriously causes the death of fish and shrimp, the growth and death of aquatic plants, and the long-term acidity of natural water bodies. Pollution will acidify the water and nearby soil, affecting the growth of crops and destroying the ecological environment. Mine wastewater contains heavy metal ions and other metal ions, which enter the environment through infiltration, seepage and runoff, and pollute the water. After precipitation, absorption, complexation, chelation and redox, it migrates and changes in the water body, ultimately affecting the health of the human body and the growth of aquatic organisms.
Second, the management of mine wastewater
(1) Wastewater treatment and resource management
1. Chemical precipitation method
The chemical precipitation method is to add a precipitant to the waste water to precipitate heavy metal ions into carbonates, hydroxides and sulfides, and the heavy metal ions are separated from the waste water in the form of aqueous metal oxides, hydroxides and sulfides. , a method of purifying wastewater. The chemical precipitation method has good adaptability to the treatment of heavy metal wastewater, so it is widely used in the treatment of heavy metal wastewater. Commonly used precipitants are lime, sodium hydroxide, sodium sulfide, and the like.
When heavy metal wastewater is treated by chemical precipitation, a large amount of heavy metal sludge is produced and needs to be disposed of or disposed of properly. For example, industrial wastewater containing 100 mg/L of Cu 2+ can produce sludge with a 10-fold heavy metal salt content. When lime is used as a precipitant, it is not suitable for treating wastewater with a large amount of wastewater and a low concentration of heavy metal ions.
2. Ion exchange method
The ion exchange method is a method in which the heavy metal ions are ion-exchanged with an ion exchange resin to reduce the concentration of heavy metals in the wastewater, thereby purifying the wastewater. The main functions of the ion exchange method are: 1 Removal of various harmful heavy metal ions to cope with increasingly stringent emission standards in the future. 2 Recovery of valuable metals in wastewater, such as gold, silver , copper, nickel, chromium, etc. 3 Improve the recycling rate of water and save the increasingly scarce water resources.
Wastewater resource management. Mine wastewater recycling includes wastewater reuse and heavy metal ion recovery. The main methods are sulfide precipitation, ion exchange, membrane separation, electrolysis, and metal replacement.
(1) Wastewater reuse
Waste water can be reused multiple times in a certain production process, as shown in Figure 1.
Figure 1 Mine wastewater reuse system
By directly recycling the wastewater or recycling it after treatment, it can maximize the use of wastewater, which can reduce the discharge of wastewater, reduce environmental pollution, reduce the replenishment of new water, save water resources, and solve the increasingly tight water supply problem. For example, a copper mine uses open-pit mine acid wastewater for sulfur removal, and the sulfur recovery rate is over 90%, which has obtained good economic and environmental benefits. The reverse osmosis process is used to treat the acid wastewater of a gold-copper mine, and the water recovery rate is up to 36.79%.
(2) Recycling of heavy metals
Heavy metals are non-renewable resources, and high levels of heavy metals in mine wastewater are necessary for the recovery of heavy metal ions in wastewater. 7%, the recovery rate of the sponge copper is 20. 53%, the recovery rate is 96.7%, after the iron-containing neutralization method and the lime-adjusted pH-iron-displacement-lime-precipitation method. Most of the copper in the wastewater is recovered in the form of sponge copper. The reverse osmosis process is used to treat the concentrate with sulfide precipitation to obtain copper slag containing 26% copper by mass. The copper recovery rate can reach 74%.
(2) Prevention of wastewater
In addition to the treatment and utilization of wastewater generated in the production process, it is also necessary to prevent the generation of wastewater and reduce the amount of mine wastewater generated from the source.
1. Excavate the drainage ditch and drain the drain. Drainage ditches are used in open pit mines and tailings ponds to intercept surface water and precipitation flowing to the stope and tailings reservoir area.
2, waterproof plugging. In order to prevent or reduce the precipitation of precipitation and surface water into the pit, backfilling and plugging with clay or cement is carried out for various crack channels on the surface near the mine, karst collapse and depressions that may seep.
3. The river is diverted. When the river flowing through the mining area has a serious impact on the mine water, it may be considered to divert the river.
Waterproof underground. 1 Rationally carry out the mining layout and adopt the correct mining method. The mining sequence and well layout should be started from the simple hydrogeological conditions. When mining in a strong aquifer or surface water, the filling method should be used as much as possible to avoid the use of large-span caving. 2 Leave the waterproof rock column to intercept the ground and various water sources underground. When the ore layer is directly below the surface water body and aquifer, and the water source cannot be drained; this method can be used when the local surface water body and strong aquifer are hydraulically connected to the ore layer through faults and fissures.
Acid wastewater prevention. 1 Seal the abandoned waste rock deposits (spray asphalt , soil cover, vegetation) to isolate the erosion of air and rain. For the waste rock accumulation area being used, it should be arranged reasonably, and the piled part (not used part) should be sealed as much as possible; for the site being used, the channel, drainage hole or layered spray asphalt can be built around it. And other inexpensive cover layers. In the arrangement of the waste rock site, as far as possible, combined with the division mining and restoration, to minimize the amount of waste rock exposed to the outside. 2 The pit is closed. The pit water flowing out of the waste tunnel usually accounts for a considerable part of the mine wastewater, and these water pollution and acidification conditions are particularly serious. For these waters flowing out of the tunnel, a method of sealing the tunnel and isolating the air may be adopted to prevent further increase of the degree of pollution or pollution of other water bodies.
(3) Daily management of wastewater
1. Daily monitoring of wastewater by enterprises
The enterprise conducts routine monitoring of the pollution factors in the wastewater according to the daily monitoring system and records it to determine whether the wastewater meets the requirements of the emission standards. When it is detected that the discharged wastewater quality does not meet the relevant emission standards, the information should be timely transmitted to the wastewater treatment system, and the discharged wastewater should be returned to the wastewater treatment system for reprocessing. In the production process, when the amount and concentration of wastewater are fluctuated, the frequency of raw water quality monitoring is increased to facilitate timely adjustment of the amount of chemicals added to ensure the quality of the effluent after wastewater treatment.
2. Daily monitoring of wastewater by government environmental protection departments
The Environmental Protection Agency conducts daily monitoring of wastewater to determine whether the environmental behavior of the company meets the requirements of laws and regulations. Enterprises should cooperate with and support the environmental protection department to conduct daily monitoring of wastewater, introduce the production process and raw and auxiliary materials used in the enterprise, the pollutants present in the wastewater and the daily concentration range. On the basis of understanding the relevant information of enterprise wastewater, the government departments conduct daily monitoring of wastewater and make legality evaluation of corporate environmental behavior.
The wastewater treatment process is a necessary process for the harmless treatment of wastewater before it enters the environment. The condition of the wastewater treatment process facility is related to the degree of wastewater water treatment, whether the wastewater can meet the requirements of the discharge standard, and even the safety of the wastewater treatment system. The daily management of wastewater treatment process facilities, including the facility's integrity rate, operation rate; the adaptability of wastewater treatment process and wastewater volume and wastewater quality; preparation and dosage of pharmaceuticals; and detection of process parameters. Timely discovery of problems in the process facilities, in order to take appropriate emergency procedures to prevent the waste water from being out of control.
Third, the conclusion
The water and soil pollution caused by heavy metals has seriously threatened China's ecological environment, food safety, people's health and sustainable agricultural development. In 2009, China's heavy metal pollution caused frequent incidents. The Ministry of Environmental Protection received 12 reports of heavy metal and metal-like pollution. The mining and selection of non-ferrous metal mines is considered to be one of the major industrial sources for discharging heavy metals.
For mine wastewater, from the aspects of wastewater prevention, wastewater resource utilization, and daily management of wastewater, strengthening the management of wastewater can reduce the amount of wastewater generated, reduce the discharge of wastewater and heavy metals, and eliminate the damage of mine wastewater to the ecological environment and the biological Poisoning of the body.
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