To resolve the contradiction between coal and water resources and protect the ecological environment of the Yellow River Basin, in recent years, CCTEG Xi'an Research Institute has built the first provincial and ministerial research platform focusing on mine water and ecological issues in the Yellow River Basin-Shaanxi Mining Area (Coal Mine) Ecological Environment Protection and Restoration School-Enterprise Joint Research Center; it has tackled key issues step by step from the aspects of mechanism, technology and process, materials and equipment, and explored an integrated technical system for "treatment, protection and use" of mine water, fundamentally realizing the full life cycle management of mine water, including water conservation and control at the source, process monitoring and supervision, and terminal purification and utilization, thus achieving "zero emission" of mine water.
For a long time, the main method of groundwater control in China's open-pit coal mines has been forced drainage, which has caused great damage to surface water and groundwater resources. Protecting water resources in mining areas and reducing the amount of drainage in mines are thorny issues faced by open-pit coal mines in the process of achieving green mining.
In response to this, CCTEG Xi'an Research Institute has developed a "key technology system for curtain water interception in open-pit coal mines" based on the perennial water replenishment conditions of river wetlands outside the boundaries of open-pit coal mines and their impact on the safe mining of open-pit coal mines and the regional hydrological environment. By overcoming the difficult problems of deep vertical concealed and close-fitting laying and connection of anti-seepage membranes, and stable troughing of ultra-deep loose strata, a narrow and long artificial impermeable zone of a certain depth is built between the surface or groundwater body and the mine pit , so that surface water and groundwater are protected in situ, surface runoff and ecological water levels are well maintained, and mining with no or little water gushing is achieved in the mine pit, thus achieving the dual benefits of water conservation and green resource development.
This technology has been applied in the open-pit coal mine in Dayan Mining Area. There are perennial rivers on the surface of the area, and the vegetation is mainly grass. The ecological environment has weak anti-interference ability. The formation of open-pit mines will cause surface water and loose layer water to infiltrate the mines, and the surrounding water level will drop significantly. After the water-cutting curtain is formed, the groundwater level in the area of about 20 square kilometers outside the curtain wall will rise to the ecological water level, solving the problem of water difficulties for local herdsmen. The vegetation diversity outside the water-cutting curtain has increased by more than 15%. In addition, the reduction in the amount of drainage in the mine further reduces the risk of slope sliding, and the slope stability coefficient has increased to more than 1.2.
The density of suspended matter in mine water is generally only 50% of that of cement sand on the surface, and it is extremely difficult to settle naturally. In response to this, CCTEG Xi'an Research Institute uses a coagulation sedimentation process to add mixed flocculants to the mine water to make the suspended matter particles condense into flocs and settle. At the same time, gravity, magnetism, centrifugal force and other methods are added on the basis of coagulation sedimentation to accelerate sedimentation.
On this basis, CCTEG Xi'an Research Institute has also developed an inorganic membrane short-process mine water treatment system. The suspended solids in the filtered mine water can be reduced to less than 1 mg/L, saving up to 80% of the floor space. The treated mine water can be used in dust reduction, flushing, firefighting and other scenes with relatively low requirements for water quality.
The high total dissolved solids in mine water restrict the higher value utilization of mine water. To this end, CCTEG Xi'an Research Institute uses a deep defluorination system coupled with a desalination membrane filtration system. High-efficiency defluorination materials can accurately remove fluoride, and reverse osmosis or nanofiltration membrane materials can pass through salt substances in mine water, so that the deeply treated mine water meets the TDS water quality detection standard requirements and can be adjusted according to the demand scenario. The treated mine water can be used in circulating cooling, irrigation, breeding, landscaping, ecological supplementation and other scenes with high requirements for water resource quality.
CCTEG Xi'an Research Institute has also developed mine water quality classification treatment technology and processes based on different water quality characteristics and resource utilization needs. It monitors and predicts mine water runoff processes in all scenarios and in all time domains, accurately controls mine water quality and quantity, and efficiently purify mine water with low consumption, optimize the deployment of clean mine water according to quality and user, and achieve efficient utilization of mine water.
In response to problems such as water shortage and fragile ecological environment in the western mining areas, CCTEG Xi'an Research Institute has developed an ecologically oriented mine water allocation and utilization technology system. Based on the ecological service functions of the mining area, it determines the ecological water demand of the mining area and regards mine ecological restoration as a prioritize water users and ensure their ecological water needs through ecologically oriented water resource allocation.
In order to alleviate the ecological degradation caused by the decline of ecological water level, CCTEG Xi'an Research Institute developed the mine water ecological recharge technology and demonstrated it in the Yimin mining area. There is a thick loose layer in the shallow part of the area, and the shallow surface layer is an important ecological in the conservation layer, affected by surrounding coal mining, the water level in the loose layer dropped significantly and the ecological function was reduced. After recharge, the groundwater level in the demonstration area turned from falling to rising, and the water level increased by nearly 2 meters, achieving a stable rise in the groundwater level in the mining area; To solve the problem of insufficient water supply during the ecological restoration process, CCTEG Xi'an Research Institute developed mine water ecological reuse technology. The technical results were demonstrated in the Heishan Mining Area, where is in a cold and arid area and is an open-pit mine that lacks water and fertilizer. In the huge dumpsite formed by mining, vegetation cannot grow naturally. The combination of soil reconstruction and bacterial fertilizer ensures the reconstructed soil moisture content and the water demand of vegetation in cold and arid areas, and accelerates the ecological restoration process of the mining area.
At the same time, CCTEG Xi'an Research Institute has developed an off-site storage technology based on the seasonal characteristics of mine water utilization. The abundant mine water in winter is stored in the water storage space. When the water demand is high in summer, the mine water stored in the water storage space is transferred out for ecological use, thereby increasing the mine water utilization efficiency to 95%. This technical system was demonstrated in the Baorixile mining area. The area is cold in winter, and mine water can no longer be used for ecological irrigation. The excess mine water cannot be absorbed. In summer, mine water has many uses and is high demand. The mine water generated in winter is transferred and stored through multiple ways, which not only makes full use of mine water, but also improves the ecological environment of the mining area.
