The low mountainous area of Helan Mountain has sparse vegetation, severe surface erosion and a fragile ecological environment. In this study, we analyzed surface soils at five different altitudes in the low mountainous area of Helan Mountain to determine their basic physical and chemical properties. the activities of four common soil enzymes and their correlations. The results showed that with increasing altitude, the soil moisture content and total porosity showed upward trends, while bulk density, organic matter and available phosphorus showed downward trends, and TC, TN and alkali-hydrolyzed nitrogen showed trends that were first decreasing and then increasing. As the altitude increased, the carbon-nitrogen ratio increased and showed a trend of first increasing and then decreasing, while soil urease and alkaline phosphatase activities showed the opposite trends that were first decreasing and then increasing, and sucrase and catalase showed steadily increasing trends. Urease activity and phosphatase activity were significantly positively correlated with soil total nitrogen. Previous studies had also found differences in various physical and chemical property indexes and enzyme activities of surface soil at different altitudes, and that the physical and chemical properties of soil and enzyme activities affect each other.

Suitability evaluation of land reclamation is an important prerequisite for determining the reuse of damaged land in mining areas. To make full use of land resources in mining areas and repair damaged land, this study takes four dumps in the eastern part of the arid desert area of northwest China as the research object, and uses the platform and slope as the evaluation unit to consider ecological land as the direction. The indicators affecting the reuse of dumps are selected as five aspects: Terrain conditions, soil conditions, location conditions, irrigation and drainage facilities, and environmental risks. The suitability evaluation index system of land reclamation based on niche fitness is constructed, and the obstacle degree is introduced to diagnose the obstacle factor. The results showed that (1) the niche fitness index of each unit in the study area was between 0.339 and 0.751, indicating that the suitability grade of reclamation for ecological land is typically low. The suitability index of the same dump platform (0.511-0.751) was generally higher than that of the slope (0.339-0.628). (2) Each factor responded differently to the obstacle degree of different units. The slope, gravel content, and drainage conditions are the key elements influencing the slope. The major obstacles for the platform are soil and drainage conditions. In soil conditions, the gravel content and bulk density of the soil are limiting factors of platform. The method developed here can be effectively used to evaluate the suitability of mining areas for reclamation. The results provide a scientific basis for the reclamation and ecological reconstruction of open-pit coal mine dumps in arid desert areas of northwest China.

Many problems exist in the ecological restoration of the waste dumps in open-pit mining areas, such as unclear site types of vegetation construction, unsuitable vegetation measures and site conditions, and poor vegetation growth. To resolve these problems, the site type classification and evaluation of the waste dump in the mining area is a key link to speed up its vegetation reconstruction. In this study, the waste dump in Wuhai treated mining area was selected as the test site. A combination of microtopography, slope direction, mulch thickness, soil hardness, soil texture, total phosphorus content, total potassium content, organic matter content, number of vegetation species, and life forms qualitative and quantitative factors were selected. After logarithmic quantification and standardized site factor correlation analysis, principal component analysis, cluster analysis and factor analysis, the site types of the waste dump were classified and evaluated. The results showed that the micro topography, slope direction and mulch thickness were the dominant factors, and they were the main factors influencing vegetation restoration in the study area. According to the combinations of these dominant factors, the waste dump in Wuhai Mining Area was divided into four site type groups and 14 site types. The site quality evaluation of the 14 site types indicated that topographic factors and vegetation factors are the main factors influencing the site quality of the waste dump, and the site quality grades were divided into four relative scores of excellent (comprehensive score greater than 7), good (comprehensive score between 6 and 7), medium (comprehensive score between 5 and 6) and poor (comprehensive score less than 5). Among these grades, 50% of the site types had site quality scores of "medium" or "poor", so the overall site quality of the waste dump in Wuhai Mining Area was below the medium level. On this basis, appropriate vegetation allocation suggestions are put forward in order to provide theoretical support for the ecological restoration in an arid open-pit mining area.

In order to clarify the ecological restoration direction, this study investigated the limiting factors of the ecological restoration of the dump of Rujigou Open-pit Coal Mine in the Helan Mountain Nature Reserve from the aspects of climate, topography, and soil physicochemical properties. The main results are as follows: (1) In terms of climate, the main limiting factors in the study area were low precipitation (<200 mm) with uneven annual distribution, high evaporation (2000 mm), low temperature, less effective accumulated temperature, and large number of gale days (≥150 days). (2) The topographic limiting factors were steep slope (30°-36°) and long slope length (10-44 m). (3) In terms of soil, the main limiting factors were high contents of sand (73.40%±2.18%) and clay (13.21%±1.37%), low porosity (30.89%±0.83%), and low contents of total nitrogen (0.67±0.05 g kg^?1), hydrolytic nitrogen (14.23±0.48 mg kg^?1) and available phosphorus (2.81±0.44 mg kg^?1). The limiting factors of the ecological restoration of the study area mainly included drought and water shortage, less effective accumulated temperature, large number of days of strong wind, steep slope, long slope length, and soil depletion. In view of the above limiting factors, countermeasures such as slope foot support, slope level arrest and consolidation, slope cover, plant measures, and muck improvement can be considered. This study provides a scientific basis and theoretical support for the selection of appropriate ecological restoration measures and improvement of restoration effectiveness for open-pit mine dumps in arid areas such as the Helan Mountains.

While promoting economic and social development of China, open-pit coal mining will also cause irreversible harm to the surrounding environment due to disturbing the topsoil. Therefore, ecological restoration measures are urgently required. Vegetation cover is an important part of mine ecological restoration work. Suitable soil structure and nutrient conditions are the basis of normal plant growth and development. In this study, the slag, sand, humic acid, diammonium phosphate (DAP) and urea were selected as the improved materials to adjust the structure and fertility of the slag and improve the slag into a suitable vegetative substrate for plant growth. From among various configurations of the vegetative substrate, the most suitable substrate for plant growth was filtered by comparing the physical and chemical properties and their effects on Alfalfa growth under different treatments. The results showed that the application of fertilizers could increase the nutrient content of the vegetative substrate and increase the pH, but the growth of Alfalfa was not optimal under the high fertilization treatment. The addition of sand could mitigate the structural problems of slag, and sand also showed a certain degree of regulation on fertility. Moreover, the addition of appropriate amounts of humic acid can enhance slag maturation and stabilize the chemical properties of the vegetative substrate. According to the results, the most optimal slag-sand-humic acid ratio for the vegetative substrate of the dump site of the Dafeng Open-pit Coal Mine is 18:1:1. The findings are expected to offer a reference for the improvement method of slag in this area, which alleviates the shortage of soil resources. It provides support for ecological environmental protection in soil source area, and also offers a new idea for the resource utilization of slag in the ecological restoration.

Coal gangue and fly ash are major industrial solid wastes containing some nutrients associated with organic or mineral matter. Vegetation restoration depends on high-quality soil in mining sites. Exploring the effects of wood vinegar (WV) irrigation and fly ash addition on the variation in chemical properties of the coal gangue substrate can provide a theoretical basis and data support for the reconstruction of mine soils and resource utilization of mine solid wastes. The indoor soil incubation experiment was conducted by adding fly ash at rates of 0, 10%, 20% and 50% to a coal gangue substrate mixed with coal gangue and raw soil. We analyzed the nutrients and salinity of the mixture of coal gangue substrate and fly ash (CGSFA) after irrigating distilled water (DW) and WV. The results showed that the addition of fly ash decreased the pH of the CGSFA mixture under DW irrigation, and WV irrigation increased the pH of the CGSFA mixture compared with DW irrigation. The addition of fly ash could increase the contents of dissolved organic carbon (DOC), available phosphorus (AP) and available potassium (AK) and decrease the contents of total organic carbon (TOC) and total nitrogen (TN) of the coal gangue substrate. Compared with DW irrigation, WV irrigation increased the contents of TOC, DOC, active organic carbon (AOC) and AP of the CGSFA mixture by 19.3%, 931.1%, 228.1% and 15.6% and decreased the contents of TN and AK by 10.6% and 35.1%, respectively. In addition, the addition of fly ash increased the contents of K⁺, Ca²⁺ and SO₄^2- and decreased the Na⁺ content in the coal gangue substrate. The irrigation of WV increased the contents of Mg²⁺, HCO₃^-, Cl^- and SO₄^2- of the CGSFA mixture and reduced the contents of K⁺ and Na⁺. Overall, fly ash addition and WV irrigation can improve the nutrients and salinity of the mixture of the coal gangue substrate. Considering the accumulation of HCO₃^-, Cl^- and SO₄^2-, it is recommended to choose 10% to 20% fly ash addition to coal gangue substrate and irrigation with WV for the reconstruction of mine soils.

In order to study the counterpoint configuration about the types of mining sites and ecological restoration technologies, open-pit coal mine dumps that had been ecologically restored, since many years, in the grassland mining area in western Inner Mongolia, were selected. A comprehensive evaluation of slope protection effect, vegetation restoration effect, soil improvement effect and engineering technology cost was carried out in order to classify the types of sites for open-pit coal mine dumps and to determine their counterpoint ecological restoration technology, so as to provide theoretical guidance and technical support for ecological restoration of the grassland mining area in western Inner Mongolia. The research results are as follows: (1) Soil thickness, slope gradient and slope aspect are the dominant factors affecting the site conditions of the dump site. Base on this, the dump site of the open-pit coal mine in the grassland mining area of western Inner Mongolia was divided into 9 types of sites. (2) For half-shade and half-sunny to thick soil gentle slope, we primarily recommend plant grid slope protection + planting + sowing + sprinkler irrigation, and the second recommendation is hexagonal brick slope protection + mortar masonry ditch + sowing + sprinkler irrigation; for half-shade and half-sunny to medium-thick soil gentle slope, we primarily recommend masonry skeleton slope protection + mortar masonry ditch + sowing + sprinkler irrigation, and the second recommendation is sowing + vegetation blanket coverage + sprinkler irrigation; for half-shade and half-sunny to thin soil gentle slope, it is recommended to use gravel capping + mortar masonry ditch. For sunny thick soil gentle slope, we primarily recommend eco bag blocking + planting + sowing + vegetation blanket coverage + sprinkler irrigation, and the second recommendation is eco bag blocking + sowing + grass curtain coverage grass curtain coverage + sprinkler irrigation; for sunny thick soil steep slope, it is recommended to use plant grid slope protection + mortar masonry retaining wall + sowing + sprinkler irrigation. For shade thick soil gentle slope, we primarily recommend eco bag blocking + planting + sowing + vegetation blanket coverage + sprinkler irrigation is preferred, and the second recommendation is planting bag stacking + mortar masonry retaining wall + sprinkler irrigation; for shade medium-thick soil gentle slope, it is recommended to use eco bag blocking + corrugated pipe drainage + sowing + vegetation blanket coverage + sprinkler irrigation; for the shade medium-thick soil steep slope, we primarily recommend eco bag blocking +sowing + grass curtain coverage + sprinkler irrigation, and the second recommendation is eco bag blocking + corrugated pipe drainage + sowing + vegetation blanket coverage + sprinkler irrigation. For thick soil platform, use of planting + sowing + sprinkler irrigation is recommended. The research results provide a scientific basis for selection of ecological restoration technologies in the grassland coal mining area in western Inner Mongolia. At the same time, with respect to the semi-arid grassland mining area with relatively fragile habitats, this research be of great significance to improve the greening benefits of the mining area and for improving the mining area and surrounding ecological environment.