Enhanced Effect of Mining Dust Diffusion on Melting of the Adjacent Glacier: A Case Study in Xinjiang, China

Abstract

Given the typical disturbances in the aqueous environment in the alpine area because of mining activities in Northwest China, a case study highlighting the enhanced effect of mining dust diffusion on the melting of the adjacent glacier is presented here. Initially, a three-dimensional numerical model of the local airflow field was established by considering the effects of both mines and glaciers using the FLUENT software. Then, the diffusion path and size range of dust particles from the mines were simulated by feeding the mining dust parameters into the above numerical model. Finally, a physical simulation experiment was performed to evaluate the influence of mining dust coverage on the glaciers. The major conclusions of this study were as follows: (1) The local airflow field in the target alpine area is controlled by the ‘heat and cold double-island effects’ formed by the mine and the glacier, and the wind circulation always takes place in a clockwise direction between the mining pit on the left and the glacier on the right. (2) In a given airflow field, there is a spread of mining dust from the mine to the glacier along the upper airflow. The arrival rates of the dust are 16.9% and 13.3% in winter and summer, respectively, and the horizontal distance of dust diffusion is inversely proportional to its particle size. (3) For an ice sample with a sectional area of 225 cm² and a volume of 1000 mL, the melting rate increased by 4.5 mL/h with an increase of dust coverage by 10%. Furthermore, when compared with a control group without dust cover, the effect of a 28% increase in dust coverage is approximately equivalent to the effect of a 1 °C increase in temperature on the ablation speed of the glacier. The study results can provide a useful reference for the selection of mining sites and the control of mining dust diffusion in alpine regions with glaciers, thereby facilitating environmentally friendly mining in alpine regions.

1. Introduction

China has the most extensive distribution of glaciers within middle- and low-latitude areas worldwide. At the beginning of this century, there were 46,298 glaciers in China covering an area of approximately 5.94 × 10⁴ km², accounting for 7.1% of the total glacial area globally (excluding the Antarctic and Greenland ice sheets) [1]. These areas are primarily distributed in the alpine and high-altitude mountainous areas of Northwest China, such as Xinjiang, Tibet, Qinghai, and Gansu [2,3], as shown in Figure 1. These areas are located deep inland and away from the sea. The Himalayan Mountains, Tianshan Mountains, and other high mountains block the humid airflow, resulting in droughts and water shortages over a vast area of Northwest China and leading to a typical alpine climate and temperate continental climate [4]. As the humid and hot airflow is blocked by the mountains, it condenses in cold and high-altitude areas, leading to the formation of snow which often accumulates annually, forming a large number of mountain glaciers [5]. These mountain glaciers, also known as the ‘solid reservoirs’, are the major sources of surface water and groundwater replenishment in the arid regions of Northwest China, thereby supporting and nourishing vast areas downstream of the glaciers [6,7,8,9,10]. Glacier mass balance (accumulation and ablation) is crucial for the socio-economic model of sustainable development and the ecological environment in the above-mentioned regions [11,12,13,14,15,16].

The colder high-altitude areas in Northwest China are rich in mineral resources. The Altai Mountains, Tianshan Mountains, Kunlun Mountains, Qilian Mountains, and other orogenic belts are rich in gold, silver, copper, iron, and other metallic mineral resources. Therefore, they form important reserves of mineral resources in China [17,18]. The distribution of the mineral resources in Xinjiang is shown in Figure 2. It can be observed that most of the metal mineral resources in Xinjiang are distributed in the colder high-altitude areas, characterized by a large number of mountain glaciers.

Dust diffusion in the alpine mining areas has become an important factor affecting the environment of adjacent glaciers. In the past few years, China’s ‘One Belt One Road’ strategy has been continuously promoted, which has led to a profound transformation in the global mineral supply-and-demand pattern. The areas for mining mineral resources have also rapidly expanded from the middle- and low-mountain belts to the alpine belt, which is spanned by a large number of glaciers [19,20,21]. The dust particles produced during the mining in colder high-altitude areas are easily lifted and diffused by the wind under special climate conditions on the plateau, including dry and low-pressure conditions. After the dust particles settle on the adjacent glacier surfaces, there is a continuous transfer of solar radiation energy and their chemical energy to the glacier through a series of physical and chemical interactions, which results in accelerated glacier ablation and material imbalance [22,23,24,25]. To develop a theoretical framework for the green mining of solid mineral resources in the colder high-altitude areas in China, it is important to assess the relationship between the typical problems caused by a mine (dust diffusion) and the typical environmental impact on mountain glaciers (glacier ablation).

To evaluate this interrelationship between the diffusion of mining dust and the melting of glaciers, researchers have conducted several studies in recent years. The major findings of these studies are discussed below.

Dust diffusion: Tang et al. [26] simulated the influence of dust particle size on dust movement, escape rate, and escape time in a mine and found that the maximum escape time decreased with the increase of particle diameter, and the escape rate decreased rapidly with the increase of dust diameter; Li et al. [27] used a Fluent simulation software discrete particle model and multi-component transport model to study the diffusion rule of blasting dust, and the results showed that dust larger than 75 microns is difficult to spread, and dust smaller than 1 micron can be spread by thermals for about 30 m.

Glacier ablation: Zhang et al. [28] showed that mineral dust covering a glacier surface could not only reduce the reflectivity of the glacier surface to solar radiation but could also continuously transfer the absorbed radiant energy and its own chemical energy to the glacier body, accelerating the glacier’s meltwater speed. Miner et al. [29] measured Qomolangma’s ecosystem on site and sampled toxic chemicals and metals. It was found that heavy metals accumulated on the glacier’s surface under the action of dry and wet deposition, which reduced the surface albedo and led to glacier flood and glacier volume loss; Du et al. [30] studied the average deformation rate of glaciers on Karlik Mountain in eastern China by using short temporal baseline and short spatial baseline interferometry. The results showed that precipitation played a leading role in glacier deformation. In winter, precipitation and temperature were low, and glacier deformation was also low. Jiang et al. [31] used annual cumulative temperature (>0 °C) and summer frost height (FLH) to reflect the influence of climatic environment on a glacier’s ablation and recession. It was concluded that the rate of glacier recession in the past 30 years was 10 times that in the past 300 years.

Although there have been many important studies on mine dust diffusion and glacier ablation, only a few studies have considered the environmental impacts of mines on glaciers. This study combined numerical and physical simulations to understand the phenomenon of accelerated glacier ablation caused by dust diffusion in alpine and high-altitude mines based on existing research results.

2. Research Plan

2.1. Research Object

According to satellite images, the Beizhan iron mine and its adjacent glacier (43°14′ N, 85°33′ E) are located in the alpine region of the Tianshan Mountains, Xinjiang Uygur Autonomous Region, at an altitude of 3500 m, as shown in Figure 3a. The climate in this region is cold and variable, with a large diurnal temperature difference (20–30 °C) and very frequent rainfall and snowfall. There is a permanent mountain glacier to the south of the mine site; the closest distance from the edge of the glacier to the mine site is 1.4 km, and the farthest distance is 2.3 km. According to the local meteorological monitoring center, the area has a long winter (October to April of the following year) and a short summer (June to July), with an average local winter temperature of 20 °C at the mine site and −20 °C in the glacier area, and an average local summer temperature of 30 °C at the mine site and 0 °C in the glacier area. Open-pit mining has been adopted at this mine for the extraction of iron minerals, as shown in Figure 3b. Mining operations such as stripping, loading, and blasting inevitably release large amounts of dust and heat, as shown in Figure 3c. Coincidentally, the glacier, located 2 km from the Beizhan iron mine, is highly susceptible to the diffusion of mining dust and exhibits accelerated ablation, as shown in Figure 3d. Therefore, in this study, the Beizhan iron mine and its adjacent glacier are considered research objects to investigate the influence of mining dust diffusion on the ablation of the adjacent glacier in the alpine area.

2.2. Research Materials and Methods

2.2.1. Mineral Dust Sample

The dust used in this experiment was obtained in situ from the glacier surface in the study area, as shown in Figure 4a. A multi-point sampling method was used for outdoor operations on the glacier near the Beizhan iron mine in October 2021. A geological hammer and a clean shovel were used to obtain the required samples, each point sampling area had dimensions of 50 cm × 50 cm, taking from the surface glacier and its overlying snow layer, and the acquired samples were placed in a cryogenic sample box. After the original samples were delivered to the laboratory, the specimens were taken out and left to stand until the snow and ice melted into water; then, the excess water was poured out, and the specimens were dried in a dryer for 24 h. The dried specimens were then pretreated with a standard sieve to remove mineral particles larger than 0.16 mm in size, as these particles were derived from the disintegration of rocks near the glacier and were not dispersed by wind from the mine area. Sieving was performed using standard sieves with apertures of 0.12 mm, 0.09 mm, and 0.05 mm. Mineral dust particles smaller than 0.05 mm were too small and were excluded, considering the operability of the experiment and the impact on the final results. The particle size classification of the mineral dust is shown in

Table 1. Mineral dust particle size gradation.

Particle Size Range (mm)	0.05–0.09	0.09–0.12	0.12–0.16
Percentage of particle size (%)	50	40	10

. The measured density of the completed, screened dust was 2100 kg/m³. The results of the dust particle size screening and density measurements provided a reliable basis for setting dust parameters in numerical simulations.

2.2.2. Numerical Simulation

Considering the distance of 2 km between the glacier and the mine site, it is not practical to study the airflow field distribution over such a large area by field measurements, so FLUENT numerical simulation is used to study the dust dispersion process. As shown in Figure 5, satellite remote sensing was initially used to obtain the digital elevation model data of the study area, which were then input into the Global Mapper software to obtain the terrain contour lines. Next, the contour lines were imported into the Sketchup software to generate a three-dimensional (3D) model of the study area. Finally, the 3D model, thus obtained, was imported into the Mesh software for the mesh division. It is to be noted that the grid near the area of concern is dense and that the grid far away from the area of concern is sparse. This improved the calculation accuracy and reduced the calculation time. After the meshing was completed, the model was imported into the FLUENT simulation software for parameter setting.

2.2.3. Parameter Settings

Based on meteorological data from local meteorological monitoring centers in the study area and measurements of dust particle size and density, the simulation model was set up as follows.

Temperature setting: The temperature of glaciers and pits varies greatly throughout the year, which causes temperature differences to vary as well. This simulation explores the dust diffusion law in winter and summer. According to the meteorological data of the local meteorological monitoring center, the winter and summer temperature settings of glaciers and mines are shown in

Table 2. Temperature settings in winter and summer.

Area	Temperature in Winter/°C	Temperature in Summer/°C
Air Fluid	0	15
Ground	10	20
Glacier Surface	−20	0
Mine	20	30

:

Dust discrete phase setting: Dust samples in the Beizhan mine were collected and sieved. It was found that the particle size of the mine dust mostly ranged from 0.05 mm to 0.16 mm, and the measured dust density was 2100 kg/m³. The detailed settings of dust parameters are shown in

Table 3. Discrete phase settings.

The Injection Parameters	Parameter Settings
Dust Density (kg/m3)	2100
Minimum Diameter (m)	0.00005
Maximum Diameter (m)	0.00016
Injection Speed /(m/s)	X = 0; Y = 1; Z = 0

.

Boundary setting: The boundaries of the 3D model were set to different types to simulate the motion of the dust after joining the wind field, as shown in

Table 4. Boundary condition parameter settings after adding discrete phase.

Area	Type	Speed/(m/s)	Boundary Condition
Glacier Surface	Wall	—	Trap
Mine	Inlet	1	Escape
Ground	Wall	—	Reflect
Glacier–Mine Wall	Wall	—	Trap
Other Wall	Wall	—	Reflect

. The boundary of the glacier surface was set as a trap to accurately track the dust particles on the glacier surface. The wall along the direction of the glacier-mine pit was set as a trap, effectively avoiding bouncing back of the dust when it arrived at the boundary, further improving the accuracy of this simulation. Due to the extension of the glacier, the dust on the ground may be blown up again, so the walls on the ground and in other directions were set to reflect.

2.2.4. Physical Simulation

The physical simulations were conducted as follows.

Step 1: A drainage hole was placed at the center of the bottom of the mold. An iron rod was inserted into this center hole at the bottom, and the joint was then sealed. Following that, 1000 mL of water was poured into the mold, and the mold was frozen in a freeze–thaw machine, as shown in Figure 6a. It was considered that exploring the mechanism of accelerated glacier melting caused by dust cover is not closely related to the distribution of glacier topography. A sample of ice with a cross-sectional area of 225 cm² was used as a study object in the laboratory.

Step 2: After the ice in the mold was formed, the iron rod was pulled out to form meltwater channels. The dust was then arranged on the surfaces of the ice, as shown in Figure 6b,c. Dust collected from the glacier was scattered on the ice surface, and real-time photographs were taken of the different dust coverings on the ice surface. These photos were then imported into the ImageJ software for measuring the coverage, as shown in Figure 6d.

Step 3: Ice ablation tests were performed outdoors. Beakers were placed at the bottom of each melting tank to measure the amount of water resulting from the ice melting at different dust coverage rates. The temperature changes were also recorded during the tests, as shown in Figure 6e.

3. Results and Analysis

3.1. Local Wind Field in the Alpine Mining Area

3.1.1. Numerical Simulation Results

As shown in Figure 7, the wind direction near the mine pit in winter was vertically upwards with a wind speed of approximately 6 m/s. As the air continued to rise, the wind speed initially increased to 15 m/s and then decreased to 6 m/s. After rising to a certain height, the air began to blow toward the surrounding low-temperature areas. The wind direction above the glacier surface was vertically downwards with a wind speed of approximately 5 m/s. Then, the air near the ground continued to blow from the glacier toward the mine pit with a maximum wind speed of 15 m/s. The distribution of the wind currents in summer was similar to that in winter; however, the overall wind speed in the study area in summer was about one-third of that in winter. There was an obvious local circulation between the mine and the glacier both in winter as well as summer.

3.1.2. Theoretical Analysis of the Simulated Results

In winter, a large amount of heat released by stripping, loading, and blasting during the open-pit mining of iron ore can increase the surface temperature of the pit to approximately 20 °C, while the surface temperature of the glacier, which is not far from the iron ore mine, can drop to approximately −20 °C. In summer, the surface temperature at the mine can reach approximately 30 °C, while that of the glacier surface remains close to 0 °C. The significant temperature difference between the mine and the glacier leads to a change in the atmospheric pressure in the alpine mining area, which in turn leads to a local atmospheric circulation, resulting in the coexistence of a heat island effect and a cold island effect.

The air near the mine warms to produce an upward motion because it is affected by both heat and cold double-island effects. As the air continues to move upwards, the wind speed initially increases and then decreases. When the air rises to a certain height, it begins to move into the surrounding low-temperature area. At the same time, the glacier surface is relatively cold. Therefore, the air flows toward the glacier and sinks, causing the air at the glacier surface to become denser and blow toward the mine pit, where the air is less dense. Finally, given the significant temperature differences in both winter and summer, an obvious local circulation forms between the mine pit (the heat island) and the glacier (the cold island), as shown in Figure 8. It is important to note that the average wind speed of the local circulation formed in winter is approximately three times that of the one formed in summer due to the larger temperature difference between the mine and the glacier in winter compared to summer.

3.2. Dust Diffusion in the Alpine Mining Area

3.2.1. Numerical Simulation Results

Mining dust particles have small particle sizes and light weights; therefore, they diffuse outwards from the mine pit under the action of the airflow field above. The diffusion paths in summer and winter are shown in Figure 9. It can be observed that the dust particles reaching the glacier surface in winter are more numerous than those in summer. The diffusion of dust particles in a large area conforms to the local circulation patterns, while the dust particles in a small area are affected by the regional atmospheric circulation and appear to be in random motion.

As shown in Figure 10, the particle-tracking function of the FLUENT software can be applied to derive the position and particle size of the dust particles captured on the glacier surface. It can be observed that larger distances between the glacier and the mine correspond to a narrow particle size distribution of dust settling on the glacier surface. The proportion of the larger particles decreases with increasing distance, while the proportion of the smaller particles increases with increasing distance. More dust particles, especially larger ones, spread to the glacier surface in winter due to greater temperature differences and wind speeds than in summer. For example, the particles with a 0.16 mm diameter account for the largest proportion of dust particles at a distance of 1.4 km in winter, while the particles with a 0.16 mm diameter rarely reach the glacier’s surface in summer.

3.2.2. Theoretical Analysis of the Simulated Results

(1)

Horizontal force and velocity of dust

When a dust particle moves at a uniform speed, the force exerted on the surrounding fluid is called drag resistance [32]. Due to the viscous dusty fluid flow, surface pressure and shear stress, which correspond to the differential pressure and frictional shear stress, respectively, are asymmetrically distributed. The resultant force of the two forces is consistent with the direction of the flow. The Stokes resistance of dust particles in a fluid [33] is the basic characteristic governing the interactions between particles and a viscous fluid, as shown in Equation (1):

$${\mathrm{F}}_{\mathrm{D}}=\frac{\mathsf{\pi }}{8}{\mathrm{C}}_{\mathrm{d}}{\mathrm{d}}_{\mathrm{p}}^2{\mathsf{\rho }}_{\mathrm{p}}\left|{\mathrm{u}}_{\mathrm{f}}-{\mathrm{u}}_{\mathrm{p}}\right|\left({\mathrm{u}}_{\mathrm{f}}-{\mathrm{u}}_{\mathrm{p}}\right)$$

(1)

where ${\mathrm{u}}_{\mathrm{f}}$ is the velocity of fluid, m/s; ${\mathrm{u}}_{\mathrm{p}}$ is the velocity of dust particles, m/s; and ${\mathrm{C}}_{\mathrm{d}}$ is the resistance coefficient of dust particles.

Drag resistance caused by the airflow is the main driving force for the movement of dust particles, and the force of dust in the horizontal direction can be calculated using Equation (2):

$$\frac{\mathsf{\pi }}{6}{\mathrm{d}}_{\mathrm{p}}^3{\mathsf{\rho }}_{\mathrm{p}}\frac{{\mathrm{du}}_{\mathrm{px}}}{\mathrm{dt}}=\frac{\mathsf{\pi }}{8}{\mathrm{C}}_{\mathrm{d}}{\mathrm{d}}_{\mathrm{p}}^2{\mathsf{\rho }}_{\mathrm{g}}{\left({\mathrm{u}}_{\mathrm{g}}-{\mathrm{u}}_{\mathrm{px}}\right)}^2$$

(2)

where ${\mathrm{u}}_{\mathrm{g}}$ is the partial horizontal velocity of a fluid; ${\mathrm{u}}_{\mathrm{px}}$ is the partial velocity of dust in the horizontal direction, m/s; and ${\mathsf{\rho }}_{\mathrm{g}}$ is the air density, $\mathrm{kg}/{\mathrm{m}}^3$.

Equation (3) is obtained after the simplification of Equation (2).

$$\frac{{\mathrm{du}}_{\mathrm{px}}}{{\left({\mathrm{u}}_{\mathrm{g}}-{\mathrm{u}}_{\mathrm{px}}\right)}^2}=\frac{3{\mathsf{\rho }}_{\mathrm{g}}}{4{\mathrm{d}}_{\mathrm{p}}{\mathsf{\rho }}_{\mathrm{p}}}{\mathrm{C}}_{\mathrm{d}}\mathrm{dt}$$

(3)

When the particle size is constant, the antiderivative of both sides of Equation (3) can be obtained and is represented by Equation (4).

$${\mathrm{u}}_{\mathrm{px}}={\mathrm{u}}_{\mathrm{g}}-\frac{4{\mathrm{d}}_{\mathrm{p}}{\mathsf{\rho }}_{\mathrm{p}}{\mathrm{u}}_{\mathrm{g}}}{3{\mathsf{\rho }}_{\mathrm{g}}{\mathrm{u}}_{\mathrm{g}}{\mathrm{C}}_{\mathrm{d}}\mathrm{t}+4{\mathrm{d}}_{\mathrm{p}}{\mathsf{\rho }}_{\mathrm{p}}}$$

(4)

It is assumed that the density of the air is 1.29 $\mathrm{kg}/{\mathrm{m}}^3$, the density of dust is 2100 $\mathrm{kg}/{\mathrm{m}}^3$, and ${\mathrm{C}}_{\mathrm{d}}$ is 0.44 at constant airflow velocity. It can be observed from Equation (4) that the dust particle size is inversely proportional to the horizontal velocity. When the particle size is the same, the horizontal velocity of dust increases with the increase in air velocity.

(2)

Vertical force and velocity of dust

Dust particles are also affected by vertical gravity. At the same density, the larger the particle size, the greater the gravity. To simplify calculations, dust particles are regarded as spheres [34].

The gravity of the dust particles is given by Equation (5).

$$\mathrm{G}=\frac{\mathsf{\pi }}{6}{\mathrm{d}}_{\mathrm{p}}^3{\mathsf{\rho }}_{\mathrm{p}}\mathrm{g}$$

(5)

where ${\mathrm{d}}_{\mathrm{p}}$ is the dust diameter, mm; and ${\mathsf{\rho }}_{\mathrm{p}}$ is the dust density, $\mathrm{kg}/{\mathrm{m}}^3$.

The buoyancy of the dust particles is given by Equation (6) [35].

$${\mathrm{F}}_{\mathrm{a}}=\frac{\mathsf{\pi }}{6}{\mathrm{d}}_{\mathrm{p}}^3{\mathsf{\rho }}_{\mathrm{g}}\mathrm{g}$$

(6)

where ${\mathsf{\rho }}_{\mathrm{g}}$ is the air density, $\mathrm{kg}/{\mathrm{m}}^3$.

The resistance of the dust particles in the vertical direction is given by Equation (7) [36].

$${\mathrm{F}}_{\mathrm{f}}=\frac{\mathsf{\pi }}{8}{\mathrm{C}}_{\mathrm{d}}{\mathrm{d}}_{\mathrm{p}}^2{\mathsf{\rho }}_{\mathrm{g}}{\mathrm{u}}_{\mathrm{py}}^2$$

(7)

where ${\mathrm{u}}_{\mathrm{py}}$ is the partial velocity of dust in the vertical direction.

As the density of air is much less than that of the dust particles, the buoyancy of dust particles in the air is ignored. When the dust particles settle in the static air, the change in the velocity can lead to a change in the resistance of the dust particles. For the dust particles moving with the horizontal airflow, their equation for vertical motion is given by Equation (8).

$$\frac{\mathsf{\pi }}{6}{\mathrm{d}}_{\mathrm{p}}^3{\mathsf{\rho }}_{\mathrm{p}}\frac{{\mathrm{du}}_{\mathrm{py}}}{\mathrm{dt}}=\frac{\mathsf{\pi }}{6}{\mathrm{d}}_{\mathrm{p}}^3{\mathsf{\rho }}_{\mathrm{p}}\mathrm{g}-\frac{\mathsf{\pi }}{8}{\mathrm{C}}_{\mathrm{d}}{\mathrm{d}}_{\mathrm{p}}^2{\mathsf{\rho }}_{\mathrm{g}}{\mathrm{u}}_{\mathrm{py}}^2$$

(8)

When the force is balanced in the vertical direction, dust particles will settle uniformly in the vertical direction, and the settling velocity at this time is known as the final settling velocity (${\mathrm{u}}_{\mathrm{py}}$). In Equation (8), when the resultant acceleration is 0, the final settling velocity can be expressed as Equation (9).

$${\mathrm{u}}_{\mathrm{py}}=\sqrt{\frac{4{\mathsf{\rho }}_{\mathrm{p}}{\mathrm{gd}}_{\mathrm{p}}}{3{\mathsf{\rho }}_{\mathrm{g}}{\mathrm{C}}_{\mathrm{d}}}}$$

(9)

From Equation (9), it can be observed that the particle size of the dust particles is directly proportional to the final settling velocity of the dust, which also explains the phenomenon that larger-sized dust particles in the air settle more quickly on the glacier surface, as shown in Figure 11.

3.3. Grading of the Dust Particles on the Glacier Surface

The particle size distribution for all of the 3550 emitted dust particles settled on the glacier surface is shown in Figure 12. It can be observed that a total of 600 particles were captured on the glacier surface in winter, indicating that 16.9% of such particles can be diffused to the glacier surface by the local circulation resulting from the heat and cold double-island effects. However, a total of 471 particles were captured on the glacier surface in summer, indicating that 13.3% of the particles could be diffused to the glacier surface by local circulation.

Lastly, the distance between the glacier and the mine pit is approximately 1.5 km, and the particles with smaller sizes can diffuse more easily to the glacier surface, while the particles with larger sizes settle prematurely and cannot reach the glacier surface. The dust particles with sizes greater than 0.16 mm would not likely affect the glacier at a distance of 2 km, while the particles with sizes ranging from 0.1 to 0.05 mm would likely settle on the glacier surface. Although only 13.3–16.9% of the particles can reach the glacier surface, the dust spreads daily from the mine pit to the glacier surface because of continuous mining activities. Therefore, the continuous accumulation of dust on the glacier surface can severely affect the ecological environment of the glacier.

3.4. Effect of Mining Dust on Accelerated Glacier Ablation

3.4.1. Physical Experiment Results

Numerical simulation by FLUENT has proved that dust is able to diffuse from the mine to the glacier surface through the heat and cold double-island effects, so it is of great significance for the laboratory to explore the mechanism of dust cover accelerating glacier ablation. The experiments were performed outdoors to replicate the actual solar radiation conditions. During the experiments, the temperature changes were recorded every 15 min, and the average temperature during each experiment was calculated. An ice specimen without mining dust cover was placed as the control for evaluating the influence of the temperature on the results, as shown in Figure 13.

(1)

Influence of dust coverage on the ice-melting rate

As shown on the left side of Figure 13, the rate at which glaciers melt increases with the dust cover and the temperature. Generally, the ice-melting rates at different average temperatures demonstrated the same trend, i.e., the average slopes of the plots at different temperatures were approximately the same. The slopes were 0.38, 0.49, 0.52, 0.42, and 0.42 when the average temperatures were 16 °C, 17 °C, 19 °C, 20 °C, and 21 °C, respectively. The average slope of the five groups was 0.45. Therefore, it can be concluded that the factor determining the effect of increasing dust coverage on the ice-melting rate was 0.45. This indicated that every 10% increase in the dust coverage increased the melting rate by 4.5 mL/h for the sample ice with a total volume of 1000 mL and a sectional area of 225 cm².

(2)

Influence of temperature on the ice-melting rate

As shown on the right side of Figure 13, the rate of melting of ice without dust coverage increased linearly with an increase in the temperature, with an average slope of 12.6. This indicated that, for each 1 °C increase in the temperature, the ice-melting rate increased by an average of 12.6 mL/h for the sample ice with a total volume of 1000 mL and a sectional area of 225 cm². Therefore, the effect of a 28% increase in dust coverage is approximately equivalent to the effect of a 1 °C rise in the temperature on the glacier melting rate. For example, the change from point A to point B is caused by the increase in the dust coverage from 0 to 27% when the temperature is constant at 19 °C, while the change from point C to point D is caused by the rise in temperature from 19 °C to 20 °C under the condition of no dust coverage. As shown in Figure 12, it can be observed that the increase in the ice-melting rate is almost the same under the two conditions.

3.4.2. Theoretical Analysis of the Experimental Results

The excessive absorption of solar radiation by the glaciers was the major cause of the glacier material imbalance. Glaciers located near mines in cold regions are easily affected by the diffusion of mining dust. As shown in Figure 14, the mineral dust is dark-colored, light-absorbing particulate matter. At the same solar radiation intensity, this mining dust can absorb more solar radiation energy than ice and snow in their original condition (i.e., without dust) [37,38,39].

X-ray diffraction analysis was performed on the dust collected from the glacier and the dust collected from the mine, and it was found that the mineral composition of both dusts was very similar, and they both contained minerals such as epidote, quartz, kaolinite, diopside, and albite, as shown in Figure 15. Combined with the results of the FLUENT numerical simulations, this is further evidence that the dust on the glacier surface comes from the Beizhan iron mine. These minerals contain metallic elements such as iron, magnesium, aluminum, and sodium, and all of these elements have low specific heat capacities and high thermal conductivities, with a greater capacity than snow and ice to absorb and release energy [40]. In addition, the minerals of the dust particles chemically react with oxygen and meltwater on the glacier surface, thereby releasing heat continuously and further accelerating the glacier melting [41]. Thus, the dust cover accelerates the glacier melting and affects the glacier mass balance, as shown in Figure 16.

4. Conclusions

(1)

The combined effects of the mine (heat island) and glacier (cold island) lead to local atmospheric circulation in alpine areas.

The significant difference in the temperature between a mine and a glacier produces ‘heat and cold double-island’ effects in an alpine area. These effects lead to the formation of a local atmospheric circulation from the glacier to the mine near the surface and from the mine to the glacier in the upper air layer. The average wind speed of such a local circulation in winter is approximately three times greater than that in summer.

(2)

The local atmospheric circulation results in the spread of mining dust to the glacier surface.

The results indicated that 16.9% and 13.3% of the dust particles from the mine can be diffused to the glacier surface in winter and summer, respectively. As the distance between the glacier and the mine grows, the size of the dust particles diffused to the glacier surface changes from variable to smaller, i.e., the proportion of particles with larger sizes gradually decreases, while the proportion of particles with smaller sizes gradually increases.

(3)

Mining dust coverage leads to accelerated ablation of the adjacent glacier.

As more mine dust covered the upper surface of an ice specimen in this study, the ice melted faster. For an experimental ice cube with a side length of 15 cm and its upper surface not covered by the mining dust, the melting volume increased by 12.6 mL/h when the temperature increased by 1 °C. When the upper surface of the ice was covered with the mining dust, the melting rate significantly increased, and the melting volume increased by 4.5 mL/h with a 10% increase in the mine dust coverage. Therefore, the effect of a 28% increase in dust coverage is approximately equivalent to the effect of a 1 °C increase in temperature on the rate of glacier ablation.