In the height of summer, waves of heat roll across the heartland of the Hulunbuir Grassland. Inside the microalgae cultivation greenhouse at the Baorixile Open-Pit Mine of China Shenhua, dense green algal liquid flows slowly through the pipes, while photobioreactors capture carbon dioxide day and night. At China's first High-Altitude, Cold-Region Mine Microalgae Biological Carbon Sequestration and Ecological Restoration Demonstration Project, the large-scale cultivation volume of microalgae has surpassed 50 tonnes, accelerating the development of a low-carbon circular model characterized by "algae-based desert control, algae-based carbon sequestration, and multi-purpose water use". This self-developed innovation has filled a domestic technological gap, providing a replicable and scalable new solution for the green development of mines in the arid, high-altitude, cold regions of Northern China.
"Microalgae cultivation requires suitable light, temperature, and an adequate CO? supply. However, in our high-altitude cold region, the biggest challenges are the extreme winter coldness and short daylight hours", recalled Wang Shi, a project technician, reflecting on the difficulties faced during the initial stages. Starting from scratch with no precedents to follow, frontline technicians and doctoral researchers collaborated closely, working day and night between the laboratory and the open-pit spoil ground.
To screen for dominant native algal strains adapted to the extreme climate of Northern Xinjiang, the team conducted hundreds of low-temperature and high-light stress acclimation tests, repeatedly adjusted pit water ratios, and continuously optimized the formulation of biological soil remediation agents. Researchers conducted field surveys and sampling on sandy slopes, meticulously calculating spraying dosages and soil improvement cycles. Breaking conventional industry practices, they ultimately formulated an innovative restoration approach of "in-situ improvement of sandy substrate without the need for soil covering", fundamentally overturning the traditional method of soil covering for greening in high-altitude cold mining areas.
Through relentless trial and error, the team achieved key technological breakthroughs. The project uses local resources, taking mine pit water and industrial CO? emissions as dual raw materials for microalgae cultivation, thereby establishing a closed-loop industrial chain. The microalgae efficiently capture carbon through photosynthesis, while simultaneously degrading nitrogen ,phosphorus and solidifying heavy metals in the water, thus purifying pit water. The treated clean water is returned to the ecological experimental area for irrigation, and the sandy soil sprayed with the algal remediation agent rapidly forms a stable biological algal crust, enabling in-situ soil improvement and fertilization of barren sandy land.
Data is the best measure of performance. The project has established a 2,100-square-meter core experimental area on sandy spoil ground, treated a cumulative 3,700 tonnes of pit water, achieved biological carbon sequestration of 1,000 tonnes, and secured multiple core invention patents in water retention improvement and microbial fertilizers. Field monitoring shows that in the experimental area, soil fertility increased by 16%, water retention capacity increased by 20%, soil microbial population increased by 35%, plant growth-promoting ability increased by 30%, and the overall ecological restoration cost reduced by over 30%; vegetation coverage increased from bare ground levels to 54%, and the highest total soil organic carbon increase reached 613.2%. The once barren gravel spoil ground is now covered with lush green grass, showcasing a harmonious integration of the industrial mining area with the grassland ecosystem.
"In the past, managing spoil grounds required either hauling in topsoil or large-scale tree planting, which involved heavy investment and slow results. With the microalgae restoration technology, we can grow forage grass on sandy land without the need for external soil transport, while simultaneously sequestering carbon and purifying wastewater. If this technology is promoted widely, it could transform ecological restoration practices in mining areas across China", said Gao Yunlong, the project leader, surveying the greened slopes. He explained that this technological system transcends a singular greening approach, integrates carbon emission reduction, water recycling, and soil regeneration, and opens a new avenue for ecological management in high-altitude cold and arid mining areas nationwide. Recognized for its outstanding technological innovation, the project won the Second Prize for Scientific and Technological Progress at the 3rd International Annual Conference on China Green Mine, serving as a benchmark case for the low-carbon ecological transformation of the coal industry.
