Evaluating Potentials of Coal-gangue-derived Building Materials Utilization in China: based on GCAM with Multi-dimensional Corrections
This study utilizes a multi-dimensional GCAM framework to reveal that China's coal gangue utilization in building materials is structurally capped at 100 Mt/yr, demonstrating that a province-differentiated, diversified strategy shifting toward power generation and mine backfill is necessary to overcome capacity limits and achieve greater environmental benefits than the current building-material-first approach.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Every year, China's coal mines produce a massive amount of rocky waste known as coal gangue. This material, which piles up to billions of tonnes over decades, is a byproduct of digging for energy. For a long time, the standard solution has been to crush this rock and turn it into bricks, cement, and other building materials. The logic seemed sound: construction projects consume enormous amounts of material, and using waste instead of digging up new resources helps both the environment and the economy. However, this approach assumes that the waste can easily reach the construction sites where it is needed, and that the rock itself is good enough for every job. As the country moves toward a greener future and produces less coal, the question of what to do with the mountains of existing waste has become urgent. The challenge is not just about finding a use for the rock, but figuring out which use makes sense where, and whether the old strategy of turning everything into bricks can actually work on a national scale.
A team of researchers from the Beijing University of Technology set out to test this long-held assumption using a sophisticated computer model designed to simulate how energy and materials move through an entire economy. They built a detailed framework that looked at the problem from four different angles at once: the quality of the rock, the distance it must travel, the full environmental cost of moving and processing it, and how technology improves over time. Instead of treating all coal gangue as the same, they sorted it into grades based on what it was actually made of. Some of it was rich in carbon and better suited for burning to make electricity; some was high in aluminum and could be processed to extract valuable metals; and the rest was ordinary rock suitable for construction. They also mapped out exactly where the waste was generated versus where the construction markets were located, calculating the cost of transporting heavy rock over hundreds of miles.
The results of this simulation revealed a hard limit that had been overlooked. The researchers found that the strategy of using coal gangue primarily for building materials is structurally capped at about 100 million tonnes per year. This limit is not caused by a lack of technology or a shortage of construction projects, but by geography and physics. The majority of the waste comes from inland provinces in the northwest, while the biggest construction markets are located along the distant eastern and southern coasts. The cost of transporting the heavy, low-value building materials over these long distances quickly exceeds the value of the materials themselves. In many cases, the transport cost would be three to five times higher than the price of the product, making the project economically impossible. Furthermore, the study showed that the construction sector is reaching a point of saturation, meaning it cannot absorb the massive volumes of waste being generated, especially when that waste has to compete with other industrial byproducts like fly ash and steel slag.
When the researchers adjusted their model to account for these spatial realities, they discovered that a huge portion of the waste could not be used for bricks or cement at all. In one scenario, this spatial mismatch reduced the potential for building material use by more than a third. However, the study did not end with a dead end. By redirecting the waste that could not be used for construction to other pathways based on its quality, the team found a way to recover a significant amount of the lost potential. The high-carbon rock was sent to power plants to generate electricity, and the high-aluminum rock was processed to extract metals. This shift allowed the system to utilize about 60 million tonnes of the waste that would otherwise have been impossible to use. When they ran the numbers again to see if this new allocation created further transport problems, they found that the system could recover even more, eventually reaching a cumulative redirection that exceeded the initial loss. This process showed that a diversified approach, using different methods for different types of rock in different places, is far more effective than trying to force all the waste into a single building material pathway.
The researchers also looked at the environmental impact of these different choices. They found that simply counting how much new material was replaced by the waste was not enough. When they included the emissions from transporting the heavy rock over long distances and the chemicals needed to process the aluminum-rich rock, the total climate benefit was significantly lower than previous estimates suggested. In fact, the net reduction in carbon dioxide was nearly 20 percent less than what would be calculated if one only looked at the displacement of virgin resources. This highlights that moving waste too far or using energy-intensive chemical processes can eat up much of the environmental gain. The study tested whether government policies, such as carbon taxes or subsidies, could force the system to use more waste. The results showed that while these financial tools could nudge the numbers slightly, they could not break the physical and geographic limits. Subsidies were found to be very expensive for the amount of climate benefit they provided, while carbon pricing offered only a small increase in usage.
Ultimately, the study concludes that the old strategy of prioritizing building materials for all coal gangue is no longer viable at a national level. The solution lies in a tailored approach where each province uses the waste that best fits its local conditions. In areas close to construction sites, making bricks remains a good option. In high-carbon regions, burning the rock for power is the logical choice. In areas with aluminum-rich rock, extraction is the path forward, provided that cleaner chemical methods are developed to reduce emissions. There is also a role for using the waste to fill in mined-out land and restore the landscape, a method that avoids long-distance transport entirely. The research suggests that trying to push more waste into the building material sector through policy alone is counterproductive. Instead, a flexible, multi-pathway system that respects the limits of geography and the specific qualities of the rock offers the most realistic and environmentally sound way to manage China's massive stockpile of coal gangue.
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