In the heart of Jiangsu Province’s coalfields, a team led by Zhimin Xu of the China University of Mining and Technology has cracked open a new pathway for managing one of the mining industry’s most persistent headaches: high-salinity mine water. Xu and his colleagues at the School of Resources and Geosciences have not just proposed a solution—they’ve engineered a system to reinject millions of cubic meters of this often-wastewater back underground, safely and strategically, over decades. Their findings, published in *Meitian dizhi yu kantan* (which translates to *Coal Geology and Exploration*), are set to ripple across North China-type coalfields, where water management has long been a costly and risky business.
The scale of the challenge is sobering. In many coal mines, millions of cubic meters of water—often laced with salts and minerals—are pumped out annually. Treating it to meet discharge standards is expensive, and even when treated, much of it is simply released rather than reused. But Xu’s team saw something others missed: an untapped opportunity to store this water deep underground, not just as waste disposal, but as a strategic resource management tool.
“Traditionally, we’ve treated mine water as a liability,” Xu explains. “But with the right hydrogeological conditions and reinjection strategy, it can become part of a sustainable cycle—reducing environmental strain while supporting operational continuity.”
The research zeroed in on Coal Mine A in Jiangsu, where the team used the Analytic Hierarchy Process (AHP) to evaluate potential underground storage zones. After analyzing storage capacity, water flow dynamics, structural integrity, and water quality compatibility, they identified the Ordovician Majiagou limestone formation as the optimal target aquifer. This 400-million-year-old rock layer, buried deep beneath the mine, offered the right porosity and permeability to absorb and store large volumes of saline water without risking leakage or contamination of overlying freshwater aquifers.
But identifying the right aquifer was only the first step. The real innovation came in designing the reinjection strategy. Xu’s team proposed a hybrid approach: a mix of underground and surface reinjection boreholes. Underground boreholes were arranged in distributed clusters with low flow rates and small diameters—ideal for gradual, low-pressure injection. Surface wells, by contrast, were centralized and designed for higher flow rates using larger-diameter pipes. Three schemes were modeled: one using only underground boreholes (400 m³/h capacity), another using only surface wells (600 m³/h), and a hybrid system combining both (600 m³/h).
Over a 30-year simulation, each scheme raised groundwater levels—but not equally. The hybrid approach delivered the best balance: a 26-meter rise in groundwater pressure, enough to store water efficiently without triggering instability. Cross-checking with empirical equations confirmed it as the safest and most scalable option.
Yet reinjection isn’t risk-free. The team scrutinized four potential failure modes: water breaking through coal seam floors, migrating along faults or collapse columns, lateral recharge from buried rock outcrops, and casing failure in boreholes. Their simulations showed that reinjection increased the risk of water inrush through coal floors by only 2.2–8.2%, keeping the pressure well below the critical threshold of 0.06 MPa/m—low enough to maintain safe mining conditions.
Faults and collapse columns posed a more localized threat. For the F16 fault and a major collapse column, the team found that increasing the column’s thickness by just 7 meters would prevent dangerous water movement—a relatively simple engineering fix.
Perhaps most critically, they evaluated borehole stability under 5 MPa of water pressure. Using COMSOL simulations and theoretical models, they found that boreholes with a 75 mm diameter could safely handle reinjection without casing collapse or uncontrolled inflow—even under high pressure.
The practical implications are profound. For energy operators in North China’s coalfields, where water management can account for up to 15% of operational costs, this technology offers a dual win: reducing treatment expenses and turning a waste stream into a managed resource. In the Juye mining area, already a proving ground for the method, early applications have shown promise in stabilizing water tables and lowering surface discharge volumes.
“This isn’t just about compliance,” Xu notes. “It’s about transforming mine water from a regulatory burden into part of a circular water system—one that supports both environmental goals and operational resilience.”
As climate pressures and water scarcity intensify, technologies like deep reinjection could redefine how the mining sector views its water footprint. For industries facing similar challenges—from shale gas to geothermal—Xu’s work offers a blueprint: rigorous hydrogeological modeling, integrated reinjection design, and proactive safety assessment. The result? A qui