Experimental study on patterns and mechanisms of water quality degradation in water-rich sand formations induced by different types of chemical grouts.

Chemical grouts are widely used in coal mining for water control and rock reinforcement, but their long-term leaching behavior and groundwater impacts are insufficiently studied, with existing hydrogeochemical methods rarely applied to engineered grouts. This study evaluates the groundwater environmental risks of chemical grouting and focuses on four typical mining grouts (urea-formaldehyde with oxalic/phosphoric acid curing agents, acrylate, epoxy resin, polyurethane) to characterize their leaching behavior, identify contaminant release processes, quantify environmental risks, and clarify release mechanisms. Laboratory leaching column experiments were conducted using a constant-flow system with silt-fine sand from the Mu Us Desert and in-situ groundwater; leachate parameters were tested periodically and analyzed via a framework integrating PCA, EWQI, and IBE. Contaminant release generally exhibits three key characteristics: initial reactive component dissolution, polymer hydrolytic degradation, and pH-driven transformation. UF-based grouts (OU, PU) form methylene-bridged networks (initial pH 4-5), with OU (999 ppm) having a lower initial TDS than PU (1505 ppm) and their acidic curing agents altering carbonate equilibrium. AS forms a gel network, with TDS release decreasing by 43% after 18 days (sulfate-dominated pollution). ER (with a hydrophobic layer) and PJ exhibit high cross-linking stability and low contaminant release. IBE assists in pollution identification, PCA explains approximately 90% of the total variation in water chemistry parameters, and EWQI classifies environmental risks as PU > OU > AS > ER/PJ, with water quality showing a gradual trend toward background conditions. This study clarifies leaching patterns and mechanisms, demonstrates the applicability of hydrogeochemical methods, thereby guiding optimal grout selection (e.g., low-leaching ER and PJ) and sustainable mining practices.