Effect of coal gangue-based porous materials on solute transport of reclamation soil in mining areas in the Yellow River Basin

In order to solve the problems of low porosity and poor fertility retention of using coal gangue alone as reclamation soil in mining areas, we investigated the influence of coal gangue-based porous materials on the transport of Cl⁻ and K⁺ in coal gangue powder, and elucidated the impact of porous materials on coal gangue pore distribution and solute transport. The convection-dispersion equation (CDE) was used to fit the breakthrough curves (BTCs) of K⁺ and Cl⁻, determining their transport parameters. By adding five different contents (0%, 10%, 20%, 25%, 30%) of porous materials to coal gangue powder, static batch tests and vertical soil column displacement tests were conducted to obtain the breakthrough curves of Cl⁻ as an inert non-adsorbing tracer and K⁺ as an adsorbing tracer. Static batch test results indicated that the addition of porous materials increased K⁺ distribution coefficient (K_d) by 19.40%-45.97%. Vertical soil column displacement tests revealed that incorporating 10%-25% porous materials could delay the transport rate of Cl⁻ by reducing saturated hydraulic conductivity (K_s) and delay the breakthrough time of K⁺ by reducing K_s and enhancing soil adsorption capacity. The application of 25% porous material could reduce the Cl⁻ concentration in the effluent by 0.34%-47.64% and K⁺ concentration by 11.86%-92.43%. The CDE model could well describe the breakthrough curves of Cl⁻ and K⁺. A composite mode with a 7.5∶2.5 (v/v) ratio of coal gangue powder to porous materials could effectively reduce solute transport.