Laboratory spectral induced polarization monitoring of phosphogypsum leachate-carbonate interactions in karst aquifer materials.

Reactive groundwater systems often involve strongly coupled hydrological, geochemical, and electrochemical processes, complicating the interpretation of hydrogeophysical observations. Karst carbonate aquifers are particularly vulnerable to contamination by acidic, sulfate-and phosphate-rich leachates derived from phosphogypsum landfills. In this study, laboratory column experiments were conducted to investigate spectral induced polarization (SIP) responses during phosphogypsum leachate‑carbonate interactions under static, dissolution-dominated, and dynamic breakthrough conditions representative of karst environments. SIP measurements were performed synchronously with geochemical monitoring of pH, fluid electrical conductivity, and major ion concentrations. Multivariate statistical analyses were applied to explore relationships between SIP parameters and evolving geochemical conditions and to aid interpretation of overlapping electrochemical behavior. Results indicate that the conductivity reflects pore-fluid ionic strength but exhibits weak linear correlations with individual ions due to the superposition of electrolytic conduction and reaction-induced pore structure modifications. In contrast, polarization signals and their frequency dependence are primarily sensitive to interface associated with carbonate dissolution and the formation or removal of secondary sulfate and phosphate-bearing mineral phases. Dual-frequency polarization features suggest the coexistence and temporal evolution of matrix-scale interfacial polarization and smaller-scale polarization associated with secondary mineral particles or surface coatings. Principal component analysis separates the dominant variability associated with bulk geochemical conditions from variations in SIP parameters related to interfacial polarization, while independent component analysis identifies statistically independent patterns that are consistent with dissolution- and precipitation-influenced electrochemical responses under heterogeneous experimental conditions. These results indicate that SIP, when interpreted in a multivariate manner and constrained by geochemical and mineralogical evidence, can provide process-sensitive information beyond bulk conductivity and help distinguish hydrologically and geochemically different reaction regimes in laboratory carbonate systems.