Environmental stability characteristics of the immobilization effect of sulfhydryl grafted palygorskite on soil-available cadmium

The stability of heavy metal immobilization amendments represents a critical factor in evaluating remediation effectiveness. To comprehensively investigate the environmental stability of a novel amendment, sulfhydryl grafted palygorskite (SGP), a series of experiments encompassing chemical exposure and sorption, incubation with simulated acid rain and thermal variations, and field validation were conducted. SGP demonstrated chemical stability across diverse media, including ambient atmosphere, aqueous solutions (H₂O, CuSO₄, and H₂O₂), and heterogeneous soil matrices, as evidenced by a maximum relative standard deviation of changes in the free sulfhydryl content and a sorption capacity below 5%. Simulated acid rain leaching resulted in a maximum cumulative leaching efficiency of less than 1%, revealing no significant impact on Cd²⁺ release from SGP-amended soil and confirming its resistance to acid rain. Thermal variance tests (-20 °C to 60 °C) demonstrated temperature-insensitive performance characteristics, with fluctuations below 10% observed in soil-available Cd regulation and Cd uptake by pakchoi. Field demonstrations in acidic and alkaline soils validated the universal stability of SGP over two years, with soil-available Cd reductions of 47.2-76.4% and grain Cd content reductions of 38.1-78.3% across seasonal variations. This study qualitatively and quantitatively assessed the stability characteristics of the SGP immobilization effect, providing theoretical support for developing new immobilization amendments and the safe utilization of contaminated farmland.