In-situ formation of CaAl-layered double hydroxides with attapulgite for synergistic remediation of soda saline-alkali soil

Novel amendment triggers in-situ CaAl-LDH formation, rapidly immobilizing soil alkalinity and carbonate. • Rapidly reduces soil pH by 2.7 units and carbonate by 83%, while cutting exchangeable Na⁺ by 76%. • Soil structure improves significantly, increasing macroaggregates 17-fold and organic matter stability by 33%. • Immediate planting is enabled, boosting pakchoi height 218% and fresh weight 70% in pots. Soda saline-alkali soils pose a severe threat to agricultural productivity due to high pH, elevated carbonate (CO 3 2 − ) concentration, and poor soil structure. However, achieving rapid alkalinity reduction and long-term stability of immobilized salts remains a significant challenge in soil remediation. This study developed a novel composite amendment comprising calcium sulfate (CaSO 4 ,), aluminum sulfate (Al 2 (SO 4 ) 3 ), and attapulgite clay (ATP) to induce the in-situ formation of CaAl-layered double hydroxides (CaAl-LDHs) for the efficient remediation of soda saline-alkali soils. Through a 150-day mineralization experiment, the amendment rapidly triggered the formation of crystalline CaAl-LDHs, confirmed by XRD, SEM, TEM, FTIR, and XPS analyses. This process effectively immobilized free CO 3 2− and hydroxyl (OH − ) into the LDHs interlayers, resulting in a significant reduction in soil pH from 10.6 to 7.9 and CO 3 2− concentration by 83%. The treatment also reduced exchangeable Na⁺ by 76% and decreased water-soluble Ca 2+ , Mg 2+ , Al 3+ , and Fe 3+ concentrations. Importantly, soil structure was markedly improved, with macroaggregates (> 1 mm) increasing by 17 folds, and soil organic matter (SOM) stability enhanced by 33% due to increased organo-mineral associations and Fe/Al oxide concentration. A pot experiment with pakchoi further validated the amendment’s practicality, which significantly improved seedling germination, increased plant height by 218%, and boosted fresh weight by 70%, while concurrently lowering post-harvest soil pH and salinity. This study presents a rapid, stable, and synergistic strategy for sustainable saline-alkali soil remediation based on in-situ LDHs mineralization, offering a promising solution for improving soil health and crop productivity. Download: Download high-res image (289KB) Download: Download full-size image