Enhanced improvement of soda saline-alkali soil by in-situ formation of super-stable mineralization structure based on CaFe layered double hydroxide and its large-scale application

In-situ super-stable mineralization technology with mineralizers (CaSO₄, Fe₂(SO₄)₃) and attapulgite (ATP) clay were applied to improve soda saline-alkali soil. The addition of mineralizers and the existence of OH and CO₃^2- in soil resulted in the formation of CaFe-layered double hydroxide (CaFe-LDH) with super-stable mineralization structure (K_sp = 1.512 × 10^-61), which was confirmed by the characterization of physicochemical properties and density functional theory (DFT) calculation. The fixation of OH^- and CO₃^2- during the formation process of CaFe-LDH led to the transformation of the existing forms of OH^- and CO₃^2- in soil from free to stable state, resulting in the permanent decrease of soil pH and CO₃^2- concentration. The effect of ATP clay on the decrease of soluble Na ions in soil through electrostatic attraction and cation exchange was also indicated. Furthermore, mineralizers (1.2 t/ha CaSO₄ and 0.75 t/ha Fe₂(SO₄)₃) and ATP clay (1.2 t/ha) were applied to 1.33 ha soda saline-alkali land, and Rumex patientia L. was seeded meanwhile for the identification of improved performance. After five months of improvement, the physical and chemical properties of soil were improved that pH, electrical conductivity (EC), the concentration of CO₃^2- and soluble Na ions, and soil bulk density decreased significantly. In addition, the emergence rate of Rumex patientia L. increased from 0% to 98.3%. All above indicated that in-situ super-stable mineralization technology with the properties of high efficiency, long-term and cost-effective (234.88 $/ha) displays excellent potential in the improvement of soda saline-alkali soil.