Method for extracting and separating salt alkali from saline alkali soil and soil improvement

A method for extracting and separating salt alkali from saline alkali soil and soil improvement, comprising the following steps:

• (1) excavating a foundation pit on a saline alkali land, building a square convex edge, setting a cylindrical partition around inner side, adding a nitric acid solution or phosphoric acid solution, and obtaining a saline alkali pool;
• (2) setting a trench around the saline alkali pool, wherein a bottom of the trench is lower than a plane of the saline alkali pool;
• and/or, setting a cylinder in a center of the saline alkali pool;
• (3) expanding a raw vermiculite to obtain an expanded vermiculite precursor, adding a catalyst and a light absorbing material, mixing evenly, and then performing a catalysis to obtain an evaporating material;
• (4) placing a trench side partition and a trench bottom partition with holes at bottom on both sides of the trench, then laying a plastic wrapping material in the trench side partition or the trench bottom partition with holes at bottom, and laying the vermiculite or the evaporating material evenly on the plastic wrapping material;
• and/or, adding the vermiculite or the evaporating material into the cylinder;
• making the saline alkali soil absorb heat, evaporate and precipitate the salt alkali under the sunlight, and enriching the salt alkali on the vermiculite or the evaporating material to obtain a vermiculite or evaporating material saline alkali mixture;
• (5) dissolving, separating and washing the vermiculite or evaporating material saline alkali mixture to obtain a saline alkali solution and the vermiculite or evaporating material for recycling;
• (6) returning the vermiculite or evaporating material to the saline alkali pool and repeating step (4) and step (5) more than three times, enriching saline alkali ions in the saline alkali soil, collecting them together for standby to realize a basically complete separation and extraction of the salt alkali in the saline alkali soil;
• (7) adding an alkali solution and an intercalation agent into the repeatedly recovered saline alkali solution for reaction to obtain an intercalated Mg—Al hydrotalcite;
• recrystallizing the intercalated Mg—Al hydrotalcite to obtain a layered intercalated hydrotalcite functional material MgAl-LDHs;
• and
• (8) modifying, crushing and sieving the expanded vermiculite to obtain a fine-grained vermiculite, then adding and returning the layered intercalated hydrotalcite functional material MgAl-LDHs and an organic matter to the saline alkali pool to comprehensively improve the saline alkali soil and achieve the control of the saline alkali land.