Composite remediation agent for groundwater remediation and preparation method and application thereof

The invention provides a composite remediation agent for groundwater remediation, which is prepared by the following steps: firing gasified slag at a high temperature of 900-1250 DEG C, expanding, cooling, pulverizing, and screening to obtain slag particles; airing and crushing the sludge, carrying out high-temperature treatment at 650-700 DEG C under the protection of nitrogen, and crushing to obtain carbonized sludge particles; under the protection of nitrogen, stirring a FeSO solution, polyvinylpyrrolidone and a NaBH4 solution, carrying out suction filtration, and washing to obtain modified nano zero-valent iron; and adsorbing the oxygen release agent on the surface of the carbonized sludge, mixing with slag, Portland cement, a filler, modified nano zero-valent iron and a pH buffer agent, pressing into flat sheets, calcining, cooling, and crushing to obtain the composite repairing agent. The composite remediation agent for groundwater remediation provided by the invention integrates multiple treatment meth