Magnetic powder for efficiently degrading Cr (VI) wastewater and preparation method thereof

The preparation method comprises the following steps: fully mixing polyvinyl alcohol (PVA) powder and Fe2O3 powder of which the particle size is greater than or equal to 400 meshes according to a mass ratio of 1/3, adding water according to a ratio, soaking, heating, and preserving heat to prepare colloid; heating, preserving heat and cooling the colloid in a drying oven, and crushing the colloid into powder 1 # with the particle size of 100-250 microns by using a blade type stirrer; 100g of the powder 1 # is mixed with 50g-100g of an aqueous solution of FeCl2 and NiCl, the concentration of the aqueous solution of FeCl2 and NiCl is greater than or equal to 10g/L, and the molar ratio of Fe to Ni in the solution is 2/1; heating and drying in a drying oven to prepare powder 2 #; the powder 2 # is heated to 360-400 DEG C in a vacuum-N2 atmosphere furnace, heat preservation is conducted, N2 is introduced in the heating process for a reaction, and black powder 3 # with the particle size being 100-250 microns is gen