Core sand for automobile engine casting and preparation method of core sand

The invention discloses a core sand for automobile engine casting and a preparation method of the core sand. The core sand is prepared from the following raw materials in parts by weight: 170-180 parts of forsterite sand, 40-55 parts of graphite sand, 35-40 parts of high-magnesium phosphate tailing slag, 40-60 parts of skarn, 25-30 parts of waste foam concrete, 40-50 parts of knar clay, 15-18 parts of coal powder, 16-20 parts of coconut coir, 14-16 parts of blast furnace gas ash, 8-12 parts of high-aluminum fine powder, 10-15 parts of calcium zirconate, 15-17 parts of hollow silica nanospheres, 2-3 parts of sodium silicate, 3-5 parts of aluminum silicate, 3-4 parts of ammonium alginate, 4-6 parts of hydroxyethyl cellulose, 4-7 parts of beta-cyclodextrin and a proper amount of water. The core sand disclosed by the invention is good in performance; in the casting process, the amount of gas evolution is small, the drying time is short, the gas permeability is good, and the wet tensile strength is high; meanwhile