Method for preparing magnesium sulphate heptahydrate by laterite-nickel ore acid leaching nickel immersing waste water

The invention relates to a method for preparing magnesium sulphate heptahydrate by laterite-nickel ore acid leaching nickel immersing waste water and belongs to the technical fields of waste utilization and environmental science. The method provided by the invention comprises the following steps of: adding magnesite into a laterite-nickel ore acid leaching waste solution and introducing the air, adjusting pH value to be 6.0-6.5 to remove iron and aluminium with enriched magnesium, then adjusting pH value to be 8.0-8.5 with lime milk to remove impurities such as nickel, lead, chromium and the like, so as to realize purification on nickel waste water, and finally carrying out concentration, fractional crystallization and vacuum drying to obtain a magnesium sulphate heptahydrate product with the purity more than 99%. According to the method provided by the invention, magnesium ion concentration in a solution is improved by virtue of a double salt reaction between magnesite powder and nickel immersing waste water, and separation of ions easy to hydrolyze such as aluminium ions and iron ions is achieved, so that originality is achieved; and primary magnesium enrichment purification and then treatment with lime are carried out, and deep purification is achieved, so that quality of a magnesium sulphate product is guaranteed.