Calcium carbide slag can be used to prepare bleaching solution. An aqueous solution containing calcium dihydroxide is provided, which is washed twice or more to remove stones and other impurities to prepare an aqueous solution containing calcium dihydroxide. Calcium carbide slag can be used to prepare bleaching solution, which can save lime, but is not conducive to stability. Therefore, attention should be paid to the following: 2CA (OH)2 + 2CL2 + CACL2 + 2H2O in the production of industrial calcium carbide. Gypsum can be produced by reaction of calcium carbide dregs with waste sulfuric acid. In addition, can also be used to build roads, and potassium rhyolite extraction potassium.