Method of recovering waste slag in quinacridone production course to prepare 2,2'-disulfonic acid ethyl benzidine

The invention discloses a method of recovering waste slag in a quinacridone production course to prepare 2,2'-disulfonic acid ethyl benzidine. The method comprises the steps of (1) pretreatment of the waste slag, (2) chemical reduction, and (3) rearrangement, wherein the waste slag produced in an oxidation step of a quinacridone pigment production course is rinsed by an organic solvent A until the waste slag is white, and is filtered and dried; or the waste slag is added into the organic solvent A for backflow treatment for 2-3h, filtered, rinsed by the organic solvent A and dried in Step (1); the chemical reduction treatment is conducted on the treated waste slag, and reacting liquid containing hydrogenated azobenzene in Step (2) is obtained; and the reacting liquid is rearranged under an acidic condition and 2,2'-disulfonic acid ethyl benzidine is obtained in Step (3). The production method of a quinacridone pigment of a co-produced 2,2'-disulfonic acid ethyl benzidine intermediate can lower the production cost effectively, solves the difficulty of the three waste treatment effectively, and has a considerable economic benefit.