The spent pickling solution, which comes from the pickling process of iron and steel, is indispensable in the manufacturing industry. Iron gets dissolved in the acid solution during the pickling process. When the concentration of metal ions in the acid solution accumulates to a certain value, it cannot to be used to wash iron and steel materials and becomes spent pickling solution that should be treated before discharge. At present, spent pickling solutions are treated via neutralization precipitation techniques in industries. This treatment method has a large discharge of wastewater, and the cost is high due to which it cannot meet the needs of green cycle in industry production. In this study, a new method, which is based on the formation of quaternary ammonium salt precipitate in a strong acid solution, is proposed to treat the spent pickling solution. The spent pickling solution was recycled and reused by precipitation separation of iron ion. The quaternary ammonium salt was recycled by dissolving the obtained precipitate in an alkali solution. The new ferric hydroxide precipitate formed and quaternary ammonium salt was returned to the solution. In the whole process, only a few amount of alkali was consumed. The removal rate of iron ion was up to 99.72%. Compared with the traditional neutralization precipitation method, the acid is not consumed and it can be reused; the alkali was consumed only for the precipitation of iron ions, not for the neutralization of the acid. The proposed method is an effective and economic method for the recovery of the spent pickling solution. It is expected to satisfy the requirements of green cycle and environmental protection in industry production.