Method for preparing flocculating agent

The invention discloses a method for preparing a flocculating agent. The method comprises the following steps of (a) collecting aged rust-oil removing agents; (b) adding ferric oxide powder or waste iron rust in the aged rust-oil removing agents, reacting for 1-2 hours, and then filtering; (c) adding iron chips to filter liquor obtained from the step (b), reacting for 1-2 hours, then filtering, and measuring the content of ferrous ions contained in the filter liquor; (d) adding an oxidizing agent, increasing temperature to 50-70 DEG C to oxidize for 1-2 hours, then reducing the temperature to room temperature, and filtering to obtain the flocculating agent. The method disclosed by the invention can be used for processing the aged rust-oil removing agents into the flocculating agent; the method disclosed by the invention can not only be used for harmlessly treating the aged rust-oil removing agents, but also be used for recycling the resources because other raw materials used for the method can be the waste iron rust and the waste iron chips in industrial production, thereby achieving higher environmental benefit and economic benefit.