Dolomite was used to neutralize the regenerated waste acid.Its effect wasn't good.After the reforms of process and equipment, the pre-hydrogen technique has been used.Two hydrogen ion-exchangers are now filled with weak acid resin, instead.And, the waste acid is made use of first to regenerate.Thus, the running period of the ion-exchangers is getting longer;the times of regeneration is get ting less ;the waste acid is fully made use of;the effluent discharge reaches the standard;and the environmental and economic benefit is great.