Abstract: There are two prerequisites while treating acidic water containing metal ions with limestone powder：1）The pH can achieve the lowest hydrolysis pH of metal ions when limestone powder react with acid；2）The pH should be higher than that of the metal ions completely hydrolyzed to form insoluble hydroxides  at the end of reaction.Using the synergistic effect of the pH rise originating from limestone powder reacting with acid promoting the hydrolysis of metal ions，the purpose of neutralization and precipitation of metal ions were achieved.Experimental results showed that the treating acidic waste water containing metal ions by limestone powder was feasible and could reduce the cost substantially. 

Key words: limestone powder, aluminum-containing wastewater, iron-containing wastewater, synergistic effect