Preparation method of polymerized iron flocculant

The invention relates to a preparation method of a polymerized iron flocculant, which comprises the steps of: mixing a certain amount of ferrous salt (or ferric salt), inorganic acid and water under stirring condition to completely dissolve iron salt; adding a certain amount of oxidant and sufficiently stirring to completely oxidize ferrous ion into ferric ion; and adding a certain amount of inorganic base and polymerization inhibitor to partially hydrolyze and polymerize ferric ion, and then aging at normal temperature for some time to obtain modified polymerized iron flocculant. Compared with the prior art, the prepared modified polymerized iron flocculant has the advantages that the stability is improved, the bonding bridging capability is enhanced, alum flower is rapid in forming and large, the coagulation effect is improved and the like; and when the modified poly iron flocculant is used under certain conditions, the water outflow quality is not significantly influenced under the condition that the flocculation effect is significantly improved.