Electroplating wastewater generally contains a large number of zinc ions, in which zinc ions exist in two forms: complex zinc and free elemental zinc. High efficiency water purification coagulants such as polyferric sulfate can directly adsorb zinc ions in elemental state for coagulation and precipitation removal. However, these coagulants can not directly adsorb and coagulate the zinc ions in the complex state, so it is necessary to destroy the complexation and change the zinc ions in the complex state into free zinc ions, and then add coagulants such as polyferric sulfate to coagulate and precipitate.

Gongyi Filter Industry Co.,Ltd found that it is very difficult to remove complex zinc by using single coagulant such as PFS and PAC, while the effect of complex alkali is better. The specific reasons are as follows: first of all, the specific surface area of the complex alkali is large, the adsorption capacity is strong, and it can adsorb a large number of suspended particles. Secondly, the composite alkali has better coagulation effect, which can accelerate the coacervation and sedimentation time in the same direction, thus greatly improving the water purification efficiency. In the process of water purification, the complex alkali is added to break the complex, then the polymerized ferric sulfate is added, and then the polymerized ferric sulfate is stirred violently to make it hydrolyze rapidly in the wastewater to form a large amount of ferric hydroxide colloid, which can adsorb some unstable complex copper ions, so as to achieve better secondary adsorption effect, and the removal rate of complex zinc is more than 95%.

In the treatment of electroplating wastewater, sodium sulfide and sodium pyrosulfite can be used as breaking agents to destroy the stability of complex metal substances, and then coagulants such as polyferric sulfate and polyaluminum chloride can be added for coagulation and sedimentation.