Hot-dip Galvanizing

Investment program for treatment of pickling acid

In hot-dip galvanisation processes the metal construction parts are coated with negatively electric metals, chiefly zinc. The surface of the metal being subjected to this process must be bright. To achieve this the parts are first pickled in a hydrochloric acid bath. In the course of time the hydrochloric acid becomes spent and has to be disposed of. The HYC-process recovers from the waste mixture valuable raw materials (iron chloride and zinc chloride) which can then be reintegrated in the processing cycle. A multiphase process removes the secondary constituents fouling the product or interfering with the separation process. The liquid is passed through an activated charcoal adsorption unit to remove the grease, inhibitors etc. from it. In a two-phase carburizing process heavy metals introduced through the steel being galvanised and the zinc used for this purpose are precipitated. The core of the unit consists of a zinc specific liquid-liquid extraction in which the iron chloride and zinc chloride are separated from one another. After passing through several retreatment phases in an evaporation unit both the FeCl2 and the ZnCl2 solutions have reached the concentration desired. 

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Source: Federal Environment Agency (UBA)