Method and formulations for removing rust and scale from steel and for regenerating pickling liquor in hot-dip galvanization process

A hot-dip galvanization process for stabilizing the surface of ferrous metals comprising steps of

• i) removing metal oxide scales and rust from said surface in a pickling stage, comprising contacting said surface with a liquid pickling composition, denoted GF2, comprising phosphoric acid, a hydrophilic polymer, a non-ionic surfactant, and an anti-smut agent, wherein said GF2 solubilizes iron oxides forming said scales and rust without solubilizing non-oxidized metal in said surface, thereby preparing said surface for zinc-coating;
• and
• ii) binding iron from said GF2 solubilized iron oxide in an insoluble iron oxalate complex by contacting said GF2 with a solid composition, denoted GF1, comprising oxalic acid, a nucleation crystallization agent, and an anionic surfactant, and removing said insoluble iron oxalate complex from said liquid composition, thereby releasing phosphoric acid in GF2 for further use;
• iii) protecting said surface by coating with a layer of zinc;
• the use of GF2 in said step i) preventing the formation of dangerous gaseous side products and resulting in a uniform and thin zinc layer, and the use of GF1 in said step ii) recovering phosphoric acid;
• wherein the combination of steps i) and ii) results in an environmentally safe and cost-effective hot-dip galvanization process.