Design, construction and operational results of a pilot plant for the treatment and valorization of pickling waste solutions

An innovative hybrid technology for both minimizing the waste production and optimizing the pickling process through the continuous control of pickling baths composition has been proposed by means of a pilot-plant installed at the Tecnozinco Srl, Carini (PA) hot-dip galvanizing plant. The recovery process has been accomplished by coupling a diffusion dialysis (DD), where HCl is recovered, a membrane distillation (MD), where HCl is concentrated, and a reactive precipitation (RP), where metal ions are recovered as iron hydroxide and ammonium/zinc chloride solution, to be used in the fluxing baths of the plant. The pilot plant was commissioned and operated using synthetic HCl solutions first and, then, real pickling liquors. Results of the long-time automatic mode operations have proven the operational stability and performance of the demonstrator. A high acid recovery of 80% and iron hydroxide with 99% of purity were achieved.