ELECTROLYTIC SEPARATION AND RECOVERY IN CAUSTIC OF STEEL AND ZINC FROM GALVANIZED STEEL SCRAP

Experiments were conducted to examine the technical and economic feasibility of a single-step process for electrochemically separating and recovering in hot caustic the components of galvanized steel. Electrochemical separation is practical because: 1. maximum anodic zinc dissolution currents yield commercially acceptable throughputs and are 1000 times greater than those for steel, 2. steel is not seriously corroded by caustic under conditions proposed and 3. the process is robust in the presence of expected aluminum, lead, cadmium and iron impurities. Stripping experiments in 5 M NaOH at 90-degrees-C indicate that a G-90 grade (275 g Zn/m2) of galvanized steel can be stripped in about five minutes at a current density of 200 mA/cm2 in a cell with parallel electrodes separated 15 to 59 mm. Tests with scrap at densities of 30 and 150 lbs/ft2 were successful at estimated current densities of about 20 mA/cm2. Residual zinc levels on the steel are less than 0.1 wt%. A technical and economic analysis of alternative technologies for separation and recovery of the components of galvanized scrap steel suggest that none are as energy efficient or cost less to the steel industry than the single-step continuous electrolytic stripping process that is the subject of this research.