Zinc is widely used in national economy, and the amount of scrap galvanized iron sheet is increasing, so it is of great significance to develop green and efficient dezincification technology from waste galvanized iron sheet. The traditional dezincification methods have their own limitations. The ultrasonic assisted technology and ion flotation technology have potential in metal recovery, and the two are combined to enhance the extraction and separation of zinc.
Waste galvanized iron sheet containing 0.78% zinc and 99.22% iron is used, as well as chemical reagents such as hydrogen chloride and hydrogen peroxide. It includes three steps: leaching, ion flotation and calcination. The effects of different parameters on the leaching rates of zinc and iron were compared between conventional leaching and ultrasonic leaching. Recovery of zinc ions in the leaching solution by ion flotation; Preparation of zinc oxide powder by calcination flotation foam.
The leaching rates of zinc and iron were affected by hydrogen oxide concentration, temperature, hydrogen peroxide dosage, liquid-solid ratio and time in conventional acid leaching. The suitable leaching conditions were determined. Ultrasonic assisted acid leaching can achieve ultra-fast dezincification. Under optimized conditions, the acid leaching time is shortened from 10min to 60s, the zinc leaching rate reaches 99.9%, and the iron leaching rate is only 0.02%. The kinetic study showed that ultrasound could enhance the extraction of zinc and reduce the activation energy of the reaction.
After four times of leaching, the theoretical concentration of zinc ions should reach 2800mg/L, but the actual concentration is 2500mg/L. After three times of leaching, the pH is 0.68, and the concentration of zinc and iron ions increases to 2160mg/L and 33.2mg/L, respectively.
In ultrasonic assisted acid leaching, the cavitation effect of ultrasound destroys the zinc coating and forms pitting corrosion, increases the contact area and accelerates mass transfer. In ion flotation, the polar end of sodium dodecyl benzene sulfonate captures zinc ions, and the non-polar end attaches bubbles to separate zinc ions.
The ultrasonic assisted acid leaching combined with ion flotation technology can achieve rapid and efficient extraction and separation of zinc from waste galvanized iron sheet with high zinc leaching rate and low iron leaching rate under optimized conditions.
