Toxic metals removal from waste waters by upflow filtration with floating filter medium. I. The case of zinc

The effectiveness of upflow filtration to remove zinc ions was studied in the present paper. Zinc ions were precipitated by employing either the conventional hydroxide route or the carbonate-enhanced route (addition of NaOH plus Na2CO3). Upflow column filtration with synthetic buoyant filter media was used for the subsequent solid–liquid separation of toxic metal precipitates. The experiments were conducted in semi-batch recirculated mode, using a pilot-scale upflow filtration column. The examined parameters were the necessary recirculation treatment time (3–4 hr) for the remaining concentrations of toxic metal to achieve the legislative limits (below 1 mg/L), the pH value (around 9.0), the initial concentration of the studied metal (10–50 mg/L), and the linear velocity of the waste solution under treatment within the column (10–65 m/hr). Under optimized conditions, the high efficiency and simplicity of the studied method for the removal of metal was demonstrated.