Abstract

This study shows the benefits of using high molecular weight cationic polyacrylamide (PAM) in the purification of wastewater discharged from a wet scrubber in secondary lead smelter for reuse. The effect of temperature, pH, filtration pressure, polymer dose and different types of filtration fabrics on filtration rate (¦_x), efficiency (¦_ε) and quality of the produced water for recycling have been investigated. Results revealed that the wastewater is a hot water suspension containing 420 g/m³ water of solid lanarkite particles (PbSO₄.PbO) submicron in diameter. Successful rapid separation of the suspended solids takes place with the use of 5 g PAM /m³ wastewater.  Separation process involves shift of the zeta potential of the solid particles to a more negative value as a precondition for adequate flocculation. Hot conditions of wastewater improves filtration rate. Although filtration pressure increases filtration rate, extra pressure may deform floc structure causing low filtration efficiency. Increasing the pH value from its original value (4.8) to 7-8 benefits the purity of the filtered water. Filtration efficiency decreases in the order: cotton, silk screen and nylon. Impregnation of the cotton fabric with polystyrene has proven to show high filtration quality, chemical and mechanical stability and long service time compared to the non-impregnated fabric.  The quality of the treated water is acceptable for recycling.

Key words: wastewater cleaning, purification, filtration, separation.