TREATMENT OF ELECTROLYTIC MANGANESE WASTEWATER BY PRECIPITATION AND HYDROPHOBIC HOLLOW FIBER MEMBRANE PROCESS

摘要

Precipitation was integrated with hydrophobic poly-vinylidene fluoride (PVDF) hollow fiber membrane process for the removal of manganese and ammonia in electrolytic manganese wastewater. Different precipitants, including NaOH, poly aluminum chloride, polyacrylamide and NH_4HCO_3, were added into wastewater and reacted with manganese to form precipitation for manganese removal. It was found that NH_4HCO_3 showed the highest manganese removal efficiency (up to 98.8%) compared with the other three precipitants. The concentration of manganese decreased from 15420 to 182.5 mg/L when the dosage of NH_4HCO_3 was 12 g/L and the settling time was 2 h. In addition, the formed MnCO_3 is an important industrial material. Subsequent membrane process provided a hydro-phobic barrier for residual manganese and a stripping channel for ammonia. Ammonia, diffused through membrane pores to the stripping solution containing sulfuric acid. Such hydrophobic PVDF membrane process enabled 99.9% removal of ammonia. During a long-term performance of membrane process, ammonia decreased sharply and stabilized at about 203 mg/L, with the removal efficiency of 99.4%. Acceleration caused by ammonia stripping to the permeate flux was found; however, it may disappear accompanied with the reduction of ammonia. Membrane fouling caused by manganese and magnesium was also found and led to a permeate flux decline. Manganese was not detected during the whole performance, showing that PVDF exhibited a good hydrophobicity and stability.