Purification of water containing heavy metals by chelating-enhanced ultrafiltration

The study has been aimed at finding out the specific features in purification of the water contaminated by Co(II) and Ni(II) ions by use of ultrafiltration in combination with chelation. Within an operating pressure range of 200 to 500 kPa, the maximum retention coefficient of Co(II) and Ni(II) ions by the UPM-20 membrane has been shown to be 95.0% and 99.9% respectively, when the poly (ethylene imine) made use of as a chelating agent. It is noteworthy that the values referred to above have been reached by use of the poly (ethylene imine) having a branched structure and a molecular weight of 70 kDa. In the case of Co(II) ions, the transmembrane flux has been shown to decrease of 40 to 15 µm/s as the concentration of a polyelectrolyte added increases, whereas it increases as the operating pressure rises. In the case of water purification from Ni(II) ions, the volume flux does not actually depend upon both the concentration of poly (ethylene imine) added and the operating pressure. It equals to ca. 30 µm/s.

The method combining chelation and ultrafiltration is shown might be in use to purify wastewaters from the heavy metal ions. The key advantages of this method are as follows: a high selectivity due to an employment of the selective polyligands and its high specific productivity at insignificant power consumption. A most suitable type of the poly (ethylene imine) to purify in an effective way water contaminated by the heavy metal ions has been found out. The dependencies reached with respect to varying the retention coefficient of ions and the volume flux against time at different concentrations of the PEI and operating pressures make evident that a rise in the operating pressure does not essentially affect the retention coefficient of the ions to be removed. In this event, the concentration of a polyelectrolyte added plays a determining role. The transmembrane flux observed at water purification from the Co(II) ions, however, depends to a great extent upon the operating pressure.