EVALUATION OF ION-EXCHANGE PROPERTIES OF FERRIC-HYDROXIDE FLOCS FOR THE REMOVAL OF HEAVY METAL WASTES USING A HIGH GRADIENT MAGNETIC SEPARATOR.

摘要

Preliminary adsorption studies showed no effect on the effluent heavy metals with a magnetite dose of 500 or 1000 mg/l but removal was lower when 200 mg/l of magnetite was used. Adsorption of metals onto ferric flocs was found to be independent of initial heavy metals concentration provided the surface available for adsorption of ions was not saturated. As surface area coverage approached saturation percent removal of heavy metals decreased. The pH of the medium was found to have a major infuence on the removal of heavy metals. A 99.9% removal of all heavy metals could be achieved at pH values greater than 10.30 - 10.50, but removal was almost totally due to precipitation.; Ferric sulphate made removal of heavy metals in a HGMS possible at lower pH values than 10.30 - 10.50. Increased magnetic field strength caused more removal of flocs for a given flow rate whereas an increase in flow rate decreased removal of flocs in a HGMS. The effect of treatment column diameters was geometric in that an increase in tube diameter caused more floc to be trapped because more entrapment area was available. The mg /in('3) of floc removed in each tube tested was the same at constant flow rate and magnetic field strength.; The floc trapped in the HGMS was removed, by turning off the magnetic field, so it could be processed for recycle of the ferric ion. On the average of 671.3 mgms of 0.1N H(,2)SO(,4) were added to the floc to produce a pH of 3.10 - 3.57. A separatory funnel was used to separate the brown-black bottom layer, containing recovered ferric hydroxide-magnetite, from the colourless top layer containing the concentrated heavy metals. The ferric hydroxide was then reused to treat a fresh batch of wastewater and the cycle repeated four times. The loss of ferric ion was between 5 - 10% during each cycle.