Use of Iron Oxides to Enhance Metal Removal in Crossflow Microfiltration

This research investigated whether iron oxyhydroxides used in conjunction with microfiltration could improve the removal of metals from a waste while maintaining adequate flux. Filtration of individual metals, a mixture of metals, and the mixture with two iron oxides were investigated. The research indicated that use of a coagulant (an iron-containing salt) might not be as important in microfiltration systems as in conventional gravity separation systems, because of the small pore size of microfilters. In some cases, filtration efficiency was relatively poor at the beginning of a treatment cycle, but in almost all cases it became excellent once a layer had built up on the membrane surface. The greatest benefit provided by iron oxides might be to reduce membrane fouling. A crystalline iron oxide such as goethite is more attractive than ferrihydrite. The flux improvement with goethite is greatest if a thin layer is deposited on the membrane surface before the contaminant metals are injected into the system, so that the goethite can trap the potentially foulant metal hydroxide particles away from the membrane surface.