A COMPARATIVE INVESTIGATION OF METAL SORPTION USING A VARIETY OF MANGANESE OXIDE MATERIALS DERIVED FROM VARIOUS SOURCES: IMPLICATIONS FOR INDUSTRIAL MINERALOGY AND GEOTECHNOLOGY DEVELOPMENT

Manganese oxides are naturally occurring minerals in soils and aquatic sediments. They have also been developed for use as applied materials derived from stock and recycled industrial waste sources. How natural, synthetic, and industrial waste-derived manganese oxide materials differ in their ability to adsorb metals from aqueous environments is poorly understood. Batch and column studies were used to measure the metal adsorption capacity of several manganese oxide materials. Specifically, the adsorption capacities of electrolytic manganese oxide (EMD) and cryptomelane (synthetic and battery waste- derived) were measured for cobalt, cerium, and lead. EMD is a synthetic, commercially available form of MnO₂ commonly used in disposable alkaline batteries; its composition is dominated by ramsdellite. Cryptomelane is a potassium manganese oxide that is a 2x2 octahedral molecular sieve structure that is common in near earth surface environments and can be readily synthesized for numerous environmental applications. The metals concentrations in aqueous solutions were measured using Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES). The data from the batch studies indicates that when used as solid-phase redox reagent in aqueous solutions containing the metals lead, cobalt, and cerium, Mn-oxides adsorb the metals at adsorption capacities ranging from 2 to >50 mg metal / g MnO₂-based material. Synthetic cryptomelane outperformed other Mn-oxide materials in adsorption studies using all three metals. EMD showed adsorption capacities up to 50 mg/ g (lead) while battery waste- derived cryptomelane showed capacities of ~16 mg metal/ g (cerium and lead). The column studies, in combination with breakthrough models, gave information regarding the rate at which adsorption occurs in the various MnO₂-based materials. The significance of these results is we can determine which features of Mn-oxides gives rise to higher adsorption capacities and we can determine the extent and at what rate the metals can be up-taken by the minerals. This information can be applied to environmental purposes such as pollution prevention (waste battery to value- added materials), water and waste water treatment processes, and soil remediation.