Removal of metals from aqueous solutions using natural chitinous materials

Four naturally derived chitinous materials, commercial cryogenically milled carapace (CCMC), mechanically milled carapace (MMC), chitin and chitosan, were assessed for their ability to remove a range of alkali, alkaline earth, transition and heavy metals from aqueous media in flow-through column trials: The materials showed a poor affinity for the alkali metals and alkaline earth metals but significantly greater affinity for transition and heavy metals. In general, chitin was the least efficient material for removal of transition and heavy metals (approximately 35%) while chitosan was most effective (> 99%). CCMC and MMC both removed > 90% of transition and heavy metals tested from solution. Batch studies conducted using copper as a reference metal demonstrated that removal was dependent on a number of variables including pH, contact time, particle size, metal concentration, metal type and the physio-chemical characteristics of the materials. Detailed analysis of the results from these studies indicate that removal is a complex process and that metals can be sequestered from solution by a number of mechanisms including adsorption, absorption and precipitation.