Copper adsorption by esterified and unesterified fractions of Sphagnum peat moss and its different humic substances

Abstract

The Cu(II) binding properties of Canadian Sphagnum peat moss, humic acid and humin extracted from the peat moss were investigated. Batch pH profile experiments indicated that the adsorption of Cu(II) is pH dependent. At pH 4.0 and 5.0 about 99% of Cu(II) was bound by all three biomasses. Time-dependent experiments showed that the binding of Cu(II) is very rapid. The Cu(II) binding capacities at pH 4.0 were 16.1 mg per gram peat moss, 28.2 mg per gram humic acid, and 17.9 mg per gram humin. More than 90% of Cu(II) bound to the biomasses was recovered by treatment with 0.1 M HCl. We showed that carboxyl groups on these humic substances are responsible for some of the Cu(II) binding by esterifying them with methanol in the presence of trimethoxymethane (trimethyl orthoformate) and observing a decrease in Cu(II) binding. Infrared analysis confirmed the esterification and base hydrolysis of the esterified biomasses corroborated that esterification (and not degradation) had occurred since the metal-binding ability was regained. Our results provide important information on the interaction of Cu(II) ions with Sphagnum peat moss and its humic fractions. This may have practical applications for the removal of hazardous copper ions from contaminated water supplies.