Abstract
Crayfish carapace, a plentiful waste in China, was applied to remove divalent heavy metal ions—copper (Cu), cadmium (Cd), zinc (Zn), and lead (Pb)—from wastewater. The adsorption capacities of crayfish carapace micro-powder (CCM) for heavy metal ions were studied with adsorbent dosages ranging from 0.5–2.5 g/L and with initial metal concentrations ranging from 50–250 mg/L. CCM particle size, initial solution pH (from 2.5–6.5), temperature (from 25–65 °C) and calcium level (from 3.5–21.5%) were also varied in batch mode. The results indicated that the adsorption capacity increases with both decreasing particle size and increasing calcium level of the crayfish carapace. The kinetic studies indicated that the adsorption could be complete within 2 h, and that the data correlated with the pseudo-second-order model. CCM recorded maximum uptakes of 200, 217.39, 80, and 322.58 mg/g for Cu, Cd, Zn, and Pb, respectively. The adsorption capacities and removal efficiencies of CCM for metal ions were three-times higher than those of chitin and chitosan extracted from the CCM.
Highlights
Contamination of aqueous environments by toxic metals is a serious global problem due to their persistence, bioaccumulation, and bio-magnification through food webs [1]
The removal efficiency increased with increasing adsorbent dosage because of the increase in surface area of the adsorbent, which in turn increased the number of binding sites (Figure 1b)
After the dosage reached 1.0 g/L, removal efficiency of copper, cadmium, and lead reached the maximum, while removal efficiency of zinc reached the maximum at 1.5 g/L
Summary
Contamination of aqueous environments by toxic metals is a serious global problem due to their persistence, bioaccumulation, and bio-magnification through food webs [1]. Most of the heavy metals are highly toxic and non-biodegradable. In China, the maximum permissible concentrations of Cu(II), Cd(II), Zn(II) and Pb(II) are 2.0, 0.1, 5.0 and 1.0 mg/L, respectively [2] They must be removed from the waste effluents in order to meet increasingly stringent environmental quality standards. Numerous methods, including chemical precipitation, ion exchange, electrodeposition, membrane separation, and adsorption had been used to treat such effluents [3]. Of these methods, traditional chemical precipitation was the most economic, but it is inefficient. Ion exchange and reverse osmosis were generally effective, but had rather high maintenance and operational costs [4]
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