Effect of Sulfate on Cu(II) Adsorption/Desorption Behavior on Ferrihydrite Colloids and Cu Speciation

摘要

Iron oxide colloids have great adsorption capacity ofheavy metalsdue to their high specific surface area. Inorganic oxyanion can causecolloid aggregation and further affect its reactivity and mobility.However, the effect of sulfate on the metal sequestration by ironoxide colloids is still unknown. In this study, using aggregation,batch adsorption/desorption, and settling experiments combined withXPS and TEM, we elucidated the sorption behavior of Cu(II) on ferrihydritecolloids and the Cu speciation change at various sulfate concentrations.Our results showed that the Cu(II) adsorption on ferrihydrite colloidswas improved by adding sulfate, but the enhancement extent obviouslydecreased at high sulfate concentrations because of the drastic diminishmentof available sites. Further desorption experiments indicated thatthe extent of Cu(II) desorption on ferrihydrite colloids was smallerthan that on ferrihydrite particles under the same conditions becauseof the physical constraints created by aggregation. Moreover, Cu speciation(dissolved, colloidal, and particulate) was controlled by sulfateconcentration, with no colloidal Cu found when the concentration exceededthe critical coagulation concentration (63 & mu;M). The study ofthe multiple interactions between ferrihydrite colloids, Cu(II), andsulfate provided the basis for a comprehensive understanding of thetransport and geochemical fate of heavy metals.

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