Adsorption of zinc onto peat from peatlands of Poland and Israel

Peat, defined as young Quaternary, mainly Holocene, organogenic sedimentary rock in the first stage of coalification, has received increasing attentio n due to its potential to act as an ubiquitous effective agent for the reco very of valuable metals, for the removal of metal ions from dumping site le achate and wastewater, or for retrospective monitoring of their migration a nd accumulation in the environment. For these purposes, adsorption capacity and binding strength of peat with respect to the metal ions under differen t conditions, as well as the mechanism of binding-release should be thoroug hly known. To date, this knowledge is still limited. In this paper, results of studies on adsorption-desorption properties of Zn2+, which is one of th e most mobile trace metals in the environment, in representative Polish and Israeli peat samples are presented. Batch studies were performed for Zn2in both single cation and a binary system (Zn-Cd) at pH 4.0. Column experim ents under saturated flow conditions with Zn concentrations of 250 and 500 mg dm(-3) in the input solution at pH 4.0 (monometallic system) were also c onducted. Finally, batch and column zinc adsorption experiments on selected peat samples were carried out using real multi-component wastes from the e lectroplating process. To assess the binding strength of peat with respect to zinc, sequential extraction by Tessier et al. (1979) modified by Kersten and Forstner (1988) was applied. The adsorption capacity for zinc of low-m oor Polish peat, which is typical for the Northern Hemisphere with pH 5.02- 6.54, was 15,800 to 33,700 mg Zn kg(-1). Lower values were found for the Is raeli peat. The presence of mass equivalent amounts of Cd showed only a mod erate suppressing influence on the uptake of Zn by different peat matter. T his suggests a weak competition of metal ions for adsorption sites availabl e, despite binding of these metals in similar mass ratios in the same most labile fractions. There was, however, a difference in the binding of Zn and Cd in the more stable fractions, where no competition between Zn and Cd oc curred. A significant difference in fractionation of Zn sorbed in batch vs, column experiments, was indicated. In particular, higher Zn enrichment in the 'insoluble organic' fraction under dynamic flow conditions was observed . Desorption experiments proved that zinc can be partially released with ac id treatment from the labile fractions. (C) 1999 Elsevier Science B.V. All rights reserved.