Journal of Hazardous Materials 161 (2009) 824–834 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Adsorption behavior of Zn(II) on calcinated Chinese loess Xiaowu Tang ∗ , Zhenze Li, Yunmin Chen MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering, Department of Civil Engineering, Zhejiang University, Zheda Road 38, Hangzhou 310027, PR China article info Article history: Received 24 August 2007 Received in revised form 9 April 2008 Accepted 9 April 2008 Available online 22 April 2008 Keywords: Adsorption Zn(II) Loess Calcination Kinetics abstract Chinese loess has proven to be effective in removing Zn(II) from aqueous solutions, but the resultant adsorbent–water slurry is difficult to separate. In this paper, the crude loess was calcinated to improve the separation efficiency of slurries in terms of sedimentary rate by increasing the particle sizes of the adsorbent. The sorption capacities of different sorbents, including crude loess, calcinated loess, de-organic crude loess and acid-treated calcinated loess, were obtained and sequenced. The adsorption capacity of the calcinated loess towards Zn(II) was found to be as high as 113.6mgg -1 . The adsorption isotherms and kinetics of calcinated loess were best-fit with the Freundlich isotherm and the pseudo-second order kinetics, respectively. The thermodynamic analysis revealed that the adsorption was exothermic and spon- taneous with a high preference for Zn(II) removal. The adsorption of Zn(II) on calcinated loess implies an ion exchange of the solute with calcite and goethite due to the observed FT-IR and XRD patterns as well as the predicted mean free energies (-11.58 to -9.28 kJ mol -1 by D–R model). The byproduct of adsorption can be purified and refreshed by using a 0.01 M HCl solution. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Zinc is one of the main pollutants in acid mining drainages. In developing countries, metal mining and metallurgy industrial departments produce large quantities of wastewater containing high concentration of Zn(II) [1,2]. Considering the toxicity of Zn(II), treatment methods have been widely developed. Chemical pre- cipitation is the most widely adopted method. Due to the low dissolution coefficient of zinc sulfide, sodium sulfide or hydrogen sulfide is always used to remove ionic zinc from aqueous solution to extremely low or nondetectable levels [3,4]. Chemical precipita- tion can also be obtained by adjusting the solution pH to alkaline states which will lead to the precipitation of Zn(II) [5]. Neverthe- less, the costs of chemical additives are high and the salinity of the wastewater will be increased, which limits the applicability of this method. Fixation of Zn(II) through ion exchange is also an optional treat- ment method. A selective elimination is possible by means of heavy metal-selective ion exchangers which exhibit a high affinity for heavy metals. However, this method is not extensively adapted to metals removal in industrial wastewater treatment [6]. Adsorption can be used to attain a similar target. Many sorbents have been developed and are being continually tested. Minerals such as apatite and goethite have been reported with excellent ∗ Corresponding author. Tel.: +86 571 87951714; fax: +86 571 85023966. E-mail address: tangxiaowu@zju.edu.cn (X. Tang). purifying capabilities for metal cations. Industrial wastes such as activated sludge, coal fly ash and iron slag have also been stud- ied for the applicability for Zn(II) removal. Natural products such as leaf [7], coca shell [8] and sea weed [9], can be used to remove heavy metals by producing activated carbons through further pro- cessing. Several kinds of natural soils have been observed to have high adsorption capacity for Zn(II) and optimum conditions have also been extensively investigated and reported [10–12]. Chinese loess is widely distributed throughout western China and has been studied as an adsorbent for Zn(II) removals from aque- ous solution in the authors laboratory. The intrinsically abundant constituent in loess is calcite. Calcite has been found to play a major role in Zn(II) adsorption [13,14]. The adsorption capacity is rather high in comparison with other adsorbents, showing potential uti- lizability in practice. In western China, the acid mining drainage is a major source of contamination to the environment. It is particularly beneficial to investigate the applicability of locally prolific loess for wastewater treatment. Since the main composition of loess is clay and silt [15], the treatment of Zn(II) in solution produces mixtures with a large amount of fine solids that are difficult to filter or precip- itate. The separation of the sorbent after equilibrating with Zn(II) solution becomes an intractable engineering problem. The main objectives of this paper are to develop a method to improve the separating properties of loess after adsorption with Zn(II) and to investigate the adsorbing behavior as well as the intrinsic uptake mechanism. Firstly, the improvement of the sed- imentary rate of the adsorbent requires an increased particle size of the sorbent that could be achieved after calcination at moder- 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.04.059