The addition of organic carbon and nitrate affects reactive transport of heavy metals in sandy aquifers Yamini Satyawali a, ⁎, Piet Seuntjens a,b,c,1 , Sandra Van Roy a,1 , Ingeborg Joris a,1 , Silvia Vangeel a,1 , Winnie Dejonghe a,1 , Karolien Vanbroekhoven a,1 a Flemish Institute for Technological Research (VITO), Boeretang 200, 2400 Mol, Belgium b Dept. Soil Management, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium c Dept. Bioscience Engineering, University of Antwerp, Groenenborgerlaan 178, 2020 Antwerp, Belgium article info abstract Article history: Received 20 May 2010 Received in revised form 15 December 2010 Accepted 16 December 2010 Available online 28 December 2010 Organic carbon introduction in the soil to initiate remedial measures, nitrate infiltration due to agricultural practices or sulphate intrusion owing to industrial usage can influence the redox conditions and pH, thus affecting the mobility of heavy metals in soil and groundwater. This study reports the fate of Zn and Cd in sandy aquifers under a variety of plausible in-situ redox conditions that were induced by introduction of carbon and various electron acceptors in column experiments. Up to 100% Zn and Cd removal (from the liquid phase) was observed in all the four columns, however the mechanisms were different. Metal removal in column K1 (containing sulphate), was attributed to biological sulphate reduction and subsequent metal precipitation (as sulphides). In the presence of both nitrate and sulphate (K2), the former dominated the process, precipitating the heavy metals as hydroxides and/or carbonates. In the presence of sulphate, nitrate and supplemental iron (Fe(OH) 3 ) (K3), metal removal was also due to precipitation as hydroxides and/or carbonates. In abiotic column, K4, (with supplemental iron (Fe(OH) 3 ), but no nitrate), cation exchange with soil led to metal removal. The results obtained were modeled using the reactive transport model PHREEQC-2 to elucidate governing processes and to evaluate scenarios of organic carbon, sulphate and nitrate inputs. © 2010 Elsevier B.V. All rights reserved. Keywords: Heavy metals Zinc Cadmium Sulphate reduction Nitrate reduction Redox processes Geochemical modeling 1. Introduction The heavy metals commonly found in the subsurface environment include Fe, Pb, Hg, As, Cr, Cd, Ni, Zn and Cu. Soils and groundwater can also become contaminated with high concentrations of these heavy metals from a variety of anthropogenic sources such as agriculture, manufacturing, mining and the land application of sewage (Ayyasamy and Lee, 2009). Toxic effects of non-ferrous heavy metals (Zn, Cd, Pb, etc.) on local ecosystems have been frequently documented (Nachtegaal et al., 2005). Among the most common heavy metals, Zn and Cd show the greatest mobility in the soil environment, therefore are of greater concern (Wilson and Bell, 1996). It has been known that the speciation of heavy metals depends on the physical and chemical characteristics of the soil. Thus, chemical stability, solubility and mobility of metal contaminants in soils and aquifer sediments are controlled by a complex series of biogeochemical processes depending on variables such as pH, redox, clay content, organic matter, microbial activity and terminal electron acceptors (TEA) (Harrington et al., 1998). Therefore, an understanding of the complex interactions between these parameters is required to predict metal partitioning, to assess the potential for groundwater contamination and to help formulate the remediation measures. The study of heavy metal mobility in soil/aquifers has attracted considerable attention. A study on Zn and Cu mobility/biogeochemical transport in the presence Journal of Contaminant Hydrology 123 (2011) 83–93 ⁎ Corresponding author. Tel.: + 32 14 335741; fax: + 32 14 321186. E-mail address: yamini.satyawali@vito.be (Y. Satyawali). 1 Tel.: +32 14 335741; fax: +32 14 321186. 0169-7722/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jconhyd.2010.12.009 Contents lists available at ScienceDirect Journal of Contaminant Hydrology journal homepage: www.elsevier.com/locate/jconhyd