Rhamnolipid biosurfactant-enhanced soil flushing for the removal of arsenic and heavy metals from mine tailings Suiling Wang, Catherine N. Mulligan * Department of Building, Civil and Environmental Engineering, Concordia University, 1455 de Maisonneuve Boulevard W., EV6.187 Montreal, Quebec, Canada H3G 1M8 1. Introduction Adverse health effects associated with exposure of arsenic and heavy metals have been reported worldwide [1,2]. These toxic elements occur naturally and may enter the environment from both natural processes such as weathering and erosion of enrichments and human activities such as mining and smelting operations. A number of remediation technologies such as excavation and landfill, thermal treatment and stabilization and solidification have been proposed for contaminated soils or solid wastes [3,4]. However, the application of these methods has been limited due to the prohibitory costs or land space requirements. The use of surfactants to enhance the removal of soil con- taminants has been widely studied in recent years. Mainly anionic and non-ionic surfactants are used for soil washing or flushing [3]. They can be used in mixtures or with additives such as alcohol and/ or salts such as sodium chloride. These agents would be most effective in promoting the mobilization of organic compounds of relative low water solubility and high lipid solubility through decreasing interfacial tension and formation of aqueous micelles. They can also be used as extractants to transfer metal ions from an aqueous to an organic phase. The possible mechanisms for the extraction of heavy metals by surfactants are ion exchange, precipitation–dissolution, and counterion binding. Polymers or foams can also be added to control the mobility of the conta- minants [3–5]. Biosurfactants are produced by bacteria or yeasts and exhibit high specificity and are consequently suited to new applica- tions. Mulligan [6] gives a comprehensive and critical review on the applications of biosurfactants (i.e., rhamnolipids, surfactin, and sophorolipids) for soil and water treatment. Biosurfactant applications in environmental industries are promising due to their biodegradability, low toxicity and effectiveness in enhan- cing the biodegradation and solubilization of low solubility compounds. A number of studies have demonstrated the feasi- bility of biosurfactant-enhanced recoveries of hydrophobic organic contaminants [6–8]. Biosurfactant-enhanced remedia- tion of heavy metal contaminated soils has also been demon- strated [4,5,9–12]. However, the use of biosurfactants to remediate arsenic contaminated soils has not been reported yet. Further research is required to investigate the role of biosurfactants in arsenic mobilization from contaminated soils or other solid wastes. In this study, column experiments were run to examine the effects of a rhamnolipid biosurfactant (JBR425) on the mobilization of arsenic and heavy metals and to evaluate the feasibility of using bio- surfactant to remove arsenic and heavy metals simultaneously from mine tailings. Process Biochemistry 44 (2009) 296–301 ARTICLE INFO Article history: Received 23 January 2008 Received in revised form 3 October 2008 Accepted 5 November 2008 Keywords: Arsenic Biosurfactant rhamnolipids Heavy metals Mine tailings Site remediation ABSTRACT Mine tailings containing high contents of arsenic and heavy metals are potential environmental contamination sources. Column experiments were conducted in this study to evaluate the feasibility of using a rhamnolipid biosurfactant (JBR425) to enhance the removal of arsenic and heavy metals from an oxidized mine tailings sample collected from Bathurst, Canada. Capillary electrophoresis (CE) analyses indicated that arsenate [As(V)] was the only extractable arsenic species in the mine tailings. The addition of rhamnolipids did not change the oxidation state of arsenic. It was found that a 0.1% rhamnolipid solution (initial pH adjusted to 11) could significantly enhance the removal of arsenic and heavy metals (i.e., Cu, Pb and Zn) simultaneously. The accumulative removal of arsenic, Cu, Pb and Zn reached 148, 74, 2379, and 259 mg/kg after a 70-pore-volume flushing, respectively. Moreover, the mobilization of arsenic and heavy metals by rhamnolipids was found to be positively correlated with that of Fe, and the mobilization of arsenic was also positively correlated to that of the heavy metals. The mobilization of co- existing metals, to some extent, might enhance arsenic mobilization in the presence of rhamnolipids by helping incorporate it into aqueous organic complexes or micelles through metal-bridging mechanisms. ß 2008 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +1 514 848 2424x7925; fax: +1 514 848 7965. E-mail address: mulligan@civil.concordia.ca (C.N. Mulligan). Contents lists available at ScienceDirect Process Biochemistry journal homepage: www.elsevier.com/locate/procbio 1359-5113/$ – see front matter ß 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2008.11.006