Effects of freezeethaw cycling on metal-phosphate formation and stability in single and multi-metal systems Erla G. Hafsteinsdóttir * , Duanne A. White, Damian B. Gore Department of Environment & Geography, Macquarie University, NSW 2109, Australia article info Article history: Received 31 August 2012 Received in revised form 28 December 2012 Accepted 9 January 2013 Keywords: Polar regions Copper Lead Zinc Contamination abstract Freezeethaw cycling may influence the chemistry, mineral stability and reaction rate during metal orthophosphate fixation. This study assessed the formation and stability of Cu-, Pb-, and Zn-phosphates in chemically simple laboratory systems during 240 freezeethaw cycles (120 days) from þ10 to 20  C, using X-ray diffractometry. In single heavy metal systems, chloro- and hydroxy-pyromorphite (Pb 5 (PO 4 ) 3 (Cl,OH)), sodalite (Na 6 Zn 6 (PO 4 ) 6 $8H 2 O), chiral zincophosphate (Na 12 (Zn 12 P 12 O 48 )$12H 2 O), and copper phosphate hydrate (Cu 3 (PO 4 ) 2 $3H 2 O) were the primary phosphate minerals that formed, and were typically stable during the experiment. Zinc and Cu-phosphate formation was reduced in multi heavy metal systems, and was substantially lower in abundance than chloropyromorphite. Successful Cu-, Pb- and Zn- phosphate formation can be expected in cold and freezing environments like the polar regions. However, field implementation of orthophosphate fixation needs to consider competing ion effects, concentration of the phosphate source, and the amount of free-water. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Orthophosphate fixation remediates contaminated soils and sediments by reducing metal mobility and bioavailability (Cao et al., 2008; Crannell et al., 2000; Ma et al., 1993). Fixation of lead and the formation of the insoluble pyromorphite group (Pb 5 (PO 4 ) 3 (Cl,Br,- F,OH)) finds the widest application (Cao et al., 2008; Hettiarachchi et al., 2000; Laperche et al., 1997; Ma et al., 1995; Nriagu, 1974). However, other metals such as Cu and Zn have also shown potential for fixation (Liu and Zhao, 2007; Xu et al., 1994). Copper phosphates can form slowly, in some cases taking over 6 months to reach equilibrium (Ayati and Lundager Madsen, 2000; Bes and Mench, 2008; Qian et al., 2009; White et al., 2012). In contrast, fixation of zinc depends largely on the phosphate source and the effects of competing ions (Cao et al., 2004; Zwonitzer et al., 2003). Due to a common geological source or co-disposal, Cu, Zn and Pb may co- occur (Chen et al., 2007; Deprez et al., 1999; Ma et al., 1994b; Pierzynski et al., 2005; Zwonitzer et al., 2003), creating the need and the opportunity to treat multiple contaminants in waters or soils. Although orthophosphate fixation is commonly used in temper- ate environments, its efficiency in cold and freezing environments is understudied. Metal contaminated soils and sediments are well- known in regions that experience cold temperatures and freezee thaw cycles, e.g. Casey, Davis and Wilkes Stations in Antarctica, Resolute in Canada and Kandalaksha Bay in Russia (Cobelo-Garcia et al., 2006; Snape et al., 1998; Stark et al., 2006; Young and Lund, 2006). At the Antarctic Casey Station, metals have been observed leaching from Thala Valley landfill into Brown Bay (Stark et al., 2005). Organisms living in cold environments, such as Antarctica, may be particularly vulnerable to contamination due to unique adaptations to these environments (Bargagli, 2008). In regard to the environ- mental chemistry, temperature changes affect mineral solubility and hydration (Dietzel, 2005; Doner and Lynn, 1989), with freezing desiccating particles and increasing solute concentration (Blackwell et al., 2010). Therefore, freezeethaw cycling has the potential to affect reaction rate and mineral stability during fixation. Although formation of the lead phosphate mineral pyromorphite is slower at 2  C than 22  C(White et al., 2012), Hafsteinsdóttir et al. (2011) showed that pyromorphite forms and is stable during 240 freezee thaw cycles (simulating 20 years of freezeethaw activity at 30 cm depth in the soil at Casey Station, Antarctica; Gore et al., 2006). However, fixation efficiency of other metals such as Zn and Cu, and of multi-metal systems during freezeethaw cycles remains understudied. This paper is the third in a series of laboratory and field exper- iments (Hafsteinsdóttir et al., 2011; White et al., 2012) which aim to assess the efficiency of orthophosphate fixation in metal con- taminated soils and sediments exposed to cold and freezing * Corresponding author. Present address: URS Australia, 53 Cleary Street, Ham- ilton, NSW 2303, Australia. E-mail addresses: erla_gud@hotmail.com, erla.hafsteinsdottir@gmail.com (E.G. Hafsteinsdóttir), duanne.white@canberra.edu.au (D.A. White), damian.gore@ mq.edu.au (D.B. Gore). Contents lists available at SciVerse ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.envpol.2013.01.007 Environmental Pollution 175 (2013) 168e177