Leaching experimens were undertaken in duplicate in 50 mL conical polyethylene centrifuge tubes (GBO, Germany). Individual tubes (67 in total) were placed on a horizontal shaker (KOS-3333, MRC, UK) for different times (15 min to 48 h) at room temperature (22°C ± 2°C) before centrifugation at µm syringe filters. pH and specific conductivity were measured by multimeters (Thermo Scientific, USA) immediately after collection. Elemental compositions of both solid and liquid samples, including procedural blanks, were determined by ICP-AES. Solid samples were pre-treated by digestion of 0.2 g sample in 10 mL 70 % HNO3 at 175°C, based on US EPA method 3051A , using a microwave digestion system (ETHOS UP, Italy). Digestion efficiency was determined by processing of US National Institute of Standards and Technology (NIST) standard reference material (SRM) 694