We report the synthesis of a new range of iron oxide-graphene oxide (GO) nanocomposites having different iron oxide content (36-80 wt%) as high-performance adsorbents for arsenic removal. Synthesized by co-precipitation of iron oxide on GO sheets that are prepared by an improved Hummers method, the iron oxide in the nanocomposites is featured primarily in the desirable form of amorphous nanoparticles with an average size of ca. 5 nm. This unique amorphous nanoparticle morphology of the iron oxide beneficially endows the nanocomposites with high surface area (up to 341 m 2 g -1 for FeO x -GO-80 having the iron oxide content of 80 wt%) and predominant mesopore structures, and consequently increased adsorption sites and enhanced arsenic adsorption capacity. FeO x -GO-80 shows high maximum arsenic adsorption capacity (q max ) of 147 and 113 mg g −1 for As(III) and As(V), respectively. These values are the highest among all the iron oxide-GO/reduced GO composite adsorbents reported to date and are also comparable to the best values achieved with various sophisticatedly synthesized iron oxide nanostructures. More strikingly, FeO x -GO-80 is also demonstrated to nearly completely (>99.98%) removes arsenic by reducing the concentration from 118 (for As(III)) or 108 (for As(V)) to < 0.02 µg L −1 , which is far below the limit of 10 µg L −1 recommended by the World Health Organization (WHO) for drinking water. The excellent adsorption performance, along with their low cost and convenient synthesis, makes this range of adsorbents highly promising for commercial applications in drinking water purification and wastewater treatment.

Musselwhite Mine in Northwestern Ontario, Canada began thickened tailings disposal in May 2010. Surface disposal of thickened tailings for the 4,000 tpd gold mine was chosen following a series of studies beginning in 2002 to investigate options to expand the capacity of the tailings management area. This technology was considered most cost effective in maximising storage capacity within the existing site footprint. The elimination of a pond for closure will reduce the risk of dam failure. Further, the non-segregating tailings are expected to be relatively impervious and saturated. These characteristics will help inhibit tailings oxidation and reduce the likelihood of acid generating and metals leaching in the long term. Musselwhite Mine is currently planning to remove the sulphide minerals from the tailings stream using a flotation plant. This paper discusses the design of the thickened tailings disposal system and presents preliminary observations on tailings deposition to date. In preparation for thickened tailings disposal the tailings management area was partitioned by an internal dyke in 2008. This has allowed tailings to be 'stacked' using the upstream method of construction in the west cell and the east cell to serve as a water management pond. The cold climate presents a special challenge to operating the thickened tailings system as there is very little precedent experience. The design has incorporated a number of contingency measures to facilitate tailings thickening and deposition in winter. Field data have suggested that the thickened tailings system is performing very well to date. The thickening plant has consistently produced underflow at about 70% solids with minimal attention. The tailings beaches are steeper than expected. The deposited tailings are non-segregating and relatively saturated. The measured in situ dry density of the tailings is higher than expected. The performance of tailings deposition is being closely monitored.

aIn the design of iron oxide-derived composite adsorbents for arsenic removal, the matrix selected for the encapsulation of iron oxide active material is critical to their arsenic adsorption performance. The ideal matrix should have a high surface area, high pore volume, and large pores that can accommodate the iron oxide nanoparticles while without causing the undesired pore filling or blockage. In this paper, we report the use of carbon nanospheres (size of ca. 28 nm) featuring high surface area, high pore volume, and hierarchical large mesopore/macropore structures resulting from nanosphere packing/aggregation as the matrix for the design of iron oxide composites. Iron oxide has been encapsulated into the carbon nanospheres with different contents (7-60 wt%). The composites have been systematically characterized for their structural, morphological, and textural properties, and investigated for their performance for arsenic adsorption. An optimum iron oxide content of 13 wt% has been established with high adsorption capacities of 416 and 201 mg g À1 achieved for As(III) and As(V), respectively, which are highest (for As(III)) or among the highest (for As(V)) reported thus far for iron oxide-based adsorbents. These are in contrast to the typically low adsorption capacities found with iron oxide composites involving other carbonbased matrices, such as activated carbon, carbon nanotubes, and mesoporous carbons. The results confirm the high potential of this class of composite adsorbents for arsenic removal. Meanwhile, the structure-performance relationship demonstrated herein is also of value to the further design of highperformance arsenic adsorbents.

An extensive study was carried out to determine the effectiveness of various sealants in retarding or preventing the production of acid mine drainage (AMD) from mine waste rock and reactive tailings. In addition to cementitious compounds, the sealants included polymer and organic based solutions. Coated and uncoated (control) samples of mine waste rock and tailings were placed in large leaching columns and the leachate solutions were regularly analyzed for parameters such as pH level, redox potential (Eh), conductivity, sulphate and the dissolved heavy metals, Fe, Ni, and Cu. Concurrent with the laboratory tests, samples were exposed to weathering effects for seven months, which included one complete winter season.Mathematical models were fitted to moving averages of the measured data to establish the relationships between pH and Eh, and conductivity and sulphate concentrations which are necessary for indicating AMD production or lack thereof. These models also enabled the estimation of the terminal pH and Eh values. The results indicate that uncoated samples produce significant AMD and that the polymer and organic based solutions were more effective in retarding AMD than the cementitious coatings. Resume-On a mene une etude poussee afin de determiner l'efficacite de divers produits d'etancheite a retarder ou prevenir la generation d'ecoulement acide de mine (EAM) provenant des rejets rocheux de mine et des residues reactifs. En plus de composes a base de ciment, les produits d'etancheite incluaient des solutions a base de polymere et de materiau organique. On a place des echantillons recouverts et nonrecouverts (controle) de rejets rocheux de mine et de residus dans de grandes colonnes de lessivage. On a analyse regulierement divers parametres des solutions de lessivage, tels que Ie niveau de pH, Ie potential redox (Eh), la conductivite, Ie sulfate et les metaux lourds dissous, Fe, Ni et Cu. En parallele avec les essais de laboratoire, on a expose des echantillons aux effets de desagregation par les intemperies pendant sept mois, parmi lesquels une saison hivernale complete. On a ajuste des modeles mathematiques aux moyennes changeantes des donnees mesurees afin d'etablir les relations entre Ie pH et Ie Eh et entre la conductivite et la concentration de sulfate, necessaires a la detection d'EAM. Ces modeles ont aussi permis l'evaluation des valeurs terminales de pH et de Eh. Les resultats indiquent que les echantillons non-recouverts produisent un EAM important et que les solutions a base de polymere et de materiau organique etaient plus effectives a retarder l'EAM que les revetements a base de ciment.

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