This paper identifies the spatial extent of bauxite processing residue (red mud)-derived contaminants and modes of transport within the Marcal and Rába river systems after the dike failure at Ajka, western Hungary. The geochemical signature of the red mud is apparent throughout the 3076 km² Marcal system principally with elevated Al, V, As, and Mo. Elevated concentrations of Cr, Ga, and Ni are also observed within 2 km of the source areas in aqueous and particulate phases where hyperalkalinity (pH < 13.1) is apparent. Although the concentrations of some trace elements exceed aquatic life standards in waters (e.g., V, As) and fluvial sediments (As, Cr, Ni, V), the spatial extent of these is limited to the Torna Creek and part of the upper Marcal. Source samples show a bimodal particle size distribution (peaks at 0.7 and 1.3 μm) which lends the material to ready fluvial transport. Where elevated concentrations are found in fluvial sediments, sequential extraction suggests the bulk of the As, Cr, Ni, and V are associated with residual (aqua-regia/HF digest) phases and unlikely to be mobile in the environment. However, at some depositional hotspots, association of As, Cr, and V with weak acid-extractable phases is observed.

Results are presented from X-ray absorption spectroscopy based analysis of As, Cr, and V speciation within samples of bauxite ore processing residue (red mud) collected from the spill site at Ajka, Western Hungary. Cr K-edge XANES analysis found that Cr is present as Cr(3+) substituted into hematite, consistent with TEM analysis. V K-edge XANES spectra have E(1/2) position and pre-edge features consistent with the presence of V(5+) species, possibly associated with Ca-aluminosilicate phases. As K-edge XANES spectra identified As present as As(5+). EXAFS analysis reveals arsenate phases in red mud samples. When alkaline leachate from the spill site is neutralized with HCl, 94% As and 71% V are removed from solution during the formation of amorphous Al-oxyhydroxide. EXAFS analysis of As in this precipitate reveals the presence of arsenate Al-oxyhydroxide surface complexes. These results suggest that in the circumneutral pH, oxic conditions found in the Torna and Upper Marcal catchments, incorporation and sorption, respectively, will restrict the environmental mobility of Cr and As. V is inefficiently removed from solution by neutralization, therefore, the red mud may act as a source of mobile V(5+) where the red mud deposits are not removed from affected land.

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Few studies have characterized reactive media for phosphorus (P) removal in passive treatment systems in terms of both batch and continuous flow experiments. This study uses basic oxygen steel slag (BOS) from a U.K. feedstock. Batch experiments demonstrated the effective removal of phosphorus with varying initial pH, initial P concentration, clast size, and ionic strength to represent environmental conditions. Continuous flow column experiments, operated for 406 days, with an influent P concentration of 1-50 mg/L (typical of domestic and dairy parlour waste) achieved removal of up to 62%; a second set of column experiments running for 306 days with an influent P concentration of 100-300 mg/L achieved a maximum effective removal of 8.39 mg/g. This figure is higher than that for other slags reviewed in this study (e.g., EAF Slag 3.93 mg/g and NZ melter slag 1.23 mg/g). XRD, E-SEM, and EDX data provide evidence for a sequential series of increasingly less soluble P mineral phases forming on the BOS surface (octa-calcium phosphate, brushite, and hydroxylapatite),which suggests that BOS may be a suitable substrate in passive treatment systems, providing a long-term P removal mechanism.

A number of emergency pollution management measures were enacted after the accidental release of caustic bauxite processing residue that occurred in Ajka, western Hungary in October, 2010. These centred on acid and gypsum dosing to reduce pH and minimise mobility of oxyanion contaminants mobile at high pH. This study assessed the effectiveness of gypsum dosing on contaminant mobility and carbon sequestration through assessment of red mud and gypsum-affected fluvial sediments via elemental analysis and stable isotope analysis. There was a modest uptake of contaminants (notably As, Cr, and Mn) on secondary carbonate-dominated deposits in reaches subjected to gypsum dosing. C and O stable isotope ratios of carbonate precipitates formed as a result of gypsum dosing were used to quantify the importance of the neutralisation process in sequestering atmospheric carbon dioxide. This process was particularly pronounced at sites most affected by gypsum addition, where up to 36% of carbonate-C appears to be derived from atmospheric in-gassing of CO(2). The site is discussed as a large scale analogue for potential remedial approaches and carbon sequestration technologies that could be applied to red mud slurries and other hyperalkaline wastes. The results of this work have substantial implications for the aluminium production industry in which 3-4% of the direct CO(2) emissions may be offset by carbonate precipitation. Furthermore, carbonation by gypsum addition may be important for contaminant remediation, also providing a physical stabilisation strategy for the numerous historic stockpiles of red mud.

There is considerable interest in the use of metallocene or lanthanocene complexes as initiators of polymerization of acrylate-based monomers. 1 We and others have demonstrated that C 2 -symmetric, dialkyl zirconocene initiatorsse.g. rac-en(H 4 Ind) 2 ZrX 2 (1, X ) Me)spolymerize methyl methacrylate to isotactic poly-(methyl methacrylate) (i-PMMA) by an enantiomorphic, site-control mechanism. 2 While syndiotactic PMMA can be prepared using sterically encumbered, lanthanocene initiators at low temperatures, 1a,c,d,g attempts to use C ssymmetric, dialkyl zirconocene initiatorssi.e., Me 2 C-(Cp)(Flu)ZrX 2 (2, X ) Me)sfor this purpose have been unsuccessful. 2b,cAs we have shown elsewhere, either cationic enolate or neutral enolate complexes of zirconium (the latter in concert with metallocenium activators) may serve as initiators of acrylate polymerization. 1h Mechanistic studies can be simplified using such compounds, as formation of these species in situ (from, e.g., metallocene dialkyls, ionic activators, and acrylates) can be slow and/ or inefficient.We have attempted to prepare bis(enolate) complexes of 1 or 2 in the hope of studying isospecific or syndiospecific MMA polymerization using cationic enolates derived from such species. These synthetic studies have met with very limited success; in one case the bis-(enolate) complex 1 could be prepared [X ) OC(Me)d CH 2 ] but this compound failed to effect polymerization of MMA in the presence of B(C 6 F 5 ) 3 , [Ph 3 C][B(C 6 F 5 ) 4 ], or [PhNHMe 2 ][B(C 6 F 5 ) 4 ]. 3 More recently, we have focused our attention on linked, Cp-amido complexes of zirconium, as these compounds are less sterically encumbered than their metallocene "analogues", a feature which facilitates the synthesis of bis(enolate) complexes. We report here our observations using this class of initiators for MMA polymerization.The prototypical complex 4 4 reacts cleanly with 2 equiv of stable, lithium enolate 5 (R ) O t Bu) 5 to provide bis(enolate) complex 3 as a crystalline, white solid (eq 1). 6

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