Environmental Toxicity Assessment of the Spilled Ajka Red Mud in Soil Microcosms for Its Potential Utilisation as Soil Ameliorant

After the red mud spill in Hungary one of the risk reduction measures was to remove the deposits from the soil surface. The residual thin red mud layer was ploughed into the soil. The aim of the present 8-month-long lab-scale microcosm experiment was to estimate the red mud amount with no adverse effects on the soil as natural habitat and to assess the mid-term environmental risk of red mud mixed into the soil. The red mud ratio mixed into the soil ranged between 0–40 %. The experiments were monitored by physico-chemical, biological and ecotoxicological methods. Mixing of 5 % red mud into the soil significantly increased the total As, Cr, Ni, Pb and Na content of the soil, but it did not exceed the Hungarian soil quality criteria. The microcosms containing 5 % red mud did not show any adverse effects on the testorganisms. Overall, 5 % red mud could be mixed into the soil without any mid-term adverse effects

Dispersal and attenuation of trace contaminants downstream of the Ajka bauxite residue (red mud) depository failure, Hungary

This paper identifies the spatial extent of bauxite processing residue (red mud)-derived contaminants and modes of transport within the Marcal and Raba river systems after the dike failure at Ajka, western Hungary. The geochemical signature of the red mud is apparent throughout the 3076 km(2) 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 mu m) 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

Mobilisation of arsenic from bauxite residue (red mud) affected soils: effect of pH and redox conditions

The tailings dam breach at the Ajka alumina plant, western Hungary in 2010 introduced ~1 million m3 of red mud suspension into the surrounding area. Red mud (fine fraction bauxite residue) has a characteristically alkaline pH and contains several potentially toxic elements, including arsenic. Aerobic and anaerobic batch experiments were prepared using soils from near Ajka in order to investigate the effects of red mud addition on soil biogeochemistry and arsenic mobility in soil–water experiments representative of land affected by the red mud spill. XAS analysis showed that As was present in the red mud as As(V) in the form of arsenate. The remobilisation of red mud associated arsenate was highly pH dependent and the addition of phosphate to red mud suspensions greatly enhanced As release to solution. In aerobic batch experiments, where red mud was mixed with soils, As release to solution was highly dependent on pH. Carbonation of these alkaline solutions by dissolution of atmospheric CO2 reduced pH, which resulted in a decrease of aqueous As concentrations over time. However, this did not result in complete removal of aqueous As in any of the experiments. Carbonation did not occur in anaerobic experiments and pH remained high. Aqueous As concentrations initially increased in all the anaerobic red mud amended experiments, and then remained relatively constant as the systems became more reducing, both XANES and HPLC–ICP-MS showed that no As reduction processes occurred and that only As(V) species were present. These experiments show that there is the potential for increased As mobility in soil–water systems affected by red mud addition under both aerobic and anaerobic conditions

Advances in Understanding Environmental Risks of Red Mud After the Ajka Spill, Hungary

In the 5 years since the 2010 Ajka red mud spill (Hungary), there have been 46 scientific studies assessing the key risks and impacts associated with the largest single release of bauxite-processing residue (red mud) to the environment. These studies have provided insight into the main environmental concerns, as well as the effectiveness of remedial efforts that can inform future management of red mud elsewhere. The key immediate risks after the spill were associated with the highly caustic nature of the red mud slurry and fine particle size, which once desiccated, could generate fugitive dust. Studies on affected populations showed no major hazards identified beyond caustic exposure, while red mud dust risks were considered equal to or lesser than those provided by urban dusts of similar particle size distribution. The longer-term environmental risks were related to the saline nature of the spill material (salinization of inundated soils) and the release and the potential cycling of oxyanion-forming metals and metalloids (e.g., Al, As, Cr, Mo, and V) in the soil–water environment. Of these, those that are soluble at high pH, inefficiently removed from solution during dilution and likely to be exchangeable at ambient pH are of chief concern (e.g., Mo and V). Various ecotoxicological studies have identified negative impacts of red mud-amended soils and sediments at high volumes (typically [5 %) on different test organisms, with some evidence of molecularlevel impacts at high dose (e.g., genotoxic effects on plants and mice). These data provide a valuable database to inform future toxicological studies for red mud. However, extensive management efforts in the aftermath of the spill greatly limited these exposure risks through leachate neutralization and red mud recovery from the affected land. Monitoring of affected soils, stream sediments, waters and aquatic biota (fungi, invertebrates and fish) have all shown a very rapid recovery toward prespill conditions. The accident also prompted research that has also highlighted potential benefits of red mud use for critical raw material recovery (e.g., Ga, Co, V, rare earths, inform), carbon sequestration, biofuel crop production, and use as a soil ameliorant

Geochemical recovery of the Torna-Marcal river system after the Ajka red mud spill, Hungary

The failure of the Ajka red mud depository in October 2010 led to the largest single release of red mud into the surface water environment. This study provides a comparative assessment of stream sediment quality in the Torna-Marcal-Rába catchment between post-disaster surveys (2010) and follow up surveys at an identical suite of 21 locations in 2013. The signature of red mud apparent in initial surveys with high Al, As, Cr, Na, V was only apparent at a small number of sample stations in recent surveys. These constitute 20 km reach of affected sediments in the immediate aftermath of the spill. Concentrations of red mud-derived contaminants are predominately associated with fine fractions of the red mud (<8 μm). This enhances transport out of the system of red mud-derived contaminants and, along with extensive remedial efforts, has substantially limited the within-channel inventory of potentially ecotoxic metals and metalloids

Alkaline residues and the environment: A review of impacts, management practices and opportunities

Around two billion tonnes of alkaline residues are produced globally each year by industries such as steel production, alumina refining and coal-fired power generation, with a total production estimate of 90 billion tonnes since industrialization. These wastes are frequently stored in waste piles or landfills, and can be an environmental hazard if allowed to generate dust, or if rainwater infiltrates the waste. This review will focus on the environmental impacts associated with alkaline residues, with emphasis on the leachates produced by rainwater ingress. Many alkaline industrial wastes can produce leachates that are enriched with trace metals that form oxyanions (e.g. As, Cr, Mo, Se, V), which can be very mobile in alkaline water. The management options for the residues and their leachates are also discussed, distinguishing active and passive treatment options. Potential reuses of these materials, in construction materials, as agricultural amendments, and in environmental applications are identified. The mechanisms of carbon sequestration by alkaline residues are assessed, and the potential for enhancing its rate as a climate change off-setting measure for the industry is evaluated. The potential for recovery of metals critical to e-technologies, such as vanadium, cobalt, lithium and rare earths, from alkaline residues is considered. Finally research needs are identified, including the need to better understand the biogeochemistry of highly alkaline systems in order to develop predictable passive remediation and metal recovery technologies

Assessing the role of bed sediments in the persistence of red mud pollution in a shallow lake (Kinghorn Loch, UK)

Red mud is a by-product of alumina production. Little is known about the long-term fate of red mud constituents in fresh waters or of the processes regulating recovery of fresh waters following pollution control. In 1983, red mud leachate was diverted away from Kinghorn Loch, UK, after many years of polluting this shallow and monomictic lake. We hypothesised that the redox-sensitive constituents of red mud leachate, phosphorus (P), arsenic (As) and vanadium (V), would persist in the Kinghorn Loch for many years following pollution control as a result of cycling between the lake bed sediment and the overlying water column. To test this hypothesis, we conducted a 12-month field campaign in Kinghorn Loch between May 2012 and April 2013 to quantify the seasonal cycling of P, As, and V in relation to environmental conditions (e.g., dissolved oxygen (DO) concentration, pH, redox chemistry and temperature) in the lake surface and bottom waters. To confirm the mechanisms for P, As and V release, a sediment core incubation experiment was conducted using lake sediment sampled in July 2012, in which DO concentrations were manipulated to create either oxic or anoxic conditions similar to the bed conditions found in the lake. The effects on P, As, and V concentrations and species in the water column were measured daily over an eight-day incubation period. Phosphate (PO4-P) and dissolved As concentrations were significantly higher in the bottom waters (75.9 ± 30.2 μg L−1 and 23.5 ± 1.83 μg L−1, respectively) than in the surface waters (12.9 ± 1.50 μg L−1 and 14.1 ± 2.20 μg L−1, respectively) in Kinghorn Loch. Sediment release of As and P under anoxic conditions was confirmed by the incubation experiment and by the significant negative correlations between DO and P and As concentrations in the bottom waters of the lake. In contrast, the highest dissolved V concentrations occurred in the bottom waters of Kinghorn Loch under oxic conditions (15.0 ± 3.35 μg L−1), with the release from the bed sediment apparently being controlled by a combination of competitive ion concentrations, pH and redox conditions