Ronan Courtney

Nutrient status of vegetation grown in alkaline bauxite processing residue amended with gypsum and thermally dried sewage sludge - A two year field study

Although the treatments for overcoming the high pH and exchangeable sodium percentage (ESP) of bauxite residue are well known, there is little information on long-term nutrient management of vegetation after rehabilitation. The present study examined the chemical and physical amendment of fine fraction residue (red mud) at the Aughinish Alumina Ltd. Bayer Plant, Ireland followed by a two-year field investigation. Gypsum and sewage sludge were incorporated into the residue and amended mud sown with Lolium perenne and Holcus lanatus. Aerial portions were harvested and nutrient composition determined annually for the first two years growth. Amended substrate was low in manganese and magnesium. After year one herbage contained adequate calcium levels, but there were deficiencies for nitrogen, manganese, potassium and magnesium. Sodium levels were not considered excessive and levels declined further in year two. Levels for nitrogen, calcium, manganese, magnesium, phosphorous and potassium were also reduced in the second year. As levels were already deficient in year one the further decreases suggest severe nutrient shortage in the residue substrate. For long-term success of revegetation of bauxite residue, even after gypsum and organic amendment, the deficiencies of nutrients in the substrate must be overcome.

Bacterial Communities Established in Bauxite Residues with Different Restoration Histories

Bauxite residue is the alkaline byproduct generated when alumina is extracted from bauxite ores and is commonly deposited in impoundments. These sites represent hostile environments with increased salinity and alkalinity and little prospect of revegetation when left untreated. This study reports the establishment of bacterial communities in bauxite residues with and without restoration amendments (compost and gypsum addition, revegetation) in samples taken in 2009 and 2011 from 0 to 10 cm depth. DNA fingerprint analysis of bacterial communities based on 16S rRNA gene fragments revealed a significant separation of the untreated site and the amended sites in both sampling years. 16S amplicon analysis (454 FLX pyrosequencing) revealed significantly lower alpha diversities in the unamended in comparison to the amended sites and hierarchical clustering separated the unamended site from the amended sites. The taxonomic analysis revealed that the restoration resulted in the accumulation of bacterial populations typical for soils including Acidobacteriaceae, Nitrosomonadaceae, and Caulobacteraceae. In contrast, the unamended site was dominated by taxonomic groups including Beijerinckiaceae, Xanthomonadaceae, Acetobacteraceae, and Chitinophagaceae, repeatedly associated with alkaline salt lakes and sediments. While bacterial communities developed in the initially sterile bauxite residue, only the restoration treatments created diverse soil-like bacterial communities alongside diverse vegetation on the surface.

Utilization of spent mushroom compost for the revegetation of lead-zinc tailings: effects on physico-chemical properties of tailings and growth of Lolium perenne.

In an attempt to promote sustainable vegetation cover on metalliferous tailings, a randomized factorial greenhouse trial of six-month duration was established to determine the effect of spent mushroom compost (SMC) amendment on the physical and chemical properties of the predominantly lead/zinc tailings. The tailings originated from the surface (20-30cm) of the partially-vegetated 76ha tailings management facility (TMF), where more than nine million tonnes of pyritic metalliferous material were deposited in an unlined land impoundment. SMC was incorporated at application rates of 0, 50, 100, 200 and 400tonha(-1), with each treatment replicated 10 times and Lolium perenne sown at a rate of 200kgha(-1). The addition of SMC was beneficent as a growing medium through improvement of the structural status of the tailings and ultimately through the provision of plant nutrients and reduction in metal concentrations. However, this improvement in the structural and chemical status of the tailings is not adequate in maintaining a sustainable vegetation cover and therefore other remedial options such as introducing a capillary break on the surface of the tailings facility are necessary.

Growth of Trifolium pratense in Red Mud Amended With Process Sand, Gypsum and Thermally Dried Sewage Sludge

Aughinish Alumina Ltd. annually produces approximately 1.5 M tonnes of alumina, 1.05 M tonnes red mud and 0.15 M tonnes of process sand residue. The residues which are stored in a mudstack are susceptible to wind erosion in a plant closure scenario. Establishment of vegetation on the residues is an attractive desirable method of suppressing dust generation. However, there are constraints in achieving vegetation growth on the residues due to the inherent high pH and sodium levels. The present study examined the use of gypsum and thermally dried sewage sludge as amendments for establishing the clover species Trifolium pratense on a red mud/process sand mix. Gypsum was applied to plots at rates of 0 and 3% (w/w) with both treatments receiving thermally dried sludge at 35 t/ha. Gypsum amendment improved chemical conditions of the substrate and increased plant yield. Plant tissue analysis indicated adequate levels for Ca and Mg but a deficiency of Mn. High Fe and Na levels were also recorded. Results demonstrate that growth of clover on red mud is possible with the addition of dried sludge and without the addition of gypsum. However, future monitoring is recommended to determine if the absence of gypsum will have a deleterious effect.

Effectiveness of a constructed wetland for treating alkaline bauxite residue leachate: a 1-year field study

Increasing volumes of bauxite residues and their associated leachates represent a significant environmental challenge to the alumina industry. Constructed wetlands have been proposed as a potential approach for leachate treatment, but there is limited data on field-scale applications. The research presented here provides preliminary evaluation of a purpose-built constructed wetland to buffer leachate from a bauxite residue disposal site in Ireland. Data collected over a 1-year period demonstrated that the pH of bauxite residue leachates could be effectively reduced from ca. pH 10.3 to 8.1 but was influenced by influent variability and temporal changes. The wetland was also effective in decreasing elemental loading, and sequential extractions suggested that the bulk of the sediment-bound metal inventory was in hard-to-leach phases. Elemental analysis of Phragmites australis showed that although vegetation displayed seasonal variation, no trace elements were at concentrations of concern.

Evaluation of Mehlich 3 for Extraction of Copper and Zinc from Irish Grassland Soils and for Prediction of Herbage Content

Abstract: The objective of this study was to determine how the extractant Mehlich 3 (M3) compared with other methods currently used in Ireland for determination of copper (Cu) and zinc (Zn) in soils. Samples from eight different mineral soil types, four of sandstone/shale and four of limestone origin, were analyzed for copper and zinc using M3 and conventional extractants. Herbage samples were taken from the soils and analyzed for Cu and Zn. Mehlich 3 results showed good correlation with ethylenediamine‐tetraacetic acid (EDTA)– and diethylenetriamine‐pentaacetic acid (DTPA)–extractable Cu and Zn. Inclusion of soil properties in multiple regression models improved the coefficients of determination. All extractants were equal in their ability to predict Cu and Zn herbage content. Differences between sandstone/shale and limestone soils in relation to herbage content were also found, with the better relationship found in sandstone/shale soils.

The potential for constructed wetlands to treat alkaline bauxite residue leachate: laboratory investigations

High alkalinity (pH > 12) of bauxite residue leachates presents challenges for the long-term storage and managements of the residue. Whilst the use of constructed wetlands is gaining in interest for its use in the treatment of alkaline waters, thus far, there is limited evidence of its suitability for treating NaOH dominated bauxite residue leachate. A series of batch trials were conducted to investigate the potential for constructed wetland conferred mechanisms (dilution water quality, contact with CO2, and substrate type) for treating NaOH solutions to levels permissible for discharge (p < 9). Results demonstrate that significant reductions in solution pH can be achieved depending on the diluting water quality. Levels achieved may not always be suitable for direct discharge (i.e. pH ≤ 9), but further reductions occur with carbonation and soil contact. The extent of pH decrease and the timeframe required are influenced by soil quality, with greater efficiency observed in soils with higher organic matter content. Decrease in solution pH to discharge permit values are possible through a combination of the mechanisms occurring in a constructed wetland. Formation of a calcite precipitate was observed in some treatments and further characterisation by XRD and XPS suggested surface coating with Na2CO3. It is therefore suggested that, under suitable conditions, constructed wetland technology can reduce leachate pH to <9 through mechanisms supporting the precipitation of sodium carbonate from solution. Further trials should investigate the activity under biological conditions representative of an operating constructed wetland.

Sustained Bauxite Residue Rehabilitation with Gypsum and Organic Matter 16 years after Initial Treatment

Bauxite residue is a high volume byproduct of alumina manufacture which is commonly disposed of in purpose-built bauxite residue disposal areas (BRDAs). Natural waters interacting with bauxite residue are characteristically highly alkaline, and have elevated concentrations of Na, Al, and other trace metals. Rehabilitation of BRDAs is therefore often costly and resource/infrastructure intensive. Data is presented from three neighboring plots of bauxite residue that was deposited 20 years ago. One plot was amended 16 years ago with process sand, organic matter, gypsum, and seeded (fully treated), another plot was amended 16 years ago with process sand, organic matter, and seeded (partially treated), and a third plot was left untreated. These surface treatments lower alkalinity and salinity, and thus produce a substrate more suitable for biological colonisation from seeding. The reduction of pH leads to much lower Al, V, and As mobility in the actively treated residue and the beneficial effects of treatment extend passively 20-30 cm below the depth of the original amendment. These positive rehabilitation effects are maintained after 2 decades due to the presence of an active and resilient biological community. This treatment may provide a lower cost solution to BRDA end of use closure plans and orphaned BRDA rehabilitation.

Plant assays and avoidance tests with collembola and earthworms demonstrate rehabilitation success in bauxite residue

Bauxite residues are a by-product of alumina manufacture from bauxite ore and are commonly disposed of in purpose-built bauxite residue disposal areas (BRDAs). Revegetation is viewed as the most effective way to landscape and rehabilitate closed BRDAS and physicochemical assessment remains the primary indicator of rehabilitation success. Little is known about the ability of keystone mesofaunal species to colonise and establish in these environments yet the long-term success of rehabilitation is dependent on residues becoming suitable habitats for such groups. Using six different residue treatments (untreated, leached, organic application, organic amended, and two revegetated field treatments) together with OECD test soil, this study assessed the characteristics of residues with plant germination and seedling development using the Rhizotest™ approach with Lepidium sativum, Sinapis alba, and Sorghum bicolor. Avoidance tests with soil mesofauna Eisenia foetida together with growth and reproduction tests for Folsomia candida were conducted to determine possibility of inhibition in residue soils. Unamended residue is inhibitory to plant growth and mesofaunal establishment. Amendment improves the physicochemical properties of the residue, and data revealed that both gypsum and organic addition is required to promote conditions favourable to plant growth and mesofauna establishment. Earthworms avoid residues with elevated Na content but will choose substrate with high soluble Ca content. F. candida preferentially moves to residues from field treatments, and both mortality and reproduction rates are comparable or superior to OECD soil. On the basis of these assays, we propose that bauxite residue can be transformed to a soil-like medium capable of supporting keystone species.

Assessing metal transfer to vegetation and grazers on reclaimed pyritic Zn and Pb tailings.

A study of the concentrations of zinc and lead in an engineered soil capping system overlying sulphide mine tailings was undertaken. Tailings geochemistry, soil cover and vegetation were monitored over a 4-year period, and a cattle grazing demonstration exercise was conducted over a 1-year period. Whilst the tailings had a relatively high pyrite content and demonstrated oxidation, a circum neutral pH was observed for the duration of the study period due to the high dolomitic content. No evidence of metal mobility into the soil cover and vegetation was observed over the monitoring period. Relatively high Zn herbage content is attributed to the glacial till component of the soil cover. Similarly, no evidence of metal transfer to grazing cattle was observed through blood and tissue analysis with Zn content not significantly different from control animals. Pb tissue content was below limit of detection.