Published in J. Environ. Qual. 33:1877-1884 (2004).
© ASA, CSSA, SSSA
677 S. Segoe Rd., Madison, WI 53711 USA
TECHNICAL REPORTS
Waste Management
Seawater Neutralization of Alkaline Bauxite Residue and Implications for Revegetation
N. W. Menziesa,*,
I. M. Fultonb and
W. J. Morrella
a Centre for Mined Land Rehabilitation, University of Queensland, St. Lucia 4072, QLD, Australia
b Alcan Gove Pty Ltd, Nhulunbuy 0881, NT, Australia
* Corresponding author (n.menzies{at}uq.edu.au).
Received for publication September 1, 2003.
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ABSTRACT
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Reaction of bauxite residue with seawater results in neutralization of alkalinity through precipitation of Mg-, Ca-, and Al-hydroxide and carbonate minerals. In batch studies, the initial pH neutralization reaction was rapid (<5 min), with further reaction continuing to reduce pH for several weeks. Reaction with seawater produced a residue pH of 8 to 8.5. Laboratory leaching column studies were undertaken to provide information on seawater neutralization of the coarse-textured fraction of the waste, residue sand (RS), under conditions comparable with those that might be applied in the field. An 0.80-m-deep column of RS was neutralized by the application of the equivalent of 2-m depth of seawater. In addition to lowering the pH and Na content of the residue, seawater neutralization resulted in the addition of substantial amounts of the plant nutrients Ca, Mg, and K to the profile. Similar results were also obtained from a field-scale assessment of neutralization. However, the accumulation of precipitate, consisting of hydrotalcite, aragonite, and pyroaurite, in the drainage system may preclude the use of in situ seawater neutralization as a routine rehabilitation practice. Following seawater neutralization, RS remains too saline to support plant growth and would require fresh water leaching before revegetation.
Abbreviations: EC, electrical conductivity • ICP–AES, inductively coupled plasma atomic emission spectroscopy • RM, red mud • RS, residue sand
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INTRODUCTION
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WORLDWIDE, MORE THAN 100 million Mg of bauxite is mined each year (Oeberg and Steinlechner, 1996). Alumina is extracted from the bauxite using the Bayer process, in which the bauxite is mixed with hot concentrated sodium hydroxide to dissolve the aluminum. The remaining solids, known as bauxite residue, are separated from the process liquor in a series of large thickeners and pumped to disposal areas. The production of residue ranges from 0.6 to 2.0 Mg per Mg of alumina produced, depending on the quality of the bauxite. Current world production of this waste is estimated at 30 million Mg per year (dry basis) (Oeberg and Steinlechner, 1996). This enormous production of saline and alkaline waste poses a major disposal problem for the industry.
Seawater neutralization of alkaline bauxite residue, which can act to lower the salinity and alkalinity of the waste, is used in a number of settings. The simplest scenario is the disposal of residue into a marine environment (Zambo, 1979; Hudson, 1987). At some refineries, seawater has been used to slurry bauxite residue to land disposal areas, achieving a partial neutralization of the material to approximately pH 9.8 (Bell and Meecham, 1979; Lewis et al., 1995). Seawater neutralization of bauxite residues at the Queensland Alumina Refinery reduces the waste pH to about 8.6 (McConchie et al., 1999), producing a stable material suitable for a range of reuse applications. Seawater-neutralized red mud has been shown to effectively neutralize acid sulfate soils, and to remove trace metals from solution (Lin et al., 2002). Seawater discharged from the Queensland Alumina neutralization process has been shown to have little adverse effect on the receiving marine environment (McConchie et al., 1996).
At Gove, in the far north of Australia, bauxite residue is disposed as dewatered slurry (60% v/v) on land. Once residue deposition is complete, the surface of the disposal area is stabilized using a vegetated soil cover. In the monsoonal environment at Gove, the success of revegetation will depend on the depth to which plant roots can extract water. If bauxite residue can be sufficiently ameliorated to permit its exploitation by plant roots, the total supply of water available to the cover vegetation will be increased, and more successful revegetation will be achieved. The use of seawater neutralization to ameliorate bauxite residue is well suited to the situation at Gove, where alternative ameliorative materials such as organic wastes (Tacey et al., 1977; Fuller et al., 1982; Hossner et al., 1986; Ward et al., 1996) are not readily available.
In this paper, we report a series of experiments conducted to evaluate seawater neutralization of bauxite residue. Preliminary studies were conducted to determine the extent of pH neutralization that can be achieved using seawater, and the rate at which this neutralization occurs. This information was then used to design larger-scale leaching column studies, and to guide a field evaluation of seawater neutralization.
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MATERIALS AND METHODS
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In the Al extraction process used at Gove, bauxite residue is separated on the basis of particle size into coarse-textured residue sand (RS) and fine-textured red mud (RM). Representative samples of RS and RM were collected from disposal ponds. The samples of RM were collected wet (60% solids) and used in this condition in subsequent analyses. The RS was air-dry when collected. The particle size distributions of these materials, as determined using a Mastersizer 2000 apparatus (Malvern Instruments, Worcestershire, UK) following dispersion with sodium hexa-metaphosphate and ultrasound, are presented in Fig. 1. The pH of a 1:5 suspension of RM was 12, and that of RS was 11.8. The electrical conductivity (EC) of these suspensions was 11 dS m–1 for the RM and 9.4 dS m–1 for the RS.
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Fig. 1. The particle size distribution of (a) residue sand and (b) red mud. The histogram bars indicate the proportion of particles in each size increment (left axis), while the solid line indicates the cumulative proportion smaller than a given size (right axis).
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Batch Neutralization Studies
Seawater batch neutralization of residue was evaluated at a range of residue to seawater suspension ratios (1:1, 1:2, 1:5, 1:10, 1:20, and 1:50). All suspensions were prepared using 200 mL of seawater and the appropriate weight of residue (1:1 200 g, 1:2 100 g, 1:5 40 g, 1:10 20 g, 1:20 10 g, and 1:50 4 g oven-dry equivalent weight). Measurement frequency was initially high (1, 5, 10, and 30 min), decreasing to hourly measurement (up to 10 h), then at 18 and 24 h. Samples were shaken end-over-end (15 rpm) continuously throughout this period. The suspension pH was measured in a stirred suspension using an intermediate junction glass electrode. Measurements were continued on the 1:50 suspension for 72 d. Measurements were also continued on the 1:2 suspension, but the seawater was replaced on a weekly basis. Suspensions were centrifuged for 40 min at 800 x g, the supernatant decanted and a fresh aliquot of seawater added. Solids were resuspended by vigorous shaking with a vortex mixer, and the regime of daily shaking and measurement continued. Four replications were made of each suspension.
A bulk sample of seawater was collected and used in all experiments reported here. The seawater had a pH of 8.07 (measured relative to IUPAC buffers) and cation composition of Na 499, Mg 55.5, K 10.3, and Ca 9.98 mM.
Data were analyzed as a completely randomized design using repeated measures analysis (SAS Institute, 1999). Comparisons between means were made using Fisher's least significant difference (LSD) test. The variance ratios and LSDs for time and interaction terms were adjusted for the degree of autocorrelation between times by the Greenhouse–Geisser epsilon (Greenhouse and Geisser, 1959).
Column Neutralization Studies
The physical characteristics of the RS fraction make it an attractive material for use as a soil replacement in rehabilitation. Column neutralization studies were undertaken to provide a more realistic simulation of the effectiveness of seawater neutralization of RS under conditions that may be achieved in the field. Leaching columns (1 m long) were prepared from 0.15-m-diameter PVC piping. The bottom end was closed using a PVC end-cap with an attached single drainage tube (8 mm in diameter). Movement of water to the drainage tube was enhanced by placing a fiberglass geotextile mat beneath the RS. Residue sand was packed into the columns in 0.10-m-thick layers to achieve a bulk density of 1.3 Mg m–3, with individual layers separated by fiberglass gauze (2- x 2-mm mesh) to aid identification of layers at sampling. Eight layers were placed in each column. A total of 50 columns were prepared.
Hydraulic conductivity of RS was determined using the method of Klute and Dirksen (1986) to aid in the selection of an appropriate leaching regime. Laboratory columns (5 cm deep) of RS were prepared by compacting material to a range of bulk densities from approximately 1.1 to approximately 1.5 Mg m–3; the higher densities being achieved by compaction of moist RS (17% gravimetric moisture content) with a hydraulic ram. Compaction produced bulk densities of 1.28 g cm–3 at 700 kPa, 1.35 g cm–3 at 1000 kPa, 1.36 g cm–3 at 2100 kPa, 1.39 g cm–3 at 3000 kPa, and 1.54 g cm–3 at 5500 kPa, the highest pressure used. A constant head of water was applied and the rate of flow monitored. Saturated hydraulic conductivity was recorded once a stable flow rate was attained. Conductivity was measured using both deionized water and seawater.
Columns were irrigated with seawater at a rate of 0.1-m depth equivalent (1.77 L) per day. This was approximately one-half of the water volume retained by the column after 24 h of free drainage (from the saturated base of the column). Water was applied as a single addition and infiltrated into the column in <1 h. Leachate was collected from four replicate columns (selected at random for each measurement) and analyzed for pH on a daily basis. Subsamples of leachate from these columns were stored at <4°C before elemental analysis. A white precipitate was noted in the collection flasks. This was allowed to settle and the supernatant filtered (0.22 µm) before elemental analysis to avoid particulate contamination. The solution concentrations of Ca, Mg, Na, K, and S were determined by inductively coupled plasma atomic emission spectroscopy (ICP–AES). Statistical analysis was performed using SAS programs (SAS Institute, 1999), with comparison between means made using Fischer's protected least significant difference (LSD) test.
To permit analysis of the residue solid phase, two replicate columns were destructively sampled after every four seawater applications. The columns were split longitudinally, then samples of each of the initial 0.10-m depth increments taken and dried at 40°C for analysis. Additional samples were taken for gravimetric moisture content determination to permit correction of the exchangeable cation measurements for entrained soluble cations. This correction was made on the basis of the gravimetric moisture content and a cation concentration estimated from the column leachate composition. Solid-phase pH and EC were measured in 1:5 residue to water suspensions. Exchangeable cations were displaced by 1 M NH4Cl at a 1:10 residue to extractant ratio and measured by ICP–AES. Ammonium was used as the displacing cation because of the high monovalent cation preference of internal exchange sites on the sodalite (Na8Al6Si6O24Cl2) present in the residue (Wong and Ho, 1995). The cation exchange capacity (CEC) was measured on samples collected after 4, 20, and 44 seawater additions. Following exchangeable cation extraction, samples were washed three times with 0.04 M NH4Cl and extracted with KNO3, and the NH4 was determined by distillation. The CEC was corrected for the volume of 0.04 M NH4Cl entrained (Sumner and Miller, 1996). Statistical analysis of solid-phase data was performed using SAS programs (SAS Institute, 1999).
Solid-phase samples (2 g) collected after 20 additions of seawater were digested with nitric and perchloric acid (20 mL of 5:1 mixture) and analyzed for Ca and Mg by atomic absorption spectroscopy. Samples of white precipitate from the leachate collection bottles were dissolved in aqua regia (3:1 HCl to HNO3) and analyzed by ICP–AES.
Field Evaluation of Seawater Neutralization
Neutralization of RS by seawater irrigation was validated at a field scale on an experimental revegetation plot. A 1.6-m depth of partially neutralized RS (reacted with approximately 20% of the seawater required to achieve complete neutralization) was trucked onto an 80- by 30-m plot and ameliorated with gypsum (CaSO4·2H2O) (30 Mg ha–1) and wood mulch (1500 m3 ha–1). However, vegetation failed to establish on the plot and further amelioration by seawater irrigation was undertaken. Seawater was distributed using small horticultural irrigation sprinklers (3-m-radius spray) configured to give overlapping spray patterns, thus ensuring a relatively uniform water distribution. Irrigation was applied at 12.5 mm h–1 for six hours per day for 30 d, giving a total application of 2.25 m of seawater.
Subsurface drainage lines, consisting of gravel and geotextile encased in 0.10 m of perforated PVC pipe, were installed at 20-m intervals at the interface of the RS and underlying RM. Eight core samples to 0.80-m depth were taken on a 10-m square grid before and following seawater irrigation. The cores were separated into 0.10-m depth increments and analyzed for pH, EC (1:5 residue to water), and extractable cations (1 M NH4Cl). No attempt was made to partition extracted cations between soluble (entrained seawater) and exchangeable. Drainage water from two subsurface drainage lines was sampled regularly during the irrigation period (10 samples over 30 d). Solution pH and EC were measured and Ca, Mg, Na, and K concentrations determined by ICP–AES following filtration to 0.45 µm. White precipitate collected from drainage lines was analyzed for elemental composition by ICP–AES following dissolution in HF (Lim and Jackson, 1982), and for mineralogy by X-ray diffraction with pattern matching using Siroquant search/match software (Taylor, 1991).
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RESULTS AND DISCUSSION
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Batch Neutralization Studies
Seawater neutralization was achieved by both a single neutralization reaction at a low residue to seawater ratio (1:50), and as a series of reactions with fresh seawater at a higher ratio (1:2) (Fig. 2). The low ratio neutralization data demonstrate that an initial neutralization to pH 9 occurs within one minute (Fig. 2), with further reaction over time to achieve a stable pH of approximately 8 for RS and approximately 8.5 for RM after 20 d (Fig. 2). For RM, a second treatment with fresh seawater at a 1:50 ratio, at the end of the reported measurement period, lowered the pH to approximately 8, whereas for RS a second treatment with fresh seawater did not markedly lower the pH. At high residue to seawater ratios (1:1 and 1:2), the pH of RM suspensions initially decreased (up to 20 min), then increased. This appears to be an effect of the relatively slow mixing achieved by end-over-end shaking, and could be reduced by vortex mixing and eliminated by ultrasonic dispersion (Branson 250, 50% duty cycle; Branson Ultrasonics, Danbury, CT). These more vigorous mixing approaches speeded equilibration, but did not alter the final pH achieved.
The regular replacement data (Fig. 2) indicate that neutralization of RS with two increments of seawater (4:1 on volume to weight basis) achieves a pH of approximately 8.5, with the decrease to approximately pH 8 achieved by five increments. In contrast, RM required six aliquots of seawater to lower the pH to <8.5, and following 10 seawater additions the pH was still slightly above 8.
The initial neutralization of residue by seawater is rapid (Fig. 3). In the context of a field-scale neutralization system, the rate of reaction of bauxite residue with seawater should not limit the application of this approach. If RS is pumped to disposal areas as a slurry with seawater, reaction to a pH of approximately 9 would probably occur in the pipe. Where neutralization by seawater irrigation is to be undertaken following deposition of RS in disposal areas, the reaction kinetics data indicate that the neutralization rate would be controlled by the rate of application of seawater, rather than by the speed of the neutralization reaction.
McConchie et al. (1999) described the seawater neutralization process as precipitation of hydroxyl ions predominantly as brucite, but also as boehmite, gibbsite, hydrocalumite, hydrocalcite, and p-aluminohydrocalcite, and of carbonate as calcite–aragonite. They report a pH of 8.6 for seawater-neutralized bauxite residue, a result comparable with that achieved here for the Gove residue.
Column Neutralization Studies
The relationship between hydraulic conductivity and bulk density (Fig. 4) is erratic at low densities, due to the presence, in some cores, of preferential pathways that permit rapid bypass flow. These low bulk density systems are not stable, and would rapidly pack to a higher density. Application of seawater to the leaching columns caused the RS sand to settle to a greater bulk density than that achieved by the initial packing. Following five applications of seawater, the columns had settled to a stable residue depth of 0.75 m, giving a bulk density of 1.38 Mg m–3. The measured hydraulic conductivity at densities greater than 1.3 Mg m–3 was relatively constant at 0.18 to 0.20 m h–1.
The hydraulic conductivity was not markedly altered by salinity (Fig. 4), though deionized water caused dispersion of the clay fraction, producing discolored drainage. While dispersion in the deionized water did not alter the hydraulic conductivity of the RS in the experimental system, this result may not be transferable to the field. In the 0.10-m-deep experimental columns, insufficient clay was mobilized by the infiltration of deionized water to cause blockage of pores. However, in the deeper RS profiles that would be used as part of a revegetation strategy, sufficient clay may be mobilized to cause blockage of pores and reduce the profile hydraulic conductivity.
An important aspect of the relationship between hydraulic conductivity and bulk density is that the conductivity is not markedly affected by increasing compaction. Even at the highest densities used, saturated hydraulic conductivity was not greatly reduced. This indicates that even compacted areas will have high infiltration rates.
The data for leachate solution composition (Fig. 5a) demonstrate a pH breakthrough at approximately 20 applications (2 m). This equates to a RS to seawater ratio of approximately 1:2, and is a reflection of the inherently more efficient nature of this system than batch neutralization. The application of seawater eluted alkalinity, which would otherwise need to be directly neutralized in the batch system. In a field setting, the displaced alkalinity would need to be neutralized by dilution with seawater before discharge to the sea (Table 1).
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Table 1. The pH of Bayer process liquor and of leachates from residue sand columns in an undiluted state and following dilution at a number of ratios with seawater.
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Excess Na (retained Bayer process liquor) was leached from the columns by the first 0.2 m of seawater (Fig. 5a). The Na concentration in the leachate then remained at a concentration comparable with that of the input seawater. Breakthrough of the other major cations from the seawater occurred in the order K (after 1 m of seawater application), Mg (after 1.7 m), and Ca (after 2.6 m) (Fig. 5b). This sequence reflects the typical lyotrophic series for these cations on soil cation exchange systems (McBride, 1994). The divalent cations, Ca and Mg, were strongly retained by the RS column (Table 2), with apparent retention efficiencies exceeding 99%. Importantly, this was achieved without any special treatment and should thus be achievable in the field. Indeed, the experimental system used, where the seawater was applied rapidly (0.1 m of irrigation infiltrating in <1 h), would have biased the system to lower efficiencies than in a field irrigation system where the same amount of irrigation would be applied over several hours.
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Table 2. The leachate volume at which cation breakthrough begins, and the mass balance of cations applied to residue sand during seawater leaching.
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It was anticipated that Ca and Mg in seawater applied to the RS column would be retained within the column as precipitates formed during the neutralization process and as exchangeable cations retained following Na displacement. However, white precipitate appeared in the leachate collection bottles from early in the leaching process. A similar white precipitate was produced in the field during seawater neutralization and was deposited at the subsurface drainage discharge. Analysis of the collected material demonstrated that it was a mixture of Ca, Mg, and Al salts. The amount of precipitate was not quantified, and the loss of this material from the column prevented the calculation of a full mass balance for Ca and Mg. However, as acid digestion of RS samples from the columns showed that only 38% of Ca and 23% of Mg applied as seawater was retained within the profile (Table 2), it appears the most of the Ca and Mg applied was carried from the column as a precipitate. Of the Ca and Mg retained within the RS profile, the majority was present as exchangeable cations.
Exchange of Ca, Mg, and K for Na on the RS appears to occur progressively from the surface, effectively forming a saturating front moving through the RS column (Fig. 6). In Fig. 6, the data for 44 applications (filled circle) are presented to represent the near-equilibrium condition. It is apparent that Mg initially occupies the exchange complex in excess of the final equilibrium condition (Fig. 6d); a result of the more rapid movement of Mg through the column than Ca. Magnesium has a higher concentration in seawater and lower affinity for the RS surface than Ca. The more rapid movement of Mg through the column results in an absence of competition from Ca, allowing Mg to occupy a greater proportion of exchange sites. Later, as the demand for Ca was satisfied in overlying layers and greater amounts of Ca moved downward through the column, a portion of the initially adsorbed Mg was displaced. During seawater neutralization, the amelioration of the residue proceeds gradually downward from the surface, rather than uniformly throughout the column. This progressive amelioration of pH, and the cation exchange complex, from the column surface (Fig. 6) indicates that a partially neutralized column consists of fully neutralized material overlying un-neutralized RS. Thus, plant roots growing into a partially neutralized RS profile would initially encounter fully neutralized material.
The cation exchange capacity was not significantly (P > 0.05) altered by seawater treatment; the mean value across sampling times and column depths was 18.1 cmolc kg–1. This is comparable with the sum of exchangeable cations (18.6 cmolc kg–1) measured after 4.4 m of seawater leaching, indicating that the correction for entrained solution effectively accounted for the soluble salt present in the samples.
Field Neutralization of Residue Sand
Fresh (untreated) RS has a pH approximately 12, an EC (1:5 suspension) exceeding 9 dS m–1, and a Na saturation of almost 100%. The RS material used to construct the field trial plot had been partially seawater-neutralized before placement, lowering the pH and EC. However, following this partial treatment, the pH of the waste remained too high to support satisfactory plant growth. Re-treatment by seawater irrigation in situ was undertaken to lower the substrate pH in an effort to produce a better environment for plant growth.
Before re-treatment by seawater irrigation, the pH of the field plot was approximately 10.5, with lower values in the surface as a result of gypsum addition. Gypsum application also produced higher exchangeable Ca through displacement of Na (Fig. 7c and 7e). Re-treatment by seawater irrigation successfully lowered the pH, EC, and extractable Na concentration (Fig. 7). Calcium applied to the residue surface as gypsum was redistributed through the profile. Additional Ca was retained from the seawater, increasing the extractable Ca content of the profile (to 0.80 m) from 2.5 to 3.9 Mg ha–1 (Fig. 7).
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Fig. 7. The (a) pH, (b) electrical conductivity (EC), and (c,d,e,f) extractable cation content of a residue sand field plot when partially seawater-neutralized (•) and when fully seawater-neutralized ( ).
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The field data also demonstrate the exchange preference effect apparent in the column studies. The initial seawater treatment produced profile extractable K concentrations of 0.32 cmolc kg–1, but further seawater treatment decreased this value to 0.26 cmolc kg–1, an effect attributed to an initial oversaturation of sites with K in the absence of competition from Mg and Ca. During re-treatment, Ca and Mg displaced K from exchange sites. The lower portion of the profile (0.5–0.8 m) shows higher concentrations of Mg, while the Ca concentration has not reached its equilibrium level.
Leachate composition data obtained from the field were generally consistent with that produced in the column study. During re-treatment with seawater irrigation, the monitored subsurface drainage lines showed a pH breakthrough, correlating with an increase in the K concentration to approximately that of seawater (Table 3). However, the Ca and Mg results from one drain were erratic, often showing concentrations exceeding those obtained during the column study, with Mg up to 800 mg L–1 and Ca up to 90 mg L–1 (Table 3). This effect may be attributed to bypass or preferential flow of seawater to the drain, or may be the result of inclusion of fine particulate material (<0.45 µm) in the measured soluble concentration.
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Table 3. The pH, electrical conductivity (EC), and elemental composition of leachate collected during seawater irrigation of residue sand in the field.
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A white precipitate was found where the drainage water ponded and following excavation of a portion of subsurface drainage system, was found to be blocking the drain pipe. This material primarily consisted of Mg (169 mg g–1), Al (54.9 mg g–1), Ca (38.2 mg g–1), and Fe (22.2 mg g–1). X-ray diffraction revealed hydrotalcite, Mg6Al2CO3(OH)16·4H2O (22-0700), aragonite, CaCO3 (41-1475), and pyroaurite, Mg6Fe2CO3(OH)16·4H2O (24-1110). This composition is consistent with the mineralogical suite suggested by McConchie et al. (1999), with the exception of brucite. This was the major Mg form reported by these authors, but was not identified in this study. The volume of precipitate was sufficient to completely clog portions of the subsurface drainage system. As subsurface drainage is considered crucial to the maintenance of suitable conditions for plant growth, the use of in situ seawater neutralization may require the replacement or cleaning of the drainage system if adopted as a routine remediation approach.
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CONCLUSIONS
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These studies demonstrate that the pH of bauxite-refining residue can be markedly reduced by irrigation with seawater. A pH of approximately 8 was achieved and is sufficiently low to permit plant growth in the neutralized residue. Seawater irrigation also replaces Na with Ca, Mg, and K, thus improving the medium's plant fertility. The salinity of the bauxite residue is reduced by seawater irrigation; however, the residue remains too saline to support most plant species. In a field situation, entrained seawater would need to be displaced by rainfall to produce a medium more conducive to plant root growth.
The loss of Ca and Mg from the neutralized sand as suspended precipitate is undesirable in a number of respects because (i) Ca and Mg are plant nutrients that are scarce in the Gove environment, (ii) formation of the precipitate resulted in clogging of the subsurface drainage system, and (iii) this precipitate will accumulate in other parts of the drainage and seawater dilution system. As clogging of the subsurface drainage system cannot be easily avoided, the in situ neutralization technique adopted in the field trial may not be a viable technique for routine revegetation. Alternative approaches, such as neutralization within a dedicated structure, may be more attractive. Such an approach would allow the precipitate to be collected and returned to the neutralized RS, to take advantage of its nutrient content.
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REFERENCES
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- Bell, L.C., and J.R. Meecham. 1979. Reclamation of alumina refinery wastes at Gladstone, Australia. Reclam. Rev. 1:129–137.
- Fuller, R.D., E.D.P. Nelson, and C.J. Richardson. 1982. Reclamation of red mud (bauxite residues) using alkaline-tolerant grasses with organic amendments. J. Environ. Qual. 11:533–539.[Abstract/Free Full Text]
- Greenhouse, S.W., and S. Geisser. 1959. On methods in the analysis of profile data. Psychometrika 24:95–112.[ISI]
- Hossner, L.R., R.H. Loeppert, H.J. Woodard, T.J. Moore, and T.L. Thompson. 1986. Reclamation and vegetation of bauxite residue. Alcoa Rep. 3. Soil and Crop Sci. Dep., Texas A&M Univ., College Station.
- Hudson, L.K. 1987. Alumina production. p. 11–46. In A.R. Burkin (ed.) Production of aluminum and alumina. John Wiley & Sons, New York.
- Klute, A., and C. Dirksen. 1986. Hydraulic conductivity and diffusivity: Laboratory methods. p. 687–734. In A. Klute (ed.) Methods of soil analysis. Part 1. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI.
- Lewis, L., J. Shim You, W. Pedersen, and E. Black. 1995. Vegetation of thickened red mud tailings deposits without the use of soil capping techniques. Light Met. (Warrendale, PA) 1995:31–34.
- Lim, C.H., and M.L. Jackson. 1982. Dissolution for total elemental analysis. p. 1–12. In A.L. Page, R.H. Miller, and D.R. Keeney (ed.) Methods of soil analysis. Part 2. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI.
- Lin, C.X., M.W. Clark, D.M. McConchie, G. Lancaster, and N. Ward. 2002. Effects of BauxsolTM on the immobilization of soluble acid and environmentally significant metals in acid sulfate soils. Aust. J. Soil Res. 40:805–815.
- McBride, M.B. 1994. Environmental chemistry of soils. Oxford Univ. Press, New York.
- McConchie, D., M. Clark, C. Hanahan, and R. Fawkes. 1999. The use of seawater-neutralized bauxite refinery residues (red mud) in environmental remediation programs. p. 391–400. In I. Gaballah, J. Hager, and R. Solozabal (ed.) 1999 Global Symp. on Recycling, Waste Treatment and Clean Technology. Vol. 1. The Minerals, Metals and Materials Soc., San Sebastian, Spain.
- McConchie, D., P. Saenger, and R. Fawkes. 1996. An environmental assessment of the use of seawater to neutralise bauxite refinery waste. p. 407–416. In V. Ramachandran and C.C. Nesbitt (ed.) 2nd Int. Symp. on Extraction and Processing for the Minimization of Wastes. The Minerals, Metals and Materials Soc., Scottsdale, AZ.
- Oeberg, N., and E. Steinlechner. 1996. Red mud and sands handling—New thoughts on an old problem. Light Met. (Warrendale, PA) 1996:67–73.
- SAS Institute. 1999. SAS/STAT software. Release 8.00. SAS Inst., Cary, NC.
- Sumner, M.E., and W.P. Miller. 1996. Cation exchange capacity and exchange coefficients. p. 1201–1229. In D.L. Sparks (ed.) Methods of soil analysis. Part 3. SSSA Book Ser. 5. SSSA, Madison, WI.
- Tacey, W.H., D.P. Olson, and G.H.M. Watson. 1977. Rehabilitation of mine wastes in a temperate environment. Annual Australian Mining Industry Council Environmental Workshop. Australian Mining Industry Council, Canberra, Sydney.
- Taylor, J.C. 1991. Computer programs for standardless quantitative analysis of minerals using the full powder diffraction profile. Powder Diffr. 6:2–9.
- Ward, S.C., G.C. Slessar, D.J. Glenister, and P.S. Coffey. 1996. Environmental resource practices of Alcoa in southwest Western Australia. In D.M. Mulligan (ed.) Environmental management in the Australian minerals and energy industries—Principles and practices. Univ. of New South Wales Press, Sydney.
- Wong, J.W.C., and G.E. Ho. 1995. Cation-exchange behavior of bauxite refining residues from Western Australia. J. Environ. Qual. 24:461–466.[Abstract/Free Full Text]
- Zambo, J. 1979. Red mud: Its properties, handling, storage and utilization. Trav. ICSOBA 15:265–277.
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ABSTRACT
INTRODUCTION
) and 1:2 (
), 1:2 (•), 1:5 (
), 1:20 (
) during the first day of reaction. Least significant difference is presented for p < 0.05.
), 2.0 m (