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Palmer, Sara J. and Frost, Ray L. and Nguyen, Tai M. (2009) Hydrotalcites and their role in coordination of anions in Bayer liquors: Anion binding in layered double hydroxides. Coordination Chemistry Reviews 253(1-2):pp. 250-267.
Hydrotalcites and their role in coordination of anions in Bayer liquors Sara J. Palmer, Tai Nguyen, and Ray L. Frost Inorganic Materials Research program, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, Australia.
1.1 Bayer Process – Origin of Red Mud..........................................................................2 1.2 Components of Red Mud...........................................................................................4
1.2.1 Iron oxides .........................................................................................................4 1.2.2 Silica minerals....................................................................................................9
1.3 Surface Chemistry....................................................................................................11 1.4 Removal of Trace Metals from Solution .................................................................13 1.5 Acid Neutralising Capacity (ANC)..........................................................................14
2. Seawater Neutralised Bauxite Refinery Residues............................................................15 2.1 Introduction..............................................................................................................15 2.2 Reaction Mechanism................................................................................................16 2.3 Formation of Hydrotalcite........................................................................................17 2.4 Adsorption of Anions on the Surface of Neutralised Red Mud...............................18
3. Layered Double Hydroxides (LDH) ................................................................................19 3.1 Introduction..............................................................................................................19 3.2 Preparation of LDH..................................................................................................22 3.3 Anionic Exchange....................................................................................................23 3.4 Reformation of Hydrotalcites ..................................................................................26 3.5 Characterisation of LDHs ........................................................................................26
3.6 LDH in the Alumina Industries................................................................................35 4. Summary ..........................................................................................................................37
16. Zone II: S-O- + H+ → S-OH 17. Zone III: S-OH + H+ → S-OH2
+
The amount of surface hydroxyl groups is roughly proportional to the reactive silica content
in the original bauxite [81]. Sodalite is a zeolite-type compound with a high surface area of
exposed oxygen atoms that react with protons [3]. Estimates for the number of surface
hydroxyl groups on red mud obtained by Chevedov et al., [3], were two orders of magnitude
higher then the average values obtained for metal oxides, [82], suggesting that a high level of
sodalite on the surface of red mud was present.
The surface charge of red mud can be derived from pH measurements and determined by
literature methods [83,84]. The point of zero charge (PZC) can be used in the determination
of the surface charge properties of materials, [83,84], and is defined as the pH at which the
net charge on the surface is zero. The PZC provides an estimate of the acidity of the oxide
surface. For most alumina and iron oxides the PZC is approximately 7-8, [85,86] with Fe2O3
and Al2O3 having PZC values of 8.5 and 9.2 respectively. The PZC of hematite has been
found to be 8.5 to 8.8 determine by potentiometric titration, [87] while goethite has a PZC of
around 8.9to 9.5 [38,88,89]. Some studies have shown that red mud has a PZC value of about
6.5, [3], while others have reported PZC values of around 8.3 [76,90,91]. Red muds
containing high silica usually have PZC values of 6.3, which suggests that the presence of
these compounds reduces the PZC value. The presence of different oxides in red mud, means
that there are not only neutral surface complexes and SOH sites at PZC, but also both
positively charged (such as FeOH2+ and AlOH2
+) and negatively charged (such as TiO- and
SiO-) surface complexes [90]. The shift in PZC to lower values is believed to be attributed to
the formation of differently charged oxide surface sites, and the release of free hydroxide
ions back into solution resulting in the increase in positive surface charge.
1.4 Removal of Trace Metals from Solution
Red mud has a strong binding capacity for heavy metals [6,12,13,15]. Red mud has the
ability to adsorb trace metals from solution onto the very fine grained iron oxides. These
finely grained particles have high surface/volume and high charge/mass ratios when the pH
of the solution is above 5, [92,93] which increases the ability of red mud to remove trace
metals. Increased adsorption efficiency can also be achieved by ensuring the solution pH is
greater than 5 [94,95]. High adsorption affinity of heavy metals on red mud is attributed to
the chemisorption reactions at the surface of the oxide components of red mud (eg. Fe2O3,
Al2O3, TiO2), however the identification of the oxide with the highest affinity for a given
metal ion has not been determined [18,19,96]. The ability of red mud to remove trace metals
from solution has been found to increase over time, where 1 kg of dry red mud was able to
remove approximately 1000 meq./kg of trace metals from solution [96]. Adsorption of heavy
metals from solution increases with increased contact of the solution with red mud, rendering
heavy metal removal a time dependent process. The metal concentrations retained in red mud
can be calculated using equation 18. Santona et al., [19], investigated red muds with high
levels of cancrinite (zeolite-like structure), and suggested that higher adsorption values
obtained were due to the presence of large quantities of cancrinite, which incorporated the
heavy metal cations in the cages and channels of its structure.
18. qe = (C0 – Ce)V / m
where, qe is the sorbent phase (mg/g), C0 and Ce are the initial and final equilibrium concentrations of the metal ion in solution (mg/litre), V is the solution volume (litres) and m is the mass of the sorbent (g).
The mechanism for the removal of dissolved metals using red mud has been proposed to be
comprised of four steps:
(i) co-precipitation of their insoluble metal hydroxides that form successive layers on the
red mud surface,
(ii) formation of kinetic intermediates [Fe2(OH)4]2+, [Fe3(OH)4]5+, [Al4(OH)8]2+, and
[Al8(OH)20]4+, at the adsorbent surface,
(iii) chemical adsorption which removes metal ions as uncharged hydroxides condensed
onto surface hydroxyl groups exposed on the red mud surface, [97] and
(iv) ion exchange.
The dominant mechanisms of removal are believed to be (i) and (iii) [98,99].
1.5 Acid Neutralising Capacity (ANC)
The abundance of amorphous and finely crystalline phases present in red mud gives rise to its
high theoretical acid neutralising capacity of 3.6 mols/kg [11,96]. Neutralised red mud, pH
8.6, retains a high neutralising capacity due to the presence of large quantities of acid
neutralising carbonate minerals and finely crystalline minerals that form weak bases.
McConchie et al., [96], determined the neutralisation of red mud is initially rapid, and
increases slowly when approaching its neutralisation limit of 3.65 mols of acid/kg after a 48
hour period. No further improvement was observed after 48 hours. The ANC of seawater
neutralised red mud can be calculated, using equation 19.
19. Total OH-alkalinity = [Na+] + 2[Ca2+] + 2[Mg2+] where [concentrations] are in mmol/g
2. Seawater Neutralised Bauxite Refinery Residues
2.1 Introduction
Bauxite refinery residues are characterised by relatively high concentrations of sodium
aluminate and sodium carbonate and a variety of anionic species. If left untreated, these
species have the potential to be detrimental to the environment. Therefore, systems have been
developed to remove these species prior to disposal. Several groups have explored seawater
neutralisation of bauxite refinery residues [10,11,100,101]. A number of alumina refineries
have implemented the neutralisation of the bauxite refinery residue with seawater prior to
disposal, and found it provided a reduction in both pH and dissolved metal concentrations.
Glenister and Thornber, [10], concluded disposal of refinery residues at pH 8 was optimal,
since at this pH chemically adsorbed Na is released, neutralising alkaline buffer minerals and
rendering most of the dissolved metal species insoluble. This coincides with the
recommended pH value outlined by environmental departments [9]. Seawater neutralisation
results in the neutralisation of alkalinity through the precipitation of Mg, Ca, and Al
hydroxide and carbonate minerals [103]. Some researchers have investigated the
neutralisation of red mud with strong acids, [77,98,103,104] and have found that the initial
addition of acid results in a rapid decrease in pH, followed by the leaching of alkaline solids
from the red mud causing a slow rise in pH.
Implementation of seawater neutralisation of red mud at Queensland Alumina Ltd. (QAL)
initially began as an alternative to the use of freshwater, [100] and led to the discovery of the
many benefits, including:
(i) a decrease in freshwater use [100],
(ii) increased settling rates of ponds due to agglomerate consolidation [105],
(iii) decreased alkalinity and sodicity in the solid refinery residue and entrained liquor
[100],
(iv) increased acid neutralisation capacity, and
(v) improved soil properties after rehabilitation.
2.2 Reaction Mechanism
The addition of seawater to un-neutralised red mud results in the formation of fine mineral
particles that flocculate into larger agglomerates. Multivalent exchange cations, Ca and Mg,
form electrostatic bridges, [106] which then act as nucleation sites for the precipitation of
magnesium and calcium hydroxides. Hanahan et al., [11], reported an increase in electrical
conductivity indicating the increase in soluble salt content. Formation of these hydroxides
reduces the concentration of hydroxide ions in solution, therefore reducing the pH of the
solution [107]. As the electrostatic conditions of the surface changes, the agglomerates
tighten, pH decreases, and elements that exhibited colloidal behaviour initially at high pH
lose stability [106]. The further decrease in pH causes the precipitation of hydroxycarbonates
of aluminium, calcium, and magnesium, where the precipitation of hydrotalcite-like
compounds, becomes favoured [11].
Seawater neutralisation does not eliminate hydroxide from the system but converts the
readily soluble, strongly caustic refinery residue into less soluble, weakly alkaline solids. The
carbonate and bicarbonate alkalinity of the waste is primarily removed through the
precipitation of calcite and aragonite [107]. McConchie et al., [96], described the seawater
neutralisation process as the precipitation of hydroxyl ions predominantly as brucite, but also
as boehmite, gibbsite, hydrocalumite, hydrocalcite, and p-aluminohydrocalcite. Most of the
boehmite, gibbsite, hydrocalumite, hydrotalcite, and p-aluminohydrocalcite was already
present in red mud, however, the reduction in pH after seawater neutralisation influenced the
continuation of crystal growth as aluminium became less soluble [96]. Menzies et al., [102],
reported the formation of a white precipitate containing hydrotalcite, aragonite, and
pyroaurite, determined by XRD. The extensive characterisation of seawater neutralised red
mud by Hanahan et al., [11], revealed the complexity of the system, identifying 15 mineral
components (XRD). The major elemental components of seawater neutralised red mud,
determined by acid digestion and ICP-MS, were Fe > Na > Al > Ca > Si > Mg [11].
Variations in reported values and components of seawater neutralised red mud are due to the
differences in physical, chemical, and mineralogical properties of red mud.
2.3 Formation of Hydrotalcite
The seawater neutralisation of aluminate liquor studies done by Smith et al., [108,109],
reported that the exact composition of the precipitate, including hydrotalcite, calcite and
aragonite, is dependent on the precipitation conditions. Smith et al., [108,109], found that the
composition of the hydrotalcite was dependent on the pH, where hydrotalcite formed at high
pH (pH > 13) had a Mg:Al ratio of 2:1 (equation 20), while those precipitated at pH 8 had a
Mg:Al ratio of 4:1 (equation 21). At high pH a more stable microcrystalline carbonate
hydrotalcite (Mg4Al2(CO3)(OH)12.xH2O) forms, due to the readily adsorbed CO2 from the
atmosphere producing a saturated carbonate solution. At lower pH (pH < 9.5) a less well
defined crystal structure forms. Due to the decrease of available carbonate in solution, the
intercalation of other anions into the hydrotalcite structure (Mg8Al2Cl(CO3)0.5(OH)20.xH2O)
is possible. The decrease in available carbonate is due to the rapid decrease in hydroxide ions
from solution resulting in a lower adsorption of CO2, and therefore a decrease in available
Identifying which mechanism is responsible for anion exchange reactions has proven to be
difficult due to: (i) the high rate of anion exchange reactions, making kinetic studies difficult,
(ii) intermediate phases formed are highly unstable and react quickly to form the new LDH
phase, and (iii) in the D-R mechanism, the dissolution of LDH takes place at the solid-liquid
interface [132].
Extensive studies by Miyata et al., [131,139,184], exposed the anionic exchange properties of
a number of species, establishing a ranking of affinity for intercalation. Hydrotalcite shows
the greatest affinity for anions of high charge density. [184,185] The affinity of monovalent
anions was determined to be OH- > F- > Cl- > Br- > NO3- > I-, while the order for divalent
anions was CO32- > SO4
2-. The carbonate anion has proven to be the preferred anion for
intercalation, and once intercalated proves very difficult to exchange with other anions. The
high affinity of carbonate in Mg,Al hydrotalcites prevents its use as an anion-exchange
material, unless precautionary steps (nitrogen atmosphere and carbonate free solutions) or
calcination are used to minimise the carbonate content in the hydrotalcite matrix.
Theoretically, LDHs have an anion exchange capacity of 3.6 mequiv./g if all the carbonate in
the general formula was exchanged [184]. Experiments conducted by Miyata et al., [184],
showed that a hydrotalcite prepared under a nitrogen atmosphere with carbonate free
solutions could obtain an anion exchange capacity of 3 mequiv./g. The theoretical capacity
value cannot be obtained due to hydroxide anions present in solution competing with the
desired anion [186]. Removal of carbonate from all sources is essential in exchange
reactions, as any carbonate present in the exchange solutions will be incorporated
preferentially to other anions. Anion exchange capacity values were determined by
comparing the anion concentrations of the initial and final solutions after the addition of a
known amount of hydrotalcite by atomic adsorption spectroscopy and the Dionex method
[186].
3.4 Reformation of Hydrotalcites
Recent studies have shown that LDHs can have a so-called ‘memory effect’ whereby a
hydrotalcite material can be thermally treated to remove water, hydroxyl, and carbonate units
from its matrix, then re-hydrated in an aqueous solution to return to its original structure
[162,187]. The restoration of the layered structure in hydrotalcites is a ‘structural memory
effect’ [188-190]. This so-called memory or restoration effect can be used effectively to
remove harmful anions, both organic [121,124] and inorganic, [160,162,191,192] from waste
water solutions.
The calcination of hydrotalcite, from temperatures of 350ºC to 800ºC, removes interlayer
water, interlayer anions (carbonate anions), and hydroxyls. The result is the formation of
periclase-like Mg,Al oxides. XRD studies have shown the collapse of the crystalline
hydrotalcite to an amorphous magnesium oxide with dispersed aluminium ions as a solid
solution [160,162,186,192]. The carbonate anions are decomposed to carbon dioxide (CO2)
and O2-, leaving O2- anions between the layers [131,184,193,194]. Re-hydrating the calcined
product regenerates the LDH, where water is absorbed to reform the hydroxyl layers, as well
as being absorbed into the interlayer along with the anion in solution [124].
Anions that are reabsorbed do not necessarily need to be the original anions, since any
available anion in the re-hydrating solution will be absorbed. For examples, the re-hydration
of calcined hydrotalcites in carbonate free solutions will yield a carbonate free hydrotalcite.
Parker et al., [186], reported a 50% decrease in adsorption in the anion exchange capacity of
LDHs due to a slight alteration in the re-formed hydrotalcite. Heating to temperatures above
900 ºC produces spinel (MgAl2O4), totally degrading the hydrotalcite lattice and preventing
any reformation.
3.5 Characterisation of LDHs
3.5.1 Vibrational Spectroscopy – Infrared (IR) and Raman Spectroscopy
Spectroscopy has been a widely used technique in the industry for the structural and
compositional analysis of inorganic, organic, organometallic, metalorganic, and polymeric
materials. Vibrational spectroscopy involves the use of light to probe the vibrational
behaviour of molecular systems, usually via absorption, emission, or light scattering
experiments. Both infrared and Raman spectroscopy give rise to a vibrational spectrum as a
set of absorption or scattering peaks, corresponding to the energies of transitions within the
sample (frequencies of vibrational modes).
3.5.1.1 Hydroxyl Stretching and Bending Vibrations
The vibrational spectra of hydrotalcites exhibit various forms of water hydroxyl-stretching
vibrations. These include water in the interlayer between the hydroxide layers, which may or
may not form bridging-type bonds with the exchangeable anions, water adsorbed on the outer
surface, and free water between layers. Water hydroxyl-stretching vibrations are intense in an
infrared spectrum, because of the large change in dipole moment, whereas, water is not
always observed in the Raman spectrum. Therefore, the comparison of the two techniques
allows for the identification of the bands associated with water and those associated with
hydroxyl stretching vibrations. Water bending modes are situated around 1600-1700 cm-1
accompanied by OH-stretching vibrations in the 3000-4000 cm-1 region [161,195-197].
The replacement of Mg2+ by Al3+, in hydrotalcites, results in stronger hydrogen bonds
between the hydroxide layers, when compared with brucite, due to Al3+ having a higher
charge and smaller ionic radius [198]. This change in O-H bond lengths can be detected in
infrared spectra with shifts to higher frequencies in the bending region, and shifts to lower
frequencies in the stretching region are associated with the strength of the hydrogen bonds
[199]. A similar observation can be seen for the lattice translation modes in the low
frequency region of the infrared spectra [200]. The OH-stretching vibration for brucite is
situated around 3570-3555 cm-1, while for Mg,Al hydrotalcites the corresponding band is
located at around 3450 cm-1. This shift is associated with the shorter O-H bonds existing in
hydrotalcite than in brucite, causing an increase in the electrostatic attraction within the
hydrotalcite layer [200].
Extensive overlapping of bands exists in the OH-stretching region of LDHs between metal-
OH bands of the hydroxide layers and the OH-bands of water. For water adsorbed on clay
minerals the OH-stretching modes of weak hydrogen bonds occur in the region between 3580
and 3500 cm-1, while strong hydrogen bonds are observed below 3420 cm-1. Water co-
ordinated to cations show stretching vibrations occurring around 3220 cm-1 [199]. Fourier
Transform IR spectra obtained by Jose dos Reis et al., [201], showed a broad band at 3400
cm-1 assigned to the ν(OH) mode ascribed to interlayer water and hydroxyl groups in the
hydroxide layers of hydrotalcite. Numerous studies conducted by Kloprogge and Frost
(summarised in
Table 4) have reported the infrared hydroxyl modes of Mg,Al hydrotalcites [199]. A broad
band around 3300-3000 cm-1 with a shoulder, sometimes visible, comprised of two or three
overlapping bands are attributed to the OH-stretching vibrations and a stretching vibration of
interlayer water. The shoulder at 3050 cm-1 was assigned to hydroxyl interactions with
carbonate ions in the interlayer [139,199,201-204], and has been attributed to the bridging
mode H2O-CO32-.
Table 4: Frequencies (cm-1) and assignments of the hydroxide layer modes of the types M-OH and M-O in the infrared spectra of Mg/Al-layered double hydroxides in comparison to brucite Mg(OH)2.
232. [9] The Guidelines, Australian and New Zealand Environment and Conservation Council
(ANZEXX) and Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ). 1 (4) (2000) Chapters 1-7.
[10] D.J. Glenister, M.R. Thornberg, Chemica. 85 (1985) 100-113. [11] C. Hanahan, D. McConchie, J. Pohl, R. Creelman, M. Clark, C. Stocksiek,
Environmental Engineering Science. 21 (2004) 125-138. [12] H.S. Altundogan, S. Altundogan, F. Tumen, M. Bildik, Waste management. 22
(2002) 357-363. [13] C. Brunori, C. Cremisini, L. D'Annibale, P. Massanisso, V. Pinto, Analytical and
Bioanalytical Chemistry. 381 (2005) 1347-1354. [14] C. Lin, M.W. Clark, D.M. McConchie, G. Lancaster, N. Ward, Australian Journal of
Soil Research. 40 (2002) 805-815. [15] C.-X. Lin, X.-X. Long, S.-J. Xu, C.-X. Chu, S.-Z. Mai, D. Jiang, Pedosphere. 14
(2004) 371-378. [16] E. Lombi, F.-J. Zhao, G. Wieshammer, G. Zhang, P. McGrath Steve, Environmental
pollution. 118 (2002) 445-452. [17] B. Diaz, S. Joiret, M. Keddam, X.R. Novoa, M.C. Perez, H. Takenouti,
Electrochemical Methods in Corrosion Research. 49 (2004) 3039-3048. [18] E. Lopez, B. Soto, M. Arias, A. Nunez, D. Rubinos, T. Barral, Water Research. 32
(1998) 1314-1322. [19] L. Santona, P. Castaldi, P. Melis, Journal of Hazardous Materials. 136 (2006) 324-
329. [20] D.J. Glenister, Chemica. 85 (1985) 100-113. [21] B.I. Whittington, Hydrometallurgy. 43 (1996) 13-35. [22] K. Solymar, J. Zoldi, T. Ferenczi, Magyar Aluminium. 26 (1989) 20-29. [23] K. Solymar, I. Sajo, J. Steiner, J. Zoldi, Light Metals. (1992) 209-223. [24] S. Prakash, Z. Horvath, Publications of the Technical University for Heavy Industry,
Series B: Metallurgy. 34 (1979) 43-63.
[25] I. Paspaliaris, A. Karalis, Light Metals. (1993) 35-39. [26] R.M. Cornell, U. Schwertmann, The Iron Oxides, Second ed., Wiley-VCH,
Weinheim, 2000. [27] P.H. Hsu, G. Marion, Soil Science. 140 (1985) 344-351. [28] D. Langmuir, Gibbs free energies of substances in the system Fe-O2=H2O-CO2 at 25
deg.C. USA. (1969) 180-184. [29] W.L. Lindsay, Chemical Equilibria in Soils, New York, John Wiley Sons. (1979)
449. [30] P. Schindler, Chimia. 17 (1963) 313-331. [31] P. Basu, Light Minerals (1983) 83-97. [32] I.I. Diakonov, J. Schott, F. Martin, J.C. Harrichourry, J. Escalier, Geochimica et
Cosmochimica Acta. 63 (1999) 2247-2261. [33] K. Ishikawa, T. Yoshioka, T. Sato, A. Okuwaki, Hydrometallurgy. 45 (1997) 129-
135. [34] F.J. Micale, D. Kiernan, A.C. Zettlemoyer, Journal of Colloid and Interface Science.
105 (1985) 570-576. [35] Y. Hotta, S. Ozeki, T. Suzuki, J. Imai, K. Kaneko, Langmuir. 7 (1991) 2649-2653. [36] V. Barron, J. Torrent, Journal of Colloid and Interface Science. 177 (1996) 407-410. [37] T. Hiemstra, J.C.M. De Wit, W.H. Van Riemsdijk, Journal of Colloid and Interface
Science. 133 (1989) 105-117. [38] T. Hiemstra, W.H. van Riemsdijk, Journal of Colloid and Interface Science. 179
458. [42] L. Sigg, W. Stumm, Colloids and Surfaces. 2 (1981) 101-117. [43] D.D. Hansmann, M.A. Anderson, Environmental Science and Technology. 19 (1985)
544-551. [44] D.E. Yates, T.W. Healy, Journal of Colloid and Interface Science. 52 (1975) 222-228. [45] S.H.R. Davies, J.J. Morgan, Journal of Colloid and Interface Science. 129 (1989) 63-
77. [46] A. Bibak, O.K. Borggaard, Soil Science. 158 (1994) 323-328. [47] F.J. Hingston, A.M. Posner, J.P. Quirk, Journal of Soil Science. 25 (1974) 16-26. [48] N.G. Holm, M.J. Dowler, T. Wadsten, G. Arrhenius, Geochimica et Cosmochimica
Acta. 47 (1983) 1465-1470. [49] R.M. McKenzie, Journal of Soil Research. 21 (1983) 505-513. [50] K. Mesuere, W. Fish, Environmental Science and Technology. 26 (1992) 2357-2364. [51] R.L. Parfitt, J.D. Russell, Journal of Soil Science. 28 (1977) 297-305. [52] R.L. Parfitt, R.S.C. Smart, Journal of the Chemical Society, Faraday Transactions 1:
Physical Chemistry in Condensed Phases. 73 (1977) 796-802. [53] E.D. Reyes, J.J. Jurinak, Soil Science Society of America Proceedings. 31 (1967)
637-641. [54] R.P.J.J. Rietra, T. Hiemstra, W.H. Van Riemsduk, Geochimica et Cosmochimica
Acta. 63 (1999) 3009-3015. [55] F.J. Hingston, R.J. Atkinson, A.M. Posner, J.P. Quirk, Specific adsorption of anions
on anions on goethite, 9th International Congress of Soil Science. 1 (1968) 669-678. [56] G.W. Bruemmer, J. Gerth, K.G. Tiller, Journal of Soil Science. 39 (1988) 37-51. [57] L. Loevgren, Geochimica et Cosmochimica Acta. 55 (1991) 3639-3645.
[58] L. Loevgren, S. Sjoeberg, P.W. Schindler, Geochimica et Cosmochimica Acta. 54 (1990) 1301-1306.
[59] B. Whittington, T. Fallows, Hydrometallurgy. 45 (1997) 289-303. [60] B.I. Whittington, B.L. Fletcher, C. Talbot, Hydrometallurgy. 49 (1998) 1-22. [61] R.G. Breuer, L.R. Barsotti, A.C. Kelly, Behaviour of Silica in Sodium Solutions,
Interscience, New York, 1963. [62] J.J. Kote, Light Metals. (1989) 45. [63] H.D. Grundy, I. Hassan, Canadian Mineralogist. 20 (1982) 239-251. [64] G. Hermeler, J.C. Buhl, W. Hoffmann, Catalysis Today. 8 (1991) 415-426. [65] M.G. Leiteizen, L.A. Pashkevich, I.B. Firfarova, D.I. Tsekhovol'skaya, Tsvetnye
Metally. (1974) 21-25. [66] S. Ostap, Hydrometallogy. 15 (1985) 1411-1414. [67] R.G. Breuer, L.R. Barsotti, A.C. Kelly, Aluminum. 1 (1963) 133-156. [68] M.C. Barnes, J. Addai-Mensah, A.R. Gerson, Colloids and Surfaces A:
Physicochemical and Engineering Aspects. 157 (1999) 101-116. [69] T. Oku, K. Yamada, T. Harato, H. Kato, Environmental Science and Technology.
29. [71] M.C. Barnes, J. Addai-Mensah, A.R. Gerson, Microporous and Mesoporous
Materials. 31 (1999) 287-302. [72] R.M. Barrer, J.F. Cole, H. Villiger, Journal of the Chemical Society A: Inorganic.
(1970) 1523-1531. [73] N.S. Volkova, D.I. Tsekhovol'skaya, N.I. Eremin, Tsvetnye Metally. 44 (1971) 31-34. [74] R.W.G. Wyckoff, Crystal Structures, Wiley, New York. Volume 1, (1963). [75] K. Zheng, A.R. Gerson, J. Addai-Mensah, R.S.C. Smart, Journal of Crystal Growth.
171 (1997) 197-208. [76] R. Apak, K. Guclu, M.H. Turgut, Journal of Colloid and Interface Science. 203
(1998) 122-130. [77] J. Pradhan, J. Das, S. Das, R.S. Thakur, Journal of Colloid and Interface Science. 204
(1998) 169-172. [78] R. Apak, G. Atun, K. Guclu, E. Tutem, G. Keskin, Journal of Nuclear Science and
Technology. 32 (1995) 1008-1017. [79] Y.G. Berube, P.L. De Bruyn, Journal of Colloid and Interface Science. 27 (1968)
305-318. [80] A. Breeuwsma, J. Lyklema, Journal of Colloid and Interface Science. 43 (1973) 437-
448. [81] L.Y.L. Li, Colloids and Surfaces A: Physicochemical and Engineering. (1993) 298. [82] H. Tamura, A. Tanaka, K.-y. Mita, R. Furuichi, Journal of Colloid and Interface
Science. 209 (1999) 225-231. [83] G. Sposito, Soil Science Society of America Journal. 45 (1981) 292-297. [84] G. Sposito, Environmental Science and Technology. 32 (1998) 2815-2819. [85] H. Hohl, W. Stumm, Journal of Colloid and Interface Science. 55 (1976) 281-288. [86] C.-P. Huang, W. Stumm, Journal of Colloid and Interface Science. 43 (1973) 409-
420. [87] L. Liang, J.J. Morgan, ACS Symposium Series. 416 (1990) 293-308. [88] C.K.D. Hsi, D. Langmuir, Geochimica et Cosmochimica Acta. 49 (1985) 1931-1941. [89] D.G. Lumsdon, L.J. Evans, Journal of Colloid and Interface Science. 164 (1994) 119-
125. [90] G. Atun, G. Hisarli, Journal of Colloid and Interface Science. 228 (2000) 40-45.
[91] V. Gupta, M. Gupta, S. Sharma, Water Research.35 (2001) 1125-1134. [92] C.A. Johnson, Geochimica et Cosmochimica Acta. 50 (1986) 2433-2438. [93] S. Yariv, H. Cross, Geochemistry of Colloid Systems for Earth Scientists, Springer-
Verlag, New York. (1979). [94] V.K. Gupta, S. Sharma, Environmental Science and Technology. 36 (2002) 3612-
3617. [95] R.N. Summers, N.R. Guise, D.D. Smirk, Fertilizer Research. 34 (1993) 85-94. [96] D. McConchie, M. Clark, C. Hanahan, R. Fawkes, The Minerals, Metals and
Materials Society. 1 (1999) 391-400. [97] K.H. Lieser, Applied Sciences. 13 (1975) 91-145. [98] V. Apak, E. Unseren, Flocculation in Biotechnology and Separation Systems. (1987),
765-771. [99] J. Gregory, Applied Sciences. 27 (1978) 89-99. [100] D. McConchie, P. Saenger, R. Fawkes, in: V.R.a.C.C. Nesbitt (Ed.), Second
International Symposium on Extraction and Processing for the Treatment and Minimization of Wastes, The Minerals, Metals and Material Society. (1996) 407-416.
[101] J. Somes, N. Menzies, D. Mulligan, Seawater neutralisation of bauxite residue. ASSSI National Soils Conference, Brisbane, QLD, (1998) 546-549.
[103] B. Koumanova, M. Drame, M. Popangelova, Resources Conservat. Recycling. 19 (1997) 11-20.
[104] E.E. Shannon, K.I. Verghese, Journal of Water Pollution. 48 (1976) 1948-1954. [105] G.A. Graham, R. Fawkes, Red mud disposal management at QAL. Proceedings of the
International Bauxsite Tailings Workshop, Perth, WA, Australia, (1992). [106] M.B. McBride, Environmental Chemistry of Soils, Oxford University Press, New
York, (1994). [107] D. McConchie, M. Clark, C. Hanahan, F. Davies-McConchie, The use of seawater-
neutralised bauxite refinery residues in the management of acid sulphate soils, sulphidic mine tailings and acid mine drainage, 3rd Queensland Environmental Conference: Sustainable Solutions for Industry and Government, Brisbane, QLD, Australia, (2000) 201-208.
[108] H.D. Smith, G.M. Parkinson, Seawater Neutralisation: Factors affecting adsorption of anionic chemical species, 7th International Alumina Quality Workshop, (2005).
[110] K. Periasamy, C. Namasivayam, Industrial & Engineering Chemistry Research. 33 (1994) 317-320.
[111] H.S. Altundogan, S. Altundogan, F. Tumen, M. Bildik, Waste Management. 20 (2000) 761-767.
[112] A.N. Ay, B. Zuemreoglu-Karan, A. Temel, Microporous and Mesoporous Materials. 98 (2007) 1-5.
[113] J. Shibata, N. Murayama, K. Sakai, H. Yamamoto, Removal of toxic metal ions with functional inorganic materials produced from wastes in non-ferrous metal industry, World Congress of Chemical Engineering, 7th, Glasgow, United Kingdom, July 10-14, (2005).
[114] Y. Kiso, Y.J. Jung, T. Yamada, M. Nagai, K.S. Min, Water Science & Technology: Water Supply. 5 (2005) 75-81.
[115] H. Hirahara, S. Aisawa, H. Sato, S. Takahashi, Y. Umetsu, E. Narita, Nendo Kagaku. 45 (2005) 6-13.
[116] S. Peng, Y. Yang, T. Chen, S. Jiang, H.f. Xu, Guisuanyan Xuebao. 33 (2005) 1023-1027.
[117] N. Murayama, M. Tanabe, R. Shibata, H. Yamamoto, J. Shibata, Kagaku Kogaku Ronbunshu. 31 (2005) 285-290.
[118] T. Murakami, H. Oshima, T. Kuwabara, T. Sato, A. Kawamoto, Mizu Kankyo Gakkaishi. 28 (2005) 269-274.
[119] S. Yapar, P. Klahre, E. Klumpp, Turkish Journal of Engineering & Environmental Sciences. 28 (2004) 41-48.
[120] T. Kuwabara, T. Sato, T. Nonaka, H. Yamamoto, M. Aizaki, Y. Fukuda, Mizu Kankyo Gakkaishi. 26 (2003) 423-429.
[121] J. Orthman, H.Y. Zhu, G.Q. Lu, Separation and Purification Technology. 31 (2003) 53-59.
[123] H.Y. Zhu, J. Orthman, G.Q. Lu, New hydrotalcite sorbents for the removal of coloured organic compounds in aqueous solutions, Sustainable Energy and Environmental Technologies, Proceedings of the Asia-Pacific Conference, 3rd, Hong Kong, China, December. (2001) 356-361.
[124] M.A. Ulibarri, I. Pavlovic, C. Barriga, M.C. Hermosin, J. Cornejo, Applied Clay Science. 18 (2001) 17-27.
[125] U. Costantino, F. Marmottini, M. Nocchetti, R. Vivani, European Journal of Inorganic Chemistry. (1998) 1439-1446.
[127] T. Lopez, P. Bosch, E. Ramos, R. Gomez, O. Novaro, D. Acosta, F. Figueras, Langmuir. 12 (1996) 189-192.
[128] A.I. Khan, D. O'Hare, Journal of Materials Chemistry. 12 (2002) 3191-3198. [129] M.C. Van Oosterwyck-Gastuche, G. Brown, M.M. Mortland, Clay Minerals. 7 (1967)
177-192. [130] M.R. Weir, J. Moore, R.A. Kydd, Chemistry of Materials. 9 (1997) 1686-1690. [131] S. Miyata, Clays and Clay Minerals. 28 (1980) 50-56. [132] A.V. Radha, P. Vishnu Kamath, C. Shivakumara, Solid State Sciences. 7 (2005)
1180-1187. [133] F. Trifiro, A. Vaccari, in: J.L. Atwood, J.E.D. Davies, D.D. MacNicol, F. Vogtle,
J.M. Lehn, G. Alberti, T. Bein (Eds), Comprehensive Supramolecular Chemistry, Solid-State Supramolecular Chemistry: Two- and Three-Dimensional Inorganic Networks, Pergamon, Oxford. (1996) 251-291.
[134] E.L. Crepaldi, P.C. Pavan, J.B. Valim, Journal of the Brazilian Chemical Society. 11 (2000) 64-70.
[135] L. Pesic, S. Salipurovic, V. Markovic, D. Vucelic, W. Kagunya, W. Jones, Journal of Materials Chemistry. 2 (1992) 1069-1073.
[136] V. Rives, Layered Double Hydroxides: Present and Future, Nova Science, New York, 2001.
[137] H.F.W. Taylor, Mineralogical Magazine. 39 (1973) 377-389. [138] G. Marcelin, N.J. Stockhausen, J.F.M. Post, A. Schutz, Journal of Physical
Chemistry. 93 (1989) 4646-4650. [139] S. Miyata, Clays Clay Minerals. 23 (1975) 369-375. [140] D.L. Bish, Bulletin de Mineralogie. 103 (1980) 170-175. [141] G.W. Brindley, S. Kikkawa, American Mineralogist. 64 (1979) 836-843. [142] G.W. Brindley, S. Kikkawa, Clays and Clay Minerals. 28 (1980) 87-91.
Molecular and Biomolecular Spectroscopy. 59 (2003) 3313-3319. [146] R.L. Frost, W. Martens, Z. Ding, J.T. Kloprogge, T.E. Johnson, 59 (2003) 291-302. [147] R.L. Frost, Z. Ding, W.N. Martens, T.E. Johnson, J.T. Kloprogge, Spectrochimica
Acta Part A: Molecular and Biomolecular Spectroscopy. 59 (2003) 321-328. [148] A. Tsujimura, M. Uchida, A. Okuwaki, Journal of Hazardous Materials. 143 (2007)
1777. [170] S.V. Prasanna, R.A.P. Rao, P.V. Kamath, Journal of Colloid and Interface Science.
304 (2006) 292-299. [171] M. Uehara, A. Yamzaki, T. Umezawa, K. Takahashi, S. Tsutsumi, Clays and Clay
Minerals. 47 (1999) 726-731. [172] T.J. Pinnavaia, Science. 220 (1983) 365-371. [173] S. Carlino, Solid State Ionics. 98 (1997) 73-84. [174] S.P. Newman, W. Jones, New Journal of Chemistry. 22 (1998) 105-115. [175] Y. Hu, P.K. Davies, Materials Science Forum. 152-153 (1994) 277-280. [176] F. Kooli, M.J. Holgado, V. Rives, S. Sanroman, M.A. Ulibarri, Materials Research
Bulletin. 32 (1997) 977-982.
[177] N. Mikami, M. Sasaki, S. Horibe, T. Yasunaga, Journal of Physical Chemistry. 88 (1984) 1716-1719.
[178] M. Sasaki, N. Mikami, T. Ikeda, K. Hachiya, T. Yasunaga, Journal of Physical Chemistry. 86 (1982) 4413-4417.
[176] T. Hibino, A. Tsunashima, Chemistry of Materials. 9 (1997) 2082-2089. [180] F. Kooli, W. Jones, V. Rives, M.A. Ulibarri, Journal of Materials Science Letters. 16
(1997) 27-29. [181] E.M. Serwicka, P. Nowak, K. Bahranowski, W. Jones, F. Kooli, Journal of Materials
Chemistry. 7 (1997) 1937-1939. [182] F. Kooli, V. Rives, M.A. Ulibarri, Inorganic Chemistry. 34 (1995) 5114-5121. [183] M. Figlarz, B. Gerand, A. Delahaye-Vidal, B. Dumont, F. Harb, A. Coucou, F.
Fievet, Solid State Ionics. 43 (1990) 143-170. [184] S. Miyata, Clays and Clay Minerals. 31 (1983) 305-311. [185] P.K. Dutta, M. Puri, Journal of Physical Chemistry. 93 (1989) 376-381. [186] L.M. Parker, N.B. Milestone, R.H. Newman, Industrial & Engineering Chemistry
Product Research and Development. 34 (1995) 1196-1202. [187] T. Stanimirova, G. Kirov, Geologiya. 92 (2000) 121-130. [188] H. Kaatuzian, A. Rostami, A. Ajdarzadeh Oskouei, Quantum Physics. (2004) 1-11 [189] N. Sui, J. Hu, J. Chen, P. Kuang, D. Joyce, Journal of Psychopharmacology. 15
(2001) 287-291. [190] S.K. Zhang, P.V. Santos, R. Hey, A. Garcia-Cristobal, A. Cantarero, Applied Physics
Letters. 77 (2000) 4380-4382. [191] H.-S. Shin, M.-J. Kim, S.-Y. Nam, H.-C. Moon, Water Science and Technology. 34
(1996) 161-168. [192] T.S. Stanimirova, G. Kirov, E. Dinolova, Journal of Materials Science Letters. 20
(2001) 453-455. [193] W.T. Reichle, S.Y. Kang, D.S. Everhardt, Journal of Catalysis. 101 (1986) 352-359. [194] T. Sato, T. Wakabayashi, M. Shimada, Industrial & Engineering Chemistry Product
Research and Development. 25 (1986) 89-92. [195] R.L. Frost, A.W. Musumeci, J.T. Kloprogge, M.O. Adebajo, W.N. Martens, Journal
of Raman Spectroscopy. 37 (7) (2006) 733-741. [196] R.L. Frost, A.W. Musumeci, W.N. Martens, M.O. Adebaj, J. Bouzaid, Journal of
1913. [206] L. Chatelet, J.Y. Bottero, J. Yvon, A. Bouchelaghem, Colloids and Surfaces, A:
Physicochemical and Engineering Aspects. 111 (1996) 167-175.
[207] T. Lopez, P. Bosch, M. Asomoza, R. Gomez, E. Ramos, Materials Letters. 31 (1997) 311-316.
[208] F.M. Labajos, V. Rives, M.A. Ulibarri, Journal of Materials Science. 27 (1992) 1546-1552.
[209] M. Valcheva-Traykova, N. Davidova, A. Weiss, Journal of Materials Science. 28 (1993) 2157-2162.
[210] J.T. Kloprogge, R.L. Frost, Journal of Solid State Chemistry. 146 (1999) 506-515. [211] J. Perez-Ramirez, G. Mul, F. Kapteijn, J.A. Moulijn, Journal of Materials Chemistry.
11 (2001) 2529-2536. [212] J.T. Kloprogge, L. Hickey, R.L. Frost, journal name. 35 (2004) 967-974. [213] J.T. Kloprogge, D. Wharton, L. Hickey, R.L. Frost, American Mineralogist. 87
(2002) 623-629. [214] V.C. Farmer (Eds), Mineralogical Society Monograph 4: The Infrared Spectra of
Minerals, (1974). [215] K. Nakamoto (Eds), Infrared and Raman Spectra of Inorganic and Coordination
Compounds, Part A: Theory and Applications in Inorganic Chemistry, 5th Edition, (1997).
[216] C. Barriga, F. Kooli, V. Rives, M.A. Ulibarri, H. Kessler (Eds), Marcel Dekker, New York, (1996) 661.
[217] O. Clause, M. Gazzano, F. Trifiro, A. Vaccari, L. Zatorski, Applied Catalysis. 73 (1991) 217-236.
[218] L. Hickey, J.T. Kloprogge, R.L. Frost, Journal of Materials Science. 35 (2000) 4347-4355.
[219] J.I. Di Cosimo, V.K. Diez, M. Xu, E. Iglesia, C.R. Apesteguia, Journal of Catalysis. 178 (1998) 499-510.
[220] C. Morterra, G. Ghiotti, F. Boccuzzi, S. Coluccia, Journal of Catalysis. 51 (1978) 299-313.
[221] R. Philipp, K. Fujimoto, Journal of Physical Chemistry. 96 (1992) 9035-9038. [222] R.L. Frost, K.L. Erickson, Journal of Thermal Analysis and Calorimetry. 76 (2004)
217-225. [223] T. Lopez, E. Ramos, P. Bosch, M. Asomoza, R. Gomez, Materials Letters. 30 (1997)
279-282. [224] F. Malherbe, J.-P. Besse, Journal of Solid State Chemistry. 155 (2000) 332-341. [225] D. Tichit, M.H. Lhouty, A. Guida, B.H. Chiche, F. Figueras, A. Auroux, D. Bartalini,
E. Garrone, Journal of Catalysis. 151 (1995) 50-59. [226] O. Marino, G. Mascolo, Thermochimica Acta. 55 (1982) 377-383. [227] G. Mascolo, O. Marino, Mineralogical Magazine. 43 (1980) 619-621. [228] G. Brown, G.W. Brindley, Mineralogical Society Monograph. 5 (1980) 305-359. [229] G.W. Brindley, G. Brown (Eds), Mineralogical Society Monograph, No. 5: Crystal
Structures of Clay Minerals and Their X-ray Identification, (1980). [230] D.M. Moore, R.C. Reynolds, X-ray Diffraction and the Identification and Analysis of
Clay Minerals, 2nd Edition, (1997). [231] J. Thorez, Practical Identification of Clay Minerals: A Handbook for Teachers and
Students in Clay Mineralology., Belgium State University Press, Dison: Lelotte, (1976).
[232] D.M. Moore, R.C. Reynolds, X-ray Diffraction and the Identification and Analysis of Clay Minerals., 2 ed., Oxford University Press, New York, 1997.
[235] H.D. Ruan, R.L. Frost, J.T. Kloprogge, L. Duong, Spectrochimica Acta, Part A: Molecular and Biomolecular Spectroscopy. 58A (2002) 265-272.
[236] S. Miyata, T. Kumura, Chemistry Letters (1973) 843-848. [237] F. Kooli, I. Crespo, C. Barriga, M.A. Ulibarri, V. Rives, Journal of Materials
Chemistry. 6 (1996) 1199-1206. [238] S. Misra, Adsorbent and substrate products and method of producing the same, US
Patent 4656156, (1987). [239] S. Misra, Synthetic hydrotalcite. US Patent 6846870, (1990). [240] W.A. Nigro, G.A. O'Neil, Method for reducing the amount of colorants in a caustic
liquor, US Patent 5068095, (1991). [241] R.B. Phillips, N.M. Fitzgerald, B.L. McCormick, Method for improving the
brightness of aluminium hydroxide. US Patent 5624646, (1997). [242] B. Schepers, G. Bayer, E. Urmann, K. Schanz, Method for removing harmful organic
compounds from aluminate liquors of the Bayer process, US Patent 4046855, (1977). [243] D.K. Grubbs, P.E. Valente, Direct synthesis of anion substituted hydrotalcite, US