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Clays and Clay,ktinerals, VoL 33, No. 3, 181-192, 1985.

INFLUENCE OF INORGANIC A N D ORGANIC LIGANDS ON THE FORMATION OF ALUMINUM HYDROXIDES

AND OXYHYDROXIDES

A. VIOLANTE 1 AND P. M. HUANG

Department of Soil Science, University of Saskatchewan Saskatoon, Saskatchewan S7N 0W0, Canada

Abstract--Hydroxide and oxyhydroxide products of aluminum were formed at room temperature at an initial AI concentration of 2 x 10 -3 M, pH 8.2, and at varying concentrations of organic and inorganic ligands commonly found in nature. The effectiveness of the ligands in promoting the formation of noncrystalline products over crystalline AI(OH)3 polymorphs was found to be in the following order: phthalate ~ succinate < glutamate < aspartate < oxalate < silicate -~ fluoride < phosphate < salicylate

malate < tannate < citrate < tartrate. The lowest ligand/A1 molar ratio at which the production ora l hydroxides or oxyhydroxides was inhibited ranged from 0.02 to 15. Above critical ligand/A1 ratios, crystalline products were inhibited and ligands coprecipitated with noncrystalline products which remained unchanged for at least 5 months. Polydentate and large ligands generally were more inhibitive than those with fewer functional groups or of smaller size.

The perturbing ligands promoted and stabilized the formation of pseudoboehmite over crystalline AI(OH)3 polymorphs in the following sequence: chloride < sulfate < phthalate ~ succinate < glutamate < silicate < aspartate < phosphate < salicylate ~ malate < tannate < citrate < tartrate. The optimal range of the ligand/A1 molar ratios for the formation ofpseudoboehmite varied, for example, from 0.005- 0.015 for tartrate to 600-1000 for chloride. Pseudoboehmite was not formed in the presence of fluoride. Key Wards--Aluminum hydroxide, Boehmite, Ligand, Precipitation, Pseudoboehmite, X-ray powder diffraction.

I N T R O D U C T I O N

The strength of retention of many anions by crystalline, poorly crystalline, and noncrystalline aluminum hydroxides and oxyhydroxides plays a significant role in governing the mobility of these anions in soils (Parfitt, 1978). The influence of organic ligands on the precipitation of AI, however, has received relatively little attention. In the last two decades, studies on the influence of inorganic ligands on the hydrolytic products of AI have been carried out for chloride, sulfate, nitrate, and perchlorate (Hsu and Bates, 1964; Hsu, 1967, 1973; Turner and Ross, 1969; Ross and Turner, 1971; Smith and Hem, 1972), silicate (Luciuk and Huang, 1974; Hsu, 1979; Wada et al., 1979; Wada and Wada, 1980, 1981), and phosphate (Hsu, 1979). Hsu (1979) found that inorganic ligands inhibited the crystallization of Al-hydroxide in the following order: phosphate > silicate > sulfate > chloride > nitrate > perchlorate. Organic ligands of low molecular weight (Kwong and Huang, 1975, 1977, 1979a, 1979b; Vio- lante and Jackson, 1979, 1981; Violante and Violante, 1980), and tannic (Kwong and Huang, 1981) and fulvic acids (Kodama and Schnitzer, 1980) also perturb the precipitation of A1 and lead to the formation of noncrystalline products and/or poorly crystalline pseudoboehmite.

I Institute of Agricultural Chemistry, University of Naples, Portici, Italy.

Materials similar to the pseudoboehmite formed in the laboratory have been found in bauxite deposits (Lippens and Steggerda, 1970) and in tropical soils (de Villiers, 1969); however, because synthetic pseudoboehmite, formed at low temperatures and pressures, is very unstable and rapidly converts into crystalline AI(OH)3 (Souza Santos et al., 1953; Bye and Robinson, 1964; Aldcroft et al., 1969; Yoldas, 1973), many geo- chemists and soil chemists have claimed that boehmite in natural environments was formed by past hydro- thermal reactions and not in the present soil environments (Hsu, 1977). On the other hand, Keller (1964) reported that gibbsite and boehmite coexist in some bauxites, suggesting that they may have formed under similar conditions.

In the laboratory, pseudoboehmite can develop in the presence of sulfate (Hsu and Bates, 1964) or in a high concentration of indifferent electrolytes, such as NaC1 (Hsu, 1967; Chesworth, 1972), indicating that in nature it may form in a saline environment . Recently, Kwong and Huang (1979a), Violante and Jackson (1979, 1981), Violante and Violante (1980), and Kwong and Huang (1981) showed that organic ligands not only promote the formation of pseudoboehmite but also stabilize it.

The objective of the present study was to examine the relative effectiveness of selected organic and inorganic ligands in promoting the formation of noncrystalline precipitation products of a luminum and of pseudoboehmite over crystalline AI(OH)3 polymorphs.

Copyright �9 1985, The Clay Minerals Society 181

182 Violante and Huang Clays and Clay Minerals

EXPERIMENTAL

Preparation of precipitation products of aluminum Aluminum hydroxides, oxyhydroxides, or noncrystalline

products were precipitated at pH 8.2 by the slow addition of 0.05 M NaOH (2 ml/min) to a solution containing A1C13 and individual organic or inorganic ligands (phthalic, succinic, oxalic, malic, salicylic, glutamic, aspartic, citric, tannic, and tartaric acids; NaCI, Na2SO,, NaF, NaHzPO4, and Na2SiO3). The reason for the adjustment of the systems to this pH was to accelerate the formation of AI(OH)3 polymorphs so as to facilitate the investigation of the influence of the perturbing ligands on the nature of the precipitation products. The A1 concentration was 2 x 10 -3 M; the ligand concentration was chosen to give ligand/A1 molar ratios (R) from 0.0025 to 1000 (Tables 1-4). For each ligand, a range of ratios was selected according to the ability of the ligand to perturb the formation of A1 hydroxides on the basis of preliminary experiments. At specific reaction periods (15 days, 1, 2, 4, 5, and 8 months), precipitation products were collected by centrifugation at 12,000 gfor 15 min.

Analyses of precipitation products of aluminum X-ray powder diffraction (XRD) patterns of the precipitates

were obtained with a Philips X-ray diffractometer with Ni- filtered CuKa radiation generated at 35 kV and 16 mA. Two milligrams of air-dried material were ground, mixed with 200 mg of spectroscopic grade KBr, and pressed into a disc. In- flared (IR) spectra were recorded on a Beckman IR 11 spec- trophotometer. The precipitation products of A1 were iden- tified by the standard methods (Jackson, 1975; Hsu, 1977; Tettenhorst and Hofmann, 1980). Suspensions of samples were deposited on carbon-coated Formvar film on copper grids and were examined with a Philips 400 transmission electron microscope. The organic C in selected precipitates was converted to COz by combustion and determined by gas chromatography using a Hewlett-Packard C-H-N Analyzer Model 185B gas chromatograph.

R E S U L T S A N D D I S C U S S I O N

Phase examinations

Table 1 lists the prec ip i ta t ion products o f a l u m i n u m (crystalline AI(OH)3 po lymorphs , pseudoboehmi te , or noncrysta l l ine materials) at the init ial p H o f 8.2 and at ligand/A1 mo la r ratios (R) be tween 0.005 and 3 after a react ion per iod o f 5 months . The prec ip i ta t ion products fo rmed var ied greatly wi th the l igands and R values o f the systems. The data obta ined at lower or higher R values than those l isted in Table 1 are discussed below.

The X R D pat terns in Figures 1 and 2 i l lustrate the influence o f different selected l igands on the precipi- ta t ion products o f a luminum. In the presence o f chlo- r ide (Figure 1A), bayeri te (4.34/~,) and pseudoboeh- m i t e (6 .65 ,~) w e r e f o r m e d at R = 50, w h e r e a s p seudoboehmi te and gibbsite (4.82 A) were fo rmed at R = 500. Chlor ide d id not inhibi t the fo rma t ion o f p seudoboehmi t e even at R = 700 or 1000 (Figure 1A). The crystal l izat ion o f AI(OH)3 po lymorphs or A1OOH was inhibi ted at R = 0.3 and 3.0 in the presence o f phospha te (Figure 1B) and at R = 0.03 in the presence o f tar trate (Figure 1C).

Oxala te l igands re tarded the rate o f crystal l izat ion o f Al -hydroxides and oxyhydroxides m o r e than as-

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Vol. 33, No. 3, 1985 Influence of perturbing ligands on preciptation products of aluminum 183

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Figure 1. X-ray powder diffractograms of A1 precipitation products formed in the presence of (A) chloride, (B) phosphate, and (C) tartrate, showing a transition from a mixture of pseudoboehmite and crystalline AI(OH)3 polymorphs to pseudoboehmite or noncrystalline materials. All the samples were aged for 4 months. R = initial ligand/A1 molar ratio.

Figure 2. X-ray powder diffractograms of A1 precipitation products formed at the initial ligand/A1 molar ratio of 0.4: (a) pseudoboehmite formed in the presence ofaspartate after 15 days of aging (unchanged after 8 months); (b) and (c) noncrystalline materials + poorly crystalline gibbsite formed in the presence of oxalate after 15 days and 2 months, respectively; (d) and (e) noncrystalline materials formed in the presence of fluoride and silicate, respectively, after 4 months of aging.

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d

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Figure 3. Transmission electron micrographs of At precipitation products formed in the presence of different organic and inorganic ligands at the initial ligand/Al molar ratio of 0.1 (mineralogical composition of the products formed is confirmed by X-ray powder diffraction): (a) bayerite + gibbsite formed in the presence of sulfate; (b) nordstrandite + gibbsite + pseudoboehmite formed in the presence of glutamate; (c) bayerite + noncrystalline materials formed in the presence of fluoride; (d) gibbsite + pseudoboehmite formed in the presence of oxalate; (e) pseudoboehrnite formed in the presence of phosphate; and (f), (g), (h) noncrystalline materials formed in the presence of salicylate, tartrate, and tannate, respectively. All samples were aged for 8 months, except for the one synthesized in the presence of salicylate which was aged for 5 months. Bar = 0.5 ~m.

Figure 4. Transmission electron micrographs of AI precipitation products formed in the presence of different organic and inorganic ligands at the initial ligand/A1 molar ratio of 1. Mineralogical composition of the products was confirmed by X-ray powder diffraction. Noncrystalline materials formed in the presence of(a) and (b) oxalate, (c) fluoride, (d) silicate, (e) phosphate, (f) salicylate; pseudoboehmite formed in the presence of (g) aspartate; and bayerite + gibbsite formed in the presence of (h) phthalate. All samples were aged for 8 months. Bar = 0.5 #m.


Figure 3

Vol. 33, No. 3, 1985 Influence of perturbing ligands on preciptati0n products of aluminum 185

Figure 4


partate but less than fluoride and silicate (Figure 2). At R = 0.4, pseudoboehmite formed in the presence of aspartate (Figure 2a) after 15 days and remained unchanged for 8 months, whereas in the presence of oxalate the A1 precipitat ion product was X-ray amorphous after 15 days (Figure 2b). Poorly crystalline gibbsite, however, appeared to form after 2 months (Figure 2c). In the presence of fluoride and silicate, all precipitates were noncrystall ine after 4 months (Figure 2d and 2e).

Figures 3 and 4 show electron micrographs of selected precipitation products o r A l formed in the presence of organic and inorganic ligands at initial R of 0.1 (Figure 3) and 1.0 (Figure 4). At R = 0.1, AI(OH)3 polymorphs formed in the presence of sulfate (bayerite and gibbsite, Figure 3a), glutamate (nordstrandite and gibbsite, Figure 3b), fluoride (bayerite, Figure 3c), and oxalate (gibbsite, Figure 3d). In many of these samples pseudoboehmite (Figure 3b and 3d) or gelatinous, shapeless materials (Figure 3c) were present. At high magnification the pseudoboehmite formed in the presence of phosphate (Figure 3e) appeared to be composed of many fibrils having a diameter of 50-80 /k. Pseu- doboehmite also formed in the presence of aspartate (Figure 4g), and bayerite and gibbsite formed in the presence of phthalate (Figure 4h) at R = 1.0.

Precipitation products of A1 synthesized at R = 0. l in the presence ofsalicylate (Figure 3f), tartrate (Figure 3g), and tannate (Figure 3h) or at R = 1.0 in the presence ofoxalate (Figure 4a and 4b), fluoride (Figure 4c), silicate (Figure 4d), phosphate (Figure 4e) and salicylate (Figure 4f) were amorphous to X-rays and showed no distinct shape.

As suggested by Wada (1977) for allophane, varia- tions and indefiniteness of both shape and size of noncrystalline materials arise from aggregation o f the particles. The aggregation of particles also is influenced by the nature and amount of the perturbing ligands coprecipitated with A1 (authors' unpublished data). Particularly, the noncrystall ine materials formed in the presence of tannic acid (R = 0.1) were heavy precipitates consisting of small particles, strongly aggregated to each other (Figure 3h). At high magnifications, noncrystalline materials commonly consisted o f submi- croscopic spherical particles (about 100 ~ in size) linked together to form a disordered mosaic (Figure 4b and 4e).

The IR spectra in Figure 5 illustrate the influence of increasing concentrations of a foreign ligand (tannate) on the nature of the A1 precipitat ion products. At the tannate/A1 molar ratio of 0.003, well-defined bands of bayerite (3440, 3470, 3560, 3660 cm -1) are easily detectable (Figure 5a). The bands at 3120 and 3360 cm- ' indicate the presence of pseudoboehmite. The bands ofbayer i te were barely detectable at higher initial tannate/A1 molar ratios (e.g., 0.007, Figure 5b) and disappeared completely at the initial tannate/A1 ratio of 0.03 (Figure 5c), whereas the bands ofpseudoboehmite

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03

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Figure 5. Infrared spectra of A1 precipitation products formed in the presence of tannic acid: (a) bayerite + pseudoboehmite (R = 0.003); (b) pseudoboehmite + trace of bayerite (R = 0.007); (c) stable pseudoboehmite (R = 0.03); and (d) noncrystalline material (R = 0.1). All samples were aged for 8 months. R = tannate/A1 molar ratio.

became more distinct. At the ligand/A1 molar ratio of 0.1, the bands of bayerite and pseudoboehmite completely disappeared and a broad asymmetr ical band was ascertained, indicating the presence of noncrystalline materials (Figure 5d).

Noncrystalline precipitation products of aluminum

From the data listed in Table 2, tartrate was the most effective o f the ligands studied in preventing the for-

Vol. 33, No. 3, 1 9 8 5 Influence of perturbing ligands on preciptation products of aluminum 187

Table 2. Order of effectiveness of inorganic and organic ligands in promoting the formation of X-ray amorphous precipitation products of AI.

L i g a n d R 2

Phthalate =~ succinate 15 Glutamate 4 Aspartate 2.5 Oxalate 1 Silicate ~ fluoride 0.4 Phosphate 0.15 Salicylate ~ malate 0.10 Tannate 0.04 Citrate 0.03 Tartrate 0.02

After 5 months of aging. 2 R = lowest initial ligand/A1 molar ratio at which X-ray-

amorphous materials were formed at pH 8.2; R values for chloride and sulfate were not determined.

mation of crystalline a luminum hydroxides and oxyhydroxides and was about 2, 5, 20, 50, and 750 times more effective than tannate, salicylate (or malate), silicate (or fluoride), oxalate, and phthalate (or succinate), respectively. The lowest tartrate/A1 molar ratio at which the formation of crystalline materials was inhibited was 0.02. On the other hand, the crystallization of pseudoboehmite was promoted even at a chloride/A1 molar ratio of 1000 (Figure 1A). Tartrate was therefore, more than 50,000 times as effective as chloride in hampering the crystallization of the precipitation products of A1.

Dicarboxylic acids (phthalic, succinic, and oxalic acids) perturbed the precipitation reaction of aluminum less than hydroxy-di(tri)carboxylic acids (citric, tartaric, malic acid) (Tables 1 and 2). Cornell and Schwertmann (1979) found that organic ligands inhibited the crystallization of ferrihydrite in a similar man- ner. Oxalate anions inhibited the crystallization of AI(OH)3 polymorphs or pseudoboehmite at R -> 1.0, whereas phthalate and succinate were effective only at R >- 15 (Table 2). Oxalate ligands which may complex A1 by forming stable 5-membered rings exhibited an inhibiting power at least 15 times greater than phthalate or succinate ligands which are capable of complexing A1 by forming unstable 7-membered rings (Violante and Violante, 1980).

Tartrate Al-complexes are much less stable than citrate Al-complexes (Sillen and Martell, 1964; Earl et al., 1979); however, tartrate had a stronger influence than citrate in retarding or inhibiting the crystallization of Al-hydroxides or oxyhydroxides (Table 2). Earl et aL (1979) demonstrated that tartrate is more strongly adsorbed on aluminous materials or more easily co- precipitates with A1 than citrate, whereas citrate shows a much stronger influence on solubilizing A1 than tartrate. Higher concentrations of tartrate anions in the noncrystalline material initially formed or in the pseudoboehmites may have retarded the transformation by

dissolution and recrystallization of these phases into AI(OH)3 polymorphs. Therefore, the influence of ligands on retarding the kinetics of the crystallization of the precipitation products of A1 was not always con- trolled by their chelating power for AI (see also Kwong and Huang, 1979c; Violante and Violante, 1980; Kwong and Huang, 1981). This behavior was particularly evident for materials formed in the presence of tannate, tartrate, citrate, oxalate, fluoride, and phosphate (see below).

Polydentate and large ligands generally are more in- fluential in inhibiting AI(OH)3 crystallization than ligands with few functional groups or of small size. This influence is evident for the precipitates formed in the presence of tannic acid (MW = 1701). Kwong and Huang (1979c, 1981) demonstrated that Al-tannate complexes have a stability constant (log k~ = 3.78) much lower than Al-citrate (log ks = 7.35) and Al-malate complexes (log ks = 5.14); however, both tannate and citrate more effectively inhibited the precipitation reaction of A1 than malate (Table 2). Furthermore, although Al-tannate complexes (log ks = 3.78) are about 10 times more stable than Al-aspartate complexes (log k~ = 2.60) (Kwong and Huang, 1979c), tannic acid and aspartic acid inhibited the crystallization of AI(OH)3 polymorphs or pseudoboehmites at R -> 0.04 and 2.5, respectively (Table 2). Thus, tannic acid was approx- imately 60 times more effective than aspartic acid in perturbing the crystallization of precipitation products of a luminum. Large molecules with many functional groups distort the structural organization of the precipitation products of A1 (Kwong and Huang, 1981) and promote their aggregation (authors' unpublished data).

Hsu (1977) considered phosphate and fluoride anions to have strong and very strong affinity for A1, respectively. Huang and Jackson (1966) showed that fluoride may break the AI-OH-A1 linkages and the OH at the edge of AI(OH)3, thus destroying the a luminum hydroxide structure. Aluminous precipitates formed in the presence of phosphate at R -> 0.15, however, were amorphous to X-rays even after a reaction period of 4-5 months (Table 2; Figure 1B), whereas in the presence of fluoride crystallization was inhibited only at R -> 0.4 (Table 2; Figure 2d; for 13% or more substi- tution of F for OH). The stronger influence of phosphate than fluoride on retarding the crystallization of precipitation products of A1 was due mainly to the larger size of the phosphate anion. Consequently, phosphate was sterically more effective than fluoride in dis- torting the structural organization of the precipitation products.

Formation o f pseudoboehmite

The formation of pseudoboehmite over crystalline AI(OH)a was promoted by the presence of certain organic and inorganic ligands. For example, pseudoboehmite was formed at R = 0.005-0.015 for tartrate


Table 3. Effectiveness of inorganic and organic ligands in promoting the formation of pseudoboehmite.

Ligand R ~

Chloride 600-1000 Sulfate 50-n.d. Phthalate ~ succinate 7-14 Glutamate 0.4-3.0 Silicate 0.3- < 0.4 Aspartate 0.1-2.0 Phosphate 0.05--0.1 Salicylate ~ malate 0.02-0.05 Tannate 0.01-0.03 Citrate 0.007-0.02 Tartrate 0.005-0.015

After 5 months of aging. 2 The range of the initial ligand/A1 molar ratios at which

stable pseudoboehmite was formed at pH 8.2 and other crystalline phases were not observed; n.d. = not determined.

(Table 3; Figure 1C), 0.05-0.10 for phosphate (Table 3; Figure 1B), 0.1-2 for aspartate (Table 3; Figure 2a), and 600-1000 for chloride (Table 3; Figure 1A). At the initial pH of 8.2, an opt imal range of R values existed for each ligand for the formation of the pseudoboehmite. The promoting effects o f organic ligands on the formation o f pseudoboehmite was apparently s imilar to the influence o f organic and inorganic ligands on the stability of lepidocrocite (Schwertmann, 1979) which is isostructural with boehmite.

Inorganic and organic ligands are arranged in Table 3 in accordance with their effectiveness in promoting the formation of stable pseudoboehmite. This sequence is similar to that for the formation o f noncrystall ine materials (Table 2), with the following exceptions: (1) silicate was more effective than aspartate in promoting the formation of noncrystall ine materials, but the latter was more effective in promoting the formation ofpseudoboehmite; (2) the format ion ofpseudoboehmi te was not noted in the presence o f fluoride; and (3) pure pseudoboehmite did not crystallize in oxalate systems.

The formation of pseudoboehmite from an init ially noncrystall ine material produced in the presence o f citrate in a few days (or even hours) after the sample preparat ion is i l lustrated in Figure 6. For a given ligand, the higher the initial R value, the slower was the rate of the t ransformation from the noncrystall ine mater ia l into pseudoboehmite (data not shown). During this transformation, the peak posi t ion o f the 020 reflection of pseudoboehmite was shifted from lower to higher 20 values with increasing sharpness o f the peak probably owing to an increase in crystallinity (Tettenhorst and Hofmann, 1980.

Bye and Robinson (1964), Aldcroft et aL (1969), and Yoldas (1973) demonstra ted that the format ion o f pseudoboehmite from the initially noncrystall ine material is a solid stage reaction. Critical concentrations of perturbing ligands in the noncrystall ine mater ial ini-

C i t r a t e R = 0.01

21 19 17 15 13 11 9 7 5

2e CuK(x Radiat ion

Figure 6. X-ray powder diffractograms of A1 precipitation products formed in the presence of citrate (citrate/A1 molar ratio 0.01) after 1, 3, 12, and 60 days of aging, showing a transformation of an initially formed noncrystalline material into stable pseudoboehmite.

tially cause a structural disorder, but then promote aggregation of particles which become less soluble (Aldcroft et al., 1969). As the reaction proceeds, the partial and gradual removal o f these ligands from the noncrystalline materials with consequent reorganiza- tion of this phase leads to the formation of pseudoboehmite (Yoldas, 1973).

When the bond between Al and the perturbing organic ligands o f the complex was ruptured by poly- merization of hydroxy A1 ions, the l iberated organic ligands seemed to facilitate deprotonat ion o f A1--OH ~ groups, promoting the formation of A1-O-Al linkages. The liberated ligands, part icularly those with strong affinity for A1, may have been readsorbed and then released again, thereby perpetuating the format ion of

Vol. 33, No. 3, 1 9 8 5 Influence of perturbing ligands on preciptation products of aluminum 189

Table 4. Organic ligands present in aluminous precipitation products formed at different ligand/A1 molar ratios.'

Ligand R 2 Minera logy 3

Ligand concen- t ra t ion

( m m o l e / k g o f sample)

Tannic acid 0.0025 Bayerite + 37 (Pseudoboehmite)

Tannic acid 0.005 Bayerite + 68 (Pseudoboehmite)

Tannic acid 0.01 Pseudoboehmite 121 Tannic acid 0.02 Pseudoboehmite 162 Tannic acid 0.04 Noncrystalline 227 Tannic acid 0.1 Noncrystalline 353 Aspartic acid 0.2 Pseudoboehmite 400 Aspartic acid 1.0 Pseudoboehmite 468 Oxalic acid 1.0 Noncrystalline 160 Salicylic acid 0.03 Pseudoboehmite 328 Salicylic acid 0.2 Noncrystalline 780 Phthalic acid 3 Gibbsite + 355

(Pseudoboehmite) Phthalic acid 7 Pseudoboehmite 593 Phthalic acid 16 Noncrystalline 880

After 8 months of aging. 2 R = initial ligand/A1 molar ratio. 3 Determined by X-ray powder diffraction; ( ) indicates small

amounts.

A1-O-A1 linkages. This process was probably related to the concentration ofligands and their affinity toward AI. Therefore, the promotion of the formation ofpseudoboehmite by relatively weak ligands was only pos- sible at sufficiently high ligand/A1 ratios. The perturbing !igands present in the precipitates (Table 4) evidently disturbed the crystallization of AIOOH. These poorly ordered Al-oxyhydroxides may have been either fine- size boehmite (Tettenhorst and Hofmann, 1980) or poorly crystalline boehmite.

At ligand/A1 molar ratios lower than the critical values (Table 3), pseudoboehmite commonly formed in the early stages of the reaction period, but with time, its XRD peaks decreased in intensity (or disappeared) and AI(OH)3 polymorphs were formed as illustrated by the phase transformation of a sample prepared in the presence ofphthalate (Figure 7a-7d). Clearly, under these conditions pseudoboehmite was not sufficiently stable and slowly dissolved. At the phthalate/A1 ratio of 7, however, pseudoboehmite remained unchanged at the end of the reaction period (Figure 7e).

The present findings provide an interpretation for the presence of pseudoboehmite in bauxite deposits (Lippens and Steggerda, 1970) and in noncrystalline boehmite-like alumina in tropical soils (de Villiers, 1969), because the organic and inorganic ligands studied are common in soils and the associated environments (Huang, 1985). Furthermore, the coexistence of gibbsite and pseudoboehmite in the systems (Table 1) studied supports Keller's (1964) suggestion that gibbsite and boehmite may have formed under similar conditions.

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R=3; 1month ~ ',

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2e CuKa Radiat ion Figure 7. X-ray powder diffractograms of A1 precipitation products formed in the presence ofphthalate: (a), (b), (c) and (d) show the transformation of unstable pseudoboehmite into gibbsite at the initial phthalate/Al molar ratio (R) of 3 during the aging; (e) stable pseudoboehmite formed at R = 7 after 5 months of aging; and (f) shows noncrystalline materials after 5 months of aging of a sample at the initial R = 15.

Perturbing ligands in precipitation products of aluminum

Table 4 shows the content (mmole/kg sample) of organic ligands in the aluminous precipitation products. It is evident that, by increasing the initial R, the


amount of perturbing ligands in the precipitate increased and the final minera log ica l compos i t i on changed. The IR spectra corroborate this observation. By increasing the initial tannate/A1 molar ratio 40 times (from R = 0.0025 to R = 0.1), however, the amount of the organic ligand in the precipitates increased less than 10 times (from 37 to 353 'mmole/kg sample). Because of the large size and complexing power of tannic acid, the presence of 227 mmole/kg of tannate inhibited the formation of crystals, whereas the presence of 400 to 468 mmole/kg of aspartate (R = 0.2 or 1), 355 to 593 mmole/kg of phthalate (R = 3 or 7), or 328 mmole/kg salicylate (R = 0.03) led to the formation of pseudoboehmite and/or gibbsite. The precipitation products of A1 containing 1600 mmole/kg of oxalate (R = 1.0), 880 mmole/kg ofphthalate (R = 16), and 780 mmole/kg of salicylate (R = 0.2) were noncrystalline. Phthalate has a much lower affinity for A1 than oxalate (Violante and Violante, 1980), so that a higher R was necessary in the presence of phthalate to promote the formation of noncrystalline materials (Ta- ble 2).

In summary, the organic and inorganic ligands studied, which are commonly present in nature, varied sig- nificantly in their ability to perturb the crystallization of the precipitation products of A1 even under mild alkaline conditions. Higher ligand/A1 molar ratio led to the inhibition of the crystallization of a luminum hydroxide polymorphs and the formation of pseudoboehmite and/or X-ray-amorphous materials. The nature of the precipitation products of A1 in terrestrial and aquatic environments may thus be substantially influenced by the kinds of perturbing ligands and the ligand/Al ratios prevailing in the environments.

ACKNOWLEDGMENT

This study was supported by Natural Sciences and Engineering Research Council of Canada, Grant A2383- Huang. Contribution no. 420, Sasketchewan Institute of Pedology.

REFERENCES

Aldcroft, D., Bye, G. C., and Hughes, C. A. (1969) Crys- talline process in aluminum hydroxide gels. IV. Factors influencing the formation of the crystalline trihydroxides: J. Appl. Chem. 19, 167-172.

Bye, G. C. and Robinson, J. G. (1964) Crystallization process in aluminum hydroxide gels: Kolloid Z. 198, 53-60.

Chesworth, W. (1972) The stability ofgibhsite and boehmite at the surface of the earth: Clays & Clay Minerals 20, 369- 374.

Cornell, R. M. and Schwertmann, U. (1979) The influence of organic anions on the crystallization offerrihydrite: Clays & Clay Minerals 27, 402-410.

de Villiers, J. M. (1969) Pedosesquioxides--composition and colloidal interactions in soil genesis during the Qua- ternary: Soil Sci. 107, 454-461.

Earl, K.D.,Syers, J.K.,andMcLaughlin, J.R. (1979) Origin of the effect of citrate, tartrate and acetate on phosphate

sorption by soils and synthetic gels: Soil Sci. Soc. Amer. J. 43, 674-678.

Hsu, P.H. (1967) Effect of salts on the formation ofbayerite versus pseudoboehmite: Soil Sci. 103, 101-110.

Hsu, P. H. (1973) Effect of sulfate on the crystallization of aluminum hydroxide from aging hydroxy-aluminum solutions: in Proc. 3rd Int. Congr. on Studies of Bauxite and Aluminum Oxides-Hydroxides, Nice, France, 1973, J. Nic- olas, ed., Sedal, Paris, 613-620.

Hsu, P. H. (1977) Aluminum hydroxides and oxyhydroxides: in Minerals in Soil Environments, J. B. Dixon and S. B. Weed, eds., Soil Sci. Soc. Amer., Madison, Wisconsin, 99-143.

Hsu, P. H. (1979) Effect of phosphate and silicate on the crystallization of gibbsite from OH-A1 solutions: Soil Sci. 127, 219-226.

Hsu, P. H. and Bates, T. F. (1964) Formation of X-ray amorphous and crystalline aluminum hydroxides: Mineral. Mug. 33, 749-768.

Huang, P.M. and Jackson, M.L. (1966) Fluoride interaction with clays in relation to third buffer range: Nature (London) 211, 779-780.

Huang, P. M. (1985) Aluminum and the fate of nutrients and toxic substances in terrestrial and freshwater environments: in Encyclopedia of Systems and Control, M. Singh, editor-in-chief, Pergamon Press, Oxford (in press).

Jackson, M. L. (1975) Soil Chemical Analysis--Advanced Course: 2nd ed., published by the author, University of Wisconsin, Madison, Wisconsin, 895 pp.

Keller, W.D. 1964. The origin of high alumina clay minerals. A review: Clays & Clay Minerals 12, 129-151.

Kodama, H. and Schnitzer, M. (1980) Effect offulvic acid on the crystallization of aluminum hydroxides: Geoderma 24, 195-205.

Kwong, Ng Kee, K. F. and Huang, P. M. (1975) Influence of citric acid on the crystallization of aluminum hydroxides: Clays & Clay Minerals 23, 164-165.

Kwong, Ng Kee, K. F. and Huang, P. M. (1977) Influence of citric acid on the hydrolytic reactions of aluminum: Soil Sci. Soc. Amer. J. 41, 692-697.

Kwong, Ng Kee, K. F. and Huang, P. M. (1979a) Nature of hydrolytic products of aluminum as influenced by low molecular weight complexing organic acids: in Proc. Int. Clay Conf., Oxford, 1978, M. M. Mortland and V. C. Farmer, eds., Elsevier, Amsterdam, 527-536.

Kwong, Ng Kee, K. F. and Huang, P. M. (1979b) Surface reactivities of hydrolytic reaction products of aluminum formed in the presence of low molecular weight organic acids: Soil Sci. Soc. Amer. J. 43, 1107-1113.

Kwong, Ng Kee, K. F. and Huang, P.M. (1979c) The relative influence of low-molecular-weight, complexing organic acids on the hydrolysis and precipitation of aluminum: Soil Sci. 128, 337-342.

Kwong, Ng Kee, K. F. and Huang, P.M. (1981 ) Comparison of the influence of tannic acid and selected low molecular weight organic acids on precipitation products of aluminum: Geoderma 26, 179-193.

Lippens, B. C. and Steggerda, J.J. (1970) Active alumina: in Physical and Chemical Aspects of Adsorbents and Cat- alysts, B. G. Linsens, ed., Academic Press, New York, 171- 211.

Luciuk, G. M. and Huang, P. M. (1974) Effect ofmonosilicic acid on hydrolytic reactions of aluminum: Soil Sci. Soc. Amer. Proc. 38, 235-243.

Parfitt, R. L. (1978) Anion adsorption by soils and soil materials: Adv. Agron. 30, 1-50.

Ross, G. J. and Turner, R.C. (1971) Effect of different anions on the crystallization of aluminum hydroxide in partially

Vol. 33, No. 3, 1985 Influence of perturbing ligands on preciptation products of a luminum 191

neutralized aqueous a luminum salt systems: Soil Sci. Soc. Amer. Proc. 35, 389-392.

Schwertmann, U. (1979) Noncrystalline and accessory minerals: in Proc. Int. Clay Conf., Oxford, 1978, M. M. Mort- land and V. C. Farmer, eds., Elsevier, Amsterdam, 491- 499.

Sillen, L. G. and Martell, A. E. (1964) Stability constants of metal ion complexes: Chem. Soc. London, Spec. Publ. 17, 390-470.

Smith, R. W. and Hem, J. D. (1972) Effect of aging on a luminum hydroxide complexes in dilute aqueous solutions: U.S. Geol. Surv. Water Supply Pap. 1827-D, 51 pp.

Souza-Santos, P., Valleijo-Freire, A., and Souza-Santos, H. L. (1953) Electron microscope studies on the aging of amorphous colloid a luminum hydroxide: Kolloid Z. 133, 101-107.

Tettenhorst, R. and Hofmann, A. (1980) Crystal chemistry of boehmite: Clays & Clay Minerals 28, 373-380.

Turner, R. C. and Ross, G.J . (1969) Conditions in solution during the formation of gibbsite in dilute a luminum salt solutions. III. Hydroxyaluminum products of reactions during the neutralization of a luminum chloride solutions with sodium hydroxide: Can. J. Soil Sci. 49, 389-396.

Violante, A. and Jackson, M. L. (1979) Crystallization of nordstrandite in citrate systems in the presence of mont- morillonite: in Proc. Int. Clay Conf., Oxford, 1978, M. M. Mortland and V. C. Farmer, eds., Elsevier, Amsterdam, 517-525.

Violante, A. and Jackson, M. L. (1981) Clay influence on the crystallization of a luminum hydroxide polymorphs in the presence of citrate, sulfate or chloride: Geoderma 25, 199-214.

Violante, A. and Violante, P. (1980) Influence o fpH, concentration, and chelating power of organic anions on the synthesis of a luminum hydroxides and oxyhydroxides: Clays & Clay Minerals 28, 425-434.

Wada, K. (1977) Allophane and imogolite: in Minerals in Soil Environments, J. B. Dixon and S. B. Weed, eds., Soil Sci. Soc. Amer., Madison, Wisconsin, 603-638.

Wada, S. I., Eto, A., and Wada, K. (1979) Synthetic allophane and imogolite: J. Soil Sci. 30, 347-355.

Wada, S. I. and Wada, K. (1980) Formation, composit ion and structure of hydroxy-aluminosilicate ions: J. Soil Sci. 31, 457-467.

Wada, S. I. and Wada, K. (1981) Reactions between alu- minute ions and orthosilicic acid in dilute, alkaline to neu- tral solutions: Soil Sci. 132, 267-273.

Yoldas, B. E. (1973) Hydrolysis of a luminum alkoxides and bayerite conversion: J. Appl. Chem. Biotechnol. 23, 803- 809.

(Received 8 August 1983; accepted 12 October 1984; Ms. 1275)

Pe3mMe--FIt~poorHcHbIe n orc~rn~pooxnc~bie npo~yxTbI aYIIOMHHI4H di)OpMHpOBa.rIHCb npn KOMHaTHOITI TeMnepaType, naqaJibnoffI XOHIIenTpaKIll4 A1 paBno~I 2 X 10 3 M, pH paBHbIM 8,2 n pa3JInqHblX KOHKeH- TpaI~nSx opraHnqecKrlX rl HeopraHn~ecxnx nnraH~loB, O6b~qHO aaxo/l~mnxcn a npnpo~e. ~dpdpeKTHBHOCTb naraH~oB a CIIOCO6CTBOBaHI, IH o6pa30aaamo HeKpttcTa.rlJulqecKttx IIpo~yxToB Ilpe~IIOqTHTeJII~HO no.rutMop- dpOM AI(OH)3 Haxo~nac~ B cJie~ytoliieM n o p ~ r e : (~TaJ/aT ~ cyKI~HHaT ~ FY/yTaMaT < acnapTaT < OKCa- naT < CHYiHKaT ~ O~TOpH~ < (])OCtl)aT < caJiitRriylaT ~ MaJIaT < TaHHaT < I~tlTpaT < TapTpaT. HaH6o2iee nn3Ka~i Be~/nqriHa MO.r/~pHoro OTHOIL]eHHH nHran~/A1, npn XOTOpO~I 3a~epTxnBanocb o6pa3oBaHne rnnpo- oKttce~ ~IJ~H oKcnr~pooi(r~ceft AI, rtaxo~a~acb s Ananaaone OT 0,02 JXO 15. B~itue KpI'ITHqeCKItX Be~r~q~H oTHomeHafi n~raaa/A1, Kp/JcTaJIJnlqecgtte IIpoRyKTBI He o6pa3oBbma~Hcb, a .rlHraRRbI oca~JlaJIHCB BMeCTe C ReKpHcTaJIJIttqeCKttMH rlpoJlyKTaMtt, KOTOpble OCTaBaJn, ICb HeI, I3MeHel-n-IhIMH B TeqenHe He MeHee, qeM 5 Meca~es. HOnn~leHTaT a 6onbtu~e naraH)Ibl nMenn 6onbtuy~o cnoco6nocT~ 3a~ep~aBaHns, aeM JmraH~, co~ep~amne MeH~mee KOnaqecTea qbyHKanOHan~H~X rpynn ann Jmra~ab~ MeHbmHX pa3Mepo~. BO3My- m a ~ o ~ e nnraH/Ib~ cnoco6CTBOBa~a n cTa6r~nn3apoBa.an qbopMapoBaHae cxopee nces~o6eMnTa, aeM xpnc- Ta~naaecKnx nOnaMOpqboB AI(OH)3 B cne~y~otueM nop~xe : xnopa/l < cyJI~qbaT < qbTa~aT ~ cy~r~HaT < rJ~yTaMaT < CI, IJn~KaT < acrIapTaT < qbacqbaT < caJItt~ttJIaT ~ Ma.rlaT < TaHItaT < I~nTpaT < TapTpaT.

OHTHMSJINHBII~I ~ana3or~ BeJIH~n~a MOJIflpHblX OTHOmenHITI nnraH/I/A1 ~ i o6pa3oBaHrDi nceB~o6eMllTa H3MeH~IJIC$I, narlpaMep, OT 0,005--0,015 a3Ia TapTpaTa ]lO 600--1000 ~nn xJmp~/Ia. I'IceBJIO6eMI, IT He o6- pa3oBl, IBa.rlc~l B npacyTcT~nn ~TopH~Ia. [E.G.]

Resiimee-- Hydroxid- und Oxyhydroxid-Verbindungen von Aluminium wurden bei Raumtempera tur und mit einer urspriknglicben A1-Konzentration yon 2 x 10 3 m, bei pH 8,2 und mit verschiedenen Konzen- trationen yon organischen und anorganischen Liganden, die in der Natur tiblich sind, gebildet. Die Wirksamkeit der Liganden bei der F6rderung der Bildung von nichtkristallinen Produkten gegenfiber kristallinen polymorphen Al(OH)3-Modifikationen geht in folgender Reihenfolge: Phtalat ~ Succinat < Glutamat < Asparat < Oxalat < Silikat -~ Fluorid < Phosphat < Salicylat ~ Malat < Tannat < Ci- trat < Tartrat. Das niedrigste Ligand/A1-Molverhaltnis, bei dem die Entstehung yon A1-Hydroxiden oder -Oxyhydroxiden verhindert wurde, liegt bei 0,02-15. Oberhalb der kritischen Ligand/A1-Verh~iltnisse wurde die Bildung kristalliner Verbindungen verhindert und die Liganden fielen mit nichtkristallinen Produkten zusammen aus, die fiber mindestens 5 Monate unvedindert blieben. Polydentat und groBe Liganden wirkten sich im allgemeinen mehr verh indemd aus als solche, mit weniger funktionellen Grup- pen oder mit geringer Gr613e.

Die st6renden Liganden f6rderten und stabilisierten die Bildung yon Pseudoboehmit gegenfiber kristallinen polymorphen Al(OH)3-Modifikationen in der folgenden Reihenfolge: Chlorid < Sulfat < Phtalat ~- Succinat < Glutamat < Silikat < Asperat < Phosphat < Salicylat ~ Malat < Tannat < Citrat < Tar- trat. Der optimale Bereich der Ligand/A1-Molverh~iltnisse fiir die Bildung yon Pseudoboehmit variierte, z.B. yon 0,005-0,015 f'tir Tartrat bis 600-1000 F~ Chlorid. Pseudoboehmit wurde in Gegenwart yon Fluorit nicht gebiidet. [U.W.]


R~sum~--Des produits d 'a luminium hydroxide et oxyhydroxide ont 6t6 formrs ~t une concentration initiale d'A1 de 2 • 10 -3 M, au pH 8,2 et ~ des concentrations varires de ligands organiques et inorganiques trouvrs c o m m u n r m e n t duns la nature. On a trouv6 que l'efficacit6 des ligands ~ promouvoir la formation de produits non-cristallins plut6t que des polymorphes AI(OH)3 cristallins 6tait dans l'ordre suivant: phthalate -~ succinate < glutamate < aspartate < oxalate < silicate -~ fluoride < phosphate < salicylate

malate < tannate < citrate < tartrate. La proportion molaire ligand/AI la plus basse h laquelle la production d'hydroxides Al ou d'hydroxides A1 a 6t6 inhibre s ' r tendait de 0,02 ~t 15. Au dessus des proportions ligand/A1 critiques, les produits cristallins 6taient inhibrs et les ligands ont coprrcipite avec des produits non-cristallins qui sont restrs inchangrs pendant au moins 5 mois. Les ligands polydentates ou larges 6talent grnrralement plus inhibants que ceux avec moins de groupes fonctionnels ou de plus petite taille.

Les ligands perturbants ont promu et stabilis6 la formation de pseudoborhmite relativement aux polymorphes cristallins AI(OH)3 selon la srquence suivante: chloride < sulphate < phthalate -~ succinate < glutamate < silicate < aspartate < phosphate < salicylate - malate < tannate < citrate < tartrate. L'r tendue optimale des proportions molaires ligand/A1 pour la formation de pseudoborhmite a varir, par exemple, de 0,005-0,015 pour la tartrate ~ 600-1000 pour la chloride. La pseudoborhmite n 'a pus 6t6 formre en la prrsence de fluoride. [D.J.]

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