The Release of Aluminum from Aluminosilicate Minerals. I. Kinetics

Abstract-The dissolution of two CaZ+-exchanged nontronite samples has been studied in 10% HC1. Early acid-dissolution studies (Osthaus, 1954) have indicated that after two hours of dissolution most of the octahedral Fe 3+ (V~Fe3+) would be removed leaving mainly tetrahedral Fe 3+ (IVFe3+) in the nontronite structure. In the present study, 57Fe M6ssbauer spectra of acid-treated samples were recorded and fitted with two octahedral Fe 3 § (2 x VlFe3+ ) and two octahedral and one tetrahedral (2 x WFe3+, 1 • lVFe3+) doublet models. The M6ssbauer spectra of acid-treated Garfield nontronite samples could be adequately fitted with two-doublet models but acid-treated Hohen Hagen nontronite samples could not. Isomer shift and quadrupole splitting values obtained from the two-doublet models corresponded to VIFea+ and not ~VFe3+, as was suggested by the Osthaus (1954) experiment. When an IVFe3+ doublet was included in the model used to fit the M6ssbauer spectra of acid-treated Garfield nontronite samples, a slight increase in the intensity of the WFe3+ doublet occurred with increasing dissolution, but this was much lower than indicated by Osthaus (1954). No trend in the intensity of the lVFe3+ doublet was observed for acid-treated Hohen Hagen nontronite. Therefore, acid treatment appears to remove VIFe3+ and WFe3+ from the nontronite structure at about the same rate. M6ssbauer spectroscopy, infrared spectroscopy and X-ray powder diffraction data indicate that the nontronite that remains undissolved following acid treatment is structurally similar to the untreated nontronite.

Section: Discussionmentioning

confidence: 99%

Site Occupancy in Nontronite Studied by Acid Dissolution and Mössbauer Spectroscopy

Luca

MacLachlan

1992

“…The dissolution kinetics of micas has been found to be both linear (Gastuche, 1963) and parabolic (Cabrera and Talibudeen, 1978;Huang and Keller, 1973;Newman and Brown, 1969). Huang and Keller (1973) also found that Si had the slowest release rate from illite.…”

Section: Kineticsmentioning

confidence: 99%

Dissolution Kinetics of Phlogopite. I. Closed System

Lin¹,

Clemency

1981

Abstract--Dry ground phlogopite was placed in deionized water saturated with COs at room temperature and pressure. The bulk solution was buffered between a pH of 5 and 6 which is close to the pH of natural weathering systems. The conditions simulated a closed system. After 1010 hr, 2.0% of the total K, 0.95% of the Mg, 0.54% of the Si, and 0.74% of the F had been released, indicating that the dissolution was incongruent. Most of the K was released within 3 min, apparently by a rapid surface exchange with hydrogen ion. One-third of the cation-exchange capacity of this phlogopite arises from cations released from the outer surfaces, while two-thirds arises from the release of more deeply seated cations. All cations exhibited decreasing release with time, the slowest being Si. The rate-controlling "factor" in the later stages is related to the release of Si. It is difficult to distinguish linear from parabolic kinetics in the later stages because of the slow rate of dissolution; however, linear kinetics is most likely. If linear kinetics is applicable, the dissolution rate of Si was 3.8 • 10 -17 mole/cm2/sec. Conclusions may be affected by the length of the experimental run.

“…The relevant properties of the minerals used in this work are listed in Table 1 ; (for a fuller description, see Cabrera and Talibudeen, 1978). Potentiometric tit~ AI( N03)3 solution.…”

Section: Mineralsmentioning

confidence: 99%

“…Therefore, little can be said, in a quantitative sense, about the nature of adsorbed AI ions from such potentiometric titration. However, the observation of the more complex buffering of adsorbed A1 than of Ai in solution points to its resistance to reaction with added OH-ions because of the strong binding of AI a § and to the existence of hydroxy-polymeric AI (Cabrera and Talibudeen, 1978) on mineral surfaces, which therefore titrate at higher pH values.…”

Section: Clays and Clay Mineralsmentioning

confidence: 99%

“…The existence of partially hydrolyzed AI ions on the surface of acid soils and clays was suggested by several authors from the study of the composition of the extracts with various salt solutions (Bache, 1974;Dalai, 1975;Bache andSharp, 1976a, 1976b;Smith and Emerson, 1976;Cabrera and Talibudeen, 1978) from the composition of the solution in equilibrium with these materials (Chakravarti and Talibudeen, 1961) and from the adsorption of AI from solution (Brown and Newman, 1973).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Release of Aluminum from Aluminosilicate Minerals. II. Acid-Base Potentiometric Titrations

Cabrera¹

1979

Self Cite

Abstract--Acidified suspensions of Al-saturated kaolinite, montmorillonite, mica, illite, and biotite in 10 -a M NaNO3 were potentiometrically titrated with 0.1 N NaOH and 0.1 N HNO3 in succession in a COz-free nitrogen atmosphere. The resulting curves were compared with those for AI(NO3)3 solutions of similar AI concentration in the supernatant solution and corrected for Al in the entrained solution in the clay.Base titrations of AI ions adsorbed on all the minerals, except montmorillonite, showed two pH inflections separated by a buffering range. With montmorillonite, there were three pH inflections similar to those for AI in solution. The first inflections in the titration of suspensions occurred at lower pHs and were less pronounced than for AI in solution. These represent the titration of HaO § sorbed during the pretreatment. The buffering by adsorbed AI ions is also less than that by A1 in solution.The OH-used up by adsorbed Al ions between the first and last inflections was equal to, or slightly greater than, the CEC of the minerals, except for mica where it was more than twice the CEC, because new interlayer surfaces were formed during the acid pretreatment. Acid titration curves of Al ions in the adsorbed and solution states showed hysteresis when related to the base titration curves. The use of two titration speeds (3 and 0.3 pH units/hr) only slightly affected the titration curves of the minerals suggesting that the observed effects were not caused by lack of equilibrium with added base or acid.