Boron isotope fractionation accompanying boron mineral formation from aqueous boric acid-sodium hydroxide solutions at 25.DEG.C..

Abstract

A series of experiments was carried out in which boron minerals were precipitated from pH and chemical composition-controlled solutions at 25°C and boron isotope fractionation accompanying the mineral deposition was measured. Borax, sassolite and sborgite were synthesized from aqueous boric acid-sodium hydroxide solutions. Borax was obtained from solutions with higher pH and sassolite from solutions with lower pH, irrespective of the mole ratio of B and Na in the solution. The fractionation factor, S, defined as S = ("B / 10B)minerai / ("B /'OB)s°luti°n increases with increasing the pH of the solution for both borax and sassolite. A cross-over point at which S=1 was found at about pH=9.5 for borax, while S was always larger than unity for sassolite. The present results of boron isotope fractionation are consistent with theoretical prediction of equilibrium isotope effects, although the experimental equilibrium constant of the boron isotope exchange reaction between B(OH)3 and B(OH)4 at 25'C is larger than that theoretically predicted (1.03-1.05 compared to 1.0194).

Boron isotope fractionation accompanying formation of potassium, sodium and lithium borates from boron-bearing solutions

“…5, all the data on S in the potassium borate system in Table 2 are plotted against the final pH of the solution phase given in Table 1. A trend is observed that the S value increases nearly linearly with increasing pH both for K2B4O7 and for suntite as in the case of borax in the previous paper (Oi et al, 1991). The slopes of the S-pH plots for the two potassium borates seem very similar to each other.…”

“…At very high pH, KBO 2 ·1.33H 2 O and KBO 2 ·1.25H 2 O are found deposited. Sodium borate system Runs in this system were conducted to examine reproducibility of boron isotopic data in the previous paper (Oi et al, 1991 ). An XRD pattern of L2B2O4 obtained is given in Fig.…”

“…To quantitatively discuss such problems, the knowledge on the exact degrees of boron isotope fractionations accompanying boron mineral formation from boronbearing solutions is certainly required. To the best our knowledge, our previous paper (Oi et al, 1991) is only one that reported laboratory experiments in which boron minerals were precipitated from boric acid solutions and boron isotope fractionation upon precipitation was measured. Unfortunately, the counterion was limited to the sodium ion.…”

Data report: boron isotope ratios in interstitial waters from Sites C0021 and C0022

“…B preferentially condenses in B(OH) 3 and 10 B is incorporated in B(OH) 4 -, leading to isotopic fractionation (Kakihana et al, 1977;Oi et al, 1991;Palmer et al, 1987). The B isotope ratio (δ 11 B) in seawater averages +39.5‰ .…”

Distribution of B, Cl and Their Isotopes in Pore Waters Separated from Gas Hydrate Potential Areas, Offshore Southwestern Taiwan

“…The ratio between the two species was controlled using the 0 00 0 00 solution pH (Kakihana et al 1977). Recent studies have shown even greater fractionation between the two B species Oi et al 1991). These isotopic characteristics can be applied to study possible sources and the B process in pore water.…”