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Boron Release from Weathering of Illites, Serpentine, Shales, and Illitic/Palygorskitic Soils

^a USEPA, Office of Research and Development, National Risk Management Research Laboratory, 919 Kerr Research Drive, Ada, OK 74820
^b USDA-ARS, George E. Brown, Jr. Salinity Lab, 450 West Big Springs Road, Riverside, CA 92507-4617

View larger version (36K): [in a new window]   Fig. 1. Cumulative B extracted as a function of sequential extractions (12 h, 1:10 w/v with 0.1 M CaCl2 for the first three extractions and 0.01 M CaCl2 for subsequent extractions). The specific surface areas were as follows: Twisselman clay loam (<250 µm), 31 m2 g–1; Traver silt loam (<250 µm), 27 m2 g–1; Morris illite (<50 µm), 62 m2 g–1; Weathered serpentine (<50 µm), 38 m2 g–1; Fithian illite (<50 µm), 52 m2 g–1; Fresh serpentine (<50 µm), 18 m2 g–1; Moreno Gulch shale (<250 µm), 30 m2 g–1; and Salt Creek shale (<250 µm), 75 m2 g–1.

View larger version (38K): [in a new window]   Fig. 2. Effects of particle size, pH, and time on (a) B concentration and (b) B release rate for Morris illite, and (c) B concentration and (d) B release rate for Fithian illite. The B release rate is expressed as the difference in the amount of B in solution between two adjacent sampling time periods divided by the sample surface area, and plotted at the mean time of the two adjacent sampling events, excluding time zero and 5 d, that is, 10, 22.5, 45.75, 105, 135, and 165 d.

View larger version (41K): [in a new window]   Fig. 3. Effects of particle size, pH, and time on (a) Mg concentration, (b) B/Mg molar ratio of release, (c) Si concentration, and (d) K concentration for Morris illite. The cation-exchange capacity (CEC) was 30.2 and 18.5 cmmol(+) kg–1 for the <2- and 2- to 20-µm fractions of Morris illite, respectively.

View larger version (28K): [in a new window]   Fig. 4. Effects of pH and time on (a) B concentration and (b) B release rate for both fresh (F) and weathered (W) serpentine (antigorite).

View larger version (45K): [in a new window]   Fig. 5. Effects of particle size, pH, and time on (a) B concentration and (b) B release rate for Salt Creek shale, and (c) B concentration and (d) B release rate for Moreno Gulch shale.

View larger version (33K): [in a new window]   Fig. 6. X-ray diffractograms of Mg-saturated and air-dried (a) Georgia palygorskite (PA), clay-size fractions of Twisselman clay loam (TWC) and Traver silt loam (TRC), and (b) fine-silt size fractions of Twisselman clay loam (TWFS) and Traver silt loam (TRFS). Cl = chlorite, F = feldspar, H = hornblende, I = illite, K = kaolinite, P = palygorskite, Q = quartz.

View larger version (39K): [in a new window]   Fig. 7. Effects of particle size, pH, and time on (a) B concentration and (b) B release rate for Traver silt loam, and (c) B concentration and (d) B release rate for Twisselman clay loam.

View larger version (39K): [in a new window]   Fig. 8. Effects of particle size, pH, and time on (a) Mg concentration, (b) B/Mg molar ratio of release (c) Si concentration, and (d) K concentration for Traver silt loam. The cation-exchange capacity (CEC) was 38.0 and 6.99 cmmol(+) kg–1 for the <2- and 2- to 20-µm fractions of Traver silt loam, respectively.

View larger version (27K): [in a new window]   Fig. 9. Cumulative HCl consumption for maintaining pH 5 as a function of time.