Fig. 5 Results of batch equilibrium experiment. a) pAl vs. pH; the imogolite line assuming congruent dissolution obeys Eq. [7]; b) pSi vs. pH; c) (pAl + 0.5 pSi) vs. pH. Closed symbols, soil:solution = 1:10; open symbols, soil:solution = 1:2.5. The linear fittings in a) and c) were performed by structural analyses (see Webster, 1997) including all data at pH >4.1 of the Bh, Bs, BC1, and BC2 horizons. Structural analyses in b) was performed separately for both pH <4.1 and pH >4.1 for each of the four lower horizons. Solubilities of gibbsite (Palmer and Wesolowski, 1992), imogolite (Farmer and Fraser, 1982), proto-imogolite sol (Lumsdon and Farmer, 1995), quartz, and amorphous SiO2 (Stumm and Morgan, 1981) were calculated for 20°C by the van't Hoff equation
