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Soil solution aluminium activity related to theoretical A1 mineral solubilities in four Australian soils
Author(s) -
HELYAR K. R.,
CONYERS M. K.,
MUNNS D. N.
Publication year - 1993
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1993.tb00455.x
Subject(s) - kaolinite , illite , soil water , chemistry , clay minerals , quartz , mineral , vermiculite , solubility , mineralogy , inorganic chemistry , geology , materials science , soil science , metallurgy , organic chemistry , paleontology
SUMMARY Four soils were treated with HNO 3 , CaCO 3 and K 2 SO 4 to enable observation of the response of the soil solution composition and the solution A1 ion activity (Al 3+ ) to the treatments and to time. The clay fraction of three of the soils was dominated by illite, kaolinite and quartz. The fourth was minated by kaolinite and iron oxides. The initial pH in 0.01 M CaCl 2 varied between 4.0 and 5.0 and the organic carbon content from 0.7 to 1.1%. The soil solutions from soils dominated by kaolinite, illite and quartz were generally supersaturated with respect to quartz and well ordered kaolinite, and unsaturated with respect to illite. The soil solutions from the soil dominated by kaolin and iron oxide were generally unsaturated with respect to quartz but still saturated with respect to ell crystallized kaolin. Within mineral groups such as Al 2 SiO 5 compounds, A1 2 Si 2 O 5 (OH) 4 (kaolinite group), and Al(OH) 3 (A1 oxide) minerals, the more soluble forms became less supersaturated or unsaturated with time for many treatments. Lime treatment usually increased the ion activity product of AI(OH) 3 in all soils, and of minerals with the composition, Al 2 SiO 5 , in the illite/kaolinite soils. Acid treatment reduced the apparent solubility of Al(OH) 3 , and the A1 silicates in the Al 2 SiO 5 , and Al 2 , Si 2 , O 5 ,(OH) 4 , mineral groups on all soils. These results are interpreted to indicate that lime treatment led to the formation of trace quantities of more soluble A1 minerals that subsequently controlled (Al 3+ ), whereas acid treatment dissolved trace quantities of such minerals leaving less soluble minerals to control (Al 3+ ). The results suggest that, in mineral soils such as these, (Al 3+ ) is under the control of inorganic dissolution and precipitation processes. These processes conform to expectations given the free energy of various inorganic aluminium compounds. Furthermore the sequence of dissolution and formation processes appears to be governed by the Gay‐Lussac—Ostwald step rule.