『Abstract
The kinetic curves of aluminum release from two variable charge
soils and a kaolinite within 48 h can be divided into three stages:
the first stage located within the initial 30 min, at which the
release rate of Al was the fastest one and the released Al dominantly
originated from exchangeable Al and amorphous Al pools. The Elovich
equation fit the kinetics data at this stage fairly well. The
moderate and the slow stages occurred within 0.5-2 and 2-48 h,
respectively. During these two stages, the released Al was mainly
attributed to Al oxides, poorly crystalline kaolinite and easily
weathered hydrous mica. The different linear equations also fit
the kinetics data at these two stages well. The rate of Al release
decreased sharply with time during the fast stage, but the rate
remained constant during the moderate and slow stages. In Ultisol,
Al oxides were the more important pool for Al release than poorly
crystalline kaolinite and easily weathered hydrous mica during
the latter two stages. In Oxisol, poorly crystalline kaolinite
was the more important Al pool. Compared to the control system,
the presence of organic acids increased the rate and quantity
of Al release from variable charge soils. The ability of organic
acids to accelerate Al release followed the order: oxalic acid＞citric
acid＞malic acid＞lactic acid. This is generally in consistent with
the magnitude of the stability constants of the Al-organic complexes.
The release rate of Al also increased with the rise in concentration
of organic acids.』
1. Introduction
2. Materials and methods
2.1. Soils and organic acids
2.2. X-ray diffraction analysis
2.3. Preparation of K-saturated soil
2.4. Preparation of H+-Al3+ saturated soil
2.5. Removal of amorphous Al oxides and free Al oxides
2.6. Experimental procedure
3. Results and discussion
3.1. Kinetics and mechanisms of Al release in the presence
of citric acid
3.2. Effect of kind and concentration of LMW organic acids on
the kinetics of Al release from variable charge soils
3.3. Implications
Acknowledgments
References