| Aluminum is a kind of important elements for human health, and tea plant is known to be a typical aluminum accumulator. The contents of aluminum in tea leaves is correlated positively with the content of activated forms especially water soluble form of aluminum in tea garden soils, the water soluble aluminum is controlled by the adsorption characteristics of aluminum in soils, furthermore the content of aluminum in tea leaves are affected. Aluminum ion has a strong ability of hydrolysis, when pH is less than 6.0, aluminum is mainly in complex ion state, and its bioavailability increases with its solubility increasing. Tea garden soil is normally conspicuously acidic. There is a high content of active aluminum in acidic soil(pH<5.5),but calcium fluoride is produced when calcium increases in slightly acidic soil. Meanwhile, the transport of fluoride is controlled by calcium fluoride, which affects the adsorption characteristics of aluminum in soil. However, when the content of calcium in soils increases and the acidity of soil decreases, the environmental geochemistry action of aluminum also change, and further affecting the assimilation and accumulation of aluminum in tea plant. Therefore, there will be of theoretical and practical significance to study systematically the adsorption characteristics and forms transformation of aluminum in tea garden soils under the existing of calcium for assessing reasonably the activities and form transforms of aluminum in tea garden soils and decreasing the content of aluminum in tea leaves by changing the soil conditions. This paper deals with the following issues: effect of interaction of Ca-Al on the adsorption capability and active of aluminum in tea garden soil, the adsorption capability of aluminum in tea garden soil when calcium existing with different pH and different content of organic matter, the active aluminum content when the supplemental aluminum was added into tea garden soil.The results from the adsorption test of aluminum in the tea garden soil under the coexisting of calcium and aluminum showed that the adsorption of aluminum in tea garden soil basically reached to equilibrium in 30 minutes or so and the absorbability of aluminum in tea garden soil enhanced, especially for the treatment of Ca/2Al. The equations of Double-constant, Elovich and 2-D Kinetics could be used to describe adsorption kinetic characteristics of aluminum in tea garden soil under the different Ca/Al ratios. The adsorption amount of aluminum for different tea garden soils increased with the increasing of the beginning concentrations of aluminum within the test concentrations of aluminum. Adsorption thermodynamics characteristics of aluminum in tea garden of different Ca/Al ratios can be described with both Freundlich equation and Temkin equation. The results from the experiment of aluminum adsorption under the different contents of organic matter and calcium showed that the adsorption equilibrium time of aluminum in the tea garden soils decreased and the adsorption capacity increased. The adsorbed amount of aluminum increased in the tea garden soil in the higher content coexistence of organic matters and calcium. The equations of Freundlich and Temkin could be used to describe the adsorption thermodynamics characteristics of aluminum in tea garden soil under the different contents of calcium and organic matter.The results from the aluminum adsorption experiment in the different solution pH with the existing of calcium in tea garden soil show that aluminum could not be adsorbed by the soil instead of dissolving of aluminum in the tea garden soil when the value of adsorption solution pH was adjusted to 1. The solubility of aluminum, however, decreased with the increase of calcium. When the beginning concentrations of aluminum were more than 100mg/L , aluminum was absorbed gradually by the tea garden soil and the adsorbed amount increased, but the increasing degree was lessen with the increasing of calcium when pH=1 under the existing of calcium, the time of adsorption equilibrium of aluminum in the tea garden soil increased up to 40 minutes or so when pH=5 with the existing of calcium, adsorption equilibrium time of aluminum in the tea garden soil was only in one minute or so, and absorbability of aluminum in the tea garden soil increased significantly with the Ca/Al ratio increasing. The adsorption thermodynamics characteristics for aluminum in the tea garden soil could be described with both Freundlich equation and Temkin equation.Results from the desorption test of aluminum in the tea garden soils showed that the desorption amounts of aluminum in the tea garden soil decreased with increasing the beginning concentrations of aluminum of adsorbing solutions whether the existing of calcium or not. Also, the desorption amounts of aluminum increased with the increasing of organic matter under the existing of calcium, especially under the lower beginning concentrations of aluminum. Whether pH was higher or lower, the desorption amounts of aluminum in the tea garden soil decreased with the increasing of the beginning concentrations of aluminum in the different Ca/Al ratios.The contents of water soluble aluminum increased and that of exchangeable aluminum decreased significantly with the increasing of calcium to aluminum ratios. When the beginning concentrations of aluminum were lower, the contents of active aluminum in the tea garden soil did not changed obviously for the different calcium to aluminum ratios. When the beginning concentrations of aluminum were higher, the contents of active aluminum decreased with the decreasing of calcium to aluminum ratio. Under the lower contents of organic matter, the contents of water soluble aluminum in the tea garden soil decreased and the exchangeable aluminum appeared to the increasing tendency. Under the higher contents of organic matter, there were not distinct changes for the contents of water soluble and exchangeable aluminum in the tea garden soil with the increasing of calcium. Generally, the higher contents of organic matter were added, the higher contents of active aluminum would be in the tea garden soil. Besides, the contents of water soluble and exchangeable aluminum in the tea garden soil increased at first and then decreased at last with the increasing of calcium whether the pH was high or low under the lower beginning concentrations of aluminum, and decreased to some extent with the increase of calcium whether the pH was high or low under the higher beginning concentrations of aluminum. Comparing with water soluble aluminum, there were not significant variation for the exchangeable aluminum but the contents of active aluminum in the tea garden soil decreased with the increasing of pH, especially under the lower beginning concentrations of aluminum. |
PDF Full Text Request