Adsorption Characteristics And Form Transformation Of Aluminum In Tea Garden Soil

Aluminum is a kind of important elements for human health, and tea plant isknown to be a typical aluminum accumulator. The cont ents of aluminum in tealeaves is correlated positively with the content of activated forms especially watersoluble form of aluminum in tea garden soils, the water soluble aluminum iscontrolled by the adsorption characteristics of aluminum in soils, furt hermore thecontent of aluminum in tea leaves are affected. Therefore, there will be oftheoretical and practical significance to study systematically the adsorptioncharacteristics and forms transformation of aluminum in tea garden soils underthe existing of fluoride and low-molecular-weight organic acids for assessingreasonably the activities and form transforms of aluminum in tea garden soils anddecreasing the content of aluminum in tea leaves by changing the soil conditions.The adsorption characteristics and forms transformation of water soluble andexchangeable of aluminum in tea garden soils under the existing of fluorideor/and low-molecular-weight organic acids, i.e. oxalic acid citric acid, malic acidand succinic acid separately were studied in the paper by the simulate test andforms analysis.Results from the adsorption test of aluminum for different tea garden soilsshowed that: the adsorbing rate were different for several tea garden soils but theadsorbing equilibrium were reached within 5 0 min for all tea garden soils, thekinetics equations of Elovich, Double-constant and Second grade can be used todescribe the kinetics characteristics of aluminum in these tea garden soils; theadsorption amount of aluminum for different tea garden soils increased with thebeginning concentrations of aluminum of adsorbing liquid within the testconcentrations of aluminum and there were slightly different in the adsorption amount for different soils; the equation of Temkin can be used to describe thethermodynamics characteristics of aluminum in the tea garden soils.Results from the adsorption test of aluminum in tea garden soils under thedifferent ratios of fluoride to aluminum showed that: the adsorption amount ofaluminum in tea garden soil decreased under the interaction of fluoride-aluminumand the more increasing ratio of fluoride the less of adsorption amount ofaluminum comparing with the control; t he two equations of Freundlich andTemkin can be used to describe the thermodynamics characteristics of aluminumin the tea garden soil when the existing of fluoride.Results from the adsorption test of aluminum in tea garden soils under theexisting of low-molecular-weight organic acids, i.e. oxalic acid citric acid, malicacid and succinic acid separately showed that: the adsorption amount ofaluminum in tea garden soil decreased under oxalic acid or malic acid or succinicacid, moreover the amount in the concentration of 10mmol/L is less than that ofin the concentration of 1mmol/L; on the contrary, the adsorption amount ofaluminum in tea garden soil increased under the citric acid and the amount in theconcentration of 10mmol/L is higher than that of in the concentration of 1mmol/L;the equations of Freundlich and Temkin can be used to describe thethermodynamics characteristics of aluminum in the tea garden soil under theexisting of the four low-molecular-weight organic acids respectively.Results from the adsorption test of aluminum in tea garden soils under thecoexisting of fluoride and one of these low-molecular-weight organic acids, i.e.oxalic acid citric acid, malic acid and succinic acid showed that: the adsorbingequilibrium time of aluminum in the tea garden soil were shorten comparing withthe control under the coexisting of fluoride and one of the low-molecular-weightorganic acids, moreover the adsorbing equilibrium times were less under the coexisting of fluoride and higher concentrations of low-molecular organic acidsthan that under the coexisting of fluoride and lower concentrations oflow-molecular organic acids; the kinetics equations of Elovich, Double-constantand Second grade can be used to describe the kinetics characteristics of aluminumin the tea garden soil under the coexisting of fluoride and one of 1mmol/L oflow-molecular organic acids, and the kinetics equations of Elovich andDouble-constant can be used to describe the kinetics characteristics of aluminumin the tea garden soil under the coexisting of fluoride and one of 10mmol/L oflow-molecular organic acids except for the coexisting of malic acid and 4F/Al,which can not be used to described with any of these five kinetics equations. Theadsorption amount of aluminum in tea garden soil increased under the coexistingof citric acid and fluoride and decreased under the coexisting of oxalic acid ormalic acid or succinic acid and fluoride. The equations of Freundlich and Temkincan be used to describe the thermodynamics characteristics of aluminum in thetea garden soil under the coexisting of one of low-molecular-weight organic acidsand fluoride.Results from the form transforms of aluminum in tea garden soils comparingwith the control showed that: (1) the contents of water soluble and exchangeablealuminum decreased under the interaction of fluoride -aluminum and further theamount of activity form were lessen with the increasing of ratios of fluoride toaluminum; (2) the contents of water soluble aluminum under the low -molecularorganic acids of 10mmol/L were higher than that of 1mmol/L, however, it is thecontrary trend for the exchangeable aluminum in general, the amount of activealuminum increased for the existing of malic acid and succinic acid and deceasedfor the existing of oxalic acid and citric acid; (3) the amount of active aluminumincreased for the coexisting of fluoride and low-molecular organic acids in the lower beginning concentration of aluminum and decreased in the higherbeginning concentration of aluminum comparing with the control, but werehigher than that of only the existing of fluoride.(4) The contents of water soluble aluminum increased with the adsorptionamount of aluminum in tea garden soil when there were or not fluoride or/andlow-molecular-weight organic acids, but the content of exchangeable aluminumincreased with the adsorption amount of al uminum in tea garden soil only withoutthe existing of fluoride and low-molecular-weight organic acids, there were nodistinguish trend for exchangeable aluminum under the existing of fluoride or/andlow-molecular-weight organic acids. In brief, the contents of active aluminumincreased with the adsorption amount of aluminum in tea garden soil when therewere not fluoride or/and low-molecular-weight organic acids, however, therewere not obvious relationships between the content of the active aluminum andthe adsorption amounts of aluminum under the existing of fluoride andlow-molecular organic acids.