Experiments were conducted to study the adsorption of Cd on two soil colloids (red soil and yellow- brown soil) and three variable-charge minerals (goethite, noncrystalline Fe oxide and kaolin) in the absence and pres...Experiments were conducted to study the adsorption of Cd on two soil colloids (red soil and yellow- brown soil) and three variable-charge minerals (goethite, noncrystalline Fe oxide and kaolin) in the absence and presence of rhizobia. The tested strain Rhizobium fredii C6, tolerant to 0.8 mmol L-1 Cd, was selected from 30 rhizobial strains. Results showed that the isotherms for the adsorption of Cd by examined soil colloids and minerals in the presence of rhizobia could be described by Langmuir equation. Within the range of the numbers of rhizobial cells studied, the amount of Cd adsorbed by each system increased with increasing rhizobial cells. Greater increases for the adsorption of Cd were found in red soil and kaolin systems. Rhizobia influence on the adsorption of Cd by examined soil colloids and minerals was different from that on the adsorption of Cu. The presence of rhizobia increased the adsorption sanity of soil colloids and minerals for Cd, particularly for the goethite and kaolin systems. The discrepancies in the influence of rhizobia on the adsorbability and affinity of selected soil colloids and minerals for Cd suggested the different interactions of rhizobia with various soil components. It is assumed that bacterial biomass plays an important role in controlling the mobility and bioavailability of Cd in soils with kaolinite and goethite as the major colloidal components, such as in variable-charge soil.展开更多
The aim of this work was to study the influence of phosphate and citrate,which are common inorganic and organic anions in soils,on the adsorption of acid phosphatase by kaolin,goethite and the colloids separated from ...The aim of this work was to study the influence of phosphate and citrate,which are common inorganic and organic anions in soils,on the adsorption of acid phosphatase by kaolin,goethite and the colloids separated from yellow-brown soil(YBS)and latosol(LS)in central-south China.The YBS colloid has the major clay mincral composition of 1.4 nm mincral,illite and kaolinite while the LS colloid mainly contains kaolinite and oxides.The adsorption isotherm of acid phosphatase on the examined soil colloids and minerals fitted to the Langmuir model.The amount of enzyme adsorbed in the absence of ligands was in the order of YBS colloid>LS colloid>kaolin≈goethite.In the presence of phosphate or citrate,the amounts of the enzyme adsorbed followed the sequence YBS colloid>kaolin>LS colloid>goethite.The presence of ligands also decreased the binding energy between the enzyme and soil colloids or minerals.With the increase of ligand concentration from 10mmol L^-1 to 400 m mol L^-1,different behaviors for the adsorption of cnzyme were found in the colloid and mineral systems studied.A sharp decrease in enzyme adsorption was observed on goethite while gradual decreases of enzyme adsorption were recorded in the two soil colloid systems.However,no any decrease was found for the amount of enzyme adsorbed on kaolin at higher ligand concentrations.When phosphate or citrate was introduced to the system before the addition of enzyme,the ligands usually enhanced the adsorption of enzyme.The results obtained in this study suggested the important role of kaolinite mineral in the adsorption of enzyme molecules in acidic soils in the presence of various ligands.展开更多
基金Project supported by the National Natural Science Foundation of China !(No. 49601011)the Natural Science Foundation of Hubei
文摘Experiments were conducted to study the adsorption of Cd on two soil colloids (red soil and yellow- brown soil) and three variable-charge minerals (goethite, noncrystalline Fe oxide and kaolin) in the absence and presence of rhizobia. The tested strain Rhizobium fredii C6, tolerant to 0.8 mmol L-1 Cd, was selected from 30 rhizobial strains. Results showed that the isotherms for the adsorption of Cd by examined soil colloids and minerals in the presence of rhizobia could be described by Langmuir equation. Within the range of the numbers of rhizobial cells studied, the amount of Cd adsorbed by each system increased with increasing rhizobial cells. Greater increases for the adsorption of Cd were found in red soil and kaolin systems. Rhizobia influence on the adsorption of Cd by examined soil colloids and minerals was different from that on the adsorption of Cu. The presence of rhizobia increased the adsorption sanity of soil colloids and minerals for Cd, particularly for the goethite and kaolin systems. The discrepancies in the influence of rhizobia on the adsorbability and affinity of selected soil colloids and minerals for Cd suggested the different interactions of rhizobia with various soil components. It is assumed that bacterial biomass plays an important role in controlling the mobility and bioavailability of Cd in soils with kaolinite and goethite as the major colloidal components, such as in variable-charge soil.
基金Project supported by the National Natural Science Foundation of China (No. 49601011)by the International Foundation for Science (IFS, No. C/2527-1).
文摘The aim of this work was to study the influence of phosphate and citrate,which are common inorganic and organic anions in soils,on the adsorption of acid phosphatase by kaolin,goethite and the colloids separated from yellow-brown soil(YBS)and latosol(LS)in central-south China.The YBS colloid has the major clay mincral composition of 1.4 nm mincral,illite and kaolinite while the LS colloid mainly contains kaolinite and oxides.The adsorption isotherm of acid phosphatase on the examined soil colloids and minerals fitted to the Langmuir model.The amount of enzyme adsorbed in the absence of ligands was in the order of YBS colloid>LS colloid>kaolin≈goethite.In the presence of phosphate or citrate,the amounts of the enzyme adsorbed followed the sequence YBS colloid>kaolin>LS colloid>goethite.The presence of ligands also decreased the binding energy between the enzyme and soil colloids or minerals.With the increase of ligand concentration from 10mmol L^-1 to 400 m mol L^-1,different behaviors for the adsorption of cnzyme were found in the colloid and mineral systems studied.A sharp decrease in enzyme adsorption was observed on goethite while gradual decreases of enzyme adsorption were recorded in the two soil colloid systems.However,no any decrease was found for the amount of enzyme adsorbed on kaolin at higher ligand concentrations.When phosphate or citrate was introduced to the system before the addition of enzyme,the ligands usually enhanced the adsorption of enzyme.The results obtained in this study suggested the important role of kaolinite mineral in the adsorption of enzyme molecules in acidic soils in the presence of various ligands.
