Adsorption Of Cadmium On Mineral-Pseudomonas Putida Composites At Different Proportions

Soil is an important part of the Earth'surface system.It connects the atmosphere,the lithosphere,the hydrosphere and the biosphere.The minerals are the main skeleton of soils,and the microorganisms are the most active components in the soil.These two solid componentes usually form mineral-bacteria composites in soils,which together affect the spices,migration and transformation of heavy metal.Because of the complexity of soils,the role of bacteria-mineral proportions in heavy metal adsorption has not been studied adequately.In this study,we selected three representative minerals whih are kaolinite,montmorillonite and goethite,and one kind of bacteria called Pseudomonas putida which are common in soils.Four mineral-bacterial composites at dry weight ratio of 0.1,0.2,0.5,1.0 were synthesized.The characteristics of the four mineral-bacteria composites and their Cd(II)adsorption capacity were obtained through Zeta potential meter,automatic potentiometric titrator,microcalorimeter,and chemical adsorption experiments.The main results are as follows:1.The particle size and automatic potentiometric titration measurement showed that the average particle size increased after the complexation between bacteria and mineral.Specifically,the average particle size of the montmorillonite-bacteria composites was larger than that of the other two mineral-bacteria composites.The surface sites of the composites increased with the proportion of bacteria.2.The kinetics of Cd(II)adsorption on mineral-bacteria indicated that the equilibrium time of Cd(II)adsorption was about 2 hours.The second-order kinetic equation fits the adsorption process well,suggesting the adsorption is chemical adsorption.3.The adsorption of Cd(II)on the composites increased with pH,namely from 3 to 8.With the increasement of bacteria,the adsorption of Cd(II)on the composites enhanced.The results of isothermal adsorption elucidated that affinity and the max capacity of Cd(II)on composites elevated with the the increasing proportion of bacteria in the composites.4.Isothermal titration microcalorimetry experiments showed that the adsorption of Cd(II)on P.putida and 1:1 mineral-bacteria of composites were endothermic process,while on the other three ratio composites were exothermic.Adsorption of Cd(II)by all composites was a spontaneous entropy increase reaction,indicating that the main products of adsorption were inner ring complexes.