Aggregation Kinetics Of Binary Systems Containing Kaolinite And Bacteria Induced By 1:1 Electrolyte

A large number of studies have shown that ion-specific effects which also known as Hofmeister effects are widely present in the process of coagulation of soil colloids and the growth of microorganisms.The interaction between soil colloid and microorganisms affects not only the formation of microbial membranes in the soil,but also the formation and stability of soil aggregates,elemental circulation,mineral weathering and many other geochemical processes.In this study,Gram-negative bacteria Pseudomonas putida and Gram-positive bacteria Bacillus thuringiensis were used as experimental strains,kaolinite colloids were used as soil mineral colloids,and instruments such as Dynamic Light Scattering and Zeta potential analyzer were used.Under the guidance of DLVO theory,the agglutination kinetics of the"bacteria-kaolinite"mixed colloid was studied.The research has obtained the following research results:?1?The hydrodynamic diameters of Pseudomonas putida and Bacillus thuringiensis were 961.2 and 1286.6 nm.Even in the 0.3 g/L bacterial suspension,even if 450 mmol/L LiNO₃,700 mmol/L KNO₃,and 900 mmol/LCsNO₃ electrolyte were added,no bacterial suspension agglomerated.?2?Under the action of three electrolytes,LiNO₃,KNO₃ and CsNO₃,there are strong ion-specific effects during colloidal aggregation,including kaolinite colloid?"bacteria-kaolinite"colloid with 0%bacterial content?,Pseudomonas putida-kaolinite mixed colloid,Bacillus thuringiensis-kaolinite mixed colloid.There are four specific points:First of all,the hydrodynamic diameters of mixed colloid containing bacteria of the same concentration which aggregating for the same time under the same concentration of different kinds of electrolytes follows LiNO₃<KNO₃<CsNO₃.For example,for Pseudomonas putida-kaolinite,when the bacterial content is 3.33% and the electrolyte concentration is 20 mmol/L,the hydrodynamic diameters of Li⁺,K⁺,and Cs⁺are 3292.8,3374.2,and 3777.8 nm,respectively;Bacillus thuringiensis-kaolinite's was 504.9,2206,and 2731.4 nm,respectively.Secondly,the colloidal aggregation rate of the mixed colloid of the same bacterial content under the same concentration of different kinds of electrolytes follows LiNO₃<KNO₃<CsNO₃.For example,for Pseudomonas putida-kaolinite,when the bacterial content is 3.33%and an electrolyte concentration of 5 mmol/L,the aggregation rates of Li⁺,K⁺and Cs⁺are 34.9,48.2,and 80.5 nm/min,respectively;B.thuringiensis-kaolinite's was 1.2,17.5,and 55.3 nm/min,respectively.Thirdly the critical coagulation concentration of mixed colloid containing bacteria of the same concentration follows LiNO₃>KNO₃>CsNO₃.For example,for Pseudomonas putida-kaolinite,when the bacterial content is 3.33%,the critical coagulation concentration of Li⁺,K⁺,and Cs⁺are 18.7,16.7,and 9.4 mmol/L,respectively;Bacillus thuringiensis-kaolinite's are 83.5,27.2,and 11.6 mmol/L,respectively.Finally the activation energy of mixed colloid containing bacteria of the same concentration follows LiNO₃<KNO₃<CsNO₃.For example,or Pseudomonas putida-kaolinite,when the bacterial content is 3.33%,he activation energy of Li⁺,K⁺,and Cs⁺are 1.5?1.4?0.7 kJ/mol;Bacillus thuringiensis-kaolinite's are 4.5?3.8?2.1?2.0 kJ/mol??3?An increase in the bacterial content leads to an increase in the stability of the"bacteria-kaolinite"mixed colloid.This stability enhancement is manifested in two points.First,the mixed colloids of different bacterial contents are inversely proportional to the bacterial content by mixing the colloids under the same concentration time with the same concentration of electrolyte.For example,for P.putida-kaolinite,the concentration of mixed agglomerates with a bacterial content of3.33,6.67,16.67,33.33,50%is 3932.5,3979.8,2477.7,604.1,464.3 nm under the action of LiNO₃ concentration of 100 mmol/L;for"B.thuringiensis-kaolinite"are 2337.1,2410.2,1808,2041.4,1432.8,1215 nm.Second,the mixed colloids of different bacterial contents are proportional to the bacteria content under the same concentration of the same concentration of electrolyte.For example,under the action of LiNO₃ concentration of 5 mmol/L,the aggregation activation energies of P.putida with a content of 3.33,6.67,and 16.67%were 1.5,2.6,and 3.9 kJ/mol,respectively;the content of B.thuringiensis was The aggregation activation energies of 3.33,6.67,16.67,and 33.33%of the mixed colloids were 4.5,3.8,2.1,and 2.0 kJ/mol,respectively.?4?The polymerization behavior in the mixed system of bacteria and kaolinite is determined by the average effect of electrostatic and molecular forces of the system,rather than by bacteria or kaolinite.This finding provides an important methodological guide for studying the polymerization behavior of"bacterial-clay"hybrid systems.?5?The composition of Pseudomonas putida and Bacillus thuringiensis has different contribution for the aggregation of the"bacteria-kaolinite"mixed colloid.The experiments have shown:under the same electrolyte,the critical coagulation concentration of the mixed colloid Pseudomonas putida-kaolinite increases significantly with the increase of the content of Pseudomonas putida;The critical coagulation concentration of mixed colloid Bacillus thuringiensis-kaolinite increased first with the increase of Bacillus thuringiensis content,and then remained unchanged.Further theoretical and computational analysis found that the increase in the content of Pseudomonas putida led to a significant reduction in the Hamaker constant of the Pseudomonas putida-kaolinite mixed colloid.The increase in the content of Bacillus thuringiensis resulted in a decrease in the Hamaker constant of the"Bacillus thuringiensis-kaolinite"mixed colloid at first,and then remained unchanged.