Influence Of Heavy Metal-Resistant Bacterium On The Surface Characteristics Of And Adsorption/Desorption Of Cu～(2+) And Cd～(2+) By Soil Colloids And Minerals

A highly heavy metal-resistant bacteria strain was screened from the soil of Tonglv mining area in Daye suburb. The influence of the bacteria strain on the surface characteristics of red soil colloid, cinnamon soil colloid, goethite and kaolin was studied. The adsorption / desorption of Cu2+ and Cd2+ ion by soil colloids and minerals as affected by the tested strain was also investigated. The researches are fundamental in explaining the microbial transformation of heavy metals in soils and the bio-geochemical behavior of heavy metals in soil environments. The studies are helpful in understanding the mechanisms of mineral-organic matter-microorganism interactions and useful for further researches of the bioremediation of heavy metal- pollutioned soils and associated environments. The main results were outlined as following:1. The screened bacteria A-l were resistant to 3mmol/L Cu2+ and 3mmol/L Cd2+ ion. The maximum adsorption of Cu2+ and Cd2+ ion by strain A-l were 395.3 and 170.7mmol/kg respectively. As compared with some other heavy metal-resistant bacteria, the tested stain not only had stronger resistance to Cu2+ ion and Cd2+ ion, but also had higher absorbability.2. The surface area of bacteria A-l was 145m2/g, which was about equal to that of cinnamon soil colloid, and was 3.5 times of red soil colloid and 7 times of kaolin. After the addition of bacterial cells, the surface areas of cinnamon soil colloid, red soil colloid and kaolin system increased by 5.1, 3.3 and 1.9m/g. The increment was of 3.0%, 8.0% and 8.7% respectively. It suggested that the contribution of the bacteria to the changes of surface area was more significant in red soil colloid and kaolin system than that of cinnamon soil colloid system.3. Within the tested pH range, the amount of negative charge of the tested systems in absence and presence of bacteria was in the order of cinnamon soil colloid > red soil colloid > kaolin, while the amount of positive charge was in the order of goethite > cinnamon soil colloid ^ red soil colloid ^kaolin. As compared with the system in the absence of bacteria, the amounts of surface positive charges in soil colloid and minerals all decreased in different degree after addition of bacteria A-l, even as high as 0.76 cmol/kg; white the amounts of negative charge in red soil colloid and cinnamon soil colloid increased in different degree, even as high as 1.24 cmol/kg. The amount of negative charge in kaolin system also decreased in certain degree. These changes were mainly concerned with these factors, (1)the surface negative charge of bacteria cells, (2) the adsorption of bacterial metabolites by soil colloids or minerals, and (Dthe adsorption of soil colloid or mineral particles on the bacterial surface with a preferred edge-on orientation. As compared with the systems in absence of bacteria, the increase rate of surface negative charge in bacteria system was smaller with the rise of pH value, but the decrease rate of positive charge was larger.4. The adsorption of Cu and Cu by the tested soil colloids and minerals fitted the Langmuir equation well (r>0.95). The maximum adsorption of cinnamon soil colloid, goethite, red soil colloid, and kaolin for Cu2+ was 431.8, 369.6, 285.1 and 100.3 mmol/L respectively at pH 5.5. Compared with the non-bacterial system, the maximum adsorption of cinnamon soil colloid and goethite system in the presence of bacteria for Cu2+ increased by 1.8%, 3.4% respectively. No marked differences were found in kaolin systems in the absence and presence of bacteria. Bacteria had no effect on the red soil colloid system. In the presence of bacteria, the Langmuir parameter K for the adsorption of Cu2+ by kaolin, cinnamon soil colloid, and goethite increased by 2.3, 0.3, and 7.5 respectively. The results showed that the interactions of bacteria with these soil components have great potentials in increasing their affinity for Cu2+, especially in goethite system. Bacteria had no effect on the affinity between Cu2+ and red soil colloid. The maximum adsorption of Cd2+...