Interfacial electrokinetic characteristics before and after bioleaching microorganism adhesion to pyrite LIU Jian-she( 建 ), WANG Zhao-hui( 慧), CHEN Hong(陈 红), ZHANG Yan-hua( 华) School of Resources Processing and Bioengineering entral South University, Changsha 410083, China , C Received 28 July 2005; accepted 8 November 2005 Abstract: Zeta potentials of pyrite and Acidithiobacillus ferrooxidans cultured by sulfur in different levels of ionic strength and pH values were measured by Coulter Delsa 440SX zeta potential determinator. Meanwhile, the effects of bacterial adhesion and bacterial concentration on zeta potential of pyrite after adsorption were investigated. The results show that with the increase of ionic strength, zeta potentials of pyrite decrease in the range of pH 2.5−10.5 and the isoelectric point(IEP) of mineral shifts to the left. It is also found that the specific adsorption on pyrite of chloride ion can affect zeta potentials of pyrite sharply. As bacterial adsorption occurs, IEP of pyrite shifts towards that of Acidithiobacillus ferrooxidans; as bacterial concentration is increscent, this tendency is even larger and more obvious. Finally, a reasonable explanation for above-mentioned experimental phenomena was given by electrical double layer model and surface ionization model. Key words: Acidithiobacillus ferrooxidans; pyrite; adhesion; electrical double layer model; zeta potential; isoelectric point 1 Introduction Zeta potential, as a critical parameter of colloidal particles, has been widely used in many fields[1-3], such as material，beneficiation and biology. As measured by electro-osmosis, fluid stream electrophoresis and microelectrophoresis, zeta potential can contribute to the analysis for mechanics of interaction between solid particles and solution component. Therefore, researchers in bio-hydrometallurgy manage to obtain some information for surface electric property using zeta potential before and after bacterial adhesion to metal sulfides. As for aspects of bacterial zeta potential, it is proved that the Acidithiobacillus ferrooxidans(A.f) growing in different substrates are varied in zeta potential. DEVASIA et al[5] pointed out that cells cultured by both ferrous iron and iron thiosulfate have shown the similar electrokinetic phenomena, namely having the same IEP. However, it is indicated that surface chemical property of cell varied with its growth condition because IEP of cells growing in sulfur substrate is variable from about 2 to 3.8. With the metal sulfides, pyrite is the most extensively-studied object, whose IEP is commonly among 6−8[6] but with the exception[7]. It is reported that as bacterial adsorption occurs, IEP of pyrite shifts towards that of A.f, which suggests modification for mineral surface property after adsorption process[8]. However, zeta potential measurement will be affected by different experimental factors like ionic strength, electrolyte composition and pH. Unfortunately, these effects are often neglected thus leading to different experimental results. Moreover, in essence, zeta potential is a potential of sliding plane(or shear plane) in electrical double layer model for solid liquid interface. So the shortage of lacking theoretical confirmation for many results of zeta potential may be made well according to electrical double layer theory. In this study, zeta potentials of pyrite and A.f cultured by sulfur in different levels of ionic strength and pH values were measured in order to contrastively discover the alternation of surface property modified by bacterial adhesion. At the same time, we tend to explain the experimental results by Gouy-Chapman-Stern model. 2 Experimental 2.1 Materials Pyrite used in experiment was well-crystallized Foundation item: Project(50374075) supported by the National Natural Science Foundation of China; Project(2004CB619204) supported by the National Basic Research Priorities Program of China Corresponding author: LIU Jian-she; Tel: +86-731-8836372; E-mail: ljscsu@263.net