矽藻土為一種礦物性黏土，為多孔洞特性結構，表面具有負電荷，被廣泛使用於工業製程之過濾程序，作為去除雜質的吸附劑。本研究主要係探討在不同水溶液條件(酸鹼度及鹽度)下，對此一黏土材料表面界達電位（ξ-potential）之影響。研究結果顯示，矽藻土的界達電位均帶負電荷，且隨著pH值及鹽度的升高所具的電位也越大，離零電荷點越遠，此乃因在高pH下，矽藻土表面上的H+將分別被OH-及Cl-所電荷交換吸引，致其表面將帶更多負電荷。此種離子交換吸引機制可合理的推衍溶液pH質和鹽度對矽藻土陽離子交換容量（CEC）之影響，將與上述的現象呈相反趨勢，即溶液pH質和鹽度越大，則矽藻土陽離子交換容量將隨之增加。 Diatomaceous earth or diatomite, a clay mineral and characteristic of pore structure and negatively polar nature in the surface, is used extensively as filter and/or filter aid for the removal of all impurities in the industrial processes. The objective of this work is to study the effects of solution parameters (initial pH and salinity) onξ-potential of the clay material. The results showed that theξ-potential decreased as the pH increased in response to the increasing number of negatively charged sites that are available due to the loss of H+ from the surface. Thus, the surface of the clay at the experimental conditions (i.e., pH ＞3.0) exhibits negative charges mainly due to the variable charge from pH dependent surface hydroxyl sites. According to the ion-exchange mechanism, it was also demonstrated that the ξ-potential thus decreased as the salinity of NaCl increased. On the other hand, it can be further expected that the cation exchange capacity thus increased as the pH and salinity of NaCl increased.