将普通砂与氧化铁涂层砂作为过滤介质进行了比较。涂层砂在中性pH下具有正表面电荷，而未涂层砂在类似条件下具有负电荷。进入过滤器的进水含有乳胶颗粒（在所有研究溶液中均带负电）或铁氢化物颗粒（在pH值大于5时带负电，但在较低pH值时带正电）。在大多数实验中，涂层介质优于未涂层介质，这一结果与预期的静电相互作用一致。包括27个参考文献、表格和图表。

Plain sand was compared with iron-oxide-coated sand as a medium for filtration. The coated sand has a positive surface charge at neutral pH, whereas uncoated sand is negatively charged under similar conditions. The influent to the filters contained either latex particles, which were negatively charged in all solutions investigated, or ferrihydrite particles, which were negatively charged at pH > 5 but positively charged at lower pH values. The coated medium outperformed the uncoated one in most experiments, a result that is consistent with expected electrostatic interactions. Includes 27 references, tables, figures.