An experimental method was developed to measure the capacity of filter media to adsorb iron(ii) ions. In addition to virgin sand, sand sampled from two water treatment plants and other filter materials namely anthracite, basalt, pumice, limestone and magnetite were tested. Used filter sands from treatment plants indicated the influence of time in use on the extent of surface coverage with the iron oxide coat. Compared to virgin filter media, used sand from groundwater treatment plants had a much higher capacity for iron(ii). The effect of pH on the adsorption capacity of virgin sand and used sand was evaluated. It was observed that the adsorption capacity of filter materials increases with increases in pH and that the used sand has 20–25-fold higher adsorption capacity for iron(ii) than virgin sand. Experimental data fitted the Freundlich isotherm model. The adsorption capacity of used filter sand was found to vary with water quality.
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