The columns effectively removed almost 100% of the dissolved Zn during the first three experiments. During experiment four, increasing amounts of Zn passed through the shell material for each subsequent 50 ml of solution passed through at 24, 48 and 72 hours. However, the shell material was continuing to retain a significant but decreasing proportion of the dissolved Zn. For example, in third run of the fourth experiment 96.8± 1.3% of the Zn from the solutions were retained on average across the three columns.