Figure 4 shows the removal efficiency of each diat- omite with respect to their cation exchange capacity (CEC).As can be seen, Zn again presents very compa- rable values in all samples, except for diatomite D1175, which despite having one of the highest CEC values (25.6 meq/100 g) is the one with the lowest removal efficiency.In the literature, very diverse CEC values of diatomites are reported, from 1.41(Shengetal.,2009) to127 meq/ 100g(Flores-Canoetal.,2013)