reagents were of analytical reagent grade, and Milli-Q water was used
throughout the experiment. Kaolin, all metal salts, iron dust, all
iron oxides, disodium ethylene diamine tetra acetic acid (Na2-EDTA), and hydrogen peroxide were purchased from Sigma-Aldrich.
Sodium borohydride was obtained from Alfa Aesar. All glassware was
cleaned with freshly prepared aqua regia, subsequently rinsed with
copious amounts of distilled water, and dried well before use. All
of the reagents were used without further purification.