Fig. 5. (a) Scanning electron micrograph taken in the untreated sediments; (b and c) Batch 1, 3 d: treated sediments with 1 mol L^-1 NaOH, 1 mol L^-1 NaNO₃, and 0.055 mol L^-1 Al(NO₃)₃ solution: the Si/Al aqueous molar ratio was equal to 0.121; (d) Batch 1, 7 d: the Si/Al aqueous molar ratio was equal to 0.096; (e) Batch 1, 21 d: the Si/Al aqueous molar ratio was equal to 0.284; (f and g) Batch 1, 42 d: the Si/Al aqueous molar ratio was equal to 14.17; (h and i) Batch 1, 42 d: sediments treated with 1 mol L^-1 NaOH, 1 mol L^-1 NaNO₃, and 0.11 mol L^-1 Al(NO₃)₃ solution: (h)cancrinite and probably sodalite crystals, and (i) a mica particle and the Fe-rich small ball crystals; (j) Batch 1, 42 d: treated with 1 mol L^-1 NaOH, 1 mol L^-1 NaNO₃, and 0.165 mol L^-1 Al(NO₃)₃ solution: cancrinite, probably sodalite, and zeophyllite crystals; (k) Batch 1, 42 d: treated with 1 mol L^-1 NaOH, 1 mol L^-1 NaNO₃, and 0.22 mol L^-1 Al(NO₃)₃ solution: cancrinite, probably sodalite, and zyophyllite crystals.