Subsurface Iron and Arsenic Removal

6 Characterization of accumulated deposits
similar to Figure 6.3, indicating that indeed the injected
water affected mainly certain soil layers. Compared to
the reference samples, amorphous iron has accumulated
up to 35.0 and 62.2 mmol.(kg.ds) -1 for well 03 and 04,
respectively.
Based on the assumption that all iron accumulates
as iron (oxy)hydroxides, it can be calculated what
portion of accumulated iron is amorphous or crystalline:
Fe crys
=Fe total
-Fe amorph
. The percentage of amorphous and
crystalline iron that has accumulated over 12 years in
12
mmol Fe.(kg.ds) -1
0 200 400 600 800
the affected layers was found to be 56-100% crystalline
near well 03 and, 67-100% near well 04. In order to
ascertain the limited contribution of iron in carbonates
on the soil grains, the carbonates were dissolved at pH
3.5-4.0 with Hydrochloric Acid at the different mesh
sizes (Kroetsch and Wang, 2006). All samples taken
in the reference well and near well 04 between 19 and
22m confirmed that the iron release during carbonate
removal was very small at