“…However, it is reported that ammonium oxalate in acid medium is effective for extracting amorphous oxides/hydroxides of both Fe and Al. 9,10,28 In the absence of catalyzing effect of light, this reagent does not dissolve crystalline Fe oxides. 9,28 At the same time, the ascorbic acid/ammonium oxalate reagent adequate for dissolving crystalline Fe oxides and does not attack silicates.…”