Effect of Photolytic Oxalate Treatment on Soil Hydroxy-Interlayered Vermiculites

The effects of Na-citrate-dithionite (NaCD), ammonium oxalate in the dark (NH 4 Ox-D), and photolytic reaction under ultraviolet radiation (NH 4 Ox-P) on the mineralogy of <2- µ m fractions of selected soils from Virginia were investigated. The NH 4 Ox-D treatment removed the smallest amounts of Al (<0.22%) and Fe (<0.50%) from all soils, indicating low levels of noncrystalline material in these materials. From the six soils examined, NH 4 Ox-P treatment extracted 5–62% more Fe and 12–300% more Al than the NaCD treatment. The NH 4 Ox-D and NaCD treatments revealed no X-ray diffraction detectable alterations to mineral phases present in <2- µ m fractions of these soils. The NH 4 Ox-P treatment, on the other hand, produced considerable degradation of hydroxy-interlayered vermiculites in these soils, as evidenced by a shift of the 14-Å X-ray diffraction maxima to lower spacings with heat treatment of the sample. The NH 4 Ox-P treatment removed variable amounts of hydroxy-Al material from the interlayers of 2:1 layer silicates, depending on their stability and degree of development.