Effect of Photolytic Oxalate Treatment on Soil Hydroxy-interlayered Vermiculites

-The effects of Na-citrate-dithionite (NaCD), ammonium oxalate in the dark (NH4Ox-D), and photolytic reaction under ultraviolet radiation (NH4Ox-P) on the mineralogy of <2-/~m fractions of selected soils from Virginia were investigated. The NH4Ox-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, NH4Ox-P treatment extracted 5-62% more Fe and 12-300% more AI than the NaCD treatment. The NH4Ox-D and NaCD treatments revealed no X-ray diffraction detectable alterations to mineral phases present in <2-/zm fractions of these soils. The NH4Ox-P treatment, on the other hand, produced considerable degradation of hydroxy-interlayered vermiculites in these soils, as evidenced by a shift of the 14-~ X-ray diffraction maxima to lower spacings with heat treatment of the sample. The NH4Ox-P treatment removed variable amounts of hydroxy-AI material from the interlayers of 2:1 layer silicates, depending on their stability and degree of development. Key Words--Hydroxy-interlayer, Iron oxide, Noncrystalline, Oxalate extraction, Photolytic reaction, Soil, Vermiculite.