Effect of photolytic oxalate treatment on soil hydroxy-interlayered vermiculites

The effects of Na-citrate-dithionite (NaCD), ammonium oxalate in the dark (NH (sub 4) Ox-D), and photolytic reaction under ultraviolet radiation (NH (sub 4) Ox-P) on the mineralogy of <2-mu m fractions of selected soils from Virginia were investigated. The NH (sub 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 (sub 4) Ox-P treatment extracted 5-62% more Fe and 12-300% more Al than the NaCD treatment. The NH (sub 4) Ox-D and NaCD treatments revealed no X-ray diffraction detectable alterations to mineral phases present in <2-mu m fractions of these soils. The NH (sub 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-Aa X-ray diffraction maxima to lower spacings with heat treatment of the sample. The NH (sub 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.