Concentration of Dioctahedral Mica and Vermiculite Using a Fluoride Solution

A SOT.U~ON containing fluoride (0.4 N NH4F, 0.1 br HC1, ~ NH4C1), pcrmi~ the concentration of dioctahedral mica end dioctahedral vermiculite in mixed clay systems. AUophane, haUoysite, kaolinite, and in particular, Mg-rich montmorfllonite, biotite, and vermiculite of clay size, are destroyed in 24-48 hr at room temperature. A salt-free, NH4-saturated sample, weighing 80 mg, is shaken in 80 ml of the fluoride solution. The residue is washed with water and X-ray diffraction patterns made. The method has use in characterizing some of the 2:1 layer silicates in clays. Anatase, if present, is also concentrated and is more positively identified by X-ray diffraction. I N T R O D U C T I O N SoME of the principal components of many soil clays are dioc~ahedral mica and expansible derivatives thereof. A method has been devised to concentrate these components by dissolution of other common major components of the clay fraction. The technique has use in characterizing some of the 2:1 layer silicates in clays and in concentrating anatase as well as the dioctahedral mica and vermiculite. The distinguishing features of the proposed method are its specificity for concentrating dioctahedral mica and dioctahedral vermiculite and its simplicity. Kiely and Jackson (1964, 1965) proposed a method for concentrating quartz and feldspar by the dissolution of the layer silicates. These authors also review other methods for the removal of layer silicates from quartz and feldspars. HasMmoto and Jackson (1960) published a method for the stepwise removal of (1) allophane, gibbsRe, and amorphous Si02 and Al~0a, (2) interlayer material, and (3) kaolinite and halloysite by initially heating successively at 110, 400, and 500~ respectively, followed by a 2.5rain boiling in 0.5 N NaOH. Brown (1953) and Rich and Obenshain (1955) employed neutral NH4F remove interlayer material from vermiculite. Rich and Cook (1963) used the