IRON OXIDE REMOVAL FROM CLAYS AND ITS INFLUENCE ON BASE-EXCHANGE PROPERTIES AND X-RAY DIFFRACTION PATTERNS OF THE CLAYS

Abstract

An improved method is presented for reduction and solution of free iron oxides from soils and clays by means of nascent hydrogen. The sample is boiled in 10% ammonium tartrate soln. in contact with metallic aluminum. The ammonia formed volatilizes, thus stabilizing the soln. at a favorable reaction of approx. pH 6.4. A relatively short digestion time (usually 15-45 min.) suffices, during which attack on montmoril-lonite, kaolinite, muscovite, and hydrous mica is unap-preciable to slight unless the lattices contain notable amts. of ferric iron. The method is decidedly less destructive to these lattices than earlier methods. Drying base-exchange material containing exchangeable basic ferric iron (clay-Fe(OH)2) caused fixation of part of the exchange iron (clay[long dash]Fe=O). The base exchange charges thus involved became nonfunctional, but were reactivated on displacement of the fixed exchange-iron by digestion in an alkaline soln. of Na tartrate. With soil clays increases in base-exchange capacity due to removal by this treatment of fixed exchange-iron ranged from 10 to 59%. The x-ray diffraction patterns of soil clays and clay minerals made after removal of free iron oxides were usually sharper and more intense than patterns of the untreated clays.