A METHOD FOR THE DETERMINATION OF FREE IRON IN SOILS AND CLAYS

A procedure for the removal of free iron from soils and clays by a single extraction at 50 °C. with sodium hydrosulphite in a citrate buffer at pH 4.75 is described. The effects of pH, temperature and reagent concentrations on the rate of removal of free iron from soils and hematite were investigated. The crystal structures of clay minerals other than nontronite were not attacked by this procedure. The single extraction removed as much or more iron than was removed by successive extractions in three procedures proposed by other workers.