The Use of Piperidine as an Aid to Clay-Mineral Identification

Abstract

It is suggested that piperidine may be useful in the identification of clay minerals during differential thermal analysis, particularly in the differenti- ation of expanding and non-expanding lattice minerals. Differential thermal analysis of two montmorillonites showing similar X-ray powder photographs indicated large differences in the distribution of cation- exchange sites. Allaway (1949) introduced the use of piperidine as an aid to clay- mineral identifcation, making use of its function as a strong base which will fill the interlattice cation-exchange positions of smectite minerals. Differential thermal analysis in an oxidizing atmosphere of acid clays which had been titrated to pH 7-5 with a 0.1N aqueous solution of piperidine gave traces which show large exothermic reactions at 300-350~ and subsequent exothermic reactions which depend on the nature of the mineral under investigation. Thus magnesium-rich montmorillonites gave exothermic peaks at around 700~ while clays typical of the nontronite group gave peaks in the 450-500~ range, The presence of aluminium in tetrahedral co- ordination was considered to be associated with exothermic peaks at 600~ Kandites sorbed insignificant amounts of piperidine and illites yielded reactions on a much smaller scale than smectites. Amines other than piperidine also produced similar effects. By comparing the rates of carbon dioxide and water production during the differential thermal examination of a piperidine-saturated clay Allaway concluded that the 300-350~ exothermic peaks were due to the oxidation of hydrogen produced by thermal decomposition of the piperidine, as more than 90 per cent. of the total carbon was unoxidized at temperatures below 430~ remaining as a black deposit of elemental carbon which was only oxidized when the clay lattice was disrupted. Carthew (1955) has confirmed some of these findings, and con- eluded that, on differential thermal curves for piperidine-saturated clay minerals, (a) nontronite and montrnorillonite give large exo- thermic peaks at 500~ and 700~ respectively; and (b) illite can be identified in mixtures with kaolinite or with montmorillonite using