Sodium hexametaphosfate interactions with illite and montmorillonite: preliminary observation on thermal behavior

The interaction of an efficient deflocculant, sodium hexametaphosphate (NaHMP), with two different illites (IMt-1 from Silver Hill, Montana USA and from Schwäbisch Hall, Würtenberg Germany) and two different Ca-montmorillonites (STx-1 from Gonzales County, Texas, USA and from Santa Rita, New Mexico, USA) was investigated.Adsorption measurements of the NaHMP anion were performed onNa-exchanged illite IMt-1 as a function of temperature by means of inductively coupled plasma technique (I.C.P.). The thermodynamic parameters of the adsorption process, together with an estimation of the maximum adsorbed amount on the Na-illite were obtained and compared to the corresponding data previously obtained for Na-kaolinite.The effect of NaHMP on the natural illites and montmorillonites was analyzed using different techniques. I.C.P. measurements of the concentration of P, Na, Si, Al, Ca, Mg, and K of the deflocculant solutions in contact with the clays were performed in order to detail the adsorption, dissolution and exchange phenomena which accompany the deflocculant activity.Thermal analysis (thermo-gravimetric, thermal-differential) and XRD measurements at non ambient temperature conditions were used to characterize the clay solid samples after the interaction with NaHMP.Thermo-gravimetric analyses indicate that NaHMP-treated illites and montmorillonites are less hydrated than natural samples, whereas the dehydroxilation reaction seems to be not influenced by the NaHMP treatment. Basal periodicity was measured via XRPD diffraction on (00l) oriented mounts of the air-dried samples in the temperature range 25 - 400°C (heating rate 2 °C/min) using a powder diffractometer equipped with an area detector. No significant variation of layer periodicity was observed, thus indicating that NaHMP molecules are adsorbed on the edge and/or in the interlayer without modifying natural layer periodicity.