Influence of water type and maturation time on the properties of kaolinite–saponite peloids

Abstract We studied the effects of maturation time and water type on the properties of peloids. The peloids were prepared artificially by mixing the same amount of solid phase of kaolin and bentonite (9:1, m:m) with hypersaline mineral water (sodium potassium chloride water) from a spring in La Malaha (Granada, Spain) and bidistilled water (oligometallic water). The liquid/solid ratio was 2:1, m:m, with periodic manual homogenization and maturation time of one to three months. The water content of the peloids was maintained constant during the entire period of maturation. The peloid properties considered were the composition of the liquid phase, the thermal behaviour, the amount of defects in the structure of the main minerals present in the solid phase (kaolinite and saponite) and the ultramicroscopic fabric of the material, determined by scanning electron microscopy (SEM) and image analysis (IA). To date, the latter aspect has been very little studied. The composition of the liquid phases changed with maturation time. Most of the parameters measured showed a tendency to increase with increasing maturation time, as a consequence of releasing ions from the clay minerals into the liquid phase. Thus, the bidistilled water became mineral water. The initial differences between the two waters employed in the mixture were maintained in the liquid phases. The investigation of the thermal behaviour of the peloid revealed that the decrease in temperature followed, with time, a fitted logarithmic curve where R 2 > 0.9. The maximum change occurred in the first stage, later cooling being slower. A statistic relationship was found between the cooling kinetic and pore size and the size of the particle aggregates measured by SEM-IA. The peloids cooled more rapidly with increasing maturation time, as in the case of saline water. Both the Hinckley index of kaolinite and Integral Breadth index of saponite changed with the maturation time of the peloid. At the end of the maturation process similar values were reached regardless of the water employed. The main effect of maturation time was the increase in the size of the particle aggregates, the formation of a fabric with a more reticular morphology, and the increase in the area occupied by the pores in the SEM micrographs.