Showing papers in "Clay science in 2012"

Effects of mineralogy of suspended materials on performance of weathered volcanic ash-based flocculant

Abstract: We examined the effect of clay mineralogy and interfacial chemistry of clay suspensions on the performance of a flocculant prepared from weathercd volcanic ash rich in allophane and imogolite, Upon addition of the fiocculant into the clay suspension and stining, fiuffY fiocs forrned and settled after a standing time. Thc absorbance of the supematant gradually decreased to near zero at an optimum addition and then increased again when more flocculant was added, The optimum fiocculant addition differed significantly among the clay suspcnsions. Inspection of the results ofthe fiocculation tests and characterization ofthe sample clays, particularly stepwise multiple regression analyses, suggested that the major factors afTecting the perfbrmance were the effective cation exchange capacity (ECEC), content of micaceous minerals and average panicle size, of which the contribution of the former two factors seemed weightier. This was interpreted as indicating the importance ofthe amount ofnegative charge on the external surfaces ofparticles in the clay suspensions.

Effects of pore water salinity on the liquid limit of mexico city clay and the swelling characteristics of its constituent minerals

Abstract: Liquid limit tests were conducted on Mexico City clay samples prepared at different pore water salinities. The results demonstrate that the liquid limit decreases almost linearly from 340% to 275% as salinity decreases from 54 to 3 gtL, and then exhibits a sharp decrease for salinities below 3 gtL. X-ray analyses indicated that smectite is the main clay mineral in the clay, and a sediment volume test on clay fractions confirmed that the smectite is ofa high-swelling type. The contents ofAl, Si, and Fe extracted with oxalate were 26,9, 37.8, and 246 glkg, respectively. Despite the fact that the smcctite in the Mexico clay is of a high-swelling type, the change in the liquid limit due to pore water salinity was opposite to that for bentonite and paddy soil composed of high-swelling smectite but was similar to that for marine clays composed of low-swelling clay minerals. This characteristic was ascribed to a dominant role ofpoorly crystalline aluminosilicates and iron (ferrihydrite) with low-swelling character over the high-swelling smectite in determining the liquid limit of the Mexico clay as the pore water salinity is changed.