pH and Hydrometer Analysis of Bentonite and Sand

摘要

Effects of pH of bentonite clay, sand and water, individually and in mixtures, is studied through hydrometer analysis techniques. Calculations show that increasing pH by sodium ion addition reduces water requirements of green sand. Principles of hydrometer analysis readings in water suspensions of solids and their density are reviewed using equations. Sodium and calcium bentonite concentrations in grams/liter water and their mixtures were related to hydrometer reading, p. Change in clay p readings, with changes in pH produced by NaOH or CH_3COOH, are shown. Higher pH from NaOH increases dispersion and gives higher p.Mixtures of sand plus clay have a concentration parameter expressed as sand plus clay in gma/1, or (S + C) per liter. Mixtures of 4, 6, 8, and 10 percent NaB at increasing (S + C) 1 develop a p curve rising slowly from 1.0 toward a limiting value, dependant on the percent NaB in the S + C mixture. At low S + C, p is usually low but then increases rapidly with S +C. At a value near 40 gms NaB/1, the S + C curve reaches p near the d = 2.65 at 40 gms NaB/1 because all the sand is trapped in the NaB dispersion. Lower percent C in S + C moves the entire curve to higher S + C for a particular p value. System sands develop p versus S +C curves that are like those of low new clay mixtures. However, when new mixtures are mulled before hydrometer analysis, the resulting curves are like those of system sands. The role of mulling in coating sands is further revealed by repeated mulling of new mixtures. The hydrometer analysis measurement appears to be a powerful tool for molding sand research and control.