A New Measure for Active Clay in Green Sand

Abstract

An alternative approach to measure active clay in green sand has been developed. While active clay determination using methylene blue adsorption is a comparison of the cation exchange capacity (CEC) of greensand to the CEC of a reference bentonite, the new technique allows direct CEC measurement by adsorption of highly selective Cu(II)-triethylenetetramine dye and subsequent quantification in a spectrophotometer. The difference in concentration of the dye before and after reaction to the greensand allows to calculate the number of adsorption sites in the molding sand, which are predominately attributed to present smectite clay minerals. The result obtained is the CEC of the molding sand, which can be used to calculate the active clay content or number of smectite clay minerals, respectively, by literature data or the CEC of a reference sample. The test procedure can discriminate among various levels of active clay content, regardless if sodium or calcium bentonite is available in silica sand. Results in this study with the new approach show repeatability with acceptable test-to-test variability when measuring green sand samples from 6 to 12% active clay. Increasing sample weight allows to discriminate active clay levels even below 4 weight-%. The new proposed method eliminates systematic errors of the methylene blue test and offers advantages in usability and accuracy.