3. Surface cleaning of silica sand
The level of iron in silica sand determines its ultimate application in glass making. Iron levels range from 0.1
Fe2O3 for the manufacture of amber and green glass, through 0.03for clear glass and less than 0.015for
table ware. The sand studied had already been processed for the manufacture of container glass and flat glass and had an iron content in the range 0.025–0.03
Fe2O3. It had already undergone high solids density scrubbing (attritioning), in the presence of sodium
hydroxide, to remove surface coatings, gravity separa- tion to remove traces of heavy mineral (ilmenite and chromite) and petroleum sulphonate activated froth flotation to remove heavily stained particles of sand. Digestion with aqua regia for 2 h had indicated that, if all surface contamination were removed, an iron level