Abstract
The U.S. Bureau of Mines investigated the use of organic binders as substitutes for bentonite in agglomerating iron ore concentrate. Over 30 organic binders were evaluated at several dosage levels in laboratory tests. The binder groups producing the greatest green pellet strengths were natural gums (guars), carboxyl methyl celluloses, and gelled starches. The nongelled and alkalized starches, starch acrylic copolymers, wood-related products, and dairy products were less effective but better than bentonite. The highest wet pellet drop numbers were obtained with binders that had a medium plate water absorption value (>500 and <10,000) in distilled water and a high slurry viscosity (>75 cp) at 6 pct solids. The highest dry compressive strengths were obtained with binders that gave the highest adhesive tensile strength (>4 kg/cm2) on iron oxide lap-joint substrates. Pellets with 0.1 pct organic binder had lower compressive strengths and reduction disintegration indices than those with 1 pct bentonite, but higher reduction rates. Pellets with carboxyl methyl cellulose and gelled starch had higher softening temperatures than those with bentonite. Overall, the most promising binder is gelled starch. Its price makes it more cost effective than carboxyl methyl cellulose, and its pellets have metallurgical properties superior to those of bentonite pellets.
