Binder Behavior on Chromite-Carbon Composite Pellets

Abstract

The influence of binders on the mechanical properties of chromite, self-reducing pellets, after subjecting to high temperatures, is analyzed in this paper. Bentonite, sodium silicate, and a combination of bentonite with carboxymethyl cellulose (CMC) were tested with different contents. All of the raw materials were characterized by chemical analysis and particle size distribution. The materials were pelletized (P1 to P7). All of the bounded green and dried pellets (P2 to P7) achieved the desired mechanical strengths, and none presented decrepitation. The best performance was obtained by the pellet P7 (4% sodium silicate as binder), with the green strength of 34 N/pellet, the dried strength of 50 N/pellet, and the strength was higher than 110 N/pellet after heat treatment at critical temperatures between 1173 and 1373 K. The unitary reduction reaction fraction was achieved after 10 minutes, at 1773 K.

Sodium Silicate Cold-Bonded Chromite Pellets for the Ferrochromium Industry – Identifying a Suitable Process

“…Figure 2a and 2b show that chromite particles are bound together by a segregated phase present on the surface of particles. The observed phase formed as a result of sodium silicate precipitation and consisted of silica gel, silicic acid, and sodium silicate 33 . EDS analysis of the area indicated by the white box in Figure 2b revealed Si, Al, and Na contents of 4.2, 4.4, and 19.4 wt%, respectively.…”

“…Several decreases in pellet mechanical strengths observed in this study occurred after local rainfall. Sodium silicate bonded refractory moulds and pellets are known to deteriorate when exposed to moisture/humid environments 33,69 . In the ferrochrome industry, the majority of oxidative sintered pellets and approximately 5% of pre-reduced pellets are stored in open, unroofed environments for extended periods before smelting procedures 14 .…”

“…Another relatively unexplored approach to prepare mechanically strong chromite pellets is the use of sodium silicate. Zambrano et al 33 prepared mechanically strong sodium silicate bonded chromite-composite pellets cured for 2 h between 900 to 1300 °C in an argon atmosphere. As far as the authors could assess, and based on personal communications with various South African FeCr producers, a feasible process to produce chromite pellets at low temperatures has yet to be realized by industry.…”