Preparation of coal-based colloidal composite binder derived from weathered coal and its application in agglomeration of Bayan Obo iron ore

Binders play critical role in determining the quality and performance of iron ore agglomerates. To develop a low-dosage and highly efficient binder suitable for the agglomeration of Bayan Obo iron ore, a novel coal-based colloidal composite binder （3Co-binder） independently developed by Central South University was investigated. The binder was prepared using high-humic-acid weathered coal from Xinjiang as the main raw material, and its preparation process and application performance in the agglomeration of Bayan Obo iron ore were systematically studied. The results indicate that the optimal preparation conditions are water-to-coal ratio of 5.5-6.0, alkali-to-humic-acid ratio of 27%-30%（mass fraction）, and alkali pre-activation time of 4-24 h. Under these conditions, 3Co-binder exhibits stable rheological behavior and maintains good flowability and stability for up to 6-10 d. 3Co-binder shows excellent compatibility with Bayan Obo iron ore. When used as replacement for bentonite in pelletizing, a dosage of only 1.5% （corresponding to 0.21% on a dry basis,mass fraction） is sufficient to achieve superior green pellet quality compared with that obtained using 2.0%（mass fraction） bentonite under comparable conditions. Scale-up simulation tests of the grate-rotary kiln process demonstrated that, under conditions of preheating temperature of 950 ℃, preheating time of 12 min, roasting temperature of 1 200-1 225 ℃, and roasting time of 20 min, the compressive strength of preheated pellets exceeds 440 N per pellet, while that of roasted pellets exceeds 2 600 N per pellet. Compared with oxidized pellets produced with 2.5% bentonite, pellets prepared with 0.21% （dry basis,mass fraction） 3Co-binder exhibit an increase in iron grade by 1.39 percentage points and an improvement in reducibility index by 4.1 percentage points. In sintering applications with high proportions of Bayan Obo iron ore, the addition of 3Co-binder significantly improves granulation behavior and enhances product quality and productivity. During secondary mixing, adding 0.3% binder （0.04% on dry basis,mass fraction） in place of part of the granulation water increases the proportion of more than 3 mm granules and optimizes the particle size distribution. As a result, the sintering productivity increases by 0.19 t/（m²·h）, and the tumbler index increased by 1.73 percentage points. Overall, 3Co-binder enables significant dosage reduction through enhanced interparticle interaction among iron ore particles, thereby strengthening granulation and bonding processes, ultimately achieving coordinated enhancement of agglomeration product quality and productivity.