The use of spent liquors from paper and pulp industry as binders for the pelletization of chromite fines

Abstract

Chromite fines must be agglomerated before being smelted in submerged arc furnaces to prevent disruptions and damage to equipment. Bentonite is the most commonly used binder for fines agglomeration in the ferrochrome industry; however, fluctuations in its availability has led to the investigation of alternative binders. Spent pulping liquors are under-utilised by-products of the paper and pulp industry, predominantly combusted for energy and pulping chemicals recovery but have shown binding potential for coal and iron ore fines. Four spent pulping liquors (sodium lignosulphonate, magnesium lignosulphonate, Kraft liquor and soda liquor) were investigated as binders for the agglomeration of chromite fines into pellets, for the industrial Outokumpu and Premus processes. The green impact strengths of the resulting pellets were found to increase with an increase in binder mass percentage, with all four pulping liquors outperforming bentonite. For the indurated compressive strength test, Outokumpu pellets were oxidatively sintered at 1200 °C, while Premus pellets were indurated in an inert atmosphere at 700 °C. For the Outokumpu pellets, all the pulping liquors produced pellets with similar or higher strengths than the control pellets made with 0.8 % bentonite. For the Premus pellets, all of the pulping liquors outperformed bentonite but had similar performances to each other. The fluxing ability of the sodium and calcium components in the pulping liquors was found to potentially be responsible for the differences in the sintered strengths of the Outokumpu pellets made with different pulping liquors. Both the inorganic and organic components of the pulping liquors were required to produce Kraft liquor pellets for the Outokumpu process with sufficiently high strengths. Lime was not found to be a suitable additive when tested with sodium lignosulphonate and Kraft liquor for Outokumpu pellets. Overall, the pelletisation of chromite fines with spent pulping liquors was found to be technically feasible and thus suitable for further application to industrial processes.