Browsing by Author "le Roux, Hendrik Pieter"
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- ItemThe use of spent pulping liquors as binders for chromite pellets(Stellenbosch : Stellenbosch University, 2023-12) le Roux, Hendrik Pieter; Görgens, Johann Ferdinand; Tyhoda, Luvuyo; Louw, Tobias Muller; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.ENGLISH ABSTRACT: Chromite fines have to be agglomerated before being smelted in submerged arc furnaces to prevent disruptions and damage to equipment and personnel. Bentonite is the most commonly used binder in the ferrochrome industry; however, fluctuations in its availability has sparked interest in alternative binders. Spent pulping liquors are under-utilised resources that are predominantly combusted for energy or cooking chemicals recovery. In South Africa, a significant focus has been placed on finding higher-value applications for spent pulping liquors. This study investigated the use of four pulping liquors: sodium lignosulphonate (NaLS), magnesium lignosulphonate (MgLS), Kraft liquor (KL) and soda liquor (SL), as binders for the agglomeration of chromite pellets for the Outokumpu and Premus processes. The pulping liquors and bentonite were tested in binder mass percentages between 0.5 % and 6.5 %. The materials were pressed into 12 mm diameter pellets using a pressure of 11.3 MPa. Green compressive strength, green impact strength, indurated compressive strength and abrasion resistance strength tests were conducted on the pellets. The green impact strengths of the pellets were found to increase with an increase in binder mass percentage. All four pulping liquors outperformed the bentonite in this test. For the indurated compressive strength test, Outokumpu pellets were oxidatively sintered at a temperature of 1 200 °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. NaLS and KL had the highest strengths. None of the binders produced sintered pellets that lost strength when exposed to water. This indicates that sintered pellets produced with pulping liquors can be stored outside and exposed to rain without negatively affecting their strength. For the Premus pellets, all of the pulping liquors outperformed bentonite but had similar performances to each other. Linear regression analyses showed that there is a statistically significant correlation between the indurated compressive strengths and abrasion resistance strengths of the pellets. This indicates that indurated compressive strength is a sufficient proxy for abrasion resistance strength. Overall, the majority of the pellets did not meet the industry targets for the strength tests. This is likely due to differences in the size, shape and density of the pellets produced in this study compared to industrial pellets. Both the inorganic and organic components of the pulping liquors were found to contribute towards the green and indurated strength of the pellets, indicating that both components are required to produce pellets with sufficiently high strengths. Despite greatly increasing the green impact strengths of pellets produced with NaLS, the addition of lime was found to be unsuitable since it greatly decreased the sintered compressive strengths of pellets produced with NaLS and KL. Overall, the pelletisation of the pulping liquors with the chromite and reductant fines in this study was found to be technically feasible. Further investigation into their implementation in industrial processes is thus recommended, with the application of NaLS and KL to the Outokumpu process being the most promising.