Effect of Na2O on formation of calcium aluminates in CaO–Al2O3–SiO2 system

Enhanced alumina extraction from kaolin by thermochemical activation using charcoal

“…The main advantages of using the charcoal instead of other inorganic fluxing materials are the chemical inertness of the carbon (i.e., did not react with the lime and metakaolinite components) as well as the completely vanishing of charcoal (even if added by high contents) from the thermal reactions medium which decomposed into gaseous phases of the carbon oxides. While, all the other different fluxing agents are strongly reactive materials (even if added by trace contents) with the transformed aluminosilicate and lime phases leading to undesirable intermediate phases which acted by lacking of the alumina leachability and minimizing the percent recovery (Pontikes et al, 2010;Yu et al, 2012Yu et al, , 2014Wang et al, 2011Wang et al, , 2017Yu et al, 2019). The recommended flowsheet for the Pyro and hydro-metallurgical 29 processing of the kaolin ore to produce alumina using lime-sinter process with the addition of charcoal is shown in Fig.…”

“…In addition to the charcoal, previous researches indicated that the common other additive of inorganic fluxing agents were MgO, A1 2 O 3 , Fe 2 O 3 , BaO, B 2 O 3 , Na 2 O, K 2 O, P 2 O 5 , MnO 2 and Cr 2 O 3 . The small amounts of these components either as chemical impurities or fluxing additives to kaolin showed undesirable effect, because these oxide materials stabilized the C 2 S β phase and hence led to preventing of the self-disintegration process (Wang et al, 2011;Yu et al, 2012;Guo et al, 2014;Yu et al, 2014;Yan et al, 2017;Yu et al, 2019;Bazhirov et al, 2020).…”

“…Moreover, the addition of charcoal would significantly improve the surface properties of the self-disintegrated sinter powders and particles and hence would increase leaching and maximize the alumina percentage recovery (APR; Qiu et al, 2004;Sizyakov et al, 2013aSizyakov et al, , 2013bDubovikov et al, 2018;Sizyakov & Brichkin, 2018;Li et al, 2019). Previous work showed that other compounds such as MgO, Al 2 O 3 , Fe 2 O 3 , BaO, B 2 O 3 , Na 2 O, K 2 O, P 2 O 5 , MnO 2 and Cr 2 O 3 , present either as chemical impurities or as fluxing additives to kaolin, were unfavourable because they stabilized the β-C 2 S phase and hence prevented self-disintegration (Wang et al, 2011;Yu et al, 2012Yu et al, , 2014Yu et al, , 2019Guo et al, 2014;Yan et al, 2017;Bazhirov et al, 2020).…”

Aluminum Mineral Processing and Metallurgy: Iron-Rich Bauxite and Bayer Red Muds

“…The autogenously pulverizable slag (calcium aluminate slag) can also be applied to leach alumina with Na 2 CO 3 and Na 2 C solutions [33,34]. The ideal composition of calcium aluminate slags is 12CaOÁ7Al 2 O 3 and γ-2CaOÁSiO 2 [35]. The slag reacts with sodium carbonate solution and yields an alumina leaching efficiency of 85% [36].…”

Characterization and Alumina Leachability of 12CaO·7Al2O3with Different Holding Times

“…Sun et al studied the ultrasonic-assisted alumina leaching and pointed that ultrasonic can improve the alumina leaching ratio and decrease the leaching temperature and sodium carbonation concentration [8]. Two-stage leaching and adding Na 2 O into slag to enhance leaching ratio were also used by Yu et al, and the results were also better [9].…”