Ludwigite ore is a typical low-grade boron ore accounting for 58.5% boron resource of China, which is mainly composed of magnetite, lizardite and szaibelyite. During soda-ash roasting of ludwigite ore, the presence of lizardite hinders the selective activation of boron. In this work, lizardite and szaibelyite were prepared and their soda-ash roasting behaviors were investigated using thermogravimetric-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microscope and energy dispersive spectrometer (SEM-EDS) analyses, in order to shed light on the soda-ash activation of boron within ludwigite ore. Thermodynamics of Na 2 CO 3 -MgSiO 3 -Mg 2 SiO 4 -Mg 2 B 2 O 5 via FactSage show that the formation of Na 2 MgSiO 4 was preferential for the reaction between Na 2 CO 3 and MgSiO 3 /Mg 2 SiO 4 . While, regarding the reaction between Na 2 CO 3 and Mg 2 B 2 O 5 , the formation of NaBO 2 was foremost. Raising temperature was beneficial for the soda-ash roasting of lizardite and szaibelyite. At a temperature lower than the melting of sodium carbonate (851 • C), the soda-ash roasting of szaibelyite was faster than that of lizardite. Moreover, the melting of sodium carbonate accelerated the reaction between lizardite with sodium carbonate.Minerals 2019, 9, 533 2 of 11 reduction followed by alkali leaching in order to recover iron and boron stepwise [9,11], and molten sodium hydroxide leaching to utilize boron individually [16][17][18].During soda-ash roasting of ludwigite ore, sodium carbonate would react with both szaibelyite and lizardite, hindering the selective activation of boron. Hence, the dosage of sodium carbonate and the roasting conditions were closely relevant to the soda-ash roasting of ludwigite ore in the roasting process. In this work, lizardite and szaibelyite were prepared, and their behaviors of soda-ash roasting were investigated, in order to shed light on the soda-ash activation of boron within ludwigite ore.
Materials and Methods
MaterialsLizardite and szaibelyite were prepared from natural ores. The as-prepared samples were dried, crushed, ground and screened to 80% passing through 0.074 mm. Chemical composition and XRD patterns of these two samples are given in Table 1 and Figure 1, respectively. The corresponding purities of lizardite (calculated by SiO 2 content in the form of Mg 3 Si 2 O 5 (OH) 4 ) and szaibelyite (calculated by B 2 O 3 content in the form of Mg 2 B 2 O 5 ·H 2 O) are 86.3% and 94.6%, respectively.
