Fluorite (CaF) is a non-renewable mineral and is employed as a flux agent in steelmaking and hydrofluoric acid production [ 1 2 ]. In China, the mineral is derived mainly from naturally occurring fluorite minerals and tailings of tungsten, and there are a few notable differences between both the production processes. Moreover, the ultimate objective of every Chinese company is to produce high-grade products (CaF≥ 97%, SiO< 1%).
2 ≥ 97%. However, although the fluorite production was efficient, the side effects of resource exploitation in China were becoming increasingly apparent, and it was difficult to maintain a steady production of high-grade fluorite, which contained more impurities than before. The two major impurities found in fluorite concentrates are carbonate (CaCO3) and silicate (SiO2). Several studies reported that all commercial fluorite production processes used froth flotation to remove the impurities [4,5,6,9,10,In the past, the fluorite concentrate’s quality index was usually CaF≥ 97%. However, although the fluorite production was efficient, the side effects of resource exploitation in China were becoming increasingly apparent, and it was difficult to maintain a steady production of high-grade fluorite, which contained more impurities than before. The two major impurities found in fluorite concentrates are carbonate (CaCO) and silicate (SiO). Several studies reported that all commercial fluorite production processes used froth flotation to remove the impurities [ 3 7 ]. Furthermore, this method was widely employed to remove gangue minerals from fluorite concentrations to further improve the fluorite grade [ 8 11 ].
2 mineral. In our previous study, the use of a two-stage depressed technology in the Jiepailing fluorite mine proved to be successful [2 ≤ 97%). This is primarily because CaCO3 in the fluorite concentrates consumes sulfuric acid (H2SO4) and is also associated with the generation of heat energy and waste volume during the furnace reactions in the acidulation of fluorite concentrate. This creates a burden on anhydrous hydrofluoric acid (AHF) manufacturers because of the increased production costs. In such cases, leaching is the easiest solution. As shown inThe Jiepailing fluorite mine is the single largest fluorite deposit in China, and has the largest ore of monolithic fluorite in Asia, and reserves 26.21 million tons of CaFmineral. In our previous study, the use of a two-stage depressed technology in the Jiepailing fluorite mine proved to be successful [ 12 ]. Thus far, a two-stage depressed process comprising one roughing and six cleaning procedures has been used for the processing of fluorite minerals. Subsequently, concentrates containing 93% fluorite, 2.5% calcite, and 3.5% sericite were obtained. Nonetheless, there is a lot of uncertainty regarding the current market and the cost of fluorite powders (93% ≤ CaF≤ 97%). This is primarily because CaCOin the fluorite concentrates consumes sulfuric acid (HSO) and is also associated with the generation of heat energy and waste volume during the furnace reactions in the acidulation of fluorite concentrate. This creates a burden on anhydrous hydrofluoric acid (AHF) manufacturers because of the increased production costs. In such cases, leaching is the easiest solution. As shown in Figure 1 , the fluorite concentrate is leached by waste hydrochloric acid (from a downstream chemical plant) after flotation.
Through this process, the calcite present in the fluorite concentrate was removed completely, but the CaF2 content increased to ~96% only and the remaining impurities could not be removed by this method. Moreover, sericite (SiO2) is a more important impurity than CaCO3 because it affects H2SO4 consumption during hydrofluoric acid (HF) or aluminum fluoride production. A number of side effects occur during the preparation owing to the hydrogen fluoride gas present in the reactor: 4HF (g) + SiO2 (s) = 2H2O (g) + SiF4 (g). Copious amounts of raw materials could be lost during production because of the high SiO2 content. Furthermore, against the background of this unprecedented situation caused by the pandemic, we need to find an effective method to desilicate fluorite concentrates before leaching.
14,17,20,21,Currently, during the direct flotation process, it is difficult to remove the silica completely via entrainment and the dissolved Ca ion might activate the sericite surface, as observed in our previous studies. In addition, further flotation cleaning was found to be ineffective. Therefore, we decided to use reverse flotation because it can be successful in cases where the gangue contains silicates (quartz or mica) and is floated with a collector of amine-type, while the valuable minerals are hydrophilic and are enriched in the underflow fraction [ 13 15 ]. This method was also reported to be the most widely used technology for the desilicification of various important minerals, i.e., iron ore and magnesite ore [ 16 18 ]. Several studies have been focusing on various amines and their derivatives that can be employed as cationic collectors in reverse flotation. Dodecylamine (DDA) is exceptionally effective as a collector of silicate minerals [ 19 22 ].
2+ ions from the chalcopyrite surface, thereby associated with the increase in the selective flotation separation between galena and chalcopyrite through the use of dextrin [2+ or Ca2+ [25,Conversely, fluorite depressants can efficiently enhance the flotation separation of sericite from fluorite. Liu and Zhang observed that citric acid (CA) might successfully eradicate Caions from the chalcopyrite surface, thereby associated with the increase in the selective flotation separation between galena and chalcopyrite through the use of dextrin [ 23 24 ]. Additionally, Gao et al. and Gan et al. reported that CA exerts sufficient depressive effects on the oleate flotation of fluorite because of its robust chelating capacity with Mgor Ca 26 ]. Thus, these studies provided us with valuable insights into our analysis.
Consequently, it is worthwhile to develop a new method to achieve desilication and purification of fluorite concentrate before acid leaching. Although we have previously formulated an efficient two-stage depressing process for mineral processing, this study addresses the need for an efficient chemical scheme for improving the separation of sericite minerals in fluorite flotation. Fundamental analyses, such as micro-flotation, batch flotation, solution chemistry analysis, ZP measurements, and FTIR were conducted for the detailed information regarding the mechanism. This pilot study was carried out in the Xinyuan fluorite dressing plant and can potentially solve several long-standing complications regarding the shortage of high-quality fluorite concentrates.