## 1 Introduction  
Scandium (Sc)--atomic number 21--lies in the periodic table of the fourth cycle III subgroup. Along with yttrium and lanthanide, scandium belongs to the rare earth family. It also has a particularity of mineralization with titanium, vanadium and iron that is not common with other rare earth elements. In the crust, the specific minerals of scandium are very rare. Moreover, there are only small economic reserves of Sc-bearing minerals including only thortveitite (Sc,Y)\({}_{2}\)Si\({}_{2}\)O\({}_{7}\), scandium phosphite ScPO4\({}_{4}\)2H\({}_{2}\)O, bazzite Be3(Sc,Al)2 Si6O18, titanium silicate mineral Sc(Nb,Ti,Si)2O5 and befanamite (Sc,Zr)\({}_{2}\)Si2O7, etc. In nature, scandium mostly occurs in ilmenite, zircon, bauxite, rare earth ore, ilmenite, V-Ti magnetite, tungsten ore, tin ore, uranium ore, coal and other minerals. In recent years, the combination of mineral processing and hydrometallurgical separation technology has been widely used in the field of comprehensive recovery and extraction of scandium, which greatly improves the concentration ratio and recovery rate of scandium. In future research and production, the recovery process of main metals and other valuable metals should be considered--with the recovery and extraction process of scandium simplified, and the production cost reduced as much as possible [1; 2; 3]. Scandium is not only rare in the crust (only 7\(\times 10^{-6}\) in the upper crust, equivalent to seven grams of scandium per ton of crust material), but also has a very low probability of forming scandium independent mineral in nature, which is only 0.4%. Current findings indicate that these rare independent minerals are mainly distributed in a few countries in Europe and Madagascar in Africa and have no real industrial value. In 1879, the Swedish chemist [PERSON] first discovered scandium in a silicon-beryllium yttrium mine and a black gold mine in Scandinavia in Europe. Scandium is normally dispersed in a number of minerals that contain other elements, like salt or sugar dissolved in water, and is not directly visible to the naked eye. Therefore, it is very difficult to obtain pure scandium metal. It took half a century from the discovery of scandium to the first successful extraction [4; 5; 6]. Scandium products are mainly used in Al-Sc alloy materials, scandium sodium halide high-intensity discharge (HID) lamps, SOFC, etc. Al-Sc alloys are mainly used in sporting goods production, automotive and aerospace industries. The higher power density of scandium zirconium-based solid electrolyte leads to the decrease of solid oxide fuel cell (SOFC) reaction temperature. Scandium lasers can be used in defense and medical fields. Scandium isotope is a common tracer in the oil refining industry. The International Adamas intelligence research center divides scandium's applications into three types: mature applications, emerging applications and future demand [7; 8; 9; 10]. Scandium chloride can be used to make high melting-point alloys. The preparation of scandium intermediate alloys by doping scandium fluoride or scandium oxide metal thermal reduction and electrolysis has been reported. Scandium metal is prepared by mixing scandium metal into aluminum alloy. Scandium metal is expensive and has a large burning-loss during smelting. In the preparation of scandium fluoride by thermal reduction method, corrosion and toxic hydrogen chloride are used, and the thermal reduction temperature of the metal is also very high. The real yield of scandium by scandium oxide thermal reduction is not high. Organic solvent extraction is one of the main methods for separating and enriching scandium. In most cases, extraction is more efficient than precipitation or ion exchange, and can be used at all stages of scandium extraction. The solvent extraction method is characterized by a simple, easy-to-grasp method, rapid and good enrichment and separation effect and large processing capacity.