China vanadium-titanium magnetite is widely distributed and rich in reserves, ranking third in China in terms of reserves and mining capacity, with proven reserves of 9.83 billion tons and prospective reserves of more than 30 billion tons [1], mainly distributed in Panzhihua-Xichang area of Sichuan, Chengde area of Hebei, Hanzhong area of Shaanxi, Yunyang area of Hubei, Xiangyang area of Guangdong and Daixian area of Shanxi. Among them, Panzhihua-Xichang area is the main metallogenic belt of vanadium-titanium magnetite in China and one of the important producing areas of similar deposits in the world. It is about 300 kilometers long from north to south, and 7 large and super-large deposits and 6 medium-sized deposits have been proved. See table 1 and table 2 for the chemical composition of raw ore and mineral processing products.

Table 1 chemical composition of vanadium-titanium magnetite in Panzhihua, Sichuan [2]

chemical composition

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titanium dioxide

vanadic oxide

cobalt

nickel

S

P

Percentage content (%)

30.55

10.42

0.30

0.0 17

0.0 14

0.64

0.0 13

Table 2 Chemical Composition of Mineral Processing Products of Vanadium Titanium Magnetite in Panzhihua, Sichuan (%)[2]

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titanium dioxide

vanadic oxide

cobalt

nickel

aluminium oxide

silicon dioxide

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Marine gasoline (abbreviation for Marine Gas Oil)

S

P

Iron-vanadium concentrate

5 1.56

12.73

0.564

0.020

0.0 13

4.69

4.64

1.57

3.9 1

0.53

0.004

Titanium concentrate

3 1.56

47.53

0.68

0.0 16

0.006

1. 16

2.78

1.20

4.48

0.25

0.0 1

Sulfur cobalt concentrate

49.0 1

1.62

0.282

0.258

0. 192

1.40

5.42

1.69

2. 16

36.6 1

0.0 19

Scandium in raw ore is mainly distributed in titanaugite, ilmenite and titanomagnetite, and its distribution in mineral processing products changes with the content of the first two minerals, and scandium exists in the form of isomorphism [3]. In titanium pyroxene, Sc3+ replaces Fe2+ and Mg2+ by isomorphism, and Fe3+ and Al3+ replaces Si4+ to achieve electricity price balance. The arrangement relationship is

Sc3+ + Al3+ →(Fe2+，Mg2+)+ Si4+

The isomorphic replacement relation of scandium in ilmenite is as follows

Sc3+ +(Fe3+ + Al3+)→(Fe2+，Mg2+)+ Ti4+

The occurrence of scandium in titanomagnetite is mainly related to ilmenite and ilmenite crystals.

Among the mineral processing products, the most scandium-rich is the electro-flotation tailings, with the Sc2O3 content reaching 77ppm, followed by iron concentrate and gravity separation tailings, with the Sc2O3 content of 63ppm and 5 1.4ppm[4] respectively. The conventional methods for extracting scandium from these raw materials are summarized as follows.

1) electric tailings and gravity tailings

Scandium is mainly enriched in titanium pyroxene. At present, there are two methods to recover scandium from pyroxene:

Acid treatment: decomposing with sulfuric acid, heating and stirring for 4-5 hours until SO2 vapor is completely removed; Or use hydrochloric acid (HCl+NaF) to decompose at 80~ 100℃ for 4~5h.

Alkaline treatment-melting with sodium bisulfate and sodium hydroxide at 500~600℃ for 65438 0 h respectively. The hydrate obtained by alkali melting method is filtered and precipitated to remove alkali, and then heated and dissolved in hydrochloric acid. Hydrate is precipitated from the solution with ammonia, filtered and calcined into oxide.

2) Titanium concentrate

Scandium is mainly enriched in high titanium slag during electric furnace smelting of titanium concentrate. When high-titanium slag is further chlorinated in a fluidized bed furnace at high temperature to produce titanium tetrachloride, most scandium is chlorinated into ScCl3 and volatilized into dust, which is collected by a dust collector after cooling, and the content of Sc2O3 can reach 736ppm[5].

3) Iron concentrate

The grade of scandium in iron concentrate is Sc2O3 20ppm. Scandium is mainly enriched in blast furnace slag during sintering and steelmaking, and can be recovered from it. The Soviet Union began the research in this field in 1950s, and used alkali-carbonate method to recover scandium from blast furnace slag. That is to say, the slag is decomposed by sulfuric acid, then the hydroxide is separated by alkalization, then scandium concentrate is prepared by carbonate treatment, finally oxalate is extracted and precipitated by thiosulfate, and then the oxalate is calcined to obtain Sc2O3.

In the 1980s, with the soaring price of scandium in the world market, there was a research upsurge of separating scandium in China, and the extraction mainly focused on titanium-containing raw materials, such as sulfuric acid waste liquid in titanium dioxide production, chlorinated dust and titanium tailings in titanium dioxide production. Domestic production units include Shanghai Dongsheng Titanium Dioxide Factory, Guangxi Xipinggui Mining Bureau, Hunan Rare Earth Metal Materials Research Institute, Jiangxi Ganzhou Cobalt Smelter, Guangzhou Titanium Dioxide Factory, etc. After entering the 1990s, the former Soviet Union countries sold a large number of past stocks, resulting in China's overproduction. The supply of scandium in the world exceeded demand, and the price of scandium dropped sharply, which directly affected the production of scandium. The research and production of extracting scandium from titanium-containing raw materials are introduced as follows.

(1) Extraction of Scandium from Waste Acid of Titanium Dioxide

When titanium dioxide is produced from ilmenite by sulfuric acid method, the scandium content in the hydrolyzed acidic waste liquid accounts for about 80% of the total content in ilmenite [6]. Most of scandium oxide produced in China comes from titanium dioxide factory. Shanghai Dongsheng Titanium Dioxide Factory, Shanghai Yuelong Chemical Factory and Guangzhou Titanium Dioxide Factory have established scandium oxide production lines. Hangzhou Sulfuric Acid Plant has put into operation an industrial plant with an annual output of 30kg scandium oxide, forming a three-stage scandium extraction process route of "continuous extraction-12 countercurrent titanium washing-chemical refining", and the product content is stable at 98-99%. At the beginning of Shanghai Yuelong Chemical Plant, scandium was enriched by P204-TBP- kerosene synergistic extraction, followed by NaOH back extraction, hydrochloric acid dissolution, 55-62%TBP (or P350) resin extraction chromatography separation and purification of scandium, and finally, Sc2O3 with purity over 99.9% was obtained by oxalic acid refining. The scandium yield of the whole method is over 70%[8].

The former Soviet Union used 0.4M P204 to extract scandium from titanium dioxide mother liquor. When the O/A ratio is1100, scandium can be almost completely separated from impurities such as titanium, iron and calcium. Scandium is back-extracted with solid sodium fluoride and then dissolved with 3% sulfuric acid. The yield of scandium is 85-90% in the scale-up test. Emperor Wen of Sui et al. [6] used P204-TBP to extract scandium from the mother liquor of titanium dioxide. First, inhibitor was added to inhibit P204 from extracting iron and titanium, and then mixed acid and sulfuric acid were used to wash and extract the organic phase, Sc2O3 that the content of TiO2 in the organic phase was reduced to 0. 1mg/l and the content of Fe was reduced to 0.5 mg/L. Feng et al. [9] used P507-N730/kloc. Nie Li et al. [10] used two-stage method to extract scandium, the first stage was extracted with P507- decanol-kerosene, and the second stage was extracted with P5709-TBP- kerosene, and scandium was enriched more than 50 times. Liu [1 1] first selectively extracted scandium with N 1923, and then added the extracted scandium to further remove impurities. The total concentration of scandium in two stages is more than 50 times. After oxalic acid refining, the purity of Sc2O3 is 99% and the recovery rate is 84%. In addition, ion exchange method [12] and emulsion liquid membrane method [13] have also been used to extract scandium from titanium dioxide wastewater.

(2) extracting scandium from chlorinated flue gas

When ilmenite is smelted by electric arc furnace, Sc2O3, like oxides such as niobium, uranium and vanadium, is stable because of its high heat of formation, and will not be reduced and remain in high titanium slag. Scandium is enriched in chlorinated flue gas when titanium tetrachloride is produced by high-temperature chlorination of this high-titanium slag. The production line built by Wuyi Branch of Fushun Aluminum Factory produces 20 ~ 30 kilograms of scandium oxide every year. Ke Jiajun et al [14] found that the content of scandium in chlorinated soot can reach 0.03~0. 12%, and the main form is ScCl3；; The process of wet extraction of Sc2O3 was studied, including unit operations such as water immersion, TBP kerosene solution extraction, oxalic acid precipitation purification and burning. The purity of Sc2O3 was 99.5% after small and large tests. From chlorinated soot to product, the recovery rate of scandium is 60%. Xie Lina [15, 16] uses low-concentration alkyl phosphonic acid (P507, P204) to directly extract scandium from leaching solution containing a large amount of Fe3+, and the scale is small. Scandium can be stripped with ethanol as stripping agent at room temperature. When zirconium was washed with 0.4%HF, the separation coefficient of scandium and zirconium reached βSc/Zr= 1893. Yang Zhifa et al. [17] extracted scandium with P5709-N235- kerosene and back-extracted at 5MHCl 60℃, which can completely separate Sc3+ from Fe3+, Fe2+, Ti3+, Al3+, Mn2+ and Ca2+. The problem of Sc3+/Fe3+ separation and phase separation are solved. When He Jinlin et al. [18, 19] extracted scandium from chlorinated soot, iron and manganese were separated by P204 extraction, and scandium was enriched 83 times by NaOH back extraction. Chemical refining uses hydrochloric acid to dissolve, TBP- concentrated hydrochloric acid to extract scandium to separate rare earth, Dowex50W-X8 exchange resin to adsorb scandium, and the purity of scandium is over 99.5%, and the yield is over 56%. Sun Benliang et al [20,265,438+0] used an organic multi-weak acid precipitant to precipitate scandium in hydrochloric acid leaching solution of chlorinated soot. After two times of precipitation and acid hydrolysis, the removal rate of iron and manganese in the leaching solution reached over 99.8%, and the precipitation rate of scandium reached 100%. Then using P204+ modifier+sulfonated kerosene as extractant, O/A= 1/20, scandium was extracted at room temperature, DSc reached 139, and the separation coefficients of scandium from iron and manganese reached 9270 and 10700 respectively. Scandium was stripped with 5%NaOH, and the stripping rate reached 99.6%. Lin Weiming et al. [22] extracted scandium with benzylated oxygen, and the yield of scandium was 98.3%.

(3) extracting scandium from titanium tailings.

Panzhihua has built a concentrator with a design scale of 6.5438+0.35 million t/a, with an annual output of 5.883 million tons of iron concentrate and 7.4553 million tons of tailings, which is in urgent need of comprehensive utilization. When Zhang [23] undertook the "Eighth Five-Year Plan" key project "Experimental Study on Comprehensive Scandium Extraction from Panzhihua Vanadium-Titanium Magnetite", it was detected that the raw ore of this iron concentrator contained 27.00g/t scandium. According to the design scale, scandium is recovered from the treated ore by 364.25t every year, with a value of 24.425 billion yuan. They use titanium tailings with scandium content of 63g/t as raw material, and can separate titanium pyroxene and feldspar from the tailings by pretreatment magnetic separation or addition treatment electric separation, with scandium content of 1 14g/t and 12 1g/t respectively. Adding cosolvent hydrochloric acid to leach scandium, the leaching rate can reach 93.64%. Scandium is leached by alkali-melted hydrolyzed hydrochloric acid, and the leaching rate can reach 97.90%. Scandium is extracted by TBP, and the extraction rate can reach 98.90%. Water was used for back extraction, and the back extraction rate was 98.00%. Then refined with oxalic acid, the product with a grade of 99.95% can be obtained, and its market price is 36,000 yuan/kg. Due to the high price and small market capacity, no factory has been built so far.

Summary:

To sum up, scandium in titanium dioxide mother liquor is ionic, and the extraction process is simple, and scandium oxide is mostly used as raw material in early production; However, the content of scandium is low (10~25ppm), which is restricted by the production of titanium dioxide (the annual output of 1000t titanium dioxide can recover dozens of kilograms of scandium oxide). Scandium in chlorinated soot exists in the form of ScCl3, so it is not difficult to recover it. The question is whether the resources of chlorinated cigarettes are sufficient. Assuming that the average content of scandium oxide is 500ppm, at least 100t chlorinated dust should be treated to obtain 50kg scandium oxide product, which is quite large. Scandium in titanium tailings mainly exists as pyroxene with silicate structure of (Ca, Mg, Al, Ti)Si2O6, which is difficult to decompose, and is often melted by acidification or alkalization at high temperature (~ 1000℃). However, the tailings yield is very large, and the absolute amount of scandium is considerable, which provides sufficient raw materials for scandium production. However, the comprehensive utilization of other resources must also be considered when dealing with tailings.

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