An example of the process of recovering vanadium from petroleum ash

Since the 1980s, power stations fueled by petroleum- processed residues have emerged. These petroleum fuels contain a certain amount of vanadium , which is about one in a million, and some as high as 1.4 per thousand (Central America). In power plants, vanadium is enriched in boiler ash and fly ash. Boiler ash is the soot deposited in the furnace, while fly ash is the fine dust collected by the dust collector. Fuel-fired power stations generate less boiler ash and more fly ash.

1. Recovery of vanadium from boiler ash

The boiler ash contains 4.4% to 19.2% vanadium and 0.2% to 0.5% nickel . Finely grinding to -100 mesh, each time with 8mol / L NaOH, leaching at 112 ° C for 4h, after three times of cross-flow leaching, vanadium leaching rate can reach 43%, 16%, 8%. The obtained leach solution can be further purified by vanadium to obtain a high-purity V ₂ O ₅ product. The remaining 33% of the vanadium in the leaching slag was further leached with 8 mol/L HCl, and Ni, Fe, and Mg in the ash were also leached, and then separated by extraction. First with 25% TBP in kerosene iron extraction raffinate with ammonia adjusted pH = 6, then 25% LIX64N kerosene solution was extracted Ni, V. Stripping with 0.3 mol/L HCl, first stripping nickel, then stripping vanadium with 6 mol/L HCl, so that 80% of vanadium can be recovered.

2. Recovery of vanadium and nickel from fly ash

Two scholars from Taiwan's Cheng Kung Univ University said that the Taiwan region burns 15 million m3 of heavy oil every year, with an annual output of 43,000 tons of fly ash. 30% of them are produced by electric dust removal, called EP ash; the other 70% are produced by cyclone separator, called CY ash. The main components are oxides of Fe, C, V, and Ni. Liquid ammonia is sprayed into the electrostatic precipitator to neutralize the acidity, so there is still 30% to 40% of (NH ₄ ) ₂ SO ₄ in the EP ash. V, Ni and (NH ₄ ) ₂ SO ₄ are recovered from these fly ash, which both recycles resources and manages the environment.

The ash was leached with 0.25mol/L NH ₃ +1mol/L(NH ₄ ) ₂ SO ₄ to preferentially leaching Ni, the leaching rate was 60%, then the leaching of vanadium with NaOH, the vanadium leaching rate was 80%. . Based on this, a 2-stage leaching process has been established. The composition of kerosene fly ash is shown in Table 1.

Table 1 Fuel fly ash composition (%)

3. Recovery of vanadium and nickel from fuel fly ash

Scholars at the University of Alexandria in Egypt proposed to recover V and Ni from fuel fly ash by pressurized acid leaching instead of sodium roasting, because sodium roasting is technically feasible but economically inefficient. They tried to have an oxygen partial pressure of 1.5 MPa at 200 ° C, a H ₂ SO ₄ concentration of 60 g / L, a liquid-solid ratio of 1 / 1 (mass), and a leaching time of 15 min. The V and Ni leaching rates were all above 95%. The iron is hydrolyzed and precipitated at 200 ° C or higher to achieve the purpose of removing iron. The leach solution is separated by electrolysis, the solution is neutralized and vanadium is precipitated with an ammonium salt, and finally calcined to obtain V ₂ O ₅ . According to analysis, this method has the following advantages over the traditional sodium oxidizing roasting method:

(1) The consumption of sulfuric acid is about 10% of soot, which is economical compared to 50% of alkali consumption;

(2) The roasting method has high energy consumption and is estimated to be 5000kJ/t soot;

(3) Pressurized acid leaching can separate Ni, V and Fe, and fully recover Ni and V.

The soot composition of this research institute is as follows:

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