Research On Process Mechanism Of The Intensified Leaching Of Vanadium From Shale By Particle Cracking With Stress Under Oxygen Pressure In Acidic System

Vanadium shale,as an advantage resource in China,has been paid attentions and studied because of its abundant reserves of vanadium.The high acid consumption,long leaching process and high impurity concentrations in leaching solution seriously restrict the development of vanadium industry of shale.Inspired by muscovite dissolution principle,the stress cracking of vanadium-bearing muscovite for vanadium enhanced extraction was proposed.The reversible conversion between CaSO₄ and CaSO₄·2H₂O is stimulated by K₂SO₄ to change local stress distribution on muscovite surface for the cracking of interfacial local area under temperature regulation,which realizes enhanced extraction of vanadium and separation of Al and Fe from source.As a result,series of key scientific problems and technical bottlenecks around vanadium extraction from vanadium shale by stress cracking were studied in this thesis.The main research contents and achievement are given as follows.Basing on process mineralogy of vanadium shale,the dissolution process of muscovite was demonstrated.After K⁺is dissolved preferentially on interface,there are a lot of charge-unsaturated oxygen atoms on the interface between muscovite's layer structure?TOT structure?and sulfuric acid solution.The charge-unsaturated oxygen atoms will attract H⁺and form interfacial hydroxyl.The interfacial hydroxyl and hydroxyl in TOT layer structure react with H⁺,the interfacial oxygen is deprived to produce lattice vacancies,which weakens the lattice bond of oxygen atoms to aluminum atoms.The increasing lattice vacancies produce more active points.H⁺can constantly react with new-born interfacial oxygen atoms to form interfacial hydroxyl,reducing the Al ligancy.The octahedral sheets are broken down and aluminum or vanadium atoms are released.The stress mechanisum between CSA interfacial growth and muscovite matrix was established.K₂SO₄ dosage,initial CaSO₄ cocnentration and system temperature have significant impacts on CSD production,CSA distribution density on matrix surface and interfacial debonding of CSA,respectively.As results of the accelating lateral growth and mutual overlaps of CSA,the stress concentration around CSA crystal corners and strain concentration in muscovite matrix adjacent to CSA crystals form.The mechanical loading passes from CSA crystals to muscovite matrix so that there are pores and microcracks appearing in the interphase.The muscovite particles are thus cracked.The new method of vanadium extraction enhanced by stress cracking of muscovite particles was proposed and the mechanism of reversible conversion among CaSO₄hydrates was established.K₂SO₄ is introduced to hydrate calcareous matters in vanadium shale,realizing CSA hydration,CSD?CSA transition and CSA interfacial growth through temperature control.The series changes reduce acid consumption,shorten leaching time and increase the V leaching efficiency during pressure acid leaching process.After adding K₂SO₄,the increase of CSA solubility and CSD supersaturation promotes CSD formation.When the temperature is below 100°C,CaSO₄ hydrates to become CSD.Once the temperature exceeds 100°C,CSD is developed into CSA by dissolution and recrystallization,which induces CSA interfacial growth.The split pores propagate in muscovite particles over time,which increases reaction interfaces between interior structure of muscovite particle and acid solution.The dissolution of vanadium is thus strengthened.The solid-phase transfer method of Al and Fe in oxygen pressure field was built under K₂SO₄ stimulation.In big pores from the interfacial debonding of CSA,Al³⁺instantaneous concentration increases significantly so that alunite nucleates and grows up in pore canals,which produces stress on pore wall.Al³⁺local concentration further increases.The precipitation of alunite is thus improved.The addition of K₂SO₄ also makes Fe³⁺precipitate in more stable form of iron sulfate?KFe?SO₄?₂?,which avoids basic iron sulfate forming in aqueous solution.The leaching efficiencies of V,Al and Fe respectively reach 90.20%,30.30%,and 5.73%after leaching for 5 h at 190°C and 2.0MPa O₂ with 15vol.%sulfuric acid solution and 7wt.%K₂SO₄ dosage.The separation coefficients of Al/V and of Fe/V are respectively 0.336 and 0.064.The enhanced extraction of vanadium and separation of Al and Fe from source are realized during K₂SO₄-assisted oxygen pressure acid leaching process.