Process And Mechanism Of Alumina Minerals Inhibiting The Oxidation Dissolution Of Pyrite In Acid Mine Water

When the primary reduction environment is destroyed by mining,pyrite is oxidized to produce acid mine water with high concentration of SO₄^2-,H⁺and metal ions.In the process of pyrite oxidation,solid film passivation layer will be formed on the surface,leading to the diffusion of water and oxygen mass transfer is blocked,and the oxidation dissolution of pyrite is inhibited.Pyrite is often co-occurring or associated with aluminum-bearing minerals,which will lead to dissolution and release of Al³⁺and form highly aluminum-acidic mine water.There are few reports on whether it will affect the oxidation dissolution of pyrite and the formation of solid film passivation layer on the surface.In this paper,the main sources of Al³⁺and the causes of acidification in typical acidic mine water in southwest China were clarified through a combination of field and indoor studies.On this basis,the formation process of the solid film passivation layer on the surface of pyrite was characterized,the microscopic interface change mechanism during the oxidation of pyrite was revealed,the influence of Al-containing minerals on the formation of secondary minerals under different Fe²⁺concentrations and p H was explored,and the regulatory mechanism of the formation and transformation of secondary minerals on the formation of solid film passivation layer on the surface of pyrite was elucidated,which has important theoretical significance for the remediation and source prevention and control of acid mine water pollution.The main research results are as follows:Typical acid mine water pollution characteristics were analyzed to clarify the influence of dissolved aluminum-containing minerals on the hydrochemical evolution of mine water.The acid mine water pollution in abandoned Dashu mining area has the characteristics of"three high and one low",namely"high iron,high aluminum,high SO₄^2-and low p H value".The acid mine water microbial community is mainly composed of A.ferrooxidans;the dissolution of aluminous clay（clay for short）in acid mine water consumes H⁺,resulting in the increase of Al³⁺concentration and p H,which promotes the hydrolysis and precipitation of iron and aluminum to produce iron and aluminum secondary minerals such as jarosite,schwertmannite and alunite,causes the change of chemical components of mine water and inhibits the acidification of mine water.The influence mechanism of Al₂O₃ and clay on the oxidation and dissolution kinetics of pyrite was revealed.The oxidation dissolution of pyrite accords with the nuclear dynamic model of solid film contraction.The addition of a small amount of Al₂O₃ and clay(Al³⁺equivalent<30 mmol/L)can promote the oxidation of pyrite,while the addition of Al³⁺equivalent≥30 mmol/L can significantly inhibit the oxidation of pyrite.The oxidation inhibition effect of clay with the same dosage is more obvious than that of Al₂O₃ on pyrite.It is mainly the formation of the secondary mineral layer on the surface of pyrite,which prevents the contact between water and oxygen and pyrite,inhibits the oxidation and dissolution of pyrite,and makes the formation and thickening of the sulfur film passivation layer on the surface of pyrite.The solid film passivation layer formed by the sulfur film and secondary mineral layer is formed on the surface of pyrite,resulting in the passivation phenomenon.The forming process of solid film passivation layer and the mechanism of inhibiting the oxidation and dissolution of pyrite were.The oxidation process of pyrite conforms to the"polysulfate-thiosulfate"pathway with or without aluminum-bearing minerals.On the one hand,the Fe³⁺concentration of the reaction system is reduced,so that the oxidation of pyrite and sulfur oxidation intermediates is inhibited.On the other hand,secondary minerals such as jarosite,schwertmannite and alunite are generated on the surface of pyrite,which prevents the surface material transmission of pyrite.In the process of pyrite oxidation,the migration rate of iron element is higher than that of sulfur element,which causes the accumulation of sulfur element on the surface of pyrite,promotes the thickening of sulfur film dominated by polysulfide chemical（Fe S_n）or iron-deficiency sulfide(Fe_1-xS),and forms a solid film passivation layer composed of sulfur film and secondary mineral layer,which inhibits the oxidation of pyrite.The regulation mechanism of aluminum-bearing minerals on the formation and transformation of secondary minerals under different Fe²⁺concentration and p H value was revealed.The dissolution of Al₂O₃ and aluminum-bearing minerals in clay and the oxidation of Fe²⁺can promote the polymerization and precipitation of hydroxyl sulfate,the intermediate product of Fe³⁺/Al³⁺hydrolysis,to produce secondary minerals under acidic conditions.Under acidic conditions（p H=2.00）with Fe²⁺concentration≥30 mmol/L,jarosite was formed by polymerization of hydroxyl sulfate.The p H value≥3.00 is conducive to the formation of schwertmannite minerals,and the mineralization process will cause the release of H⁺and promote the transformation of schwertmannite minerals into jarosite,which indicates that the dissolution of aluminum-bearing minerals under acidic conditions will promote the formation and transformation of schwertmannite minerals.To sum up,Al³⁺is released by the dissolution of aluminum-bearing minerals（Al₂O₃ and clay）in acid mine water,which promotes the formation of secondary minerals on the surface of pyrite under the interaction of iron and aluminum hydrolysis and co-precipitation,so that sulfur elements accumulate on the surface,forming a solid film passivation layer composed of secondary mineral layer and sulfur film,which inhibits the oxidation and dissolution of pyrite.At the same time,the release of Fe²⁺and dissolution of Al³⁺during the pyrite oxidation process can regulate the formation of secondary minerals and mineral phase transformation on the surface of pyrite,which is conducive to the formation and thickening of solid film passivation layer,and has important reference significance for the prevention and remediation of acid groundwater environmental pollution.