Fe(?)-induced Oxidation And Transformation Of Realgar At The Earth's Surface

Realgar mine is a unique mineral in China.Due to mineral smelting activities,a large amount of tailings were produced.With the scouring of rainwater and surface runoff,the chemical forms of arsenic in realgar can be transformed to harm people's health.The ferrous was widespread in nature,and often used for stabilization of arsenic waste residue.However,the mechanism of the oxidative dissolution and mineral phase transformation of realgar induced by ferrous is not clear.In this study,the transformation behavior and mechanism of arsenic in realgar minerals were investigated,which taking from Shimen town,in order to provide theoretical basis for the release and safe treatment of realgar tailings.?1?X–ray fluorescence spectrum analyzer?XRF?,X–ray diffraction photometer?XRD?and X–ray photoelectron spectroscopy analyzer?XPS?were used to study the basic properties of the realgar.The mineral sample was mainly composed of As,S and Si,and the mass percentage of arsenic in the mineral was 68.3%,the main crystalline substance was realgar?As₄S₄?.As was all as As?II?,60.68%of S existed in disulfide and 39.32%existed in polysulfide,and O was water molecules and hydroxyl groups adsorbed on the surface,through the element valence state analysis.In the range of pH 2-12,the realgar surface had a negative charge,and BET was only 0.01 m² g^–1.The analysis results provided basic parameters for subsequent research.?2?Oxidant quenching experiment and density functional theory were combined to study the oxidative effect of ferrous on realgar.The oxidative dissolution behavior and mechanism of arsenic in realgar were revealed.Under the pH 6.5,the realgar oxidation rate was extremely slow.However,ferrous(Fe?II?/As?5.4×10^–2)promoted the oxidative dissolution of arsenic in realgar,and the dissolution rate of arsenic in realgar increased with the decrease of the addition.In the process of ferrous activated oxygen molecules,the resulting high price iron?Fe?IV??might be the main oxidant.The pH could also affect the oxidative effect of ferrous on arsenic in realgar,which could not play a good oxidation role under acidic and alkaline conditions,while the oxidation effect was significant in neutral conditions.?3?XRD,the geochemical software of Phreeqc,Fourier transform infrared spectroscopy?FTIR?and Scanning electron microscope?SEM?were used to analyze the physical and chemical properties before and after the reaction of the samples.The effect of pH on stability of realgar was studied and then the stable transformation mechanism of the arsenic in realgar induced by Fe?II?was obtained.The addition of ferrous(Fe?II?/As>5.4×10^–2)could not only induce the dissolution of arsenic in realgar,but also stabilized the arsenic in realgar.With the increase of Fe?II?/As molar ratio,the concentration of arsenic in the solution gradually decreased.The ferrous was oxidized to form the amorphous ferrihydrite,which adsorbed the arsenic in the solution.And with the increase of the addition of ferrous,the production of the amorphous ferrihydrite increased.The products were coated on the surface of the realgar mineral,which was difficult to release arsenic into the environment.The addition of excess ferrous accelerated the rate of oxidant production.The oxidant was consumed by a large amount of ferrous in solution,thus the stable rate of arsenic was greater than the oxidation rate.