Preparation Of Monoclinic Crystal System FeS And Its Heavy Metal Purification Mechanism

Non-ferrous metal smelting process to prepare sulfuric acid and mining industry,etc.all produce a large amount of strong acidic wastewater containing arsenic and heavy metal ions,which is extremely harmful to the environment.At present,sulfidation method can convert heavy metal ions and arsenic into insoluble sulfide in a strong acidic environment,thus achieving efficient separation of heavy metals and arsenic,which is a common purification technology in industry nowadays.However,due to the strong competitive effect of large amount of H⁺in strongly acidic wastewater,the utilization rate of traditional sulfidation agent is low and hydrogen sulfide gas is easily produced,which not only causes waste of chemicals but also has serious safety hazards.How to improve the utilization efficiency of S^2-and reduce the escape of H₂S is essential for the deep purification of heavy metal ions and arsenic in strongly acidic wastewater.In this paper,based on the excellent adsorption properties of iron-sulfur compounds on heavy metals and arsenic,monoclinic magnetic pyrite with high activity was prepared by different methods and applied to the purification of copper and arsenic plasma in dirty acid as a slow-release donor of S^2-in strong acidic system.The"structure-efficiency"relationship was established.The main research findings are as follows.（1）The evolution of pyrite calcination products under nitrogen atmosphere:pyrite→monoclinic magnetic pyrite→hexagonal magnetic pyrite→metathionite;calcination temperature has a significant effect on the phase transformation of pyrite calcination process,650-700℃monoclinic magnetic pyrite has the fastest transformation rate;the monoclinic magnetic pyrite thus prepared has the characteristics of porous,large specific surface area;monoclinic magnetic pyrite is used for tainted acid copper,arsenic ion Separation,under the best conditions,the removal of copper 67%,arsenic 25%,proving that the monoclinic magnetic pyrite prepared by calcination of pyrite is less reactive.（2）The evolution law of calcination products of iron powder and sulfur under nitrogen atmosphere:iron powder and sulfur→monoclinic magnetic pyrite→hexagonal magnetic pyrite;temperature and iron-sulfur ratio have a greater influence on the phase transformation of calcination products,and the transformation rate of monoclinic magnetic pyrite is the fastest at 450°C.The surface of monoclinic magnetic pyrite prepared by iron and sulfur in the ratio of 1:1 is rough and porous.The experimental results of the separation of copper and arsenic ions in dirty acid showed that monoclinic magnetic pyrite was highly efficient in the purification of copper and arsenic,with the removal rate of 93.17%for copper and 66.46%for arsenic,which proved that the monoclinic magnetic pyrite prepared by iron powder and sulfur had good reactivity.（3）The evolution of pyrite and iron powder calcination products under nitrogen atmosphere:monoclinic magnetic pyrite→hexagonal magnetic pyrite→meteoric iron sulfide;temperature and time have a greater impact on the phase transformation of calcination products,monoclinic magnetic pyrite begins to appear at 450℃,with the extension of calcination time,the content and transformation rate of monoclinic magnetic pyrite are increasing,and the structure changes from a reticulated structure to rods and short columns.The experimental results of the thus prepared monoclinic magnetic pyrite for purification of foul acids showed that the removal rate of copper was 94%when the amount of P450-4（Calcined at 450℃for 4h）was 5 times the theoretical molar amount and the reaction temperature was 80°C;the removal rate of arsenic reached 97.19%when the amount of P450-4 was 10.5 times the theoretical molar amount,the reaction temperature was 50°C and the reaction time was 30min,which proved that the monoclinic magnetic pyrite with good reactivity.（4）The reactivity of monoclinic magnetic pyrite prepared by the three methods was in the order from high to low:pyrite calcined with iron powder>iron powder with sulfur>pyrite.The surface of the monoclinic magnetic pyrite calcination product obtained from pyrite with iron powder showed a loose and porous nano-submicron structure,while the surfaces of the other two calcination products existed mostly in a massive,slightly porous and dense state;the mechanism of copper/arsenic removal was a sulfide reaction with monoclinic magnetic pyrite,which led to the formation of Cu S/As₂S₃ precipitate by combining copper/arsenic with sulfur,and the reaction process was in accordance with Avrami kinetic model,the reaction is controlled by a mixture of diffusion and chemical reaction.