Treatment of Cyanide Tailings with Persulfate Oxidizers at Different Temperatures AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY23080004

Chinese Library Classification Number:TF09

Citation Information:

Cyanidation is still the main gold extraction process，but it is accompanied by a large number of cyanide tailings，whose composition is complex and difficult to deal with. If it is directly stored without treatment，it will occupy a large amount of land，bring environmental pollution problems and a serious waste of resources，so the study of its harmlessness，minimization，resource comprehensive treatment process is crucial for the ecological environment and metal resources recycling. Compared with the fire method，the wet reaction conditions are more moderate and controllable，the reaction speed is fast，and the adaptability to the raw ore is strong，etc. It has a wider development prospect. At present，the advanced oxidation technology of persulfate （PS）has attracted extensive attention from researchers，which has the advantages of high stability，easy operation，low price，etc. The activation of SO₄^·− radicals has the characteristics of long half-life，wide pH application range，and strong oxidizability，etc. In this paper，persulfate was used as the oxidant，persulfate was used as an oxidizing agent to treat cyanide tailings，focusing on the effect of temperature on the leaching process and the oxidation reaction mechanism of pyrite. Through chemical analysis，X-ray diffraction analysis （XRD），scanning electron microscopy （SEM）and other means，the changes in the leaching rate of ferric ions during the oxidation process，the enrichment of gold，the changes in the main mineral types before and after leaching，and the types of free radicals and their contributions were systematically analyzed. The results showed that the iron leaching rate gradually increased with the increase of reaction temperature，and the leaching rate reached 93.69% at 90 ℃. Macrokinetic analysis showed that the leaching process conformed to the pseudo-primary kinetic model，with a reaction rate constant of 0.0897 h⁻¹，an apparent activation energy of 41.177 kJ·mol⁻¹，and a chemical reaction as the main rate-controlling step. XRD and SEM results showed that the cratering and corrosion cracking of the pyrite surface worsened with the increase of temperature，but no diffraction peaks of other iron minerals appeared at the end of the leaching process，which indicated that the leaching process was mainly the dissolution reaction of FeS₂，not a simple oxidation and desulfurization reaction. At 90 ℃，cyanide tailings quality loss rate of 52.8%，the gold content of 1.19 g·t⁻¹ enriched to 2.88 g·t⁻¹，the aggravation of corrosion of pyrite was conducive to the exposure of the gold and silver wrapped in pyrite，and to increase the subsequent leach agent and its contact area，which contributed to the subsequent recovery of gold and silver treatment，contributing to the subsequent recovery of gold and silver processing. Methanol （MeOH）and tert-butanol （TBA）were added as active species bursting agents in the persulfate oxidation system to investigate the free radical species and their contributions in the system. The results showed that the decomposition of pyrite in cyanide tailings under ambient conditions was mainly attributed to the direct oxidation of S₂O₈²⁻，but the oxidation potential of PS itself was low，and pyrite could not be oxidized effectively. With the increase of leaching temperature，persulfate absorbed external energy to induce the homolytic decomposition of O–O bonds，and the contribution of oxidation by SO₄^·− and HO· radicals increased，and the contribution of HO· oxidation could reach 94.13% at 90 ℃. At the same time，the significant decrease in pH during the oxidation process was favorable for the generation of free radicals through HSO₄⁻ decomposition pathway. During the oxidation process，the oxidation mechanisms of SO₄^·− and HO· radicals on pyrite were similar，both preferentially reacted with S atoms，but due to the coordination number limitation of S atoms，the neighboring Fe atoms at this time had a stronger affinity compared to the radicals，and the preferential oxidation of Fe atoms would further promote the deep oxidation of S atoms. This might be the fundamental reason why the physical phase of FeS₂ remained unchanged during the oxidation process. During the experiment，phosphoric acid was used to mask Fe³⁺，and it could be seen that at lower temperatures，the lower Fe³⁺ content of iron ions had less influence on the leaching rate，but when the temperature increased，the large amount of Fe³⁺ production was conducive to the destruction of the S–S bond，and at the same time realized the cyclic conversion between Fe²⁺/Fe³⁺，which promoted the generation of free radicals and further enhances the leaching rate. However，the activation mode of energy transfer was still dominant in the whole oxidation process，supplemented by the activation mode of electron transfer with Fe²⁺ as the electron donor. This indicated that the effect of temperature on PS treatment of cyanide tailings was mainly reflected in the change of the reaction rate constant （k）and Gibbs free energy （ΔG）in the radical generation reaction，which in turn affected pH of the reaction system and the composition of the oxidized substances.