Study On Phase Transformation Law And Technology In Sulfuric Acid Curing And Water Leaching Process Of Secondary Copper Smelting Dust

The efficient recovery of secondary copper smelting dust can effectively alleviate the shortage of strategic metal resources such as copper,zinc,lead and tin in China,and solve the problem of environmental pollution,it is of great significance to promote the development of circular economy in our country.In this paper,the technology and theory of sulphuric acid curing-water leaching were studied for the recovery of valuable metals and the removal of fluorine and chlorine from secondary copper smelting dust,the phase transformation law of secondary copper smelting during sulfuric acid curing was clarified.The research results of the paper are as follows:（1）The thermodynamic results showed that the curing process in addition to Sn O₂,control the suitable temperature zinc,Cu,Pb and Sn phase can be converted to the corresponding sulfate.TheΔr G_m^?of Cu Cl reacts with H₂SO₄,when in 109.81℃above less than 0.The Gibbs free energy of Sn O₂ reacts with H₂SO₄ is always positive,the reaction is not spontaneous.And Sn and Sn O are more easily converted to Sn（SO₄）₂.In addition,Sn²⁺and Sn⁴⁺in the solution are easily hydrolyzed during the leaching process of the curing products,and the separation of Sn from Zn and Cu can be realized by controlling the p H value of the solution.（2）The amount of sulfuric acid and the curing temperature are the main factors affecting the conversion efficiency.Sufficient amount of sulfuric acid is conducive to the phase conversion.The copper in smelting dust is mainly Cu Cl,which does not react with concentrated sulfuric acid at low curing temperature,resulting in copper leaching rate of only 27.73%.For zinc and lead,the curing process is not affected by experimental factors,and the corresponding sulfate is easily produced.In the process of water leaching,the leaching rate of tin begins to decrease when the p H of the solution is greater than-0.2.Under the optimal conditions,the removal rates of F and Cl are 76.54%and 99.07%,respectively,and the leaching rates of Zn,Cu,Sn and Pb are 98.73%,96.64%,0.65%and 0.25%,respectively.Realizing the efficient separation and enrichment of valuable metals Cu,Zn from Pb and Sn,efficiently volatile removal of fluorine and chlorine,and reduce the amount of acid.（3）The curing experiment of pure substance further revealed the phase transition law of copper smelting dust during curing.In the pure substance curing experiment,Cu Cl and Cu S are greatly affected by the curing temperature.Cu Cl basically does not react with concentrated sulfuric acid at 150℃,and the leaching rate of copper is only 7.24%,the curing products and leaching residue are in the form of cuprous,and the XRD peaks of Cu S curing products at150℃correspond to Cu SO₄·H₂O and Cu S,and the copper leaching rate is 60.50%during water leaching.With the increase of temperature,the curing products of both products change into Cu SO₄.Zn O,Zn S,Pb and Pb Cl₂ are easy to be converted into corresponding sulfates in the curing process and are less affected by experimental factors.Sn O₂ does not react with concentrated sulfuric acid,while Sn O and Sn will generate different valence state of tin sulfate under different acid content.When the molar ratio of acid content is 2.6,the curing products of both are mainly Sn（SO₄）₂·2H₂O,which is greatly affected by the solution p H in the process of water leaching.The hydrolysis begins when the p H is greater than 0,and can be completely hydrolyzed when the pH is 1.2～1.4.The hydrolyzed product is SnO₂.