Study On The Process Of Recovering Lead Oxide From Spent Lead Paste By Leaching Of Hydrometallurgy And Solution Synthesis

Spent lead paste is a difficult problem of resource utilization.The traditional pyrometallurgical recovery process not only has high energy consumption,but also has environmental problems,such asSO₂ pollution.The traditional hydrometallurgical recovery process is complicated and the electrolysis efficiency is low.Therefore,many researchers are exploring an environmentally friendly and efficient hydrometallurgical recovery process of spent lead paste.In this study,a process of recovering lead oxide from spent lead paste by hydrometallurgy is explored.Firstly,the spent lead paste was desulfurized with NaOH as desulfurizer,and the optimal desulfurization conditions were explored,and the kinetics of desulfurization process was analyzed.Then,the desulfurized lead paste was leached with acetic acid to obtain lead acetate solution,and the optimal conditions of acid leaching process were explored.After that,PbO was synthesized by using the lead acetate solution leached with simulated desulfurized lead paste and NaOH liquid phase,and the crystal forms ofβ-PbO andα-PbO were analyzed.Finally,the feasibility of PbO recovery from spent lead paste by hydrometallurgy was verified by using the lead acetate solution leached from the desulfurized lead paste.The main results are as follows:（1）The optimum conditions of desulfurization reaction are:molar ratio of NaOH to PbSO₄ is 2.40,desulfurization reaction time is 30 min,liquid-solid ratio（m L/g）is 2:1,stirring rate is 300 r/min,and reaction temperature is 35℃.Under this condition,the desulfurization rate reaches95.40%,and the loss rate of Pb in desulfurization process is less than 1%.The kinetic analysis results show that the reaction process of NaOH desulfurization spent lead paste is controlled by internal diffusion,and the apparent activation energy is 4.045 k J/mol in the temperature range from 25℃to 55℃;（2）The optimum conditions for acetic acid leaching desulfurization lead paste are as follows:at room temperature（about 25℃）,the molar ratio of acetic acid to total Pb in desulfurization lead paste is 2.00,the molar ratio of hydrogen peroxide to PbO₂ in desulfurization lead paste is 1.25,the reaction time is 30 min,and the liquid-solid ratio（m L/g）is 10:1.Under the conditions,the leaching rate of Pb is 96.14%.（3）By changing the way of NaOH addition,two crystal forms of PbO （β-PbO andα-PbO）were obtained by simulating the synthesis of lead acetate solution leached from desulfurization lead paste and NaOH liquid phase.The purity ofβ-PbO andα-PbO reached 98%and 99%,respectively in 20 min.The results showed that the intermediate Pb₃O₂（OH）₂ was formed by the reaction,and the triangular cone coordination structure formed by Pb and O atoms in Pb₃O₂（OH）₂ is similar to the crystal structure of the two PbO products,thus the productβ-PbO could be obtained by the decomposition of Pb₃O₂（OH）₂.The crystal structure of orthorhombicβ-PbO was unstable if the way of adding NaOH was changed.With the participation of NaOH dissolution exothermic process,the final product of Pb₃O₂（OH）₂ decomposition was tetragonalα-PbO with more stable crystal structure.Therefore,the two crystal forms of PbO could be distinguished by changing the way of NaOH addition.（4）The experimental results of PbO synthesis from lead acetate solution leached from actual desulfurized lead paste and NaOH in liquid phases showed that the synthesis ofβ-PbO could not be carried out normally,and the reaction product was Pb₃O₂（OH）₂.The results showed that the synthesis ofα-PbO could be carried out normally,and the optimal synthesis conditions are as follows:the initial reaction temperature is 95℃,the molar ratio of NaOH to Pb is 2.50,the stirring rate is 300 r/min,the reaction time is 20 min,and the NaOH dosing method is:NaOH particles quickly mixed with deionized water of equal mass and then put into operation.The purity ofα-PbO reached 99.37%.（5）It is feasible to recover PbO from spent lead paste by the proposed hydrometallurgy in practical application.α-PbO can be obtained from spent lead paste by desulfurization,acetic acid leaching and hydrometallurgical synthesis successively.