Research On Clean Conversion Mechanism Of Preparation Of Lead Oxide From Lead Components In The Spent Lead Paste By Shortened Process

In China,more than 3.5 million tons of waste lead paste,containing nearly 2.5million tons of lead,are discarded every year.Given the complicated composition of waste lead paste,such as 5%-10%physical impurities,1%-2%chemical impurities,and various forms of lead components（e.g.,Pb SO₄,Pb O₂,Pb O,and Pb）,the disposal of these waste lead paste has become the focus and difficulty of the secondary lead industry.Although it has achieved mechanical disassembly sorting and high-efficiency smelting,the process is still too long and exists many nodes for production and emission.Therefore,it is an urgent need for the industry to further shorten the process,lower energy consumption,reduce pollutant discharge,improve product benefits,and thereby achieve green development.This paper selected the waste lead paste as the target and investigated the clean conversion mechanism of lead oxide preparation from lead components in the spent lead paste by the shortened process around three key tasks,including impurity separation,lead conversion,and sulfur conversion.On the basis of revealing the properties of the spent lead paste and the existing states of each component,an efficient method of particles destabilization and fine separation was developed.Moreover,employing nitrite as a lead conversion agent,this study explored the transformation mechanism of NO₂^--Pb O₂-Pb and established the economic coupling transformation of lead components and NO₂^-recycling pathway,which reduced the consumption of redox agents.Furthermore,by using triethylene tetraamine（TETA）and Na₂CO₃as sulfur conversion agents,the study explored the deep conversion mechanism of Pb SO₄and developed a technology for efficient sulfur conversion and preparation of high purity lead oxide.Finally,a complete process chain of clean recovery of waste lead paste with high electrochemical activity lead oxide was formed by integrating the above three parts,which realized the reduction of the waste lead paste recovery cost and emission reduction of air pollutants at the source.This paper mainly draws the following conclusions:（1）Using alkyl phenol polyoxyethylene polyoxyethylene ether（APEP）as the emulsifying dispersant,this study designed and self-made a forced dispersion device with twin hydrocyclones and a mixed power fine screening device,which carried out emulsifying dispersion and fine separation of physical impurities of waste lead paste.It was found that APEP containing hydrophilic/hydrophobic groups could effectively reduce the agglomeration and adhesion effect and realize the liberalization of target individuals.Under 0.1 mg/L of APEP and p H of 5,the emulsification and dispersion effect of APEP is excellent.Compared with the initial state,the Zeta potential of the waste lead paste particles was increased by 4.41 times,and the average particle size was decreased by 63.64%.In addition,with the help of a forced dispersion device with twin hydrocyclones and mixed power fine screening device,the removal rates of plastic,lead grid/powder,and fiber reached 99.75%,82.54%,and 99.65%,and the entraining rates of lead paste are only 0.17%,0.06%,and 0.36%,respectively.（2）In the system of dilute sulfuric acid,Pb O₂can be rapidly reduced to Pb SO₄and Na NO₃by lead conversion agent（Na NO₂）.When the n（Na NO₂/Pb O₂）is 1.1:1,the reaction time is 38 min,and the liquid-solid ratio is 4:1,the conversion rate of Pb O₂can reach 99.79%.Under neutral or alkaline conditions,Na NO₃can react with Pb to produce product A（yellow orthogonalβ-Pb O with layered structure,1-2μm）and Na NO₂,and realizes the regeneration cycle of Na NO₂without NO and NO₂release.In the reaction process between Pb and Na NO₃,n（Na NO₃/Pb）,reaction temperature,and reaction time greatly influence the lead conversion.When the n（Na NO₃/Pb）is 3:1,the reaction time is 7.8 h,and the reaction temperature is 83℃,the oxidation efficiency of lead reaches 99.75%.In addition,the conversion time of Pb is longer than that of Pb O₂in the coupling conversion process of lead paste.The control step of Pb oxidation process is the surface chemical reaction control,and the apparent activation energy of Pb is 47.688 k J/mol.（3）TETA can coordinate with Pb SO₄in the lead paste to dissolve solid Pb SO₄.When the n（TETA/Pb SO₄）is 1.3:1,the reaction time is 11 min,the liquid-solid ratio is 2:1,and the reaction temperature is 30℃,the leaching efficiency of Pb SO₄can reach 99.93%.The density functional simulation results show that the HOMO of TETA is mainly near N2 and N3,and the E_HOMOis-4.7294 e V,indicating that amines of TETA are easy to give electrons and form coordination bonds with vacant orbitals provided by metal ions during the adsorption process.It forms an ion couple with a sulfate ion.The stable configuration of the coordination compound formed by TETA and lead is mainly ternary ring chelate with four coordination compounds（binding energy-0.3174 a.u.）.The control step is a surface chemical reaction,and the apparent activation energy of Pb SO₄is 47.5212 k J/mol.（4）Pb CO₃precursor can be prepared from TETA-Pb solution by Na₂CO₃.Simultaneously,chemical impurities separation and TETA regeneration can be achieved.The lead precipitation rate and Na₂SO₃concentration were increased with the mole ratio of Na₂CO₃to Pb in solution,while the secondary Pb SO₄leaching rate and Na₂CO₃utilization rate were decreased with the C/Pb.It is more appropriate with the C/Pb about 1.0.In a nitrogen atmosphere,Pb CO₃precursor was pyrolyzed at400℃for 2 h to obtain product B（rod-shaped red tetragonalα-Pb O,1-2μm）.Both product A and B have high purity,and their impurity content is only 0.0204%and0.0233%,respectively.Moreover,the initial capacity of battery A and battery B prepared by product A and product B exceeded the theoretical capacity.Their cycle life reached 482 times and 518 times,respectively,both greater than 350 times required by the national standard（GB/T 22199-2008）.（5）Integrating the impurity separation,lead conversion,and sulfur transformation,this study created the clean process and equipment for preparing power materials（Pb O）from the spent lead paste.Furthermore,the pilot-scale test was carried out,and the operation stability,element material flow,economic benefit,and environmental benefit of the process were analyzed.The total recovery rate of Pb in this process is about 99.65%without lead-free steam,SO₂,and other gaseous pollutants generation.Meanwhile,the content of impurities in product A and product B is only 0.0478%and 0.0259%,respectively,with a gross profit of 4233.88 yuan per ton of lead oxide product.Therefore,the process has good technical,environmental,and economic feasibility and excellent industrial application prospects.