Study On Leaching Process Of Spent Lead Battery Paste With Organic Acid And Preparation Of Ultrafine Lead Oxide By Calcination At Low Temperature

Discarded and spent lead acid batteries are hazardous wastes which could cause serious damages to both eco-environment and human health if treated and pilled improperly. Since the noxious lead dust and SO2 emission in the traditional pyrometallurgy, it is urgent to develop clean lead recovery technology for the sustainable development of secondary lead industry, among which lead paste is the most difficult part for recovery and disposal. In this thesis, lead paste was leached with organic acid to produce lead citrate precursor which would prepare ultra-fine lead oxide when calcinated at relatively low temperature. And there are also some efforts attached on systematical research on the theories and principles related to this technology. The main researches include the following contents:1. Characterization of lead paste in spent batteriesThe lead paste studied in this thesis comes from the crushing and separation device of Hubei Jin Yang Co., LTD. Before leaching experiments lead paste would be first pre-treated such as neutralizing, drying, crushing and further separation. Then chemical analysis and hydrometallurgy leaching was conducted by using part of the paste whose particle size is less than 120μm, which accounts for 80% by mass, and its specific gravity is 6.95 g/cm3. The major mineral constituents of lead paste are PbO, PbO2, and PbSO4. And the main components are PbSO4 (56.5-64.5%), PbO2 (29.5-32.5%), PbO (4-5%) and Pb (0.5-5%) by mass. In addition, there are trace impurities as Sb and Fe.2. The conversion of lead paste in the citric acid-sodium citrate systemThe hydrometallurgical converting law of PbO, PbO2, or PbSO4 leaching with the mixture of citric acid and sodium citrate in the different proportions respectively has been studied. Calculating by stoichiometry method and characeriation of XRD, FT-IR SEM and TG, it was found that the leaching product is Pb(C6H6O7)H2O at pH=3-4 who has board flake shape with particle size of 10-50μm, while the precipitate is Pb3(C6H5O7)2·3H2O at pH=5-6 which is thin scales shape with particle size of 1-10μm. And the converting law of simulative paste consisting of PbO, PbO2, PbSO4 and Pb in the citric acid-sodium citrate system is nearly the same with that of the single component. Having accomplished the leaching study of simulative paste, experiments were conducted to study the effect of the dosage of leaching reagent, temperature and time on both desulphurization rate of lead paste and recovery rate of lead paste by using the real lead paste. The optimal condition was found to be:3:1 of mol ratio of citric acid to total lead,9:5 of mol ratio of sodium citrate to total lead,2:1 of mol ratio of hydrogen peroxide to lead dioxide,1/5 as the starting paste/water mass ratio,8h of leaching time.The results of SEM/EDX showed that in leaching process, PbO2 and PbO reacted quickly, while PbSO4 reacted relative slowly. And since during the reacting process the particle size of PbSO4 reduced continuously, the reaction of generating lead citrate from PbSO4 fited well with the core-shrinking model. The leaching of PbSO4 in the citric acid and sodium citrate solution fited the kinetic equation:1-(1-a)1/3=Kt+B. The apparent activation energy was 67.82 kJ-mol"1 and the leaching process was controlled by chemical reaction procedure. Initial study indicates that about 40% of Fe entered in solution, while Sb can reach to 80% to the utmost extent.3. The conversion of lead paste in the acetic acid-sodium citrate systemThe product prepared by leaching of PbO, PbO2 and PbSO4 in acetic acid and sodium citrate solution was deduced to be Pb3(C6H5O7)2·3H2O by stoichiometry method. The optimal condition for leaching real lead paste was found to be:8:3 of mol ratio of acetic acid to total lead,4:3 of mol ratio of sodium citrate to total lead,2:1 of mol ratio of hydrogen peroxide to lead dioxide,1/5 as the starting paste/water ratio,2h of leaching time. The temperature increase had a positive impact on both desulphurization rate of lead paste and the morphology of the crystallized lead citrate. The smaller size of lead citrate particles (<5μm) was formed at room temperature, thus resulting on the difficulty in the filtration process. However recrystallization of the precursor could deal with the filtration difficulty by appropriately changing the particle size of the precursor resulting from optimizing the crystallizing duration and temperature. Moreover, the crystallizing process could remove the impurities into the filtrate which would lead to cleaner lead citrate precursor.4. Preparation of ultra-fine Lead oxide from lead citrateTG-FTIR analysis of the lead citrate precursor revealed that the thermal decomposition process of lead citrate in air was approximately divided into dewatering stage, main organic constituent decomposing stage and burning stage. TG-FTIR data of two kinds of lead citrate showed that dehydrating crystal water was the initial reaction of thermal decomposition, and subsequently organic matters were produccd within 200-280℃, the main products were CO2 thereafter. The final products from two kinds of lead citrate were mainly both PbO and Pb. Calcination temperature played a crucial role in the decomposition of lead citrate in air. The main product of Pb(C6H6O7)-H2O at relatively low temperature was a-PbO, (3-PbO and Pb, while at relatively higher temperature it was P-PbO. And if prolonging the calcination duration at the temperature of 400-450℃, Pb3O4 would be produced. And the calcinating products of Pb3(C6H5O7)2·3H2O at different temperature was similar with those of the Pb(C6H6O7)·H2O, except that no PbsO4 could be formed by prolonging the duration. Through electrochemical test by self-made micro-electrode, ultra-fine lead oxide has shown regular redox mechanism, good reversible property and cycle stability, which promised certain application prospect.The result of this study could guide the utilization of hydrometallurgy method on recycling of spent lead-acid battery; combining the traditional hydrometallurgy and the metal complexes theory would enrich the extraction and recovery of metal by using organic acid, it also could direct the hydrometallurgical recovery of other E-waste.