| Due to stable performance and low price, lead-acid batteries still occupy more than50%market share of secondary battery. At present, spent lead-acid batteries are mostly be recycled by pyrometallurgical process which has the risk of environmental pollution. Our group previously researched on converting spent lead paste into superfine leady oxide powder by calcination at low temperature of lead citrate precursor obtained in citric acid/sodium citrate leaching system. The leady oxide powder can be directly used to prepare active materials of new lead-acid batteries. But there are large amounts of impurities such as Fe, Sb, Cu, Zn and so on exist in the spent lead paste. For hydrometallurgy of recovering lead-acid battery current,the method of removing impurity has rarely been studied. A lot of impurities such as Fe, Sb, Cu, and Zn will enter the waste paste and residues in leady oxide powder affect the lead-acid battery performance. Therefore, the transformation of these impurities and their impacts on the electrochemical performance of the battery are needed to be further studied. Based on these key issues, much research has been done and the main achievements in this thesis include:1. Comparison of the properties of leady oxide powder prepared by leaching of simulated lead paste and traditional leady oxide powderAccording to the composition of spent paste, simulated lead paste was confected using analytical reagents (65%PbSO4,29.5%PbO2,4.5%PbO,0.5%Pb). The simulated paste was leached with citric acid/sodium citrate system to obtain lead citrate, which was then roasted at375℃to generate novel leady oxide powder. The physical and electrochemical properties of novel leady oxide powder were compared with traditional leady oxide powder. The water absorption value of novel leady oxide powder is220mL/kg, oxidation degree is81%, acid absorption value is0.256g/g, apparent specific gravity is1.612g/cm3and average particle size is0.831μm. The water adsorption value of novel leady oxide powder is two times of traditional powder but the particle size is far smaller than the traditional powder. Novel leady oxide powder and traditional leady oxide powder were prepared to2Ah batteries. For novel leady oxide powder,20h rate discharge capacity is3.204Ah,1C rate discharge time is53.82min and the capacity retention rate is less than 80%after150cycles. The results include that novel leady oxide powder shows far greater initial discharge capacity but poorer cyclic performance than traditional leady oxide powder.2. The transformation of Fe in the leaching process and its impacts on battery performance and failure mechanismContent of Fe in the waste paste is0.157%. First, the transformation rule of Fe2O3/Fe3O4in different ratios of citric acid/sodium citrate (different pH) was studied. Leaching pH has little effect on reaction of Fe2O3/Fe3O4with citric acid/sodium citrate. The ratios of ferric oxide and ferroferric oxide in the filtrate are relative high as13.2%and10.4%when pH is around3-4.Fe2O3/Te3O4were introduced into simulated lead paste with the weight ratio of Fe to lead paste as0.01%,0.05%,0.1%,0.5%and1%. The transformation rule of Fe in the leaching system of citric acid/sodium citrate and residual amount in leady oxide powder were studied. Fe transfers into the filtrate to a larger extent when the content in the lead paste is lesser. The properties of leady oxide powder obtained from lead paste with Fe are similar to the leady oxide powder from pure simulated lead paste. The results of CV tests indicate that Fe has a negative effect on the self-discharge of leady oxide powder.The leady oxide powder with Fe was prepared to2Ah battery to investigate the impacts of Fe on battery performance. The results are as follows:For Fe, the higher content is, the poorer battery performance is. When the content of Fe reaches1%,20h rate discharge capacity reduces to1.817Ah,1C rate discharge time reduces to36.09min, discharge capacity loss is23.56%and the capacity decays to80%of the initial capacity after20cycles. Through dismantling the spent batteries with Fe, it can be concluded that the variable valences of Fe will form micro-cell inside the battery which result in the generation of large amount of irreversible lead sulfate and leads to the degradation of cycle performance of battery.3. The transformation of Sb in the leaching process and its impacts on battery performance and failure mechanismContent of Sb in the waste paste is0.202%. First, the transformation rule of Sb in different ratios of citric acid/sodium citrate was studied. Leaching pH has a certain influence on reaction of antinomy with citric acid/sodium citrate:The lower pH is, the less the reaction of Sb is. When pH is1, the ratio is the highest as71.39%.Sb were introduced into simulated lead paste with the weight ratio of Sb to lead paste as0.01%,0.05%,0.1%,0.5%and1%. The transformation rule of Sb in the leaching system of citric acid/sodium citrate and residual amount in leady oxide powder were studied. Sb transfers into the filtrate to a larger extent when the content in the lead paste is lesser. The properties of leady oxide powder obtained from lead paste with Sb are similar to the leady oxide powder from pure simulated lead paste. The results of CV tests indicate that Sb promotes the increase of PbO2reduction peak which is conducive to the formation of PbO2.The leady oxide powder with Sb was prepared to2Ah battery to investigate the impacts of Sb on battery performance. The results are as follows:For Sb, when the content of Sb is less than or equal to0.5%, cycle life increases with the increase of content, and the battery capacity retention rate remains at around80%after160cycles. Through dismantling spent batteries with Sb, it can be concluded that less content of Sb can impede the growth of PbO2, but high content of Sb will generate a-PbO2, which easily generates a large number of irreversible lead sulfate and leads to the cycle performance of battery degradation. Sb in electrolyte will make negative self discharge.4. The transformation of Cu in the leaching process and its impacts on battery performance and failure mechanismContent of Cu in the waste paste is0.001%. First, the transformation rule of CuO in different ratios of citric acid/sodium citrate was studied. Leaching pH has little effect on reaction of CuO with citric acid/sodium citrate. The ratio of CuO in the filtrate increases with the decrease of pH; when pH is1, the ratio is the highest as17.88%.CuO were introduced into simulated lead paste with the weight ratio of Cu to lead paste as0.01%,0.05%,0.1%,0.5%and1%. The transformation rule of Cu in the leaching system of citric acid/sodium citrate and residual amount in leady oxide powder were studied. Cu transfers into the filtrate to a larger extent when the content in the lead paste is lesser. The properties of leady oxide powder obtained from lead paste with Cu are similar to the leady oxide powder from pure simulated lead paste. The results of CV tests indicate that Cu promotes the increase of oxygen peak.The leady oxide powder with Cu was prepared to2Ah battery to investigate the impacts of Cu on battery performance. The results are as follows:Cu does not significantly affect2h rate discharge capacity,1C rate discharge time and cycle performance of battery. But the self-discharge capacity loss increases as the amount of Cu increases. When the content of Cu is1%, the loss of capacity is17.06%. Through dismantling the spent batteries with Cu, it can be concluded that Cu on the positive plate has no effect the active substance. Cu in electrolyte will make negative self discharge.5. The transformation of Zn in the leaching process and its impacts on battery performance and failure mechanismContent of Zn in the waste paste is0.001%. First, the transformation rule of ZnO in different ratios of citric acid/sodium citrate was studied. Leaching pH has a great influence on reaction of ZnO with citric acid/sodium citrate:ZnO is leached entirely into filtrate when pH is between1and5and only part ofZnO is reacted when pH is between5and8.ZnO were introduced into simulated lead paste with the weight ratio of Zn to lead paste as0.01%,0.05%,0.1%,0.5%and1%. The transformation rule of Zn in the leaching system of citric acid/sodium citrate and residual amount in leady oxide powder were studied. Zn transfers into the filtrate to a larger extent when the content in the lead paste is lesser. The properties of leady oxide powder obtained from lead paste with Zn are similar to the leady oxide powder from pure simulated lead paste. The results of CV tests indicate that Zn promotes the increase of PbO2reduction peak which is conducive to the formation of PbO2.The leady oxide powder with Zn was prepared to2Ah battery to investigate the impacts of Zn on battery performance. The results are as follows:When the content of Zn is0.1%, the battery capacity retention rate remains at around80%after200cycles. When the content of Zn is over0.1%and content of Sb is over0.5%, the cycle performance of battery gets poorer. Through dismantling the spent batteries with Zn and solification, formationg, it can be concluded that less content of Zn is liable to generate4BS(4PbO-PbSO4) in the formation procedure which is good for cycle performance, but high content of Zn will generate3BS(3PbO-PbSO4) in the formation procedure which is not good for cycle performance. Zn in electrolyte can protect the negative plate.6.Analysis of the impacts of impurities in actual spent lead paste on battery performanceThe performance of battery made by leady oxide powder prepared from spent lead paste was studied. It was found that the20h rate discharge capacity is1.834Ah,1C rate discharge time is39min and the capacity decays to less than80%after3Ocycles. So to remove the impurities in the lead paste is necessary. |
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