The Study On The Lead Paste Desulphurization Process Of Damped Lead Acid Battery In A Rotating Packed Bed Reactor

Lead paste as the major composition in damped batteries has an important role in the process of lead recycling. Lead acid batteries which are improperly disposed of will corrode and contaminate the soil and the ground water. Therefore, it is necessary to improve pathways for recycling them, which is related not only to the sustainable development of lead acid battery industry, but also the reduction of the lead pollution to the environment and human health. However, low liquid-solid mass transfer rate in conventional reactors leads to the significant limitation for industrial application of Pb-paste desulphurization using hydrometallurgical process. In this article, Pb-paste desulphurization in a rotating packed bed (RPB) reactor, a reactor with high mass transfer performance, is firstly reported. It was found that RPB markedly intensified the desulphurization process in a very short contact time, within a second, thereby achieving a continuous desulphurization process. Furthermore, the mechanism of desulphurization process was investigated by the theory analysis of micromixing and mass transfer mechanism in the RPB. The main contents and findings are summarized as followed:1. The desulphurization process was investigated in stirred tank reactor (STR) with sodium carbonate and sodium hydroxide as the desulphurization transforming agents and lead sulfate (PbSO4) as the raw material. The effects including concentration, the molar ratio of desulphurization agent and PbSO4, temperature on the desulphurization process were explored. The results indicated that the increase of desulphurization agent concentration and the molar ratio was beneficial to the process. When the desulphurization agent had an excess of 20%, the best desulphurization degree could be achieved. Temperature had only a small affect. It took 12 min (720 s) or 6 min (360 s) to make the desulphurization degree reach 99.7% or 99.5% by using sodium carbonate and sodium hydroxide.2. The desulphurization process of PbSO4 was further performed by using RPB as a reactor. The effects of rotating speed, feeding flow, molar ratio, agent concentration and temperature and were studied. The results showed that the desulphurization degree increased with the increase of desulphurization agent concentration, rotating speed and feeding flow rate. The optimum desulphurization conditions were the rotating speed of 1500 rpm and the feeding flow of 1100 mL/min. Temperature had an obvious effect on the desulphurization degree only at a low reactant concentration. In a very short contact time, within a second, only one cycle liquid-solid contact could make the desulphurization degrees of PbSO4 reached 99.5% when Na2CO3 had an excess of 20% and NaOH had a reaction with a theoretical stoichiometric ratio. As compared to STR, it was greatly shortened by at least 2 orders of magnitude.3. Based on the above optimum results, the desulphurization process of real lead paste was investigated in the RPB. It was found that it took 10 min (600 s) or 14 min (840 s) for STR to make the desulphurization reach 97% or 99% by using sodium carbonate and sodium hydroxide as desulphurization agents and a homogenizer rotating speed of 9000 rpm. However, to obtain the same desulphurization degree, the desulphurization time in the RPB with a rotating speed of 1500 rpm is less than 1 s, which is greatly shortened by at least 2 orders of magnitude.The results proved that the RPB reactor could greatly intensify the desulphurization process of lead paste, and it exhibited a great potential for the industrial application of lead paste desulphurization.