Research On The Theory And Technology Of The Flue Gas Desulfuirzation Process By Spent Zn-MnO₂Batteires

Zn-MnO₂batteries still account for a considerable share in the field ofdry battery consumption markets because of the lower price and they aredifficult to be replaced completely by other kinds of batteries, although theircapacity is lower compared with alkaline manganese batteries. As all kinds ofbatteries have a problem of serving life, the number of large waste batterieswill increase with the creasing consumption of batteries, and there is onexception of Zn-MnO₂batteries. Therefore, researches on recycling of spentZn-MnO₂batteries as second resources can not only reduce environmentalpollution, but also meet the requirements of sustainable development. Theemission of the flue gas containing sulfur dioxide is one of the most importantreasons that cause atmospheric pollution, even acid rain disaster. Therefore,eliminate or reduce the atmospheric pollution caused by SO₂gas emission hasbecome an important global issue.This article has discussed the history and current situation of recyclingof spent Zn-MnO₂batteries and the flue gas desulfurization technology, andsummarized the advantages and disadvantages of existing technology. In viewof recent reports about the recycling of spent Zn-MnO₂batteries which oftenfocus on the recovery of Mn and Zn products and are lack of the fullutilization of the electrolyte, and so on, spent Zn-MnO₂batteries are selectedas raw materials and the feasibility of desulfurization is verified on the basisof phase analysis of spent Zn-MnO₂batteries cathode, anode and electrolyte,the absorption mechanism is analyzed. Then the absorption capacity ofdifferent absorption solutions are compared which are obtained by dealt withthe cathode material from spent batteries under different conditions, and thefiltrate obtained by ammonia wash the cathode materials as absorptionsolution is the best choice. Meanwhile, the influence of temperature on SO₂absorption efficiency is investigated and the absorption of different depth ofdischarge of spent Zn-MnO₂batteries is compared. The results show that: thecathode of spent batteries mainly consists of a mixture of α-MnO₂, Mn₂O₃Mn₃O₄phase and minor Zn(NH₃)₂Cl₂,ZnCl2phase. However, ZnCl2willdisappear after washed by distilled water. The surface morphologyobservation results show that the cathode materials are formed by crystalaggregates with different size, and the crystal aggregates are formed by a great mount of micropores and micrparticles. There are many rocks ofparticles with different size on the negative electrode surface, which areverified mainly to be unsolvable zinc complexes Zn(NH₃)₂Cl₂. The electrolyteof spent Zn-MnO₂batteries is of weak alkaline, which verifies the feasibilityof absorbing SO₂using spent batteries. Furthermore, the solution obtained bywashing the positive electrode with low concentration ammonia is of muchbetter desulfurization efficiency than that with distilled water directly, and isvery similar to conventional ammonia desulfurization, and40℃is theoptimum to absorb SO₂at a range of30-70℃. The cathode active material ofnew batteries is α-MnO₂, besides that, Mn₂O₃Mn₃O₄phase also appear inspent batteries with different depth of discharge. With the increase of depth ofdischarge, a series of weak peaks are discovered, the main peaks becomelower and move rightwards slightly; the surface of most particles becomesmore and more roughly and the gaps between microparticles become biggerrelatively in the cathode materials. Meanwhile, the relative content of zinccompounds increases slightly according to EDS. The experiments of SO₂absorption show that the more serious the depth of discharge is, the better thedesulfurization efficiency will be.