Study on the preparation of Mn–Zn soft magnetic ferrite powders from waste Zn–Mn dry batteries

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Abstract

Using waste Zn–Mn dry batteries, waste scrap iron and pyrolusite as raw materials, Mn–Zn soft magnetic ferrite powders were prepared through the process of simultaneous leaching, purification and co-precipitation. The experimental results indicated that the leached yields of Fe, Mn and Zn were 92.02%, 96.14% and 98.34%, respectively. The leached liquor was purified through these processes of sulfuration precipitation, fluorination precipitation and double salt precipitation deep purification process. Therefore, high removal yields of impurities could be achieved. Removal yields were as follows: Ca 99.7%, Mg 92.33%, Al 96.48%, Si 63.64%, Cu 99.86%, Pb 98.51%, Cd 53.0% and Ni 78.72%. Among these co-precipitation powders, the average mass content of the main components were Fe 41.41%, Mn 13.92% and Zn 4.49%, and the mass ratio of Fe:Zn:Mn was 69.2:23.3:7.5. Compared with the theoretical prescription (Fe:Mn:Zn = 67.3:24.4:8.3), the absolute errors of main components were Fe +1.9%, Mn −1.1% and Zn −0.8%. Because of content impurities in co-precipitation powders (Ca < 0.0028%, Mg < 0.0053%, Al < 0.0084%, SiO2 < 0.0023%, Pb < 0.0031% and Cu < 0.0010%), the qualities of these gained co-precipitation powders could compete with the demand for the preparation of soft magnetic ferrite. The magnetic properties also demonstrated that the soft magnetic ferrite samples, which were made from the co-precipitation powders prepared by used batteries, had the same qualities as PC30 made by the TDK Company.

Introduction

The environmental impact of mercury bearing in used batteries attracts much of the attention of the domestic media (Wang and Wang, 2003). It is a fact that used batteries can cause environmental pollution. However, we should understand that the main compositions of Zn–Mn waste dry batteries are iron, zinc and manganese (Nie, 2002). In addition, at the meeting of “the first high-tech forum of china environmental protection” held in Zhuhai and “the third academic seminar of environmental simulation and pollution control” held at the Tsing-Hua University, many environmental experts appealed that it was only one option in developing a recycle economy in order to implement a sustainable development strategy in China (Qian, 2003). A recycle economy is a type of ecological economy that has three principles: reduction, recycle and utilization. Hence, it is meaningful that spent batteries are treated as an important second resource and some novel methods on the utilization of spent batteries should be developed.

For years, many countries all over the world, according to their own specific characteristics, developed many kinds of treatment technologies for waste Zn–Mn dry batteries. These technologies were roughly divided into two types, pyrometallurgical processes and hydrometallurgical processes. In the case of the pyrometallurgical processes, such as the Japanese patent’s reports (Krondo, 2000, Oshima et al., 1997), the raw material of ferrite can be acquired and recycled by the reaction of crushing, roasting and magnetic separation (Yasunori et al., 1999), and manganese, zinc and mercury could be gained by vacuum-aided recycling system technology. In the case of the hydrometallurgical processes, zinc and manganese dioxide were prepared through processes of leaching, purification and electrolysis with waste Zn–Mn dry batteries (Zhong and Mei, 1988, Mauro et al., 1994, Cleusa et al., 2001). Xia introduced another method where mercury and plastics were first reclaimed by vacuum treatment and then the ferrite could be prepared from those remains through neutralization and oxidation reactions (Xia and Li, 2000). Generally, pyrometallurgical processes have certain economic benefits, but the roasting process can produce secondary pollution. Although we can avoid secondary pollution in a vacuum, pyrometallurgical processes are seldom used in industry because of the high cost of investment and operation. The utilization of hydrometallurgical processes is comprehensive, but the procedure is long and the reagent is heavily consumed. Wastewater discharged in hydrometallurgy processes may also cause secondary pollution. Thus, these disadvantages prevent the industrialization of the hydrometallurgy process. Therefore, it is necessary and meaningful to develop a new kind of technology having economic feasibility and environmental benefit conspicuous to deal with the waste Zn–Mn dry batteries.

Iron, manganese and zinc are not only the main components of waste Zn–Mn dry batteries, but they are also the main components of Mn–Zn soft magnetic ferrite. Therefore, based on a large amount of our research on the preparation of Mn–Zn soft magnetic ferrite (Peng and Tang, 2003, Tang et al., 2003), a study on the preparation of Mn–Zn soft magnetic powders from waste Zn–Mn dry batteries has been conducted. In this paper, the craft theories and conditions on preparation of Mn–Zn soft magnetic ferrite powders from waste Zn–Mn dry batteries has been investigated; and Mn–Zn soft magnetic ferrite powders, having a much lower impurities content, were successfully prepared.

Section snippets

Materials

Waste Zn–Mn dry batteries were collected from the Garbage Station of the Central South University. Pyrolusite was supplied from Hu’nan Xiangtan. Iron scraps were acquired from the Mechanical Plant of Central South University. The chemical analysis results of these raw materials are shown in Table 1.

Auxiliary reagents including ammonium sulfide, ammonium fluoride and ammonia were chemically pure. The ammonium acid carbonate was used for the agriculture. Manganese sulfate, zinc sulfate and

Flow chart

The experimental flow chart is given in Fig. 1.

Leaching process

First, the used batteries are dismantled into scrap and powder. In the leaching experiment process, H2SO4 is first poured and then pre-treated waste Zn–Mn dry batteries. Pyrolusites are slowly added and reacted for 2–3 h. In order to reduce Mn(IV) to Mn(II), iron scraps are finally added and allowed to react another 2–3 h. The final pH value is adjusted by milk of lime. In the primary stages of leaching, three main components of Fe, Mn and Zn are

Leaching process

According to these conditions (Peng and Tang, 2003, Tang et al., 2003), the leaching experiments are carried out. However, our studies focus on the condition tests of the amount of H2SO4 consumed and the time of the leaching procedure. The experimental results are shown in Fig. 2, Fig. 3.

From Fig. 2, Fig. 3, it can be seen that the leached yields of Zn, Fe and Mn increase gradually with the leaching time and as the amount of H2SO4 increases in molar excess. As the three main components approach

Conclusions

Based on our results, we make the following conclusions.

  • (1)

    The research demonstrates that high quality soft magnetic ferrite powders can be prepared from waste Zn–Mn dry batteries.

  • (2)

    Compared with the traditional ceramic method and co-precipitation method, this technology does not need to be separated into main components. Therefore, the production process and periods are simple, as well as the industrialization.

  • (3)

    The comprehensive utilization of the Fe, Mn and Zn in the waste Zn–Mn dry battery has

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