A new insight of recycling of spent Zn–Mn alkaline batteries: Synthesis of Zn_xMn_1−xO nanoparticles and solar light driven photocatalytic degradation of bisphenol A using them

Highlights

• Zn_0.5Mn_0.5O nanoparticles synthesized using SABs were cylinder with 60 nm diameter.

• Adsorption equilibrium of BPA on Zn_xMn_1−xO nanoparticles were achieved in 40 min.

• Decomposition yields of BPA were increased with light irradiation and Zn_xMn_1−xO nanoparticles.

• The findings have positive effects on solving the recycling of SABs.

Abstract

This work focuses on the synthesis of Zn_0.1Mn_0.9O, Zn_0.3Mn_0.7O, and Zn_0.5Mn_0.5O nanoparticles using Zn–Mn spent alkaline batteries (SABs) as raw materials and their applications for photocatalytic degradation of bisphenol A in water. Zn–Mn SABs were manually dismantled into scrap (including plastics, copper cap, zinc crust, and carbon rod) and powder. The mashed zinc crust and pretreated powder were successively added into H₂SO₄ and NH₃⋅H₂O, and the formed precipitates were characterized. The yield (wt) of synthesis of Zn_0.5Mn_0.5O (ZnMnO₃) nanoparticles was 57.1%. The synthesized Zn_0.5Mn_0.5O nanoparticles were cylinder, with a length of 60 nm. Afterwards, the removal efficiencies of bisphenol A (BPA) under solar light irradiation with the recovered Zn_xMn_1−xO nanoparticles were investigated: (1) the adsorption equilibrium of BPA on Zn_xMn_1−xO nanoparticles could be achieved after approximate 40 min. The saturation absorbance of BPA was about 32.40 ± 4.76 mg g⁻¹, 20.40 ± 3.60 mg g⁻¹, and 14.50 ± 4.55 mg g⁻¹ by Zn_0.1Mn_0.9O, Zn_0.3Mn_0.7O, and Zn_0.5Mn_0.5O nanoparticles, respectively; (2) compared with the 21.7 ± 1.6% degradation of BPA (only solar light irradiation for 180 min), the combination of solar light irradiation and Zn_0.1Mn_0.9O, Zn_0.3Mn_0.7O, and Zn_0.5Mn_0.5O nanoparticles could lead to 59.41 ± 4.32%, 83.43 ± 2.73%, and 71.22 ± 4.79% decomposition yields of BPA, respectively. These findings have positive effects on solving the recycling of SABs, decreasing the cost of catalysts, and the problem of organic pollutant in water.

Introduction

Zn–Mn alkaline batteries are usually used by the portable electronic devices requiring small electric power, such as radios, remote controls, cameras, and toys [1], [2], [3]. Since 2002, more than 15 billion Zn–Mn batteries have been produced annually in China [4]. Moreover, the world-wide consumption of batteries is also significant. Most of the spent alkaline batteries (SABs) are discarded as waste, although the SABs are classified as hazardous waste. Thus, the recycling of wasted batteries is significant not only to environmental safety and human health, but also in economical point of view to resource and materials.

To solve environmental problems and utilize secondary material resources, a great effort has been made to recycle the SABs in the last two decades [5], [6]. However, the recycling with an unadorned purpose of waste treatment is not an attractive business, particularly in developing countries where economic interests supersede environmental obligations. Some researchers have proposed the separation of valuable metals from Zn–Mn SABs with the application of phosphonic acid, phosphinic acid extractants, and trialkyl phosphine oxides [7]. Nevertheless, it is considered that these processes are not predominant for reducing the recycling cost. Most recovery of valuable metals from SABs is generally carried out by precipitation and thermal treatments via ammoniacal or acidic leaching processes to yield reusable oxides or ferrites [8], [9], [10]. Most of the methods of recovering valuable metal components from SABs do not necessarily catch the fancy due to limited applicability and low commercial value of the end product.

Recently, using SABs as raw materials to synthesize Zn–Mn ferrite magnetic materials has been developed owing to the presence of adequate amounts of Mn, Zn, and Fe in them. Zn–Mn ferrites are extensively used in transformers, electromagnetic gadgets, information storage systems, and biomedical devices because of their high magnetic permeability, saturation magnetization, dielectric resistivity and relatively low eddy current losses [11], [12]. However, it is worthy to note that the reactant contents have to be adjusted with lots of pure reagent when SABs were directly used as precursors. In addition, the synthetic process also affects the performance of Zn–Mn ferrites [13].

In our previous work, nano materials were successfully synthesized using some plants [14], [15], [16], [17], which could enhance the efficiencies of photocatalytic degradation on organic pollutant in water [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32]. In this work, a convenient synthesis of Zn_xMn_1−xO nanoparticles using Zn–Mn SABs was reported and the removal efficiencies of bisphenol A (BPA, an endocrine disruptor) under solar light irradiation with them were investigated. These findings cannot only reduce the cost and simplify the synthesis process of Zn_xMn_1−xO nanoparticles, but also have positive effects on solving the recycling of SABs as well as the problem of organic pollutant in water.