Introduction

China holds a leading position in the global production of electrolytic manganese. Approximately 80% of the world’s electrolytic manganese output comes from China. Currently, the amount of manganese slag accumulated in China has exceeded 100 million tons, and an additional 13 million tons are added each year, accounting for over 98% of the global output [1, 2]. The main distribution areas are Guangxi, Hunan, Guizhou, Yunnan, Chongqing, and Liaoning, which are rich in manganese resources. It is estimated that for every ton of manganese metal produced, approximately 7–10 tons of waste residue will be generated [3–5]. In China, most electrolytic manganese producers adopt the wet storage method to handle electrolytic manganese residues [6]. This open-air storage method not only consumes a large amount of land resources but also the harmful substances in the electrolytic manganese residues are highly likely to seep into the surrounding water bodies and soil, posing a serious threat to the local ecological environment [7, 8]. Therefore, it is particularly urgent to develop economic, efficient, and environmental-friendly technologies for the harmless and resourceful treatment of electrolytic manganese slag, to accelerate the processing of the accumulated electrolytic manganese slag, promote the sustainable development of China’s electrolytic manganese slag industry and related downstream industries, and thereby indirectly contribute to the growth of the regional economy [9]. Songtao County in Guizhou Province is rich in manganese resources and is part of the “Manganese Triangle” core area. In July 2021, the National Development and Reform Commission, the Ministry of Industry and Information Technology, the Ministry of Natural Resources, and the Ministry of Ecology and Environment jointly issued the “Notice on Strengthening Manganese Pollution Control and Promoting the Adjustment of the Manganese Industry Structure.” In November of the same year, the “Opinions on Deepening the Battle Against Pollution Prevention and Control” issued by the Central Committee of the Communist Party of China and the State Council clearly proposed to comprehensively improve the pollution control in the “Manganese Triangle” area in the Wuling Mountains region at the junction of Chongqing, Hunan and Guizhou provinces. On March 27, 2022, the Ministry of Ecology and Environment released the “Technical Specifications for Pollution Control of Manganese Sludge,” which is the first national ecological environment standard in China specifically formulated for the pollution control technology of manganese sludge. This specification details the pollution control technical requirements for manganese sludge during collection, storage, transportation, pre-treatment, utilization, filling, backfilling, and landfilling, as well as the relevant requirements for monitoring and environmental management. Manganese slag belongs to the second category of general industrial solid waste. Its moisture content ranges from 20% to 30%. It contains a large amount of soluble sulfates such as manganese sulfate and ammonium sulfate, as well as heavy metals such as zinc, copper, nickel, and cobalt. The composition is complex and the treatment is very difficult [10, 11]. With the rapid development of industries such as metallurgy, coal mining, and forging, a large amount of industrial solid waste such as slag, steel slag, and fly ash has been produced. Due to the failure to handle and utilize them in a timely and effective manner, they have been discarded and piled up disorderly. Therefore, the goal proposed by the Guizhou Provincial People’s Government in the “Guizhou Province’s 14th Five-Year Plan for National Economic and Social Development and Long-Term Goals until 2035”—that “by 2025, the comprehensive utilization rate of industrial solid waste will reach 70%”—allows for the harmless disposal and comprehensive utilization of the filter residue from electrolytic manganese production, which can absorb a large amount of electrolytic manganese waste and turn it into a resource, aligning with national policy directions and the development plans of Guizhou Province [12].