## 1 Introduction  
Copper was one of the first metals processed by humans and has been an important material in the development of civilization. Copper has become a major industrial metal, ranking third after iron and aluminum in terms of quantities consumed. Copper anode slime (CAS) is an important industrial by-product generated at the bottom of electrorefining tanks during copper electrolytic refining, and contains significant amounts of gold, silver, selenium, tellurium, platinum-group precious metals and lead, bismuth, antimony, copper, and other valuable metals. Therefore, CAS is one of the main raw materials for the extraction of rare precious metals [1]. China is a major copper-producing and copper-consuming country. According to the United States Geological Survey, the global production of refined copper in 2021 was 26,000 billion tons, and China produced 10,000 billion tons of refined copper [2]. Almost all of China's known silver resources are associated with non-ferrous metals, of which lead and zinc deposits account for 51.4% and copper deposits account for 34.9% [3]. In the first quarter of 2022, raw gold production within China reached 83.401 tons, of which 65.009 tons was mineral gold and 18.392 tons was non-ferrous by-product gold [4]. The production of copper, lead, and other non-ferrous metals is steadily growing, and the by-products of their refining processes have become important raw materials for the extraction of gold, silver, and other valuable metals [5]. Table 1 lists the composition of CAS from various refineries and regions. The high contents of heavy metals in CAS indicate that it is an important raw material for the extraction of precious metals [6]. On one hand, the recovery of metals from CAS can bring considerable economic benefits. On the other hand, CAS is a kind of hazardous waste, in which heavy metals such as Cd, Pb, and As may cause an environmental and ecological threat [7]. Therefore, it is necessary to develop novel green technologies for PMs recovery from CAS with the constraints of environmental regulations and the requirements in revenue increase. The key to all methods is to achieve the separation of precious metals (gold, silver, etc.) from valuable metals (lead, bismuth, etc.). The prominent approaches that have been developed to treat CAS include the traditional pyrometallurgical process, combined Kaldor furnace dressing-metallurgy method, hydrometallurgical methods, and combined pyrometallurgical and hydrometallurgical half-wet method. The pyrometallurgical process is currently the mainstream process because of its large processing capacity and strong adaptability to a variety of raw materials. First, a precious metal lead alloy is produced by high-temperature reduction smeling. Subsequently, the obtained alloy is oxidized and smelled to remove Pb and produce a Au-Ag-Pt alloy. Finally, Ag and Au are obtained by electrolysis. However, this method is usually characterized by high energy consumption, low purity of the recovered Ag, and air pollution during recycling (including SO\({}_{2}\), PbO, As\({}_{2}\)O\({}_{3}\), and Sb in the soot). In recent years, an improvement to the traditional firing process, i.e., the Kaldor furnace process [16], as well as the vacuum distillation process were developed. The Kaldor furnace process is used to complete the reduction and oxidation of anode slime in a Kaldor furnace. This method has advantages such as equipment processing capacity, short operation time, less metal backlog, low energy consumption, small amount of flue gas, and good operating environment. However, the equipment investment is high, and the furnace charge return volume increases the cost of late slag treatment [16; 17]. A previous study developed an integrated hydrometallurgical process consisting of leaching, solvent extraction, and cementation. The leaching agent was HCl + H\({}_{2}\)O\({}_{2}\), and the extractants included Cyanex272 and LIX 63. The overall recoveries of Au and Ag from anode slime were 91.4% and 96.9%, respectively [18].