1. Introduction
Tellurium is majorly used as an alloying element [
1] in the production of free-machining low-carbon steel and copper alloys to enhance its machinability without altering the conductivity. Tellurium-based catalysts are mainly employed for hydrogenation, oxidation, and halogenation reactions of organic compounds. Tellurium compounds are applied in the processing of rubber-based compounds as vulcanizing, accelerating agents, and batteries [
2]. It has also been widely used in cadmium tellurium-based solar cells [
3]. Tellurium, as mercury cadmium telluride, is utilized in thermal imaging applications as a sensor material. Tellurium in its very pure form is used for electronic applications. Large-scale commercial production of CdTe solar panels and Bi
2Te
3 in refrigeration technologies in recent years has significantly increased the demand for tellurium [
4]. The world reserves of tellurium are 24,000 tons contained mostly in copper resources. The average world production of tellurium is estimated at 450–500 tons per year [
5]. Tellurium is majorly produced in the United States, Peru, Japan, and Canada. Processing 500 tons of copper ore usually produces 1 pound (0.45 kg) of tellurium. Tellurium’s main source is the anode slime produced during the electrolytic refining of blister copper. Tellurium and selenium were separated using the copper cementation technique [
6].
Halli et al. [
7] studied the electrochemical recovery of tellurium from metallurgical industrial waste. The highest tellurium recovery through pregnant leach solution via electrowinning is 55 wt% purity in the produced deposits, whereas electro-deposition followed by spontaneous redox replacement is 64 wt%. The processing of cemented telluride has been carried out through a hydrometallurgical process with minimal discharge from copper refining. Rheea et al. [
8] recovered tellurium through a series of unit operations involving leaching, precipitation, and electro-winning steps. Yue et al. [
9] fabricated a hierarchical hybrid membrane for efficient recovery of tellurium from photovoltaic waste.
Li et al. [
10] studied the leaching behavior of metals via an alkali fusion-leaching route from copper anode slime for the preliminary separation of metal values. Under optimal conditions, leaching recoveries of nearly 97% Se, 98% As, 86% Sn, and 76% Pb were achieved under optimal conditions leaving the platinum, silver, gold, and tellurium values in the residue.
Gómez-Gómez et al. [
11] synthesized tellurium-based nanoparticles and concluded that Te nanoparticles strongly affect biofilm biomass. An efficient and cost-effective radiochemical technique was developed by Sankha Chattopadhyay and Sujata Saha Das [
12] to separate tellurium from reactor-irradiated TeO
2 targets with good yield and high quality.
Jin et al. [
13] studied the electrochemical recovery of fine tellurium powder from hydrochloric acid media via mass transfer enhancement. A turbulent cylindrical reactor having a large surface area cathode was employed for the recovery of tellurium as microscale Te powder from dilute solution with a recovery rate of 96.1% and a current efficiency of 84.3% while effectively suppressing the undesired reactions of chlorine generation and TeO
2 production. Fan et al. [
14] found out the conditions for sodium hydroxide leaching of tellurium with a solid to liquid ratio of 1:6 and free caustic concentration in a solution of 30–40 g/L, with a temperature of 120 °C. Fan et al. [
15] extracted high-purity bismuth along with tellurium while treating the residue of zinc anode slime by sulfation roasting, leaching, and electro-deposition processes.
Guo et al. [
16] have investigated the recovery of Te from high tellurium-bearing resources by leaching using alkaline sulfide followed by sodium sulfate precipitation. More than 90% Sb and Te leaching efficiency was achieved under optimal conditions. Furthermore, with respect to other metals, such as antimony, arsenic, and cadmium, leaching and releasing studies have been reported by several authors [
17,
18,
19,
20], which is summarized briefly in this section. Antimony release characteristics of blast furnace slag, mining waste rock, and tailing sand were investigated in static immersion and dynamic leaching tests by Ren et al. [
17] and they concluded that the Sb release capacity of the three samples was in descending order of tailing sand, blast furnace slag, and mining waste rock. Zhang et al. [
18] studied the leaching and releasing characteristics and regularities of antimony and arsenic from antimony mining waste rocks, blast furnace slags, and tailings. It was suggested that a lower solid–liquid ratio and small particle size improve the leaching efficiency. The concentration of heavy metals, chemical speciation, and leaching characteristics of antimony ore tailings was analyzed by Zhou et al. [
19]. The results show that the concentrations of Sb, As, and Hg in the leachates increased with increasing solid–liquid ratio, decreasing particle size, and increasing temperature. Meng et al. [
20] aimed to identify the microbes involved in regulating Cd solubility and reveal possible mechanisms. It has been reported that anaerobic microbes, such as anaerolineaceae played an important role in shaping the microbial community in soil and regulating the Cd solubility.
The continuous removal and recovery of tellurium in an up-flow anaerobic granular sludge bed reactor were reported to recover Te from very dilute solutions (Mal et al. [
21]). Recovery of tellurium from de-copperizing leach solution of copper refinery slimes by a fixed bed reactor packed with copper cuttings was studied [
22]. This study showed to enhance the recovery of copper telluride from a de-copperizing leach solution at 80–90 °C temperature and linear velocity of 3.7 cm/s. Recycling of copper telluride from copper anode slime processing was reported by Xu et al. [
23] and Xu et al. [
24]. Tellurium and copper were selectively recovered from copper telluride through hydrothermal leaching under the optimized conditions of 5 mol/L NaOH, 5:1 liquid to solid ratio, 150 °C temperature, and 2 h reaction time. During this process, copper was enriched in the solid residue as copper oxide, and more than 95% of tellurium was selectively dissolved in the solution. Recovery of tellurium from aqueous solutions by adsorption with magnetic nanoscale zero-valent iron is reported by Yu et al. [
25] and from chloride solutions using tri-iso-octylamine by Mandal et al. [
26].
Even though several researchers tried to recover tellurium from different raw materials to the best of our knowledge, there is no attempt to develop a process flowsheet to recover tellurium from waste anode slime having high tellurium concentration. In this study, optimum conditions were developed to recover Te and Cu from anode slime having the following composition Cu: 31.8%, Te: 24.7%, and As: 0.96%, towards a sustainable copper mining industry.