Recovery of Precious- & Rare Metals from Electric Wastes
and Industrial By-products ; Focusing on Circular Economy

(폐기물과 부산물로부터 귀금속 및 희소금속 회수에 관한 기초연구 ; 순환경제의 구현 )

Massive recycling of waste mobile phones: Pyrolysis, physical treatment, and pyrometallurgical processing of insoluble residue

(Park et al.; ACS Sustain. Chem. & Eng., 2019, vol.7, pp.14119-14125)

Waste of electrical and electronic equipment (WEEE) has diversified due to the rapid development of the information technology (IT) industry. Specifically, a significant amount of mobile phones are thrown away because technical trends lead to the faster replacement of goods. The reuse or repair of mobile phones has long been in decline due to rising product complexity and shortened life cycles. Unlike general waste, waste mobile phones (WMP) include various heavy metals and hazardous substances. Lead, cadmium, mercury, PVC, and halogenated flame retardants are examples of those that pollute the environment. Mobile phones also contain significant amounts of resource materials derived from precious metals, carbonaceous materials, and inorganic parts. Valuable metals can be recovered from the lead frame (copper), solder (lead and tin), case (iron and aluminum), and IC chip (gold, silver, and palladium), which particularly increases the recycling rate of mobile phones.5 Among the various parts, printed circuit boards (PCBs) are considered to be essential to the urban mine industry due to integrated platinum group metals (PGMs). The global recycling of waste PCBs is mainly concentrated in Asia. The current recycling status of PCBs in China and South Korea were reviewed in recent publications.
The smelting treatment of insoluble residue was mainly covered to simulate the recovery procedure of precious metals in the molten state. Slag composition was controlled by incorporating different compositions of synthetic fluxes. Recovery rate was significantly influenced by the terminal velocity of metal particles in the liquid slag in association with slag viscosity and silicate structures.
Oxide composition of insoluble residue, different fluxes (A, B, and C), and prospected slag compositions illustrated in the CaO−Al2O3−SiO2 ternary phase diagram at 1500 °C.
Material flow from experimental results calculated as complete leaching of PCB and smelting process of insoluble residue through slag C.

Thermodynamics of gold dissolution behavior in CaO-SiO2-Al2O3-MgOsat Slag System

(Han, Swinbourne and Park; Metall. Mater. Trans. B, 2015, vol.46B, pp.2449-2557)

Gold is a bright yellow, dense, soft, malleable, and ductile metal and has been a valuable and highly sought-after precious metal for coinage jewelry and other arts since long before the beginning of recorded history. Physically, gold is the most ductile of all metals, is a good conductor of heat and electricity, and reflects infrared radiation strongly. Chemically, it does not react with water, dry or humid air, and most corrosive reagents, so these are the reasons why it is well suited for use in coins and jewelry and as a protective coating on other more reactive metals.
Consequently, in the present study, gold solubility in the CaO-SiO2-Al2O3-MgOsat slag system was measured at 1773 K at pO2 = 10-10 atm to pO2 = 10-8 atm using a CO–CO2 gas mixture over a wide range of compositions, i.e., 8 to 40 mass pct CaO, 26 to 50 mass pct SiO2, and 0 to 36 mass pct Al2O3, to determine the dissolution mechanism of gold in the calcium silicate-based slags.
Iso-gold solubility contours in the CaO-SiO2-Al2O3-MgOsat system at 1773 K.

Thermodynamics of Indium Dissolution Behavior in FeO-bearing Metallurgical Slags

(Han and Park; Metall. Mater. Trans. B, 2015, vol.46B, pp.235-242)

Indium (In) represents a minor percentage of the earth’s crust. Its concentration is comparable to that of silver, which is about 0.1 mass ppm, and ranges from 50 to 200 ppb in the earth’s crust. The average indium content in zinc deposits ranges from less than 1 to 100 ppm. Indium is usually produced as a minor by-product in the lead and zinc smelting and refining processes. It is a rare and valuable metal that is used in a variety of industrial applications, such as liquid crystal displays (LCDs), semiconductors, low-temperature solders, infrared photodetectors, and solar cells.
Low-cost FeO-bearing metallurgical slags are more interesting than synthetic CaO-SiO2-Al2O3 slag for pyrometallurgical processing of In-containing waste materials. Nevertheless, the indium dissolution behavior in FeO-bearing metallurgical slags is controversial. Because the fayalite slags can be easily obtained from copper smelters after smelting, the FeO-bearing slag system can potentially be used as an economic flux in pyro-recycling. Therefore, in the current study, indium solubility in the FeO-SiO2-Al2O3-CaO-MgOsat slag system was measured at 1573 K using a CO-CO2 gas mixture over a wide range of compositions to determine the dissolution mechanism of indium in FeO-bearing slags.
Iso-indium solubility contours in the FeO-SiO2-Al2O3-5CaO-MgOsat slag system at 1573 K.

Dissolution Behavior of Indium in CaO-SiO2-Al2O3 Slag

(Ko and Park; Metall. Mater. Trans. B, 2011, vol.42B, pp. 1224-1230)

Indium is usually produced as a minor by-product of Pb and Zn smelting and refining processes. Primary production peaked at just over 600t in 2007, falling back to around 520t in 2009. China has emerged as the world’s leading producer of indium, as its output has increased from 73t in 1999 to a peak of 320t in 2006. In 2009, China accounted for just over half of the total world output of indium. Growth in demand has prompted an increase in recycling; indium is most commonly recovered from ITO sputtering targets and LCD screens, which are its main applications. It is also used in low melting point alloys and compound semiconductors. Recently, the pyro- and hydrometallurgical recycling of indium-containing electric parts and dental materials has been termed “urban mining” due to the very high cost and scarcity of indium. However, the mechanism of indium dissolution into slags and fluxes, which is crucial for determining the operating parameters, is not fully understood.
The literature contains only two experimental studies on the distribution of indium between Pb and slags. The dissolution mechanism of indium, however, was not established in these experiments.
In the present study, therefore, the solubility of indium in the CaO-SiO2-Al2O3 slag was measured at 1773 K (1500 oC) and under a highly reducing atmosphere over a wide range of compositions within the liquid area in the slag system in order to elucidate the dissolution mechanism of indium in metallurgical slags under reducing conditions.
Iso-indium solubility contours in the CaO-SiO2-Al2O3 system at 1773 K.