precious-metal-bearing fraction (PMB fraction)
Also known as: precious metal fraction · precious-metal fraction · PMB
Material streams generated from waste containing economically recoverable quantities of precious metals such as gold, silver, platinum, and palladium, typically sourced from electronic waste components.
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What is precious-metal-bearing fraction?
What it is
The precious-metal-bearing fraction refers to any material stream containing economically recoverable quantities of precious metals such as gold (Au), silver (Ag), platinum (Pt), and palladium (Pd) [5]. These fractions are typically generated from waste streams like e-waste, where these metals are used in small but critical components due to their conductivity and corrosion resistance [2][5].
How it works
The recovery process for precious metals from waste streams generally involves several stages. Initially, the waste material undergoes mechanical pre-processing, such as shredding, to liberate different material types. This creates a shredder light fraction (SLF), which can be rich in metals like copper, tin, lead, zinc, silver, and gold, alongside plastics and other non-metallic materials [2]. Subsequent steps often involve thermal or chemical treatments. Pyrolysis, a thermal decomposition process in the absence of oxygen, can be applied to SLF to separate organic components from metals, enriching the metal concentration in the solid residue [2]. This solid product, after pyrolysis, shows enriched concentrations of copper, zinc, lead, and precious metals, making them more amenable to industrial recovery processes [2]. Chemical methods, such as selective scavenging from aqueous solutions, can also be employed to concentrate precious metal ions down to very low levels [1][3].
Economics and operational realities
The economics of recovering precious metals from waste are driven by the fluctuating market prices of these commodities and the efficiency of the extraction processes. While e-waste contains valuable elements, their concentrations are often low, requiring high volumes of feedstock to yield meaningful quantities of recovered metals [5]. The initial capital expenditure for advanced recycling technologies, such as pyrolysis units or sophisticated chemical extraction systems, can be substantial. Operational costs include energy for thermal processes, chemicals for hydrometallurgical routes, and labor. The heterogeneity of waste streams, particularly e-waste, presents a challenge, as material composition can vary significantly, affecting process efficiency and the consistency of recovered outputs [2]. Margins can be thin due to these high processing costs relative to the low concentrations of target metals, especially when commodity prices are unfavorable. The decreasing concentration of precious metals in newer electronic devices, such as smartphones, further complicates the economic viability of recovery efforts over time [5].
precious-metal-bearing fraction across recycling sectors
How this plays out in practice, sector by sector.
E-waste recycling business
In the e-waste recycling sector, the precious-metal-bearing fraction is a primary driver for economic recovery, despite the low concentrations of these metals in individual devices. E-waste, or Waste Electrical and Electronic Equipment (WEEE), contains a range of valuable materials, with precious metals like gold, silver, palladium, and platinum being among the most valuable [5]. These metals are found in circuit boards, connectors, and other electronic components. The process typically begins with manual dismantling or mechanical shredding of e-waste to separate different material streams. The resulting metallic fractions, particularly those from printed circuit boards, are then processed further to concentrate and extract the precious metals. This often involves pyrometallurgical (high-temperature smelting) or hydrometallurgical (chemical leaching) methods. The operational economics are challenging due to the high volume of e-waste required to accumulate sufficient quantities of precious metals, the complexity of separating these metals from other materials, and the significant capital and operational costs associated with advanced recovery technologies. Price volatility of precious metals directly impacts the revenue generated, making consistent returns difficult. Furthermore, the trend of decreasing precious metal content in newer electronic devices, such as smartphones, means that recyclers need to process even larger volumes of waste to maintain recovery levels [5].
Lead Acid Battery Recycling
The term "precious-metal-bearing fraction" is generally not directly applicable to lead-acid battery recycling. Lead-acid batteries primarily contain lead, lead compounds, sulfuric acid, and plastics. While they are a significant waste stream requiring recycling due to their hazardous content and the value of lead, they do not typically contain precious metals in economically recoverable quantities. Therefore, the operational focus and economic drivers in lead-acid battery recycling are centered on the recovery of lead and plastics, rather than precious metals. The processes involved are designed for lead smelting and plastic reprocessing, not for the extraction of gold, silver, or platinum group metals.
Common questions about precious-metal-bearing fraction
Plain-English answers to what people most often ask.
How does the concentration of precious metals in e-waste affect recycling costs?
Is it economically sound to recover precious metals from all types of e-waste?
What are the main risks in recovering precious metals from e-waste?
Citations & references
Peer-reviewed and published sources underpinning this entry. Numbered markers [n] in the text above link here.
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Characteristics of Nanocomposites Formed on the Steel Surface Contacting with Precious Metal Solutions
O. M. Lavrynenko et al. · 2019
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The PGE-Au Mineralisation of the Skaergaard intrusion: precious metal minerals, petrography and ore genesis
N. Rudashevsky et al. · 2023
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