The recycling of printed circuit boards (PCBs) is one of the most technically complex and strategically important activities within the industrial circular economy. PCBs are composite materials in which high-value metals such as copper, aluminum, tin, and precious metals are embedded in a fiberglass and epoxy resin matrix. Stokkermill technology addresses this complexity through a dry refining process, designed to recover metals from electronic waste without chemical treatments, fully aligned with environmental and industrial standards in the United States.
The core of the PCB recycling process is impact delamination, carried out using an Impact Mill (IM). Unlike traditional blade shredding systems, the impact mill does not cut the material. Instead, it applies high-energy impact forces. PCB fragments are accelerated at high speed and projected against armored surfaces, exploiting the different elastic behavior of the materials involved.
The inert matrix, composed of fiberglass and epoxy resin, is rigid and brittle and therefore pulverizes instantly upon impact. Metals, due to their ductility, absorb the impact energy through plastic deformation. Copper, aluminum, and tin detach cleanly from the substrate without breaking, forming compact, spheroidal metal granules. This process produces free, clean metal particles with preserved density and commercial value, free from organic contamination.
Material discharged from the impact mill is ideally suited for gravity separation, thanks to the significant density and shape differences between metal granules and inert powder. Gravity separation tables efficiently exploit these physical characteristics to separate heavy metals from light non-metallic fractions.
During this stage, most plastics and fiberglass are removed, reducing the overall material volume by approximately 80%. The heavy fraction is concentrated into a single stream, producing a mixed metal concentrate consisting of copper, aluminum, and precious metals. This output is already plastic-free and is widely accepted by U.S. and international smelters as a high-grade mixed metal feedstock.
For operations aiming to maximize the economic value of recycled PCBs, the process can be enhanced with an optical metal sorting module. This technology is particularly effective on fine particle sizes, where traditional eddy current separators lose efficiency.
The mixed metal concentrate is analyzed by high-resolution optical scanners operating on the RGB color spectrum. Each individual particle is identified by its color and directed into the appropriate sorting channel. This allows the recovery of high-purity copper, clean aluminum, and a separate fraction containing brass and gold-plated contacts. The final result is metal outputs with purity levels exceeding 99%, ready for direct melting and offering maximum market value.
In the United States, chemical PCB refining involves high capital and operating costs related to environmental permitting, hazardous chemical handling, emissions control, and fixed operational expenses that are largely independent of throughput. For this reason, Stokkermill technology intentionally stops at the production of a high-grade metal concentrate, positioning itself at the most economically efficient point in the recycling chain.
The dry refining approach eliminates chemical risks, significantly reduces operational complexity, and supplies smelters with a clean, concentrated feedstock that can be processed at peak efficiency.
