PCB design and manufacturing coincides with social and ecological responsibility.
PCB recycling processes must meet global requirements and comply with global directives.
Controlling e-waste must become a priority for the PCB industry.
My family and I live in a rural area, miles away from the nearest town. Just to the north of our property, a very old bridge spans a small creek. One day, while walking across the bridge, something in the creek caught my eye: an empty oil bottle bobbing gracefully next to an old boot. At second glance, I noticed a tire and some plastic bottles lying next to the creek.
I pondered if oil from the bottle had trickled into the creek, and wondered at the fact that the boot and tire would take up to 80 years to decompose. It was a sad realization that the plastic bottle might take 450 years to eventually break down into smaller pieces of high-density polyethylene.
Of course, printed circuit boards don’t purposely float down creeks, on a mission to harm the environment. Yet, all of us—whether we’re involved in PCB design or manufacturing—have a social responsibility to protect the environment and act as ecological stewards. PCB recycling processes are a part of this larger equation. PCBs have a ratio consisting of 40% metals, 30% organic materials, and 30% ceramics. Therefore, recycling processes recover approximately 99% of copper, copper-beryllium alloys, beryllium oxide, aluminum, tin, gold, silver, platinum, palladium, and lead from a PCB board.
The Recycling Process for PCBs
Once a product completes its operational life-cycle, consumers consider the product and everything inside it as trash, or e-waste. This e-waste can either travel to a landfill—where solvents and other chemicals can possibly bleed into the soil—or to a recycling center. Recycling a PCB recovers the precious metals and components, and turns the trash into treasure.
PCB recycling begins with the physical process of drilling/sorting the boards to remove components, and then cutting the boards into smaller chunks. This process removes capacitors, motors, batteries, plugs, semiconductors, LEDs, fasteners, and other parts from a PCB. Additionally, magnetic separators pull ferromagnetic materials away from non-ferrous metals and any non-magnetic waste. The Waste Electrical and Electronic Equipment Directive (WEEE Directive) and the Restriction of Hazardous Substances Directive (RoHS) require different recycling methods for those components.
From a management perspective, sorting metals from ceramics, fiberglass, and other materials becomes much easier in small sections. Sorting also performs the essential task of removing any undesired materials from the recycling process.
Different PCB Recycling Processes
After cutting and sorting PCB boards, most firms rely on either pyrometallurgy, hydrometallurgy, or electrochemical processes to break down the boards and retrieve precious materials.
The pyrometallurgical process includes heating the PCB to a high temperature in order to recover the material. For example, early recycling methods relied solely on the extractive process to roast, smelt, and refine precious metals from e-waste. Reverberatory furnaces heat to temperatures ranging from 1400 to 1600 Co and convert lead, tin, and oxides to a liquid form.
At the beginning of PCB manufacturing processes, carbothermic reactions pair chemical reactions with high temperatures to reduce iron impurities for removal from tin/lead solder dross—or the waste from wave soldering. In addition, co-combustion and gasification processes convert organic materials into carbon monoxide and hydrogen gases by combining high temperatures with oxygen and steam to produce electrical power.
Hydrometallurgical processes utilize aqueous leaching agents consisting of nitric acid, sulfuric acid, and aqua regia to recover metals. Depending on the type of materials, hydrometallurgy breaks down into sub-processes that involve using solvents to separate contaminants from desired materials, the addition of ions to a precipitation agent that changes the material from a liquid state to a solid-state for separation, and loaded ion-exchange to extract captured metal ions.
Electrochemical processes work with crushed materials by dissolving metals in solvent, removing any foreign materials such as resin, and then recovering the metals. The process occurs through the use of positive and negative electrodes plunged into aqueous solvents. Connecting the electrodes to a power source causes the metals to deposit on the cathode—or negative electrode. The oxygen-generating reaction by the electrolysis of water at an anode causes the copper to dissolve after the removal of the resins.
Newer PCB recycling processes use biotechnology to recover precious metals and copper. With this approach, microbes bind metal ions found in the external environment to compounds for the recovery of metals. Ferrous ion oxidation bacteria generate ferric ions for the oxidation of ferrous iron and the extraction of copper.
Can PCB Recycling Processes Harm the Environment?
The intention behind all PCB recycling processes is to not cause additional harm to the environment. While extreme heat changes metals both chemically and physically, the process also uses energy, and can release toxic dust and gas containing dioxin and lead.
Aside from using energy, pyrometallurgy also requires increased investment costs. Some of those costs cover the equipment needed to recycle metals. Other costs cover waste air processing that prevents hazardous dust and particulates from entering the air.
Although pyrometallurgy involves the use of high-tech methods, the process has taken an ugly turn. Firms have the tendency to send e-waste to Africa and China to use low-tech heating methods to remove impurities. In some of those locations, regulations do not apply. Instead, workers use open fires to burn non-metal waste materials while attempting to retrieve precious metals.
Unless used correctly, hydrometallurgy can also be harmful to the environment. Without the proper wastewater treatment equipment, wastewater can contain acids and metallic ions.
PCB Recycling Offers a Different Type of Value
Although material recovery offers cost benefits and market value, removing the different types of pollution caused by old PCBs adds to the ecological value of our surroundings. Just as companies have a process for design, they should also have PCB recycling processes in place. High volumes of toxic elements should no longer flow into groundwater basins or mist into the air. Removing toxic elements from our environment, while emphasizing life cycle analysis and sustainability improves the quality of life for all global citizens.
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