It takes a whole lot of engineering to make a device work as well as possible. As I’m sure you know by now, electrical engineers and hardware engineers like to use valuable materials in their products, as these materials often have desirable properties. Gold and silver, for example, conduct electricity extremely well, and neodymium is a powerful paramagnetic substance. Aluminum is used in surplus, so this is less desirable, but it is recycled nonetheless.
When you give your old devices to a tech recycler, you are one of millions that do the same. In this way, recyclers are able to obtain thousands of tons of material in bulk at a very low price, so they earn much more than their money back when the device is through. This is why they can make money this way, but you or I cannot; we just don’t have the resources to get massive quantities of technology.
When they first bring in the electronic scrap, most of it consists of old PCB. This type of waste is relatively easy to obtain gold from and results in a high return on investment. They separate the PCB material from other waste via magnets, filters, and conveyor belts, which take the PBCs to a shredder which will completely tear apart the waste. The shreds are then left in a solvent, which will completely dissolve the printed fiberglass and leave just the copper, gold, silver, aluminum, platinum, etc. This scrap metal is then separated again to ease the rest of the process. Many recyclers have their own methods for doing this, including but not limited to using a mixture of nitric acid and hydrochloric acid (otherwise known as Aqua Regia) to dissolve out the gold and platinum, but leave other metals untouched. Regardless of the process chosen, the separate metals are then melted down and purified so that they can be sold. This typically results in an impressive profit, but another benefit that these companies receive is tax benefits. Tech recycling is a huge industry, and without them, landfills would be overflowing with random tech junk.
So go ahead and let your old junk go. It might end up in your spouse’s wedding ring later in life.