When discarded mobile phones gather dust in drawers and obsolete computers are piled in corners, we might never have imagined that these forgotten electronic wastes contain a "urban mine" - the content of precious metals such as gold, silver, and copper in discarded circuit boards far exceeds that of natural ores. And the key to unlocking this mine is the water-selective recycling equipment for discarded circuit boards, which, like a silent gold miner, allows resources to be reborn through the washing of water. The working process of this equipment is a perfect synergy of technology and environmental protection. First, there is the "preprocessing of disassembly": workers separate components such as capacitors and chips from the circuit boards, leaving a pure substrate; Second, there is the "crushing and screening": the crusher crushes the substrate into millimeter-sized particles, and the sieving machine sorts them by size, paving the way for subsequent separation; Third, the core "water-selective separation": particles of different sizes are fed into the water-selective tank. Metals (with high density) sink under the impact of water, while non-metals (such as resins and fiberglass with low density) float with the water, easily achieving "recovery of gold and copper while diverting plastics". Finally, the enriched metal particles are purified to become shiny industrial raw materials, while non-metals can be used to make building materials or fuels. Throughout the entire process, no strong acids or alkalis are used. Instead, water and physical principles are relied upon, completely avoiding the secondary pollution of traditional pyrometallurgical and hydrometallurgical recycling. Its value lies not only in "turning waste into treasure", but also in "double empowerment". From the resource side, one ton of discarded circuit boards can extract 30 grams of gold, 200 grams of silver, and 50 kilograms of copper - a figure far exceeding the average grade of natural gold mines (about 3 grams per ton). According to the data of an environmental protection company: after introducing this equipment, the annual processing of 12,000 tons of discarded circuit boards recovers 360 kilograms of gold and 600 tons of copper, equivalent to reducing the mining of 200 tons of gold and 3,000 tons of copper, directly saving primary mineral resources. From the environmental protection side, it frees circuit boards from the fate of "landfill-pollution": if an unrecycled circuit board is buried underground, its lead and mercury will seep into the soil and pollute the water; after water-selective treatment, harmful substances are locked in the recycling process, achieving "zero landfill and low emissions". More importantly, this equipment has caught the rhythm of the times. Today, under the "double carbon" goal, circular economy has become the core path of green development. Water-selective recycling of discarded circuit boards not only reduces the carbon emissions of resource extraction, but also reduces the environmental burden of electronic waste disposal, perfectly meeting the requirements of sustainable development. In electronic waste processing industrial parks in Zhejiang, Guangdong, and other places, this equipment has become a "standard configuration", driving the "urban mine" from concept to reality. It is the epitome of technology empowering environmental protection: without complex chemical reactions or high pollution treatment costs, it simply uses physical principles to solve the "recycling dilemma" of electronic waste. When the water washes over the circuit board particles, it separates not only metals and non-metals, but also the boundaries between "waste" and "saving", and "pollution" and "greenness". The water-selective recycling equipment for discarded circuit boards, like a low-key "gold miner", allows the treasures of urban mines to be rediscovered in the rhythm of water. It tells us: environmental protection is not sacrifice, but innovation; resources are not exhausted, but can be recycled and reused. In the blueprint of a green future, the more such "gold miners" there are, the closer we will be to the dream of a "waste-free city".