1. Used PCB circuit boards from mobile phones and computers contain valuable metals like gold and copper, making their recycling value over 30 yuan per kilogram, significantly higher than that of waste paper, glass bottles, and scrap iron. 2. PCB circuit boards typically show three main colors on their surface: gold, silver, and light red. Gold is the most valuable, followed by silver, with light red being the least valuable. 3. These colors indicate whether manufacturers have used cost-effective materials. The circuits inside mainly consist of pure copper, which oxidizes easily and thus requires protective coatings. 4. Contrary to common belief, large areas of circuit boards are often gold-plated rather than made of copper.