Gold mining from gold sources, such as natural ores, electronics, and other industrial wastes, is not yet feasible in terms of environmental costs and production efficiency. The trace quantity of Au in the aqueous solution limits its effective capture and extraction through conventional methods. Here, we report a homogeneous, spontaneous, and selective Au-capture method via iron electrocoagulation. Exhibiting a strong electronegativity that distinguishes Au from other metals, water-dispersed Au ions are readily adsorbed by in situ crystallized positively charged ferrous colloidal nuclei. This process involves no chemicals, but it can be performed using an insignificant cell voltage, 0.2 V, with an extraction efficiency of ∼100%. Interestingly, Au0 sponge flocs are obtained in the precipitate, indicating a synchronous reduction reaction. By demonstrating the success of electronic waste and gold-ore pilot tests, we suggest that this approach might be feasible for industrial use. This research opens a new path in the development of sustainable technologies for gold extraction, thereby contributing to a scalable circular economy.