Geothermal energy, while a clean and renewable energy source, generates waste brine that can hinder operations. However, this brine presents a valuable opportunity for resource recovery. This study demonstrates a facile method to extract silicon, a critical component for lithium-ion batteries, from geothermal brine. Through a two-step process involving silica precipitation and magnesiothermic reduction, we successfully produced high-quality silicon with a porous structure. The extracted silicon exhibits promising electrochemical performance, demonstrating its potential as a sustainable and cost-effective anode material. By effectively utilizing residual geothermal brine as a precursor for silicon anodes, this study offers a sustainable and economically viable solution for addressing both waste management and the increasing demand for high-performance battery materials. The extracted silicon exhibits a high initial capacity of 2736 mAh/g at a current density of 200 mA/g, with a capacity retention of 24% after 300 charge–discharge cycles. This research highlights the importance of maximizing resource utilization from geothermal energy, contributing to a more circular and environmentally friendly energy sector, particularly in the development of sustainable routes for silicon production.