Copper is an important metal for many purposes, such as electrical wiring, plumbing, and various industrial applications. However, it often ends up in the waste-streams of mining, manufacturing, and electronic recycling processes. Traditional methods of Cu recovery, such as pyrometallurgy and hydrometallurgy, are effective but expensive and hazardous, involving high temperatures and/or toxic chemicals. Greener and more innovative methods are needed to sustainably recover these precious materials.

The RPR is an open system designed as a long, narrow, and shallow (97, 37, and 7 cm, respectively) circuit resembling an oval racetrack with a 10 L capacity (see image). A photovoltaic panel powers a motor, which drives a paddle wheel at an optimized rate of 20 rpm and forces the solution around the track at 0.15–0.25 m s–1. The blades of the paddlewheel were designed with a backward-facing curve, which improved energy efficiency by minimizing contact with the solution while still creating the turbulent flow needed to disperse and homogenize the photocatalysts and Cu ions. The RPR offers several advantages, including relatively low construction and operational costs (as it is made from PVC), scalability, ease of maintenance, high treatment capacities, and the flexibility of adjusting the solution depth depending on the amount of solar irradiance. The platform has been tested with deionized water (pH 5.7), tap water (pH 7.1), and seawater (pH 8.5) with 250 mg L–1 Cu(II) solution in 10 L of water, and has a conversion efficiency of Cu(II) ions of about 97, 95, and 81% within 30 minutes of operation at temperatures of 25–28 °C in the Atacama Desert. Further to this, the recovery of metallic Cu was approximately 94, 93, and 80%.