Rhodium recovery from acidic wastewater using radiografted chelating adsorbents

Platinum group metals (PGMs), particularly rhodium (Rh), are rare and vital for industrial applications, with Rh being scarcer (≈ 20 t/y) than platinum (Pt) and palladium (Pd). Its high cost and limited supply emphasize the need for efficient recovery from industrial waste. New radiografted chelating adsorbents, created through irradiation, offer a sustainable, cost-effective alternative to existing extraction methods. They exhibit high efficiency, selectivity, and reusability, making them ideal for recovering and recycling Rh from industrial wastewater.

This study investigates the effectiveness of radiografted chelating adsorbents for recovering rhodium (Rh) from acidic wastewater, with a focus on functionalized materials both with and without loaded silver (Ag). Rhodium, a critical platinum group metal (PGM), is highly valuable yet scarce, making efficient recovery methods from industrial waste essential. However, Rh's complex chemistry in acidic environments often complicates its extraction and recovery. Traditional methods like solvent extraction and ion exchange adsorption have limitations, driving the need for alternative recovery techniques.

The adsorption efficiency of these radiografted materials was assessed across a wide range of hydrochloric acid (HCl) concentrations under both static and dynamic conditions. Radiotracer ¹⁰¹Rh was employed to monitor and quantify Rh adsorption. The results demonstrate that the radiografted chelating adsorbents exhibit high distribution coefficients (Kd, LogKd ≈ 3) and significant adsorption capacities (Qc > 74 mg/g), which are comparable or superior to commercial resins, particularly under varying pH conditions. Notably, selective recovery of Rh was achieved even under extreme competitive conditions, with the presence of 21 additional metal ions. These findings suggest that amine and amide-based adsorbents presented in this study could provide a sustainable and cost-effective alternative to conventional methods for Rh recovery from industrial waste. A proposed recycling cycle based on these new radiografted chelating adsorbents is shown in the picture.