Electrochemically Assisted Calcium Silicate Utilization for Phosphate Recovery

Abstract

Electrochemical pH-swing systems have demonstrated significant potential across diverse applications, including chemical production, carbon capture, and water treatment. However, conventional systems predominantly depend on costly ion exchange membranes, which are often plagued by fouling and scaling challenges. Here, we introduce an ingenious electrochemically assisted calcium silicate (EACS) system capable of achieving a rapid pH swing from 8.5 to 10 within 1 h through the in situ utilization of H⁺ and OH^– ions, eliminating the need for membranes. The EACS system incorporates a novel 3D-printed porous basket holder designed to house calcium silicate particles and a rod-shaped Ru–Ir anode. Under closed-circuit conditions, the packed calcium silicate reacts with H⁺ generated at the anode, releasing Ca²⁺ into bulk solution, while OH^– produced at the cathode accumulates, resulting in an elevated bulk pH. This mechanism enables the EACS system to achieve exceptional phosphorus recovery efficiency (88.4%–96.6%) from various waste streams, with energy consumption as low as 24.4 kWh kg P^–1. Long-term continuous flow experiments demonstrate that periodic replacement of depleted silicate minerals sustains system efficiency and stability. Furthermore, comparative analysis reveals that while carbonate and silicate minerals are functionally viable, silicate minerals exhibit superior performance in removal kinetics, product purity, and reduced carbon emissions. Notably, the effluent from the EACS system, enriched with Ca²⁺ and characterized by a high pH, exhibits potential for direct air carbon capture. The proposed EACS system offers a transformative approach to environmental remediation and industrial applications, leveraging the fundamental principle of pH-swing to open new avenues for sustainable solutions.