Selective Separation between Ammonium and Potassium in a Membrane-Separated Magnesium-Based Electrochemical Process

Abstract

Increasing trends in global food and water demands alongside growing environmental concerns press the need for developing new wastewater management strategies. Modern wastewater treatment facilities should provide nutrient recovery and recycling, localized production capabilities, and low energy consumption. Magnesium-based electrochemical wastewater treatment processes are one technology option with the potential to address these needs by providing opportunities for simultaneous recovery of valuable resources from waste streams. In this system, phosphate and ammonium coprecipitate with the magnesium released from the sacrificial anode, producing struvite, NH4MgPO4, as a fertilizer. This technology also eliminates the disadvantages of the commonly used chemical precipitation method of struvite recovery, including magnesium salt dosing, and adding base to the system for pH control, due to in situ magnesium corrosion and hydroxide production at the magnesium anode surface.In this presentation, we specifically focus on a membrane-separated electrochemical process with a solid magnesium electrode. A complex synthetic water matrix including key ions such as ammonium, potassium, and phosphorus with other background salts was made for the anodic chamber to simulate animal liquid manures. Sodium sulfate solution was used as the supporting electrolyte on the cathodic chamber. Two different cation exchange membranes (CEMs) were placed between the two compartments to separate the anolyte from the catholyte. All experiments were conducted under OCV (no external energy input), and ion concentrations in each chamber were tracked over time using ion chromatography to perform kinetic study. The produced precipitates from each experiment are collected and have been characterized by scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) to identify the morphology and purity of the produced solid precipitates. Furthermore, X-ray diffraction (XRD) and Fourier-transform infrared spectrometry (FT-IR) were used to exactly identify the nature of the precipitates. Experimental results indicate that magnesium electrode corrosion under OCV in the anolyte will decrease ammonium separation through the CEM to the catholyte compared to potassium.