Tailoring phosphate mining waste into high‐performance geopolymers: A sustainable process for selective CO 2 / N 2 separation

This study investigates the performance of eco‐friendly geopolymers synthesized from phosphate mining waste for CO 2 /N 2 separation. Two distinct geopolymeric adsorbents were developed using a consistent formulation (35% metakaolin, 19% phosphate mining tailings, 11% NaOH, 11%, 13% Na 2 SiO 3 , 22% water, w/w) but employing different processing methods to yield granular particles (MPW) with a size of 0.112 ± 0.038 mm and spherical beads (MPWE) with a 3 mm diameter. The MPW exhibited a superior textural framework with a surface area of 298 m 2 /g and a micropore volume of 0.1150 cm 3 /g, significantly outperforming the MPWE in adsorption capacity. Kinetic studies revealed that the MPW achieves a CO 2 capacity of 2.50 mmol/g (21°C and 101 kPa), with significantly faster adsorption rates and substantially higher affinity compared to N 2 . The Avrami model best described the CO 2 kinetics, while N 2 adsorption followed the intraparticle diffusion model. Breakthrough curves for single and binary mixtures (CO 2 /N 2 ) were successfully described by a dynamic model based on mass, energy, and momentum balances. Under the specific dry‐gas breakthrough conditions investigated here, MPW exhibited an apparent dynamic separation factor of ( = 91) at 21°C and 101 kPa. Cyclic adsorption/desorption experiments revealed a slight decrease in CO 2 adsorption due to interactions between CO 2 and the adsorbent, with CO 2 desorption observed at low temperatures, although desorption is more effective at higher temperatures. These results highlight the potential of phosphate waste‐based geopolymers as sustainable, promising adsorbents for industrial carbon capture.