Purification of natural palygorskite clay: Process optimization, cleaner production, mineral characterization, and decolorization performance

This study presents a cascade process for the purification of natural palygorskite (Pal) clay. The purification conditions were optimized using response surface methodology, resulting in the production of highly purified palygorskite (PPal) adsorbent with a purity of approximately 99.9%. The PPal adsorbent exhibited a rod-like morphology with single-crystal dispersion, and dimensions ranging from 20 to 50 nm in diameter and 50 to 200 nm in length. PPal demonstrated high efficiency in the separation of methylene blue (MB) and Congo red (CR) from dye wastewater. Under optimal conditions, with an initial dye concentration of 200 mg/L, pH of 7, adsorption time of 120 min, and adsorbent dosage of 0.2 g, PPal achieved adsorption capacities of 49.27 mg/g for MB and 44.82 mg/g for CR, corresponding to removal efficiencies of 98.54% and 89.63%, respectively. The fitting of Langmuir and pseudo-first-order kinetic models indicated that the adsorption of MB and CR onto palygorskite was spontaneous, monolayer chemical adsorption. Multiple mechanisms, including physical adsorption, electrostatic attraction, ion exchange, and hydrogen bonding, controlled the adsorption process. The estimated production cost of PPal is approximately 3000 ¥/t. The three-step purification approach for producing high-purity palygorskite demonstrates promising and sustainable technology. Considering cost-effectiveness, purification efficacy, and renewability, PPal proves to be an efficient adsorbent for cationic dyes, such as methylene blue. It exhibits strong technical and economic feasibility for future commercialization and industrial-scale wastewater treatment applications.