Sustainable utilization metal ions of acid leaching clay wastewater to fabricate adsorbents for high-efficient removing Congo red and Methyl violet

Abstract

Recycling waste into efficient adsorbents to remove pollutants again provides a compatible solution for the sustainable development of water resources. Here, Mg2+, Al3+, and Fe3+ metal ions from oxalic acid leaching mixed-dimensional palygorskite clay wastewater were successfully converted into mixed metal oxides (MMOs) through a simple precipitation-calcination process. MMOs prepared under different precipitation pH conditions or different washing schemes were used to remove the anionic dye Congo red (CR) and cationic dye Methyl violet (MV). The relatively pure Mg-Al-Fe MMO obtained at pH 13 with thorough washing had ultrahigh adsorption capacity for CR, up to 1369 mg/g. In the presence of sodium oxalate byproducts without washing, the prepared MMOs containing Fe3O4, sodium carbonate, and carbon byproducts had higher removal capacities for cationic dye MV, with a maximum of 1098 mg/g. Moreover, the series of MMOs exhibited strong removal capability for CR + MV mixed dyes and satisfactory cycle stability. This work provided a new perspective on the sustainable utilization of mineral resources and water resources.