Rapid and efficient synthesis of energy-saving cool pigments and environmental restoration materials using rare earth secondary resources

This paper proposes a method for the short-process recovery and reuse of rare earth secondary resources. Low-value rare earth polishing powder waste (WP), trichromatic phosphor waste (WT), NdFeB permanent magnetic waste (WN), and SmCo permanent magnetic waste (WS) were used as the raw materials. Based on the concept of combinatorial chemistry, energy-efficient cool pigments and environmental remediation materials were synthesized by a solid-phase method. The results showed that the synthesized materials had fluorite-type and garnet-type structures. In terms of cool pigments, doping with different rare earth permanent magnets can enrich the color (including yellow, green, brown, gray, and blue) and cause fluctuations in the near-infrared (NIR) reflectance (59.05- 99.54 %) and NIR solar reflectance (55.32- 95.64 %). Yellow fluorite-type pigments (WP: WT = 1:1) have the highest NIR reflectance (R = 99.54 %), while brown fluorite-type pigments (WP: WN = 1:0.1) and blue garnet-type pigments (WP:WS = 1:0.1) have relatively high NIR reflectance, 88.18 % and 59.30 %, respectively. The synthesized pigments possessed better chemical stabilities and thermal insulation performance. In terms of environmental remediation materials, the adsorption capacities of fluorite-type materials for F- and PO43- can reach 84.03 mg/g and 85.3 mg/g, respectively. In summary, materials synthesized from rare earth waste exhibit excellent potential for use in energy-efficient wastewater treatment and promote the sustainable utilization of secondary rare earth resources.