Cool coatings with hibonite blue pigments prepared with nickel recovered from waste Watts bath

This work is focused on waste nickel ions recovery from Watts bath in the preparation process of hibonite blue pigments with NIR reflective properties. Ca 1-x La x Al 12-x Ni x O 19 (x = 0.5) pigment was prepared by combustion synthesis using a real Watts bath wastewater as Ni 2+ source and was subsequently annealed at temperatures between 800 to 1300°C, for 1 hour. The immobilization process of nickel in the hibonite blue pigments was confirmed by testing the stability of the obtained pigments in acidic and alkaline solutions for 18 hours. Ni 2+ doped hibonite pigments show high total solar reflectance. The Ca 0.5 La 0.5 Al 11.5 Ni 0.5 O 19 sample annealed at 1000°C for 1 hour showed the highest total solar reflection (72.6 %) and excellent colorimetric CIE L*/a*/b* parameters (82.7/-10.2/-30.7). The same sample was dispersed in an acrylic paint and applied onto a metal sheet showing good coating characteristics and lower temperature during IR irradiation.