Ceramization of heavy metals in (Ba1−XMx)Al2Si2O8 celsian solid solutions and recycling as pigments

Ceramization of several heavy metals (M = Cr, Fe, Co and Ni) in celsian lattice has been studied by sintering up to 1500 °C of its oxides with BaCO3, Al(OH)3 and SiO2 in order to obtain (Ba1−X Mx)Al2Si2O8 solid solutions. Cr3+ enters in solid solution forming cationic vacancies up to x = 0.5 (both celsian and hexacelsian coexist), Fe3+ and Co2+ only up to x = 0.1 (both celsian and hexacelsian coexist), melting at higher x values, while Ni only forms solid solution at low x (0.02), coexisting hexacelsian and celsian, and at higher x NiAl2O4 spinel crystallizes. However, the use of glass-forming mineralizers such as borates increases reactivity and monophasic celsian is obtained in the case of Co-celsian solid solution (adding 10 wt% of glass-forming agent) at only 1000 °C/3h of sintering temperature. These powders have been reused as ceramic pigments and leaching test is performed in order to classify the resulting solid solutions for its landfill disposal (Council Directive 1999/31/EC on the waste landfill).