Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-II-3IMPROVEMENT OF CALCIUM FLUORIDE CRYSTALLIZATION INA FLUIDIZED BED REACTOR WITH MULTIPLE INLETSAbstractA. Garea, R. Aldaco, A. IrabienDepartamento de Ingeniería Química y Química Inorgánica, ETSII y T,Universidad de Cantabria, Avda. Los Castros, s/n, 39005 Santander, Spain.Tel. + 34 942201588; Fax. + 34 942201591; E-mail: gareaa@unican.esThe limited natural resources of fluorspar, calcium fluoride, and the world consumptionof fluorspar for chemicals production, stabilised around 4 million of tons in 2004 (WorldMineral Statistics, 2004) require to make an effort in the sustainable management of the rawmaterial as well as the valorization and recycling into the production processes.The fluoride recovery process to obtain synthetic calcium fluoride consists on acrystallization process in a fluidized bed reactor, which is proposed as an alternative to theconventional precipitation in the BREF document on Best Available Technology in commonwaste water and waste gas treatment and management systems in the Chemical Sector(European Commission, 2003).Previous works were focused on the study of the fluoride removal and recovery assynthetic CaF 2 by crystallization in a fluidized bed reactor working with standard fluoridesolutions at laboratory scale [1-3], and the pilot plant scale operated with industrialwastewaters [4].A model of crystal growth of calcium fluoride was reported by Aldaco et al. [5-7], fromthe fitting of growth rate data to the variables: supersaturation, seed particle size, andsuperficial velocity in the fluidized bed. The crystal growth model was based on theaggregation and molecular growth mechanims, while the nucleation process related to finesformation was described by a nucleation rate equation as a function of the supersaturation [7].As fines formation leads to a reduction of the process efficiency in terms of the amount ofcrystallization product recovered in the reactor, it is important to focus on the undestanding ofthe mechanims of fines formation in order to minimize this effect, mainly by means of thecontrol of supersaturation.Using the concept of distribution of local supersaturation along the reactor, achieved bymultiple feed points, Costodes et al. [8] reported results of crystallization efficiencies up to94 % for the nickel hydroxy-carbonate recovery. The efforts to undestanding of themechanisms involved in the fluidized bed were also referenced for the removal ofphosphorous [9, 10].79