Removal and cementitious immobilization of heavy metals: chromium capture by zeolite-hybridized materials obtained from spent fluid cracking catalysts

An alternative for the reutilization of spent catalyst industrial residue for removal and immobilization of heavy metals is presented. A solid containing about 80% (w/w) of NaA zeolite was hydrothermally synthesized by reconversion of a spent catalyst discarded from a fluidized-bed catalytic cracking unit (FCC). The obtained material (ZFCC) was afterwards used for Cr(III) removal from aqueous solutions. Chromium cation was incorporated in the zeolitized structure by ionic exchange in liquid media, and the exchange level was determined by atomic absorption spectrometry. To analyze the viability of final disposal for the chromium sludge obtained using this methodology (Cr-ZFCC), cement mortars containing Cr-ZFCC in variable percentages were prepared and their mechanical and metal retention properties were evaluated. Mechanical strengths and drying shrinkage shown by mortars containing not more than Cr-ZFCC 5% (w/w) were similar to those corresponding to control mortars without zeolitic additions. Leaching tests indicated that mortars with Cr-ZFCC 5% (w/w) produce an effective immobilization of Cr(III) and should be considered as a viable alternative for safe chromium disposal.