טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentElina Ofer Rozovsky
SubjectStabilization of the Ferrite Crystal as Part of a Process
Aimed at Heavy Metals Removal from Industrial
Wastes at Ambient Temperature (ATFP)
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Dubowski Yael
Full Thesis textFull thesis text - English Version


Abstract

Removal of heavy metals (HM) from industrial wastewater is of primary environmental importance. The seeded ambient temperature ferrite process (ATFP), in which heavy metals are removed from solution by their incorporation into the structure of ferrite, is an attractive alternative for both complete metals separation and generation of stable sludge. Despite its potential, the fresh ferrite immediately after its synthesis is not completely stable.

The current research investigated the effect of several selected treatments on the stability of Co- and Ni-ferrites. Six treatment methods were examined in this work (exhaustive oxidation, stoichiometric addition, pH2 rinsing, pressing, aging and coating), while chemical and physical characterization of the treated precipitates were used to evaluate the effectiveness of each method. Leaching was the main chemical evaluation parameter. Three from these six methods were determined as the most effective for treating the precipitates: rinsing with pH2 water (for removal of unstable solid intermediates), coating the ferrites with a magnetite layer, and one week of aging at 90oC and pH12. The coating extent can be determined by the desired leaching reduction as an exponential correlation was found to be between these two factors.

The combined final treatment was tested on many kinds of ferrites which differed in their generation pathway, generation temperature (~25oC and 90oC), generation pH, metal to iron ratios, and in metal Me incorporated into the ferrite (Co(II) and Ni(II)). In all Co(II)-ferrites acid rinsing (pH2) reduced leaching by a factor of 2 and after aging at the best operational conditions this reduction factor reached 6. The Ni(II)-ferrites generated by the ATFP resulted in higher reduction factors, indicating that different ferrites were generated from different metals, while the proposed final treatment was relevant for all. In Ni(II)-ferrites generated quickly at 90oC several different phases were formed indicating that most of the Ni(II) wasn't incorporated into the ferrite lattice. In these precipitates, after the acidic rinsing the Ni(II) leaching increased and the coating was also not very effective. On the other hand, aging at high temperature at high pH stabilized these solids and the leaching after such aging decreased drastically.

The whole ferrite process (e.g. synthesis and final treatment) was found to be more economic and environment friendly than the common precipitation method of the ions as metal hydroxides.