טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentKlas Sivan
SubjectRemoval of Toxic Metals from Industrial Wastewater by their
Stable Incorporation into Ferrites at Ambient
Temperatures: Process Development and
Modeling
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Ori Lahav
Professor Yael Dubowski
Full Thesis textFull thesis text - English Version


Abstract

This work is devoted to the development of a novel process for the removal of toxic metals from wastewater. Ferrites containing different levels of six non-iron metal ions were first synthesized at 90ºC. The chemical composition, unit-cell sizes and dissolution behavior were assessed. Together with an extensive literature survey, the degree of incorporation was found to be (in terms of x MexFe3-xO4, Me is a non-iron metal) 1.0, 1.0, 0.78, 0.49, 0.35, and 0.0 for Zn(II), Co(II), Ni(II), Al(III), Cd(II) and Cr(III) respectively. The dissolution rate of the ferrites indicated that the chemical stability increased with increasing Me content for all of the ferrites except for Cd, which demonstrated an opposite behavior. The water exchange rate between the inner and outer hydration shells around a dissolved metal was found in this work to be associated with the distribution of Me inside the ferrite particles and to be correlated with the maximal incorporation degree trend. The only exception to this rule was Cd(II). This was attributed to its large ionic radius. The order of incorporation in ferrites precipitated at 30ºC was in agreement with that attained at the 90ºC synthesis. However, only around two thirds of the maximal incorporation attained at 90ºC was possible, probably as a result of the high Fe(II) concentration that was found to be required in the synthesis performed at ambient temperature. It was thus postulated that Me hinder the process because less Fe(II) is present to drive the reaction. Dissolution rates of ferrites produced at 30ºC increased with increasing Me content, in contrast with the results obtained at the 90ºC synthesis. This observation was shown to be associated with higher amount of water molecules incorporated into the ferrite structure during synthesis at ambient temperatures. From overall process efficiency standpoint it was concluded that the ATFP is capable of producing a highly stable end-product at relatively high Fe/Me ratios (>10), while >97% of the wastewater volume is treated to comply with Me regulation levels. Increasing the synthesis temperature will increase the incorporation level and stability and reduce external Fe demand. This can be economically attained by a simple separation process.