טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAdva Zach-Maor
SubjectRemoval of Water Pollutants by Immobilized Magnetite
(Fe304) Nano-Particles
DepartmentDepartment of Chemical Engineering
Supervisor Professor Emeritus Semiat Raphael
Full Thesis textFull thesis text - English Version


Abstract


The main objective of the research was to develop an efficient process for removal of  pollutants from aqueous solutions using immobilized iron oxide nano-particles.

Permanganate modified granular activated carbon (GAC) was impregnated with ferric chloride solution resulting in immobilized iron oxide nano-particles carbon (nFe-GAC). Batch adsorption experiments revealed high efficiency of phosphate, copper and chromium removal, by the newly developed adsorbent. Maximum adsorption capacities of 435 mg PO4/g Fe and 588 mg Metal/g Fe were obtained. These values are much higher compared with other adsorbents used towards these pollutants removal.

The adsorption mechanism of the pollutants by the nFe-GAC included two steps: a fast initial sorption followed by much slower adsorption process. This two-step differential sorption rates is a characteristic of adsorption by iron oxides. It was demonstrated that the latter is the rate-determining step for the process. Innovative correlation of the diffusion mechanism with the unique adsorption properties of the synthesized adsorbent is presented.

A new approach to the Thomas model was established. The new approach is based on two-step differential sorption rate coefficients.  By implementing this approach excellent model prediction was obtained. By applying this approach a transition point, at which diffusion becomes the predominant adsorption mechanism, was defined for the first time. This point significance is not only scientific but also practical as it could contribute to scale-up design of two stages adsorption processes.

The effect of varying parameters, such as feed flow rates, feed pH, initial phosphate concentrations and adsorbent bed height were examined and described using the modified Thomas model.

Adsorption mechanism was determined both on the molecular level - using advanced analytical methods and on the bulk level - through batch and fixed-bed experiments. Results revealed phosphate was bonded to the nFe-GAC predominantly through bidentate surface complexes. It was established that phosphate was adsorbed to the magnetite surface mainly via ligand exchange mechanism. The diffusion process continued regardless of interface interactions, revealing some of the outer magnetite binding sites for further phosphate uptake.  

Matrix reusability was demonstrated through successive fix-bed adsorption/regeneration cycles, both for the phosphate and the heavy metals.  Regeneration was found to be predominantly a surface reaction, at which the regenerant ions replace the adsorbed ions only at the surface outer biding sites.

Finally phosphate recovery experiments were carried in order to examine the feasibility of a zero liquid discharge (ZLD) process, using the nFe-GAC for phosphate removal from aqueous solutions.