Phosphate and thermal stabilization of heavy metals in dredged sediments

Author

Peter Kuria Ndiba, New Jersey Institute of Technology

Document Type

Dissertation

Date of Award

Fall 1-31-2009

Degree Name

Doctor of Philosophy in Environmental Engineering - (Ph.D.)

Department

Civil and Environmental Engineering

First Advisor

Lisa Axe

Second Advisor

John R. Schuring

Third Advisor

Hsin Neng Hsieh

Fourth Advisor

Trevor Tyson

Fifth Advisor

Daniel Watts

Abstract

Treatment and reuse of dredged harbor sediments in construction as an alternative to disposal reduces costs and conserves resources. This research focused on leachability of metal contaminants subsequent to phosphate addition and thermal treatment at 700 °C. X- ray absorption spectroscopy (XAS) in combination with principal component analysis, target transformation, and linear combination revealed that in the untreated sediments Zn precipitated as the relatively soluble smithsonite (ZnCO₃) (67%) and adsorbed to hydrous iron oxides (15%) and hydrous manganese oxides (18%). Phosphate addition and calcination resulted in sparingly soluble phases, hopeite (Zn₃₍PO₄)₂.4H₂O) (22%), and spinels, gahnite (ZnAl₂O₄) (44%) and franklinite (ZnFe₂O₄) (34%). Sequential extraction revealed similar shifts in metal forms from labile to recalcitrant residuals for Ni, Cu (spinels), Mn (crystalline oxides), Pb (phosphate mineral), Cd (alumino-silicate), and Co (adsorption to cryptomelane). The U.S. EPA toxicity characteristic leaching procedure (TCLP) confirmed both phosphate addition and calcination reduced leachability of metals with the combined treatment achieving up to an 89% reduction. In beneficial reuse, the synthetic precipitation leaching procedure (SPLP) revealed that impact to groundwater criteria can be achieved in the treated sediments but will be dependent on the applied dilution attenuation factor (DAF). This research demonstrates the importance of evaluating speciation alongside leaching behavior in developing accurate prediction and assessment of risks posed by waste materials.

Recommended Citation

Ndiba, Peter Kuria, "Phosphate and thermal stabilization of heavy metals in dredged sediments" (2009). Dissertations. 894.
https://digitalcommons.njit.edu/dissertations/894