Heavy metal immobilization through phosphate and thermal treatment of dredged sediments

Peter Ndiba, Lisa Axe, Thipnakarin Boonfueng

Research output: Contribution to journalArticlepeer-review

65 Scopus citations


Disposal of dredged sediments is expensive and poses a major challenge for harbor dredging projects. Therefore beneficial reuse of these sediments as construction material is highly desirable assuming contaminants such as heavy metals are immobilized and organics are mineralized. In this research, the effect of the addition of 2.5% phosphate, followed by thermal treatment at 700°C, was investigated for metal contaminants in dredged sediments. Specifically, Zn speciation was evaluated, using X-ray absorption spectroscopy (XAS), by applying principal component analysis (PCA), target transformation (TT), and linear combination fit (LCF) to identify the main phases and their combination from an array of reference compounds. In dredged sediments, Zn was present as smithsonite (67%) and adsorbed to hydrous manganese oxides (18%) and hydrous iron oxides (15%). Phosphate addition resulted in precipitation of hopeite (22%), while calcination induced formation of spinels, gahnite (44%), and franklinite (34%). Although calcination was previously used to agglomerate phosphate phases by sintering, we found that it formed sparingly soluble Zn phases. Results from the U.S. EPA toxicity characteristic leaching procedure (TCLP) confirmed both phosphate addition and calcination reduced leachability of heavy metals with the combined treatment achieving up to an 89% reduction.

Original languageEnglish (US)
Pages (from-to)920-926
Number of pages7
JournalEnvironmental Science and Technology
Issue number3
StatePublished - Feb 1 2008

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • Environmental Chemistry


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