ABSTRACT
This chapter discusses the high level treatment of metal bearing wastes, the advantages offered by metal removal through adsorption onto iron hydroxides are increasingly attractive. Adsorption is capable of removing many metals over a wider pH range and to much lower levels than precipitation. As the adsorbents are conventionally used just once before disposal along with the removed metals, and as the process works best when large quantities of ferrihydrites are present, the ferrihydrites often become the dominant component of the sludge produced. The unattached adsorbent is an amorphous iron oxyhydroxide solid commonly called ferrihydrite. It was prepared by titrating a 10-2 M Fe(NO3)3 solution with concentrated base until the solution reached pH 11.0 ± 0.5. After terminating each run at a given pH, the column was backwashed to remove collected particulate metals. The Fe-coated sand has properties similar to unattached ferrihydrite in removing metals over a wide pH range.
