Characterization and treatment of wastewater produced during the hydro-metallurgical extraction of germanium from fly ash

Abstract

The present work dealt with the characterization and treatment of liquid wastes produced during the hydrometallurgical recovery of germanium (Ge) from fly ash. The main metals causing reasons for environmental concern were arsenic (As), nickel (Ni) and antimony (Sb). Precipitation using calcium hydroxide (hydrated lime) was the most efficient method for treating wastewaters with high levels of As, Sb and Ni (up to 99.9% removal). However, relatively large quantities of sludge were produced due to the large doses employed. Reverse osmosis (RO) also proved to be an efficient method achieving heavy metal removals of over 90%. Large quantities of concentrate were produced which required subsequent treatment by lime precipitation. A combined treatment of RO and lime precipitation of the resultant concentrate stream yielded a 97.5% removal of metals. At the same time, a stream with a concentrated level of catechol was obtained that could be reused in the extraction of Ge.