Evaluation of the mobility of heavy metals in the sediments originating from the post-galvanic wastewater treatment processes.

Abstract

The article presents the assessment of heavy metals mobility in sediments from the process of galvanic wastewater treatment (pH 2.5, Co 1.5mg/L, Cr6+ < 0.02mg/L, Cr(total) 62mg/L, Cu 110mg/L, Ni 129mg/L and Pb 59mg/L) based on the use of hydroxides (Ca(OH)2, NaOH) as well as inorganic and organic sulphur compounds (Na2S, sodium dimethyldithiocarbamate (DMDTC), sodium trithiocarbonate (Na2CS3), trimercapto-s-triazine trisodium salt, TMT). The leachability was assessed after 1, 7, 14 and 21days of sediment contact with the leaching agent (deionized water). FeCl3 was used as a coagulant. The efficiency of metal removal changed within a range of 99.67-99.94% (for NaOH), 98.80-99.75% (for TMT), 99.67-99.92% (for DMDTC), 99.67-99.91 (for Na2CS3). The heavy metal content in the obtained precipitates changed within the following ranges: 0.1-0.2g/kg (Co), 9.8-14.7g/kg (Cr), 23.6-39.8g/kg (Cu) 30.5-43.2g/kg (Ni), 24.3-33.1g/kg (Pb) and 12.2-18.7g/kg (Cd). The leachability tests revealed the release of 34-37% of Cd, 6.4-7.5% of Ni and 0.06-0.07% of Cu after using an excess of Na2CS3 as the precipitant. The use of NaOH resulted in the release of 0.42-0.46% of Cr from the sediment, and the use of TMT 0.03-0.34% of Ni. The best immobilization of heavy metals was observed in the case of the precipitate resulting from the use of DMDTC as a precipitating agent. The findings may be useful for predicting the mobility of heavy metals in the sludge and assessing the risk involved so as to support their removal and management.