Removal of heavy metals from CRUD and slime dam material using soil washing and bioremediation
Date
2008-12
Authors
Shumba, Trust
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
A substance called CRUD (Chalk River Unidentified Deposit) was deposited together
with gold tailings to the East Paydam tailings dam. Previous research conducted on
the material has shown that the crud leaches Mn and Ni at concentrations that are
above their acceptable risks limits as well as Zn which leaches at concentration
slightly below its acceptable limits thereby posing an environmental risk. The main
objective of the research was to test the hypothesis stating that soil washing in series
with bioremediation can be used to remove the heavy metals from the material from
the East Paydam tailings dam.
Various laboratory and pilot scale tests were conducted to investigate critical soil
washing and bioremediation parameters and their respective influence on the
treatment process. Laboratory work involved column tests and batch tests. These tests
were crucial in determining the critical parameters for the pilot scale tests such as the
selection of the suitable lixiviant from the four that were investigated. The optimal
concentration of the lixiviant was also determined together with the optimum soil:
liquid ratio. These parameters were employed in the pilot scale tests. Pilot scale tests
involved soil washing in series with bioremediation. The bacterial growth over the
bioremediation period was also determined. Precipitation of the heavy metals from
leachate was investigated by varying the pH and temperature.
Results showed that the soil from the East Paydam can effectively be treated by soil
washing in series with bioremediation. Oxalic acid was selected for soil washing of
the payable slimes at a concentration of 0.001M. However, material that contains high
amount of CRUD (deeper down the slime dam) required the relatively concentrated
0.1M oxalic acid and mechanical agitation. Bioremediation was determined to
increase the amount of heavy metals that was leached from the material from the East
Paydam slimes dam. Precipitation of the heavy metals at a pH of 12 achieved up to
98% removal of heavy metals from leachate.
Description
Thesis (MScEng (Process Engineering))--Stellenbosch University, 2008.
Keywords
Metals -- Toxicology, Soil washing, Bioremediation, Dissertations -- Process engineering, Theses -- Process engineering, Soil remediation, Contaminated sediments