Effect of tailings composition on enzyme-induced carbonate precipitation stabilisation: a baseline study

The successful application of biocementation by way of enzyme-induced carbonate precipitation (EICP) in sandy soils has generated research interest in the use of EICP in tailings stabilisation. Initial efforts to apply EICP for tailings stabilisation have encountered significant challenges due to the complex and often inhibitive chemical environment (e.g. the presence of heavy metals and flotation collectors) for urease enzyme activity. This study explores the inhibitory effects of common heavy metals found in tailings (e.g. Cu2+, Ni2+ and Co2+) and flotation collectors (sodium isopropyl xanthate and potassium amyl xanthate) on the EICP process. Strategies to overcome the inhibition are also explored. An increase in the inhibition effect due to increasing metal concentrations was observed and, among the metals tested, Cu2+ had the highest inhibition, followed by Co2+ and Ni2+. Xanthates also reduced urease activity. Adding L-cysteine to the EICP treatment solution improved urease activity and subsequently carbonate precipitation, which was likely to be brought about by protecting the enzyme from the inhibitory effects of heavy metals. EICP-treated specimens (in one treatment cycle) achieved an unconfined compressive strength of up to 1·68 MPa and demonstrated improved stiffness and dilative behaviour when sheared in direct simple shear space.