Tailings co-disposal case study – art or science?

Abstract

Murray Zircon Pty Ltd operates the Mindarie Mineral Sands Project in South Australia comprising a mine and concentrator plant. The program for environmental protection and rehabilitation (PEPR) approved by the South Australia Department of Manufacturing, Innovation, Trade, Resources and Energy (DMITRE) requires diligent management of the tailings deposition and overall mine rehabilitation processes. The mining licence was granted based on a maximum permitted operational footprint of the open area of the mine. Mining at Mindarie follows the 'moving-hole' concept whereby topsoil and overburden is removed, ore is mined, tailings are deposited in the mined-out space and are then capped by overburden. The moving hole must advance at approximately 10 m per day. Consequently, it is imperative that dewatering, consolidation and stabilisation of deposited tailings happens quickly. Tailings are treated using a high molecular weight polymer which rapidly releases clean water for reuse in the concentrator plant. The polymer binds the coarse and fine particles together to create a non-segregating deposit and accelerates the consolidation rate. Polymer dosing regimes for the tailings have historically relied on a visual interpretation of the material entering the tailings cells to determine the optimum dose; however, it is the consolidation rate and associated strength gain that determines when overburden replacement can begin. To provide an improved assessment of the impacts of dosage on consolidation, geotechnical testing was undertaken on material treated with different polymer levels. A recent development for the Mindarie mine is to adjust the natural acidic pH of tailings to a slightly alkaline level using lime. This was done in order to overcome a throughput bottleneck in the slimes thickener and reduce polymer dosing levels in the slimes thickener and tailings applications. The impact of lime addition on polymer dosing, together with the effect of lime on tailings consolidation properties is also investigated.

Polymer-modified tailings deposition – ongoing testing and potential storage efficiency opportunities

“…The results suggest that polymer treatment has the potential to significantly improve the overall performance of this type of mining operation, with particular benefit in the timely rehabilitation of mining land to agriculture. Furthermore, modelling suggests that the mining process could be optimised to the treatment by use of longer tailings cell sizes within the strip mining process; however, this aspect of the project is the subject of a parallel paper (Beveridge et al 2015).…”

Large strain shearing behaviour of untreated and polymer treated clayey silt slurry specimens

“…Owing to the increased application of forms of PT, studies to characterise the effects PT may have on post-deposition geotechnical behaviour of the treated slurry have been undertaken. Broadly, these studies have indicated the following effects of PT: lower consolidated densities at a given vertical effective stress and higher permeability at a given density (Jeeravipoolvarn et al 2009;Yao 2012;Manzotti et al 2014;Beveridge et al 2015;Gholami & Simms 2015;Reid & Boshoff 2015;Riley et al 2015;Znidarcic et al 2015;Reid & Fourie 2016, 2018aAbdulnabi et al 2022), higher undrained shear strengths at a given density (Jeeravipoolvarn et al 2009;Yao 2012;Beier et al 2013;Manzotti et al 2014;Cooling & Beveridge 2015;Gholami & Simms 2015;Reid & Fourie 2016Abdulnabi et al 2022) and higher CSL elevation (Reid & Fourie 2016), and various contrasting outcomes when examining the effects of PT on brittleness in undrained monotonic or post-cyclic shearing (Beier et al 2013;Gholami & Simms 2015;Reid & Fourie 2017) and drastically different penetrometer responses (Reid and Fourie 2018a), with a summary of recent studies provided by Reid and Fourie (2018b).…”