Solseng, PB & Wuolo,RW 2010, '‘Free’ water from thickened tailings', in R Jewell & AB Fourie (eds), Paste 2010: Proceedings of the Thirteenth International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 505-514, https://doi.org/10.36487/ACG_rep/1063_45_Solseng
(https://papers.acg.uwa.edu.au/p/1063_45_Solseng/)
Abstract: Recent trends in tailings disposal are aimed at disposal without ‘dams’. Although tailings basins (and dams) 
can be designed, constructed, operated and closed safely and very economically, recent initiatives have 
focused on minimising the use of hydraulic structures for containing tailings. These initiatives have been 
(and should be) driven by decisions based on considerations for water supply and economic considerations 
associated with minimising risk from (1) the potential adverse environmental impacts with the ‘free’ water 
from thickened tailings, (2) having a dependable tailings management system for operating tailings dams, 
and (3) public perception with tailings dams. In most cases, water is the key factor in the evaluation of risk 
with tailings disposal. This paper will address some of the concepts used to estimate the quantity of ‘free’ 
water that is available from thickened tailings for recycling (if water shortage is a consideration) and to 
assess the potential risks for this ‘free’ water to cause adverse environmental impacts. Predictive flow 
modelling of thickened tailings, drainage, and the hydrologic settings in which thickened tailings are 
deposited is a key tool in quantifying ‘free’ water production. The movement of ‘free’ water from the 
thickened tailings will be discussed in the paper. Once the quantity of ‘free’ water is known, the associated 
risk may be evaluated more accurately. Two case histories will be presented that illustrate the concepts; one 
involving thickened tailings/paste from a soda ash facility in Wyoming, USA and one from flu gas 
desulpherisation (FGD) sludge from a coal-fired power plant in North Dakota, USA. General concepts for 
tailings disposal, with minimal use of ‘dams’ on projects that are currently under development, will also be 
discussed. The benefits, as well as the challenges of having ‘free’ water available within the thickened 
tailings during disposal will be addressed. Finally, ‘free’ water from thickened tailings and sludge must also 
be accounted for when evaluating the thixotropic characteristics of these materials. The role that salinity 
plays on thixotropy must be considered when designing containment structures for thickened tailings. This 
paper will discuss the thixotropy of thickened tailings and FGD sludge.