Experimental Study of Evaporation from Saline Tailings

Many of the mining operations in Western Australia are located in arid and semiarid regions where there is a severe scarcity of freshwater. Most of the processing is carried out using ground water from paleochannels. Much of this ground water is very saline, with concentrations approaching saturation in many cases. The potential rates of evaporation in the region can be very high (over 3 m∕year). With careful management, tailings deposited subaereally in this region can achieve high strengths and densities due to evaporation. However, high salinity results in a severe reduction in the rate of evaporation from the tailings, thereby inhibiting consolidation due to evaporation. This paper presents the results of laboratory evaporation tests carried out to examine the mechanisms by which this reduction occurs. In these tests, all tailings samples with saline water formed salt crusts on the surfaces during evaporation, resulting in evaporation rates that were markedly low compared with those from equivalent freshwater tailings samples. This was the case even if the salinity was low. From measurements made on these samples, it is concluded that the most important mechanisms for reduction due to the salt crust are the increase in surface reflectivity and the increase in the surface resistance to moisture transfer. The vapor pressure reduction in the air due to the salinity of the tailings water is also a factor.