Coal mining has been an important industry in many parts of the world including Australia. Large amounts
of brackish water need to be pumped out to the surface from the workings of mines and good quality water isalso needed for various coal cleaning operations. Several processes such as mill, flotation and refining cause
mine water quality deterioration with low pH, high sulphate content and different dissolution of dissolved ions
[1]. Therefore, treatment of the contaminated water from a coalmine prevents serious damage to receiving
waters and their ecosystems and can be reclaimed for other purposes. Water management in mining advocates
a sustainable approach of using non optimal water instead of fresh water sources. Use of wetlands for mine
waste water treatment in order to remove inorganic pollutants and the application of lime and sulphides,
followed by ion exchange in precipitation of heavy metals were studied [2,3]. Although, a number of
technologies have begun to address the treatment of mine water, very few studies have focused on low energy
and chemical free treatment techniques. The main aim of this study is to develop a technology that can
produce a high quality effluent along with low energy consumption without any usage of chemicals.
The use of membrane separation technologies in brackish water treatment are the result of the tightening of
environmental regulations being placed on industry [4]. Membrane distillation (MD), a thermally driven
physical separation process, comprises of four configurations such as direct contact membrane distillation,
sweeping gas membrane distillation, air gap membrane distillation and Vacuum Membrane Distillation (VMD)
[5]. A convective transport process occurs in VMD using a vacuum pressure on permeate side of the
membrane to reduce the pressure below the saturation pressure of feed solution. The hydrophobic nature of
the membrane prevents liquid solution from entering its pores and assists in the creation of a liquid-vapor
boundary layer. The VMD system has a number of advantages over conventional MD techniques. Perhaps the
most significant advantage is the production of pure distilled water at lower operating temperatures, resulting
in lower operating costs [6]. Therefore, lower energy requirements are needed to achieve similar flux rates
compared to other distillation and desalination processes [7]. VMD is a promising technology that has the
potential to become as important as conventional distillation and pressure driven membrane technologies for
water desalination [8]. Experimental monitoring of the performance of VMD and studying the sensitivity of
flux to feed flow rates, temperatures and vacuum pressures will help to identify specific correlations that these
parameters have on flux, contaminant removal, and thereby increasing reuse potential and treatment
optimization.
2. Theoretical Background
Various types of mass transport mechanism are identified such as Knudsen flow model, viscous flow
model, ordinary molecular diffusion model and/or a combination of the above to describe the flux through a
MD system [5]. Both molecule-molecule and molecule-pore wall interaction occurs in a VMD process, hence
the mass transport within the Knudsen-viscous transition region is considered [5]. For this case, the equation
(1) is used to determine the clean water mass flux N (kg/m2
-s), however, it is noted that the saturation pressure
on the RHS of the equation (part of ) is a function of heat transfer which in turn dependent on the mass