Coal Preparation » Environmental Improvement
A Handbook is provided with this report.
This study was undertaken to identify the impacts of using saline mine water as coal preparation process water and the reuse of plant water as a means of reducing fresh water use and approaches to maintaining optimum plant efficiency. It examined the interaction between dissolved electrolytes, hydrophobic and hydrophilic solids and air bubbles and how they impact on coal preparation unit operations.
Availability of good quality water in sufficient quantities is seen as an emerging issue in the Australian coal industry. Potential approaches to meet this challenge are to reduce water consumption in coal preparation, increase recycling or use saline mine water if it is available on the minesite. With the last two options, the impact of dissolved salt build up on plant product quality and the efficiency of separation processes need to be understood.
The aim of the work was the establishment of the important physical forces which control the behavior of solids, liquid and air bubbles in CHPP separation processes and linking these with process performance in an environment of changing water quality. This new understanding allows the manipulation of these surface forces in a manner that mitigate negative effects of saline water use and thus maintain optimum process efficiencies.
This project studied the coal preparation processes that are impacted by salinity including flotation, filtration and sedimentation to clarify the effect of salt on these processes. This information was combined with the insight gained from basic surface chemistry studies, including particle-particle interaction forces by Atomic Force microscopy to understand how these processes are affected by salinity. This connection between practical impacts and the underlying surface forces controlling these effects is being used to formulate systematic approaches to mitigate any negative impacts and exploit positive effects to operational advantage. Operational guidelines for coping with the negative effects and enhancing any positive effects are provided.
From the process point of view, saline water has a positive impact in terms of improved flotation recovery or conversely reduced flotation reagents consumption especially when high concentrations of divalent cations such as Mg+2 and Ca+2 and divalent anions such as SO4-2 are present. The extent of this effect depends on the type of coal. For filtration and sedimentation rates, the impact of saline water is negative in the absence of flocculant addition, contrary to what may be expected from the Double Layer theory. Fortunately the use of flocculants has such an overwhelming positive impact on filtration and sedimentation rates that it overshadows the effect due to the salts and in that situation, the presence of the salts in most cases results in clearer sedimentation overflow with less residual solids.
The information acquired is presented in this report and a handbook linking the science to potential operational issues in a comprehensible manner that will provide plant operators with the capacity to determine unfavorable conditions and how best to deal with the situation. The benefit to the industry of is the improved management of coal preparation plants in an environment of changing water quality. Fresh water importation would be reduced as more mine water is used and recycled, contributing to corporate sustainable development goals.