Ian Wark Research Institute
ARC Special Research Centre
ARC Special Research Centre
Research Area: Colloid science, physics, environmental and chemical engineering
Degree: Honours
Supervisor: Prof
Jonas Addai-Mensah
Description: Mineral waste tailings dewatering and disposal of pose a major technological and environmental challenge to mining and mineral processing industry worldwide. Hydrometallurgical processes used in the separation of minerals in ore bodies involve the production of fine particles and utilization of large volumes of water, generating equivalently large volumes of intractable waste tails of low solids density. As high-grade ore deposits are exhausted, the mineral industry is forced to increasingly mine and process low grade ores. Consequently, tailings generation has increased at a much faster rate than the installed capacity for disposal in recent years.
The dewatering of colloidally stable tailings is conventionally achieved by flocculant-mediated, gravity-driven sedimentation in thickeners. Notwithstanding recent advances made in thickener technology for improved dewatering rate, only a modest thickened pulp solids loading can be achieved. Thus to date, a more effective treatment method is yet to be found to drastically reduce tails water content before or during impoundment. The failure by conventional dewatering (flocculation & sedimentation) methods to achieve acceptably high tails consolidation with minimum water retention over long periods of time warrants recourse to a novel dewatering approach. Tails solids loadings in excess of those in conventional thickener underflows may be achieved mechanically by centrifugation and filtration or electroosmosis. For stable tails dominated by particles and pores of colloidal dimensions however, the high hydraulic resistance to flow that must be overcome at high solids volume fraction in order to initiate water drainage renders both centrifugation and filtration processes ineffective and costly. In this case the application of electric field to move water out of a concentrated pulp (electroosmosis), or cause charged particles in a dilute dispersion to move towards an electrode (electrophoresis) offers an economically viable alternative to industry for improved dewaterability of tailings (1-7).
Anode (+) Charged particle capillary wall Cathode (-)
Electrosomotic flow of solution containing ions through
a capillary of charged particle walls due to electric potential difference
V applied between 2 electrodes at a distance X.
For an effective electrokinetic dewatering, both electroosmosis and electrophoresis may be coupled with conducive, interfacial chemistry, particle interactions and pulp network structure. To date however, due to paucity of combined knowledge and understanding of colloid "engineering" and electroosmosis/electrophoresis, the optimization of the underlying and inter-linked processes for maximum dewaterability has not as yet been fully achieved.
In the proposed study, particle-solution interfacial chemistry, particle interactions and electroosmotic/electrophoretic dewatering behaviour will be investigated as a function of industrially-relevant pulp chemistry and applied DC electric field. Flocculated and unflocculated concentrated dispersions prepared from colloidal size, clay particles will be characterized and investigated. Tails pulp chemistry will be manipulated as a function of solution/dispersion conditions (ionic strength of electrolyte, flocculant concentration, pulp solids volume fraction and high pH) at a fixed temperature (~ 25oC).
References
1) RH Sprute and DJ Kelsh, Dewatering and densification of coal waste by direct current laboratory tests, United States Bureau of Mines Report 8197.
2) NC Lockhart, Electroosmotic dewatering of clays, I. Influence of voltage, Colloids and Surfaces, 6 229-238 (1983).
3) NC Lockhart, Electroosmotic dewatering of clays, II. Influence of Salt, Acid and Flocculant, Colloids and Surfaces, 6 239-251 (1983).
4) NC Lockhart, Electroosmotic dewatering of clays, III. Influence of Clay type, Exchangeable cations and Electrode materials, Colloids and Surfaces, 6 253-269 (1983).
5) NC Lockhart, Electroosmotic dewatering of fine suspensions, Recent Advances in Solid � Liquid Separation, 242-274 (1986).
6) JQ Shang and KY Lo, Electrokinetic dewatering of phosphate clay, Journal of Hazardous Materials, (1-3) 55 117-133 (1997).
7) AT Yeung, Electrokinetic flow in porous media and their applications, Advances in Porous Media, (Ed. Corapcioglu, M.Y.) 2, Elsevier Amsterdam, 309-395 (1988).
