Paper 87_Rule:text 9/26/08 1:58 PM Page 45 RULE, C.M. Energy considerations in the current PGM processing flowsheet utilizing new technologies. Third International Platinum Conference ‘Platinum in Transformation’, The Southern African Institute of Mining and Metallurgy, 2008. Energy considerations in the current PGM processing flowsheet utilizing new technologies C.M. RULE Anglo Platinum Management Services Energy efficiency is currently a significant area of interest due to the Eskom power situation, which led to severe power impacts to the PGM, and indeed whole SA primary industries, in early 2008. Anglo Platinum has focused on energy efficiency for a number of years, especially in the concentrator operational area. New comminution technologies have been aggressively developed, which have shown real metallurgical efficiency gains as well as significant energy efficiency and saving potential for Anglo Platinum’s total electrical consumption as the company expands into a growing PGM demand market. This paper illustrates this programme activities, potential and considerable achievements to date. Introduction autogenous or ‘SAG’, and less often, fully autogenous, Energy efficiency in the mineral processing industry is an ‘FAG’ milling. In recent years mills have become larger area currently much in focus in South Africa. The recent and larger following worldwide mining industry trends for major power cuts in January 2008 brought home to the realizing economy of scale benefits in unit equipment. The population how precarious the Eskom supply-demand size of PGM industry concentrators has dictated that few equation actually is. The mining industry is a major power very large mills have been installed – mining practice in the consumer and Anglo Platinum is one of the largest mining industry is manually intensive underground operations so industry consumers. It is imperative that Eskom customers throughputs required in related concentrators have been deal with this situation as a matter of priority. constrained. It is not expected that this tenuous power availability The mineralogy of platinum group metals has dictated situation will be changed for the better for a number of fine grinds to optimally liberate and hence make available the valuable components for recovery by froth flotation. years due to the long lead times in the installation of The circuits have over time become more complex – primary, large capacity, thermal power generation. Medupi current practice is for so called MF2 circuits, with and Kusile power plants are scheduled for full regrinding after an initial milling and flotation stage, (Rule commissioning in 2016 and 2017 respectively. and Anyimadu, 2006). The circuit that arose from the low Unfortunately this situation has coincided with unique recoveries obtained on more complex and fine grained resources demand for the minerals industry in South Africa silicate associated ores became more and more prevalent. – driven by the behemoth of Chinese economic growth. Typically the majority of Platreef and UG2 ores and altered Anglo Platinum has invested significant time and Merensky ores show a higher tendency in these ‘poor resources in defining potential energy efficient metallurgical response’ characteristics. This is graphically comminution technology and indeed has taken a holistic illustrated in Figure 1 showing typical PGM speciation in look at the demands of becoming more energy efficient in plant tailings of a Western Bushveld UG2 concentrator the processing route for optimal PGM extraction in its (various AR mineralogy reports). processing flowsheets. The increasingly complex and fine grained mineralogy and the pursuit of higher metals extractions not only Concentrator circuit design and operation naturally leads to more complex concentrator circuits and finer grinds, it logically leads to impacts on the quality of The PGM industry has, relative to the other base metal the flotation final product produced. In order to obtain processing operations, typically, a complex concentrator reasonably high metallurgical recoveries, the final product circuit design with usually multi-stage and fine grinding grade is necessarily lower. The concentrator products and flotation. This has arisen due to the inherent high metal dispatched to the next stage of the process, smelting, are prices for the precious metals contained in the ores mined typically low grade when the proportions of metal sulphides and drives the pursuit of better metallurgical extraction and value metals are compared to the silicate gangue efficiency. Thus it has made good business sense to spend minerals. This is one consequence of the pursuit of metals money both on capital and at an operating level to recovery. Hence a relatively large proportion of the overall maximize metals recovery. energy employed in the PGM industry is consumed in the Typically, depending on their vintage, the comminution combined concentrating and smelting operations. Logically technologies employed have been gyratory, jaw and cone then this represents an ideal opportunity to become more crushing and tumbling mills, ball mills and semi- energy efficient. ENERGY CONSIDERATIONS IN THE CURRENT PGM PROCESSING FLOWSHEET 45 Paper 87_Rule:text 9/26/08 1:58 PM Page 46 8 8 6 9 7 2 5 5 7 6 8 5 8 6 7 6 7 7 7 8 6 7 5 7 6 7 6 9 6 8 7 7 7 5 Figure 1. Photomicrographs sourced from an MLA investigation report on tailings from a Western Bushevld UG2 tailings sample showing the complexity of the liberation challenge; note that each particle shown has a PGM phase shown in red. These ‘attached’, ‘middlings’ and ‘locked’ composite particles are all sub 100 micron Figure 2. Schematic of the architecture for process monitoring at Anglo Platinum concentrators Installed power—comminution and smelting feedstock is the concentrator’s product flotation Comminution has been estimated to consume directly concentrate. Currently, of this total installed electrical around three per cent of all world electrical power. In power within Anglo Platinum, tumbling mills and IsaMill resource rich countries such as Australia, Peru, Chile and equipment represents 195 MW ‘nameplate capacity’ and South Africa the minerals processing industry consumes furnaces at the smelters some 185 MW ‘nameplate much higher proportions of overall energy use. capacity’. This represents some 380 MVa of the installed 1 Anglo Platinum currently has installed some 1 GVa of GVa (or 1 000 MVa) – i.e. nearly 40% of Anglo Platinum’s Eskom power capacity. This should be seen in the light of a total Eskom consumer load. total installed Eskom power capacity of roughly 38 GVa. A major portion of this power is installed to drive the unit equipment for the processes of comminution and smelting. Flowsheet and technology optimization as an energy Comminution is the process of rock size reduction, i.e. usage optimization route crushing and grinding. This size reduction is necessary to The pursuit of more optimal processing efficiency has liberate the value minerals that naturally occur together in gathered pace in recent years. Anglo Platinum is in a period the run of mine ore. After liberation, froth flotation provides the primary separation process. Typically a mass reduction of significant mining and processing capacity expansion, to 1–5% of the original ore feed to the concentrators is related to meeting an ever growing PGM market demand. A achieved in this step. trend over this period has been the ever increasing Smelting is the second major separation process in the exploitation of the UG2 reef horizon and the development PGM industry—it is carried out in electric furnaces; the of the Eastern Bushveld PGM operations. 46 PLATINUM IN TRANSFORMATION Paper 87_Rule:text 9/26/08 1:58 PM Page 47 The more complex PGM mineralogy and the chromite This expansion process at Anglo Platinum has seen a spinel content of the UG2 reef has introduced a level of number of fundamental benefits: processing complexity that was not required when PGMs • A modernization and rationalization of the concentrator operations were mainly Merensky focused. The key to more capacity employed. This can be seen in the trend in energy efficient and better extraction metallurgy lies in recent years of older and smaller plant being made exploiting the mineralogical properties of the ores. redundant and replaced by new plant with larger and The plethora of new expansion and replacement mining fewer units of process equipment and flowsheet projects and the arising need to understand the geology, modification. metallurgy and mineralogy has been addressed by the - In the last two years some 47 old and small tumbling establishment of state-of-the-art mineralogical and mills have been replaced with newer larger mills and metallurgical analyses and pilot plant facilities within 5 new mainstream, 3 MW IsaMills for regrinding Anglo Platinum and at the supporting Anglo American duty, Research facilities. This has led to a better than ever - A further 22 old and small tumbling mills will be understanding of the ore characteristics and hence the replaced in the next five years. extraction processes required and the development of a - 22 IsaMills in both ‘mainstream inert grinding’ number of new strategies in flowsheet design and applications or MIG and concentrate regrind, the technology application. A feature of this has been the industry referred, ultra fine grinding application or opportunity to install both greenfield and brownfield UFG, will be operational by the middle of 2010— capacity