Tailings management – Drying out in the desert

Water is the ever looming issue on mine sites. Particularly for minerals processors. 
This issue is compounded by the dry, and often remote location of many mines in Australia, which makes access to water suitable for processing difficult.  
Gindalbie's Karara iron ore mine is no different.  
In building its tailings management system, which typically consume high levels of water, the miner aimed to dramatically reduce its ­water requirements and produce tangible water savings. 
It hired Bis Industries, which worked with FLSmidth, to design a system that emphasised the miner's focus on water management. 
The two companies commissioned and designed an advanced dry tailings management system. 
This system at Karara will be the first of its type in dry tailings in the country. 
Dry tailings systems are considered ideal for dry climate mining operations, such as in Australia and  for the Karara mine in Western Australia's Mid West in particular. Along with a cut in water usage (which is achieved through process water recycling and the virtual elimination of water losses through evaporation and seepage), other benefits of dry tailings systems include a significantly smaller tailings storage footprint as well as improved site rehabilitation potential. 
According to Gindalbie's managing director Tim Netscher, the Karara mine has incorporated a clarification process into the overall ore ­benefication process which allows the de-watering of tailings to produce tailings that are dry and inert, which allows for the application of a state of the art tailings management system. 
"The resulting tailings comprise a dry, inert material composed predominately of silica that will be stockpiled and progressively rehabilitated," Netscher said. 
The system has been designed and engineered by FLSmidth, and will see a RACHO stacking conveyor used on site to stockpile these tailings. 
The technology behind the mobile stacking conveyor to be utilised at the mine is reportedly well proven, with more than 25 systems working throughout the world, operating at more than 12 000 tonnes per hour. 
At Karara, a vacuum belt filter will reduce the retained moisture of the iron ore tailings to around 15 per cent, giving the tailings the consistency of wet sand. 
After this the tailings will then be delivered to the designated storage area by conveyor and dispersed by the mobile stacking conveyor. 
An area of four kilometres square has been allocated for this tailings storage. 
According to FLSmidth, by comparison a more traditional pond storage system would use an area of about 52 kilometres square to store the tailings that Karara is projected to generate. 
"This is the case if the area required for such a pond storage system is based on a three metre deep pond, for a fully lined six metre deep pond these space requirement would be halved, however even at six metres deep the total area required is still significantly more than that allocated for the dry storage tailings system." 
Filling this tailings storage will be a site specific designed GPS controlled mobile stacking conveyor that will run for just over 370 metres. 
Constructed of space frame truss sections, it is mounted on crawler tracks that are able to level and move individually to maintain the required levelling and alignment as material is continuously stacked.  
The conveyor has been designed to climb or descend a 10 per cent slope while operating, and a 20 per cent slope when travelling with an empty, non running belt. 
Initially operating at 14.6 million tonnes per annum (eight million tonnes of dry magnetite concentrate production), the system has been designed to meet the increased output from the processing plant as Stage 2 of the ­Karara iron ore project comes on line. 
When fully operational the mobile conveyor system will stack the tailings approximately 90 metres high (in three stages) over a 20-plus year period. 
Bis Indsustries director Jim Ahearn, who led the team which investigated storage methods at Karara, said a mobile stacking conveyor system offered a number of benefits for the project and would help the miner in meeting its site and minerals processing water reduction target of 30 per cent. 
"We examined a number of ­options," Ahearn explained, "and finally arrived at the mobile stacking conveyor solution as more environmentally appealing, much less water dependent, and ultimately lower cost for our customer". 
Ahearn went on to say that in choosing the FLSmidth RAHCO system fit a number of criteria in the mine's aim of water reduction. 
According to Bis the geotechnically stable dry tailings – which are composed most of silica – will provide a secure and workable base for the mine's future reclamation and revegetation program. 
The dry nature of the tailings will make them easier to work with, and as there is no water to remove – as would be the case with traditional tailings dam rehabilitation programs – it significantly cuts down on the program's time. 
"This tailing strategy will cement our environmental credential by simultaneously delivering several significant environmental benefits," Netscher said.

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