WATER MANAGEMENT
FLSmidth Deep Cone Thickener as part of a project to convert the subaqueous tailings pond to a paste-filled impoundment over ten years ago. The TTD plant was expanded in 2008, accelerating the rehabilitation of the dam, largely removing free water from the surface of the Cerro de Lobo tailings facility for storage in a new dedicated water dam, Cerro de Mina.
An unintended consequence of the reduction of water in the Cerro de Lobo tailings impoundment has been a build up of dissolved metals and thiosalts in the plant process water as the overall volume of process water was reduced. As the plant uses lime for pH control in the flotation process, and these metals increase in concentration, associated lime use would accelerate the precipitation of gypsum, creating multiple maintenance problems with scaling in the plant.
A water treatment plant installed in the 1990s was re-commissioned as a temporary solution while a permanent solution was put in place.
After a design phase led by an international consulting engineer, SOMINCOR contracted FLSmidth for the detailed design and supply of the necessary equipment for a Fenton-HDS water treatment plant. Under a joint process review, and an additional pilot testing campaign, FLSmidth was able to double the throughput capabilities of the plant using the same equipment sizes as originally specified, using the proprietary FLSmidth MaxR process.
The new plant, currently under construction, will initially accept water from Cerro de Mina, sparge the incoming water with hydrogen peroxide to convert the thiosalts to sulphates, and then, in a series of conditioning and reaction tanks, precipitate the dissolved heavy metals as hydroxides, combined with carefully precipitated calcium sulphate, before settling the precipitates in a 30 m diameter Eimco Clarifier. The MaxR process uses a controlled recirculation of clarifier underflow, conditioned with the necessary quantity of fresh lime to reduce the levels of dissolved metals and sulphates.
The final clarified overflow will be conditioned with CO 2 to bring the pH in line with requirements for the plant process water.
There is an occasional need for discharge of water from the operation and in order to meet this, the overflow will be further treated by reverse osmosis as required, depending on the season and water condition.
Driving change
Dr Hubert Fleming, Anglo American’ s Global Lead for Water Management, is keen on“ driving change and defining our water future.
“ The world needs water. According to the World Economic Forum, a shortage of clean fresh water presents the greatest global, societal and economic risk over the next decade. By 2030, the global population is expected to reach 8.5 billion and the human race could face a 40 % water shortfall. This means that we have little to spare; steps must be taken to ensure water is conserved as much as possible, starting now.
“ With around 75 % of our mining operations located in high water-risk regions, we recognise the need to conserve water wherever possible. Most of the water is used by our tailings disposal facilities – where we store the non-valuable parts of ore after separating the valuable fraction – and through the control of dust on our haul roads.
“ Effectively managing water shortages also mitigates the risk of operational disruptions and presents an opportunity for us to play a leadership role in water catchments. We are six years into an ambitious 10- year water strategy, focussing on achieving water resilience. Our success so far can be attributed to two areas of focus: driving operational excellence and investing in technology.
“ To achieve operational excellence, we have set quantifiable water usage goals for every site worldwide, targeting a 14 % reduction from our projected water consumption by 2020.
“ In 2015, for the third year in a row, we managed to exceed the 2020 target by achieving an estimated 16 % water saving against our projected
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