WATER MANAGEMENT
resulting data can effectively inform short-term and long-term actions .”
Responding to the GISTM ’ s water balance concerns will need a better understanding of evaporation fluxes and variability . Measuring evaporation from TSFs is a field of growing interest and research , with important gains being made in the scientific assessment of what has previously been an estimation . While annual potential evapotranspiration ( PET ) in semi-arid environments like southern Africa reaches volumes often exceeding three times the annual rainfall , the actual evaporation volumes from the TSF are controlled by the hydraulics of the porous medium . An improved knowledge of evaporation effects assists design engineers to understand the development of the pore water flow within the body of the TSF – allowing better assessments of TSF stability to be made .
Beyond the on-site water balance and actual water volumes and fluxes in the TSF , best practices in water management emphasise a broader water stewardship approach . A leading mining company has even targeted zero-use of fresh water on its mines , recognising that water conflict could threaten its social licence to operate . These pressures for water stewardship beyond GISTM standards speak to trends emerging in the public space , guiding mines to adopt water strategies that will build resilience within the business . In future , such an approach is likely to be vital when accessing finance and markets .
Dewatering by pontoon
Weir Minerals is a global supplier of pontoon barge solutions for mining , which are typically used for three main site dewatering applications - process water make-up , water reclaim for onsite processes and tailings fluid management .
The floated pumps perform a variety of tasks including providing process make-up water and collecting site ground water ; as well as recycling water from tailings for use in the mill process or complementary uses such as dust suppression . Utilising the floated pumps in a ‘ dredge-like ’ approach to capture tailings for additional processing allows sites to recover valuable ore or to remove solids to increase the storage capacity of a tailings pond .
Deep well pumping is commonly used in permanent mine face depressurisation dewatering , dyke mounted tailings dewatering & process water supply dewatering applications . But Weir argues : “ Using deep-well pumping systems can lead to problems with inadequate water ingress into the well ( ie recharge rates ) leading the well to run dry or the pump to operate with air entrancement in the water which causes problems for pump health . This style of pump is also sensitive to handling solids , which can cause premature mechanical failure . Due to the nature of the pump system configuration ( pumps installed at the bottom of a deep casing ), the replacement of deep well pumps requires specialised equipment & personnel which can make it an expensive process .”
In comparison , it says pontoon barge systems are more reliable as barges decant from the top of the pond therefore pumping cleaner water than a deep well system . Pumping cleaner water through the system means reduced pump maintenance requirements and provision of cleaner recycled water being used in the mill circuit .
“ One of the greatest advantages of pontoon barges over deep well pumping is that pontoon barge systems allow for flexibility with water level fluctuations . These systems self correct for changes in water level and require only minor mooring adjustments whereas a deep well pumphouse will need to be moved further up the wall of the dyke to accommodate fluctuating water levels as tailings ponds grow . And by comparison , deep well pump systems requires allocation of time and heavy machinery , and potentially the creation of a new well .”
Kris Kielar , ETO Dewatering Product Manager , explains : “ We had a customer using static deep well pumps enclosed in pump houses on the dyke wall . The pond level increased around five metres annually and so these pump houses had to be relocated further and further up the wall .”
This relocation process cost the customer C $ 1.2 million and took up to six weeks to complete each time , so Weir Minerals provided a solution to integrate the existing pumps and pump houses with a Multiflo ® AC steel hull pontoon barge system . Using the Multiflo ® pontoon barge system allows the customer to move the now floated pump house in only a few
20 International Mining | MARCH 2022