PASTE & FILTERED TAILINGS further to 70 wt %. The TSF is provided with peripheral spigots . This site deposits a low-yield stress underflow that spreads and fills the TSF , while producing a 1-3 % slope . The standard surface stacking management plan with layering of fresh tailings with a dry cycle between layers is used . An advantage of surface stacking technology can be seen in the water balance . This site produces a high rate underflow with 875 m 3 / h ( 3,850 gpm ) water . Of this , the pastetype thickener recovers 518 m 3 / h ( 2,280 gpm ). This 518 m 3 / h is significant as it is 20 % of the 2,500 m 3 / h of water being pump from the Yellow River . Without the use of the paste-type thickener , the 875 m 3 / h of water would have been sent to a slurry pond . In an arid climate with long winters , the potential of recovering much of this water would be low . The use of the surface stack with a paste-type thickener recovered , right at the thickener , 59.1 % of the water received from the high rate thickener . The TSF management has been as planned with increased water recovery at the thickener , no free water on the TSF , the rapid drying , and the low-risk TSF being achieved .
Case study 2 : South Africa
The second case study is an iron mine , Khumani , in South Africa . For this greenfield sitt , due to the arid climate and available water , the regulators required a minimum water use of 0.09 m 3 per tonne of product *. The use of a surface stack with P & TT was the only acceptable method that met this stringent requirement . The plant has a high-water method ( jigs and classification ) to recover the iron . The TSF system used twostage thickening with a 90 m ( 295 ft ) diameter WesTech Titan™ traction high rate thickener at the beneficiation plant . The underflow is sent to an 18 m ( 59 ft ) diameter WesTech Deep Bed paste-type thickener near the TSF . A second phase , two years later , duplicated this system giving total dry tailings of 21,600 t / d . The TSF is in a shallow valley about 5 km from the beneficiation plant and uses the standard surface stack management with layers of non- Newtonian underflow < 500 mm thick , diverting to another part of the TSF allowing each layer to dry . The material dries to a low moisture with large cracks before the next layer is placed . Pumping transports the P & TT to periphery distribution spigots with a series of booster centrifugal pumps . Just like the first case study , this site shows the surface stacking claims have being met for more than 15 years .
Case study 3 : Brazil
The third case study is a bauxite plant , Paragominas , in northern Brazil . This greenfield plant is in a semi-tropic climate averaging 1.8 m of rainfall annually . The site now has installed a second phase using parallel circuits , each with a WesTech 70 m concentrate thickener and a WesTech 45 m HiDensity™ thickener for the tailings . The concentrate is pumped to the aluminium plant and the non-Newtonian tailings are surface stacked . An important takeaway from this site is that there is no real limit to how fine the particles can be for surface stacks with P & TT . There is a rule of thumb for the minimum amount of fines . It states that 20 % of the weight must be finer than 20 μm . However , there is no maximum for minus 20 μm material . As the amount of material passing 20 μm increases , the yield stress versus wt % relationship simply shifts to lower wt %. For example , as presented earlier in case study 1 , the proper yield stress was achieved at 70 wt % solids . For this bauxite site , the stream characteristics ( particle size distribution , mineralogy , etc . combine to have the proper yield stress produced at 35 wt % solids . With the proper yield stress achieved , the rapid drying , angle repose , and ease of TSF management are the same for both sites . Periphery spigots are used for normal surface stacking site management techniques , layered deposition with drying cycles . The 35 wt % non- Newtonian underflow is placed in < 0.5m depths , then allowed to dry 4-8 weeks to reach 65 wt % between layers . This case study provides very strong evidence for low-risk of failure TSF because the mine conducted a drill-core study of the TSF . The construction of the TSF is in a valley next to the beneficiation plant and includes features like diverting the river in the valley around the TSF , dividing the TSF into two areas with a berm between them . This provides access for periphery spigots for deposition across , as well as around its TSF . The mine ’ s evaluation of the success of their TSF used drill cores collected from the full TSF on a relative grid pattern . The cores were analysed in 0.5 m sections . With the TSF being in operation for more than 12 years at the time of the study , part
Moisture distribution curve for 0.5 m sections of up to 30 m deep drill cores
of the stack was over 30 m deep . The samples were analysed for moisture content , PSD , and the yield stress of the material . An article ** concluded that there was “ significant homogeneity in terms of physical character regardless of spatial distribution .” The moisture content to 30 m deep was a relatively consistent 33-34 % ( see distribution figure ). The rheology study reported apparent viscosity of 30 MPa . s , a very stable material that would require “ huge energy to make it flow .” The final moisture was independent of variables like season , discharge flow rate , and layer depth .
The desirable benefits of surface stack with P & TT have been realized for these three case studies . The TSFs are very stable with no free water . The technology predicted increase in water recovery is significant and a major cost advantage . Rapid drying in wet or dry climates is a function of the high solids content and the deposition method . Drill-core study of an active site showed the uniform moisture content through 12 years of operation , a stable low-risk TSF . These benefits are easily achieved with the straight forward TSF management . The P & TT technology deserves high marks with a proven track record , the path has been tried . Starting with the critical function of producing the non- Newtonian underflow and through the subsequent stages , these combine for successful surface stack installations .
IM
* T . du Toit , M . Crozier , ‘ Khumani Iron Ore Mine Paste Disposal and Water Recovery ’, The Journal of The Southern African Institute of Mining and Metallurgy , Volume 112 , March 2012 . ** Bretas , et . al ., ‘ Geotechnical and Rheological Characterization of Bauxite Mining Tailings ’, 7th International Conference on Tailings Management , Chile 2021 .
JULY 2022 | International Mining SUPPLEMENT P11