TAILINGS
wt % were typical although the target was 68 wt %. The retrofit included adding 2 m of wall height and replacing the full thickener mechanism together with a new diluting feed system , higher torque capacity and low drag rakes . After the restart , the plant was able to increase the underflow density to 64-65 wt %. Testing showed that achieving 68 wt % should be possible with about three hours of mud retention time .” This thickener has a dual floor slope with a 10 degree inner slope and 7.125 degree outer slope . These are relatively low floor slopes , typical for high rate thickeners where the underflow can flow hydraulically .
The new feed system on this thickener included E-Duc feed dilution to reduce the feed concentration from 40 wt % to 12 wt % for better flocculation . “ This system works very well and resulted in greatly improved overflow clarity at lower flocculant dosages . The lower than targeted underflow density though has been expensive for the company in terms of requiring modifications to their TSF .”
They add that mud transport within a thickener is dependent on several factors including floor slope and raking . At low underflow concentrations the mud generally behaves in a Newtonian fashion . As the concentration increases the mud begins to develop a yield stress , or resistance to flow . With Newtonian characteristics , the mud flows to the bottom outlets hydraulically . As the yield stress increases , that mud needs more force to get it to flow to the outlets . Deep Cone Thickeners designed for high yield stress muds use 30 degree floors to provide a lot of that force using gravity .
“ One example of the difference can be seen at a northern Chile copper mine , where their latest 125 m tailings thickener has a 3:12 floor slope compared with 2:12 floor slope on their previous designs . This increases the mud volume and retention time as well as the centre depth . This change has resulted in a 1-2 wt % increase in the underflow density .”
Another retrofit project with high density thickeners involved 3 x 60 m tailings thickeners at another copper concentrator in Chile . That project was originally built using box truss rake designs and these types of rake arms tends to build up mud within the rake structure . The rakes were replaced using a low drag tubular design that allowed the underflow density to improve by about 2 wt %, from 61-62 wt % up to 63-64 wt %.
The authors state : “ Typical methods of improving the raking capacity involve using deeper and longer blades to move more material and cover more area . In looking at the raking capacity for the Kazakhstan DCTs , it became apparent that something else was needed to produce the results the customer was looking for .
FLSmidth has been seeing market success with its new AFP2525 filter with which it says customers can expect an average of 93 % availability and up to 95 % recovery of process water . AFP2525 filters for Buenaventura ’ s San Gabriel are expected to be delivered by the end of July . Installation and commissioning will be in Q3 and Q4 . Additional filters for Torex ’ s Media Luna are scheduled for shipment in April with installation and commissioning also occurring in Q3 and Q4
Their High Compression tailings thickeners were only able to produce about 61 wt % underflow and they wanted 68 wt %. Just adding low profile rakes and steepening the floor would probably get them up to about 65 wt %, but probably not 68 wt %. To improve further , higher raking capacity was needed . A spiral inner blade design was conceived where the second rake blade was essentially shifted to connect the first and third blades on adjacent long and short arms , making for long spiral blades in the inner area that connect between the long and short rake arms . This effectively triples the raking capacity in the inner area .”
CFD modelling for the mud bed was used in the spiral blade development to look at the mud bed retention times with and without the spiral blade and truss rakes . The results were very promising and resulted in a much tighter mud bed residence time distribution . This ultimately resulted in the adoption of the Inner Spiral Blade for the Kazakhstan DCTs .
“ Thickeners are not particularly efficient or consistent in terms of mud retention time , meaning there is a wide variation in mud retention times . Some material typically ratholes , or short circuits to the underflow outlets very quickly . That material doesn ’ t have time to thicken up and results in low underflow densities . Other material tends to stay in the thickener for long times , resulting in high yield stress and correspondingly high torque . By over-raking and improving the efficiency in the mud bed the thickener can operate with more even and consistent mud retention time , producing higher underflow densities while running at lower torques .”
Rhosonics ’ SDM ECO
In the dynamic world of mining , efficiency , and environmental responsibility go hand in hand . One technology at the forefront of this balance is the new SDM ECO from Rhosonics , a non-nuclear density meter for slurries . Vitor Braz , Global Sales Manager , told IM : “ Traditionally , dewatering concentrated slurry – achieved via thickeners or filter presses – posed challenges in maintaining optimal density levels , and inline density meters enable real-time monitoring and controlling of slurry density . By continuously tracking density variations , operators can swiftly adjust parameters to keep density at the desired setpoint , maximising water recovery . This not only enhances operational efficiency but also reduces water consumption , a critical sustainability goal in mining .”
He adds : “ Moreover , proper density management is paramount for the safety of tailings storage facilities . Accurate density monitoring with the SDM ECO upstream from the tailing ’ s disposal facilities helps prevent disasters such as tailings dam failures , mitigating environmental hazards , and ensuring regulatory compliance . In the quest for responsible tailings management , accurate density measurement is non-negotiable . With the SDM ECO , mining operations can navigate this challenge with confidence , safeguarding both their operations and the environment .”
Rhosonics ' new SDM ECO non-nuclear density meter for slurries
58 International Mining | APRIL 2024