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David Romo Paterson & Cooke, Chile Ray Martinson Paterson & Cooke, Chile New Projects: Conventional or High Density Tailings?

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Presentation on theme: "David Romo Paterson & Cooke, Chile Ray Martinson Paterson & Cooke, Chile New Projects: Conventional or High Density Tailings?"— Presentation transcript:

1 David Romo Paterson & Cooke, Chile Ray Martinson Paterson & Cooke, Chile New Projects: Conventional or High Density Tailings?

2 Every new mining project has to define the most important aspects for the business: Mineral resources model Mine explotation design Methallurgicall process The challenges of new mining projects After that, the main consumptions of the process have to be evaluated: Water consumption Energy consumption At the end, the projects have to define what to do with the waste of the process: Sterile material Tailings 2

3 In this case Paterson & Cooke office in Santiago was in charge of the definition of tailings management system of the project. Aim of the study The aim of this presentation is to show the issues we had to face and what we did to deal with them, in order to support the definitions of the Client. “What we have to do is to look at the whole picture of the problem” 3

4 1.Project overview 2.Tailings deposit location 3.Bench scale tests 4.Conceptual trade off: conventional or thickened tailings? 5.Semi pilot test work 6.Reviewing the solution 7.Conclusion Content 4

5 The study adresses a new project of Sociedad Punta del Cobre, the greatest medium copper mining company in Chile. It is a gold-copper mine located at the IV region of Chile, around 300 km north of Santiago It is located in a desert area, the annual rainfall is less than 200 mm. The project considers a plant to process over 15,000 tpd The tailings deposit considers a capacity over 100 million tonnes 1. Project Overview 5


7 Based on satellite survey, 11 potential sites were identified closer than 30 km to the plant. The storage target was 150 million tonnes. A comparison was done considering: Conventional tailings pumping head Recovered water pumping head Dam wall volume Existing human activity Three alternatives were selected to complete the trade off comparison 2. Tailings Deposit Location 7

8 The evaluation of each alternative considered: Storage capacity of 80 million tonnes Processing plant of 17,000 tpd Conventional tailings with 55%cw Sand wall from cycloned tailings The results were the following: 2. Tailings Deposit Location Alternative 2 Alternative 4 Alternative 5 PLANT LOCATION ParameterUnitAlternative 2Alternative 4Alternative 5 Starting wall volumeMm³ Final wall volumeMm³ Final wall heightm Slurries and water pipeline lengthm Total installed powerkW1,2496,6697,759 Plant make-up waterm³/t Due to lower Capex and Opex, lower installed power, best plant make- up water and lower environmental impact, Alternative 2 was selected. 8

9 In order to get slurry design parameters, bench scale tests were done on samples of each UGM and on a composite. The samples were got from metallurgical bench scale tests. The average p80 was 148 μm, 61% less than 75 μm and Sg of 3.03 Sedimentation tests were done by Delkor: Magnafloc 338 was the best floculant, floc dose between 6-12 g/t and dilution of 13%cw Depending on the sample, a paste thickener could produce tailings between 68.5% %cw, being the expected average equals to 71.5%cw. 3. Bench Scale Tailings Tests 9

10 A range of rheology was measured in rotational viscometer. The unsheared yield stress, for the expected operational thickening points, was determined between 15 and 40 Pa, which is considered a low rheology. The rheology reduction was measured at 30%, so the expected fully sheared yield stress was between 10 – 28 Pa. At the average thickening point the expected fully sheared yield stress was 19 Pa. 3. Bench Scale Tailings Tests 10

11 In order to estimate the beach slope at the deposit, a flume test was done on the composite sample. The limitations of flume tests for predicting beach slopes are well known, so the measured values were reduced by considering two reduction factors: evaluating the average slope in the middle of the flume and also considering a reduction of 30%. 3. Bench Scale Tailings Tests With those considerations, at the average fully sheared yield stress of 19 to 20 Pa at the deposit, a beach slope of 1.5% was estimated for the purpose of pre- feasibility engineering 11

12 The main aspects to figure out in the project in terms of the prefeasibility study were as follows: Deposit location Tailings management system Dam wall and storm water system design The dam wall and storm water system design were undertaken by Knight Piesold Chile. Two different options for tailings management system were evaluated: Conventional tailings option: low density tailings, cyclons operation, slimes transport, tailings sand wall and tailings discharge at the deposit from the wall. Thickened tailings option: high density tailings, wall constructed with borrowed material and tailings discharge at the end of the deposit. 4. Conceptual Trade off: Conventional or Thickened Tailings? 12

13 4. Conceptual Trade off: Parameter Conventional tailings systemThickened tailings system Solids concentration64% CW 70% CW Thickener(1) × Ø48 m high rate thickener, yield stress < 15 pa (1) × Ø48 m paste thickener, yield stress < 80 Pa Tailings transport Gravitational flow through 4,300 m HDPE pipeline Gravitational flow through 700 m HDPE pipeline Tailings classification cyclones No cyclones or pumping slurries systems were considered Sand transport slurry pumps TDH 20 m Slimes transport Gravitational flow through 1,475 m steel pipeline Recovered water transport barge pumps and water pumps TDH 230 m Starting dam wall 1.8 Mm³1.0 Mm³ Final dam wall 12.5 Mm³6.5 Mm³ Beach slope 0.3%1.5% Plant make-up water 0.46 m³/t0.40 m³/t Installed power 3,100 kW1,700 kW 13

14 4. Conceptual Trade off The thickened tailings system was selected because of: Lower capex Lower installed power Lower plant make up water Lower volume of water within the deposit Greater opportunities to improve the using of the deposit facilities Wall Thickener Plant Location Tailings discharge 14

15 Semi pilot tailings tests were done in order to improve the knowledge of tailings on a larger scale. The p80 was 218 μm μm Fine fraction less than 75 μm was 56%-60% Slurry behaviour tests were done by P&C Johannesburg: Natural pH 7.8 Slurry conductivity over 40 mS/cm (sea water) Slurry naturally settling 5. Semi Pilot Tailings Tests 15

16 Semi pilot thickening tests were done by Outotec in a Ø190mm x 4 m thickener: Magnafloc 338 was the one of the best floculants, floc dose grew up to 17 g/t and dilution was 12%cw Optimum flux rate was 0.4 t/m².h Expected U/F solids concentration 65%-73%cw Unsheared yield stress between Pa Two options were proposed: One 55Øm high compression thickener Two 38Øm high compression/paste thickeners 5. Semi Pilot Tailings Tests 16

17 A range of rheology was measured in rotational and tube viscometer. A great difference between the rheology of both samples was measured. Even the rheology was 6 times greater than the measured one at the PFS study. A rheology reduction of 60% was measured on these samples 5. Semi Pilot Tailings Tests 17

18 4 m flume tests were done to estimate the beach slope. The experience and test data analysis were done with the support of Professor Andy Fourie. Both samples showed different behaviour, due to the different lithology. The beach slope estimation considered a safety factor of 50% over the measured slope. At the average solids content for the thickener operation of 70% CW, the average beach slope was estimated on 1.6% 5. Semi Pilot Tailings Tests 18

19 6.1 Tailings Pumping Because of the higher rheologies measured at semi pilot test work, pump stations are required for tailings transportation from thickener(s) to the deposit. Depending on the option of thickening circuit the pumping system is as follows: 6. Reviewing the Solution Pump station(1) × Ø55 m thickener (2) × Ø38 m thickener Underflow discharge (1 + 1) 20 m/15 m 250 kW centrifugal pumps 2 × (1 + 1) 20 m /15 m 200 kW centrifugal pumps Transport to deposit(1 + 1) 25 m/20 m 200 kW centrifugal pumps 19

20 6.2 Filtered tailings Bench top filtering tests were done by Delkor, but the filtration rates were very poor for vacuum and pressure technologies. In spite of those results, an evaluation of filtered tailings system was done. The area of the deposit is not suitable to dispose tailings in stock piles. This is because of the maximum expected value for the hydrographic basin storm flow which reaches 211 m³/s. As a result, a water dam as well as an evacuation tunnel had to be considered in this evaluation. Finally the filtered tailings option resulted into a Capex over 2.4 times the thickened tailings option. 6. Reviewing the solution 20

21 The study developed for this new project of Sociedad Punta del Cobre ended into the following conclusions: The site conditions are the most important aspects that define which type of dewatering system is the best. The topography and the hydrographic basin storm determine the design of the deposit and the tailings management system. The other very important aspect are the pumping distances. If the material presents good conditions to be thickened or filtrated, a complete test plan must be done to support every engineering evaluation. Bench scale or pilot tests are recommended to be done for each stage of engineering. In this case, thickened tailings clearly has technical advantages over conventional and filtered tailings systems. The expected plant make-up water is 0.4 m³/t and the installed power is 2,700 kW For feasibility engineering, the final selection of the thickening circuit and the study of disposal strategies will be important issues to address. 7. Conclusion 21

22 We want to acknowledge to all people who worked with us, from Knight Piesold Chile, Multical, Delkor, Outotec, Mr. Andy Fourie and to Pucobre S.A. Acknowledgements 22

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