HEAP LEACHING AERATION: SCIENCE OR ART?

Transcription

1 HEAP LEACHING AERATION: SCIENCE OR ART? J. Menacho and W. Cifuentes, De Re Metallica Ingeniería Ltda., HydroProcess 2013, Sheraton Hotel, Santiago, Chile, July 2013.

2 CONTENTS MOTIVATION FUNDAMENTALS REVIEW CASE STUDY STATE OF THE ART FINAL REMARKS 2

3 WHY AERATION IS NEEDED? Because the ultimate oxidative agent in the leaching of metallic sulphides is always the OXYGEN: 2Fe +3 + CuS = Cu Fe +2 + S 0 ½ O 2 + 2Fe H + BACTERIA = 2Fe +3 + H 2 O ½ O 2 + CuS + 2H + = Cu +2 + S 0 + H 2 O And, also because the cheapest oxygen source is the ambient air. 3

4 HARD CLIMBING FOR THE AIR IRRIGATION WETTED SURFACE LOW MOISTURE ZONE VADOSE ZONE AERATION LIQUID DRAINAGE SATURATED ZONE 4

5 REVIEWING FUNDAMENTALS: LAMINAR AND TURBULENT FLOW Laminar flow of fluid through porous media is described using Darcy s law: ΔP μ = q ΔL k If the resistance (m/k) remain constant, the pressure gradient (DP/DL) is proportional to the velocity q of the fluid. But as the flow becomes turbulent, the pressure drop increases faster than the velocity. In such a case the Forchheimer s equation applies: ΔP ΔL μ = q + βρq k 2 5

6 GAS SLIPPAGE AT LOW PRESSURE If the Darcy s law applies to any fluid, then ρ g μ ρ g? μ ρ g L L A L A K = k k = K ; K = k K = K L L A A L μ ρ g μ ρ g μ L L A L A Klinkenberg (1941) found large discrepancies between permeability measured to air and that measured with water. He suggested that interaction between the gas molecules and the capillary walls produces a gas slippage which reduces the viscous drag and increases the gas permeability. Then, μ L b ρ g A K = K 1 + A L ρ g P μ L m A 6

7 HYDRAULIC AND PNEUMATIC CHARACTERISTIC CURVES The van Genuchten equation (1980) is often used to model the effect of liquid content on conductivity. In that case: θ - θ θ - θ R R K θ = K L L θ - θ θ - θ S R S R Similarly, 1/2 1/m 1-θ - θ 1 - θ - θ R R K θ = K A A θ - θ - θ S R RGAS θ - θ - θ S R RGAS m 1/2 1/m 2 m 2 7

8 SOLUTION TO THE FLOW PROBLEM The Richards equation (continuity and momentum coupled equations) under apropriate B.C. drives to the relations q = q(t) and q = q(t). For the liquid phase: Unidimensional form of the Richards equation: θ dh = K + 1 t z dz q = q(t) and q = q(t) B.C. θ z,0 = θ 0 K h + z = q 0,t z θ L,0 = 0 ; t 0 z 8

9 PNEUMATIC SYSTEM DESIGN L P θ S θ; N θ,σ θ P0 θ S θ; N θ,σ θl = δ 9

10 CASE STUDY 10

11 DRM BIOLEACH PLANT MODEL... MINE PLAN BLASTING Stacking Wetting Irrigation Drainage Aeration PLS SX/EW Copper Cathodes Raffinate 11

12 RELEVANT PARAMETERS Depth, m Parameter Mass, t 6,387,271 6,387,271 2,129,090 2,129, , , ,697 Height, m Area, m 2 197, , , , , , ,138 Apparent density, t/m Initial porosity, / Current porosity, / Sat. Hyd. Conductivity, m/s 1.45E E E E E E E-03 CuT grade% CuS grade, % Ore density, t/m Initial ore moisture, % Mean irrigation rate, L/h/m THIRD FLOOR SECOND FLOOR FIRST FLOOR 12

13 THEORETICAL OXYGEN CONSUMPTION Cpy: Cc: Cv: Without Biomass Production: CuFeS 2 Fe SO 2 H O 3 O CuSO 5 FeSO 2 H SO Cu S 2 Fe SO H O 1.5 O 2 CuSO 4 FeSO H SO CuS Fe SO H O 1.5 O CuSO 2 FeSO H SO Py: 2 FeS 2 H O 7 O 2FeSO 2 H SO With Biomass Production (g Biomass/g Consumed Fe 2+ = ) Cpy: Cc: Cv: Py: CuFeS Fe SO CO NH H O O C H O N CuSO 3 FeSO H SO Cu S Fe SO CO NH H O O C H O N 2 CuSO 2 FeSO CuS CO NH H O O C H O N CuSO FeS CO NH H O O C H O N Fe SO H SO

14 OVERALL OXYGEN DEMAND Mineralogical Component Initial Weight Fraction, % Reacted Weight Fraction, % Mass, t kmol of Mineral Cu 2 S (Chalcosite) ,195 45,204 CuS (Covellite) ,396 56,437 CuFeS 2 (Chalcopyrite) ,455 FeS 2 (Pyrite) , ,443 Mechanism O 2 Demand, kmol Total O2 Mass, kg Total O 2 Volume, m 3 Air Volume, m 3 Air Flow Rate, m 3 /h Ferric 2,595,078 83,042,494 68,890, ,450,014 47,840 Leaching Fe(III) 2,639,529 84,464,932 70,070, ,350,113 48,660 Regeneration Overall Air Flow Rate, m 3 /h 96,500 14

15 LIQUID EFFLUENT VECTORS 15

16 HYDRAULIC CONDUCTIVITY EVOLUTION 3 L/h/m 2 6 L/h/m 2 10 L/h/m 2 16

17 LIQUID SATURATION PROFILES 3 L/h/m 2 6 L/h/m 2 10 L/h/m 2 17

18 MOISTURE PROFILES 3 L/h/m 2 6 L/h/m 2 10 L/h/m 2 18

19 HYDRAULIC/PNEUMATIC CONDUCTIVITY V/S SATURATION (0-18 m) 19

20 HYDRAULIC/PNEUMATIC CONDUCTIVITY V/S SATURATION (52-54 m) 20

21 MAXIMUM AIR FLOWRATE 3 L/h/m 2 6 L/h/m 2 10 L/h/m 2 21

22 AERATION EFFECT ON COPPER PRODUCTION AVG. T 27.1 C 25.5 C 24.0 C LESS AIR HIGHER TEMPERATURE (Within a range) LESS AIR LESS PRODUCTION Half aeration % Quarter aeration % 22

23 CURRENT CHALLENGES Isotropic Ideal aeration ENVIRONMENTAL AIR PERFORATED PIPES BLOWER Pressure, Flowrate Head losses along the lines ENVIRONMENTAL AIR PERFORATED PIPES Strip Lenght BLOWER 23

24 CURRENT CHALLENGES Strip Height Height gradient ENVIRONMENTAL AIR Pressure, Flowrate PERFORATED PIPES BLOWER Strip Height ENVIRONMENTAL AIR Side leakage BLOWER Pressure, Flowrate Liquid saturation effect PERFORATED PIPES 24

25 TECHNOLOGY MAP ROAD Rio Tinto, Spain (since 1500): Natural convection Codelco Low Grade Sulphide Leach (1976): Natural convection, finger damp geometry Girilambone, Australia (1998): Forced aeration, blower and perforated pipes BHP Billiton (2004): Air distribution system composed by tubings provided with holes to liberate the air from those tubings and a protective element surrounding outside the holed tubings. Netafim (2013): Aeration system composed by aeration pipes connected to a spaced emitter net and the aeration pipes extend through the bed toward the basal layer. 25

26 THE STATE OF THE ART Main Features: Use of gas emitters replace holes Tridimensional arrangement when possible Advantages: Air-emission points may increase from 0.5/m 2 to 10/m 2 Balanced pneumatic nets are possible to implement Tridimensional arrangement increases overall aeration Strong technical support process-oriented. 26

27 THE STATE OF THE ART 27

28 MODEL-BASED LEACH AUTOMATIC CONTROL SYSTEM Main Application + DB Server CONTROL MODEL-BASED Plant Network Gateway Irrigation Flow + Rate Flushing Control Main Matrix Pressure + Flow Repository Level Sub Matrix Control Pressure + Flow BHP Billiton CLUSTER PROJECT, Minera Escondida,

29 MODEL-BASED LEACH AUTOMATIC CONTROL SYSTEM BHP Billiton CLUSTER PROJECT, Minera Escondida,

30 Cobre Soluble, % Razón de Lixiviación, L/h/m2 MODEL-BASED LEACH AUTOMATIC CONTROL SYSTEM 8-month plant run (2012): +2 higher copper recovery points Granulometría, %-100# We do not irrigate just to promote uniform application, but to MAXIMISE COPPER RECOVERY BHP Billiton CLUSTER PROJECT, Minera Escondida,

31 MODEL-BASED LEACH AUTOMATIC CONTROL SYSTEM BHP Billiton CLUSTER PROJECT, Minera Escondida,

32 MODEL-BASED LEACH AUTOMATIC CONTROL SYSTEM A natural step is to include the aeration as part of the automatic control for bioleach applications BHP Billiton CLUSTER PROJECT, Minera Escondida,

33 FINAL REMARKS Forced aeration practice in sulphide heap leaching has not progressed too much since its first application at Girilambone in Excess in aeration not only does not guarantee enough oxygen availability for the sulphides but also remove latent heat from the strips making kinetics slower. Uneven aeration may affect 2% to 4% copper production. Introduction of the newest technology ideally supported by robust monitoring and automatic control system should produce significant improvement in the aeration practice. 33