Methodology to Determine Management Strategies Objective-3 Milestone-1 CRLX0401 (AMD Treatment Component)

Transcription

1 Authr(s): Dave Trumm, CRL Energy Ltd CRL Ref : B Title: Methdlgy t Determine Management Strategies Objective-3 Milestne-1 CRLX0401 (AMD Treatment Cmpnent) Client Name : Client Address : FRST Distributin : (ther than client) Date f Issue : 3 August 2006 This reprt must be quted in full except with permissin frm CRL Energy Ltd

2 Methdlgy t Determine Management Strategies (Objective 3) 1.0 Intrductin The verall gal f Objective 3 is t prvide ptins t reduce impacts t acceptable levels. Impacts are defined as acid mine drainage (AMD) and neutral mine drainage (NMD) with high arsenic levels. Althugh, water quality targets are typically set by resurce cnsent fr a discharge pint frm a mine site it is up t mine peratrs t decide hw t meet these targets. Objective 3 prvides: Optins fr mine peratrs t meet targets Methd t select ptins Cnfidence t stakehlders that mine peratrs have ability t meet targets The questins that Objective 3 addresses are: What preventin / remediatin ptins are available t meet water quality targets? Fr each ptin: What is the ptential effectiveness? What is the risk f failure? What are the limitatins? What is the relative cst? What parameters need t be measured t select ptins? Why are these imprtant? Hw much data n each parameter is necessary? Hw are preventin / remediatin ptins selected using critical parameters? Hw are the preventin / remediatin ptins implemented? Management strategies can be divided int tw categries: Upstream Cntrl and Dwnstream Cntrl. Upstream Cntrl invlves preventing and/r minimising mine drainage thrugh verburden management strategies. Dwnstream Cntrl invlves treatment f mine drainage using water treatment systems. Selectin f apprpriate Dwnstream Cntrl strategies is presented in the fllwing sectins. 2.0 Methd t Select Apprpriate AMD Treatment Step 1. Data cllectin: Determine AMD water chemistry by sampling mnthly fr apprximately ne year Field Measurements: ph, cnductivity, temperature, disslved xygen, Fe 2+ cncentratin Labratry Analyses: Fe, Al, Mn, Ni, As (disslved and ttal cncentratins), sulphate, ht acidity, titratins prepared in the field and labratry analysed fr metals (disslved and ttal) - see Appendix A fr Titratin Methdlgy Determine range f flw rates and respnse f flw t precipitatin events, either by spt sampling r preferably via data lgger. Als determine effect f flw variatin n water chemistry by sampling during these events. CRL Energy, Ltd. 2

3 Step 2. Step 3. Step 4: Step 5. Step 6. Step 7. Dcument surface tpgraphy and available land area fr treatment systems Determine treatment gals (water quality endpints) and requirements fr remediatin ptins. This includes using the titratin results frm step 1 t establish the apprpriate treatment level (including amunt f neutralizing material required): Use the labratry results fr metals t calculate acidity Tabulate all results and graph titratin results. Use the results f Objective 2 t determine the degree f impact anticipated frm this site. Reprt this t the grup f parties that are t decide the level f acceptable impact (typically this will include the respnsible party, the reginal authrity, and nn-gvernmental rganisatins). Use the acceptable level f impact t determine the level t which metals and ph shuld be reduced Select the apprpriate treatment level (NaOH equivalent frm titratin results) t lwer cncentratin f metals and ph t acceptable levels Use treatment gals t determine mass f cntaminants t be remved frm AMD (assume cntaminants t be remved as hydrxides, 5% slids by weight). This data is necessary t design apprpriately-sized settling pnds. Kg/day CaCO 3 cnsumed Kg/day Fe(OH) 3 remved Kg/day Al(OH) 3 remved Kg/day MnO 2 remved Other metals/metalids Select ptential remediatin ptins using cllected data and flw chart. See Appendix B fr an explanatin f the tw basic treatment strategies, Appendix C fr flw chart, and Appendix D fr a descriptin f the mst cmmn treatment methds, including an evaluatin f effectiveness, limitatins, and indicative csts. Undertake pilt trials t determine mst cst-effective remediatin ptins Design system using prgrams such as AMD Treat Divert nly the amunt f AMD that can be treated with systems Cllect data n a regular basis (weekly, frtnightly, r mnthly) Cllect samples frm inlet t systems and utlets (stagger samples accrding t residence times f systems) Field: ph, cnductivity, temperature, disslved xygen, Fe 2+ cncentratin, flw rate Labratry: Fe, Al, Mn, Ni, As, Ca (disslved and ttal), sulphate, ht acidity t backgrund ph, ht acidity t ph 8.3, alkalinity AMD treated in these field trials can be used in ectxiclgy experiments t determine if remediatin is sufficient fr recvery f the ecsystem. Analyse Data Caculate residence times in systems Calculate remval rates f cntaminants Calculate treatment efficiencies CRL Energy, Ltd. 3

4 Step 8. Determine effectiveness in reducing mrtality rates f macrinvertebrate cmmunity Based n the results f the field trials, select system(s) based n effectiveness, implementability, and cst (see Appendix D) Effectiveness: a qualitative assessment f hw effective each alternative is expected t be in meeting the treatment gals. This includes an assessment f the expected successful duratin f each remedial activity. Implementability: a qualitative assessment f the practicability f implementing each alternative based n the cmplexity f the required technlgies, site-specific cnstraints (such as space availability, terrain, etc.), and the amunt f experience the cnstructin cmmunity, in general, has with using these technlgies. Cst: an rder-f-magnitude cst estimate t allw cmparisn f the alternatives frm a cst standpint. These estimates are develped using qutatins by vendrs and estimating values. CRL Energy, Ltd. 4

5 Appendix A AMD Titratin Methdlgy CRL Energy, Ltd. 5

6 AMD Titratin Methdlgy Equipment: 20% NaOH Digital (r therwise) titratr ph, cnductivity meter Prtable Merck Phtmeter SQ 300 t measure Ferrus irn 0.45 micrn syringe filters (10) Abut 10 bttles fr lab analysis fr metals (100ml, nitric preserved) Flasks fr titratins (250ml) Methdlgy: RAW AMD 1. Fill small vial fr measuring Fe 2+ cncentratin 2. Measure and recrd Fe 2+ cncentratin 3. Fill flask with AMD (250ml) 4. Filter 100 ml thrugh 0.45 micrn filter int 100ml bttle fr lab analysis fr disslved metals (Fe, Al, Mn, Zn, Ni) 5. Recrd ph, cnductivity f remaining AMD in flask First Titratin 6. Empty flask, rinse in AMD, refill with untreated AMD 7. Titrate with 0.05ml 20% NaOH 8. Stir sample 9. Filter 100 ml thrugh 0.45 micrn filter int 100ml bttle fr lab analysis fr disslved metals (Fe, Al, Mn, Zn, Ni) 10. Recrd ph, cnductivity f remaining AMD in flask Secnd Titratin 11. Repeat Steps 6-12 using 0.10ml NaOH Third Titratin 12. Repeat Steps 6-12 using 0.15ml NaOH 13. Cntinue titratins each time adding 0.05ml mre NaOH than last titratin until ph reaches 7 CRL Energy, Ltd. 6

7 Appendix B Ptential Remedial Strategies fr AMD CRL Energy, Ltd. 7

8 Ptential Remedial Strategies fr AMD Remediatin f AMD using passive remediatin technlgies can be placed int tw brad categries: xidising and reducing strategies. AMD is generated thrugh an xidatin prcess, which results in the dminant cntaminant, irn, being present in tw states, ferrus (Fe 2+ ) and ferric (Fe 3+ ). Remediatin systems emplying the xidising strategy remve irn frm the AMD by cntinuing the xidatin prcess such that all ferrus irn is xidised t ferric irn, and nce the ph has been raised sufficiently, precipitated ut f the AMD as ferric hydrxide (Fe(OH) 3 ). In remediatin systems using the reducing strategy, irn catins and sulphate are reduced and cmpunds such as FeS 2, FeS, and H 2 S are frmed, thereby remving irn and sulphate frm the AMD. In the xidising strategy, alkalinity is added t the AMD water by the disslutin f limestne r ther alkaline materials, and DO is added by aerating the AMD water. Typical remedial systems that emply the xidising strategy are pen limestne channels and diversin wells. In the pen limestne channel, limestne is placed alng the sides and bttm f culverts, ditches, r stream channels. The limestne diversin well is an active treatment methd in which limestne gravel is added t the well peridically. These systems typically require a steep tpgraphy in rder t generate the necessary aeratin and t prevent armuring f limestne by metal hydrxides, which can inhibit the disslutin f limestne. Settling pnds usually cmplete the system t capture and stre metal hydrxide precipitates. Fr the reducing strategy, DO is stripped frm the AMD water using a system that creates an anaerbic envirnment, and alkalinity is then added by the disslutin f limestne. After the ph is raised, metals nt already remved as sulphides precipitate as metal hydrxides. Typical remedial systems that emply this strategy are anaerbic wetlands, anxic limestne drains, and successive alkalinity prducing systems (SAPS), als knwn as vertical flw wetlands (VFWs). In anaerbic wetlands, water is passed thrugh rganic rich substrates and disslved metals are reduced. Sme wetlands may have a layer f limestne at the base t increase ph. Anxic limestne drains are buried trenches filled with limestne gravel. Under anxic (lw DO) cnditins, the limestne des nt cat r armur with irn hydrxides. VFWs are a cmbinatin f an anxic limestne drain and an rganic substrate. Sulphate reductin and irn sulphide precipitatin can ccur in the cmpst material whilst the underlying limestne adds alkalinity t the AMD. These systems typically require that the AMD remain in the system lng enugh fr reductin reactins t ccur. The chice between apprpriate strategies is based n the water chemistry (largely DO cntent and ferrus/ferric (Fe 2+ /Fe 3+ ) irn rati), flw rates, surface tpgraphy, and available land area. CRL Energy, Ltd. 8

9 Appendix C Flw Chart t Chse Amng Passive Treatment Systems CRL Energy, Ltd. 9

10 Fe cncentratin high Fe 3+ < 10% DO < 2 Fe 3+ > 10% Steep tpgraphy Nt steep tpgraphy Large flat area Lng narrw land area Large flat area Lng narrw land area Reducing System: ALD + Settling Pnd Oxidising System: Diversin Well Steep OLC Limestne Sand Dsing (all pssibly with settling pnd) Oxidising System: OLC with access fr dzer t break up xides Reducing System: VFW + Settling Pnd Anaerbic Wetlands Reducing System: VFW + Settling Pnd Anaerbic Wetlands (bth with very lng residence times) Oxidising System: Limestne Leaching Bed Slag Leaching Bed (bth with settling pnd) Fe cncentratin lw Al cncentratin high Al cncentratin lw DO > 2 DO < 2 Lng narrw land area Limited land area - steep Large flat area Large flat area Lng narrw land area Lng narrw land area Large flat area Oxidising System: Limestne Leaching Bed Slag Leaching Bed (bth with settling pnd) Reducing System: ALD Oxidising System: Diversin Well + Settling Pnd Reducing System: Anaerbic Wetlands Reducing System: VFW + Settling Pnd Anaerbic Wetlands (bth with very lng residence times) Oxidising System: OLC r OLD Limestne Sand Dsing Flw chart t use t select amng AMD passive treatment systems (prduced by Dave Trumm). CRL Energy, Ltd. 10

11 Key t use t Chse Amng the Passive Systems (fr lw ph AMD). By Dave Trumm (CRL Energy) 1. Fe cncentratin high Fe cncentratin lw Fe 3+ % lw t high (10-100%) (see nte 1 belw) Fe 3+ % lw (<10%), DO <2 (see nte 2 belw) Steep tpgraphy oxidising Diversin Wells (pssibly with settling pnd) Steep OLC (pssibly with settling pnd) Dsing AMD with limestne sand (pssibly with settling pnd) Nt Steep tpgraphy Lng narrw land available oxidising Gentle OLC with access fr dser t breakup rcks peridically (pssibly with settling pnd) Large flat area available oxidising r Reducing Oxidising Limestne leach bed with very carse rcks and gd flushing system+settling pnd Slag leach bed with very carse slag and gd flushing system+settling pnd Reducing VFW with very lng residence time in rganic layer+settling pnd Anaerbic Wetlands with very lng residence time (must design fr accumulatin f sludge) Organic Bireactr? 5. Lng narrw land area available reducing ALD+settling pnd Large flat area available reducing VFW+settling pnd Anerbic wetlands 6. Al cncentratin high (see nte 3 belw) Al cncentratin lw (see nte 4 belw) Limited land area available, steep tpgraphy oxidising Diversin wells+settling pnd Lng narrw land area available, steep r nt steep tpgraphy oxidising Open limestne channels Dsing AMD with limestne sand Large flat area available oxidising Limestne leach beds+settling pnd Slag leach beds+settling pnd 8. DO < DO > Lng narrw land area available reducing ALD Large flat area available reducing Anerbic wetlands 10. Lng narrw land area available oxidising Open limestne channels / Open limestne drains Dsing AMD with limestne sand Large flat area available oxidising r Reducing Oxidising Strategy Limestne leach beds Reducing Strategy VFW (but need lng residence time at high DO) Anerbic wetlands (but need lng residence time at high DO) CRL Energy, Ltd. 11

12 Nte 1: Nte 2: Nte 3: Nte 4: Treatment cnsideratins: AMD highly xidised Fe(OH) 3 readily precipiates if ph raised Oxidising strategy apprpriate but must prevent armuring f limestne and must capture hydrxide precipitates. Primary cncern is t remve Fe. If Fe remains prevalent thrughut the remainder f the passive treatment system, perfrmance will deline ver time frm armuring in cnjunctin with general hydraulic cnductivity reductins frm irn sludge depsitin. If use reducing treatment strategy need t strip DO, reduce Fe 3+ t Fe 2+ prir t cntact with limestne Add flume/hlding pnd prir t system Treatment cnsideratins: AMD nt highly xidised Fe 2+ will readily xidise t Fe 3+ upn additin f DO Treatment cnsideratins: Acidity in AMD mstly frm ph and Al cncentratin Al(OH) 3 readily frms at a ph f abut 6, hwever aluminium hydrxides geneally d nt armur limestne t the same extent as irn hydrxides Oxidising strategy apprpriate but must incrprate settling pnd fr strage f hydrxides Treatment cnsideratins: Acidity in AMD mstly frm ph Precipitatin frm metal hydrxides a minr cncern ALD = Anxic Limestne Drain, OLC = Open Limestne Channel, OLD = Open Limestne Drain, VFW = Vertical Flw Wetland CRL Energy, Ltd. 12

13 Appendix D Descriptins f AMD Passive Treatment Systems CRL Energy, Ltd. 13

14 AMD Passive Treatment Systems This sectin underway. Fr each system will prvide the fllwing: Descriptin f system Effectiveness f treatment Limitatins Indicative cst Systems t be included: Oxidising strategies: pen limestne channels diversin wells Limestne leach beds Slag leach beds Aerbic wetland (with/withut limestne) (high ph) Dsing AMD with limestne sand Fundatin drains Reducing strategies: anaerbic wetlands anxic limestne drains vertical flw wetlands (SAPS) CRL Energy, Ltd. 14