Heap-Leach Cyanide Solution Tank Selection Mining

Heap-Leach Cyanide Solution (Sodium Cyanide NaCN at 100-1000 ppm CN-Free in Alkaline pH 10.5-11.5 Lime-Buffered Barren and Pregnant Leach Solution Recirculated Through Crushed-Ore Heap Pad for Gold and Silver Dissolution as Au(CN)2- and Ag(CN)2- Complex Ion at Carlin-Trend Nevada, Cortez, Goldstrike, Round Mountain, Cripple Creek, Fort Knox, Mesquite, Castle Mountain, and Latin-American Heap-Leach Mine Operations) — Process-Water and Adjacency Tank Selection at Heap-Leach Gold and Silver Mining

Heap-leach cyanide solution (sodium cyanide NaCN; CAS 143-33-9 sodium cyanide briquette + solid + 30% solution; dissolved at 100-1000 ppm CN-free in process water buffered with hydrated lime Ca(OH)2 to pH 10.5-11.5 to suppress HCN gas evolution; recirculated through crushed-ore heap pad at 0.005-0.015 gpm/ft2 application rate for 60-180-day leach cycle to dissolve gold + silver as Au(CN)2- + Ag(CN)2- soluble cyanide complex ion per the Elsner equation 4 Au + 8 NaCN + O2 + 2 H2O -> 4 NaAu(CN)2 + 4 NaOH; pregnant leach solution at 0.5-5 mg/L Au + 5-50 mg/L Ag + 100-500 ppm CN-free pre-recovery; barren solution at 50-300 ppm CN-free post-Merrill-Crowe zinc-precipitation or activated-carbon CIC adsorption gold-recovery step; on-site solution makedown at 30% NaCN solution from rail-delivered solid briquette via specialized makedown tank with caustic-buffered dissolution; HCN gas evolution at pH below 9.3 is ACUTELY FATAL at 100-300 ppm air concentration per OSHA 29 CFR 1910.1000 + MSHA 30 CFR 56/57 + ACGIH TLV-Ceiling 4.7 ppm HCN; full-facility cyanide-management discipline per International Cyanide Management Code + ICMI Signatory + Auditor framework + ASTM D6888 + D7237 free-CN + WAD-CN + total-CN distillation analytical framework + EPA Method 9010 + 9012 + 9013 + 9015 cyanide analytical framework) is the dominant gold-and-silver-extraction chemistry at modern open-pit + low-grade heap-leach gold + silver mining operations across Nevada (high-grade gold belt, Cortez, Goldstrike, Round Mountain, Hycroft), Colorado (Cripple Creek), Alaska (Fort Knox, Pogo), California (Mesquite, Castle Mountain), Mexico (Pinos Altos, La Herradura), Argentina (Veladero, Cerro Vanguardia), Chile (Maricunga district), Peru (Yanacocha, La Zanja), Australia, Africa, and Asia, providing 60-90% gold recovery + 30-70% silver recovery from 0.3-2.0 g/t low-grade ore at one-third the capital and one-half the operating cost of conventional milling + cyanide-in-pulp circuits.

U.S. and Canadian heap-leach throughput is concentrated at major gold producers (Barrick Gold + Newmont Corporation + Kinross Gold + Coeur Mining + SSR Mining + Hecla Mining + Equinox Gold + Centerra + Eldorado Gold + Pan American Silver) with primary sodium-cyanide producers (Cyanco Bulk Distribution Winnemucca Nevada + Sasol Sasolburg South Africa + Orica Yarwun Queensland Australia + Chemours Memphis Tennessee + Anhui Shuguang Group China). Bulk sodium-cyanide is delivered as 1-tonne flow-bin or rail-car solid briquette at on-site solution-makedown plant operation; cyanide solution is internal to the mine + never shipped off-site outside ICMI-certified intermodal cyanide-isotainer specification.

The eight sections below cite OSHA Hazard Communication 29 CFR 1910.1200 + 1910.1000 cyanide ceiling-limit + MSHA 30 CFR 56/57 surface-and-underground-mine cyanide standard + International Cyanide Management Code + ICMI Signatory Mine + Producer + Transporter + Auditor framework + EPA Method 9010 + 9012 + 9013 + 9015 cyanide analytical + ASTM D6888 free-CN + D7237 weak-acid-dissociable + total-CN + EPA NPDES + state-specific mining-discharge permit + EPA SPCC + state-specific cyanide-bearing tailings + heap-pad code + Indian Country Environmental + EPA RCRA Subtitle C + Bureau of Land Management Mine Plan of Operations + Forest Service Plan of Operations + State Reclamation Bond + Mine Safety and Health Administration MSHA training + cyanide antidote kit + emergency-medical-response framework at routine operating practice at North American + Latin-American + Australian + African + Asian heap-leach gold-and-silver mine operations.

1. Material Compatibility Matrix

Heap-leach cyanide solution at typical 100-1000 ppm CN-free + pH 10.5-11.5 lime-buffered alkaline composition is a moderately corrosive caustic-alkaline cyanide-bearing solution with low chemical-corrosion risk against most polymeric construction at the dilute working-strength specification but with absolute regulatory + life-safety controls overlay. Note the operating-discipline controls: pH-control discipline (pH below 9.3 drives HCN gas evolution at fatal air concentration; continuous pH monitoring + automated lime-dosing trim is mandatory; pH-low alarm + interlock at 9.5 + emergency-shutdown at 9.0 is standard heap-leach plant practice), HCN-detection discipline (continuous fixed-point HCN gas detector at solution-pond + tank + makedown-plant + electrowinning-cell area at 4.7 ppm Ceiling alarm + 10 ppm shutdown + portable HCN monitor + escape-respirator at every worker is mandatory under MSHA + ICMI), spill-and-containment discipline (every solution tank + pond + pipe + valve at heap-leach circuit requires double-liner + leak-detection + secondary-containment per state-specific cyanide-bearing tailings code + EPA SPCC + ICMI Standard of Practice 4.4), wildlife-protection discipline (open ponds at greater-than-50 ppm WAD-CN are prohibited under ICMI Standard of Practice 4.6 + state mining-discharge permit; ponds must be netted + fenced + hazed to exclude waterfowl + wildlife; cyanide-bearing solid + liquid waste discharge to pond is permitted only at less-than-50 mg/L WAD-CN), and copper-zinc-iron contamination discipline (copper + zinc + iron + nickel + cobalt + mercury cation impurities in process water consume free CN as Cu(CN)4 (3-) + Zn(CN)4 (2-) + Fe(CN)6 (4-) complex ion, drive HCN gas evolution at acidification, and complicate cyanide-destruction chemistry; raw-water analysis + impurity-budget management is routine).

The dominant industrial pattern at North American + Latin-American + Australian + African + Asian heap-leach gold-and-silver mine operations is welded-carbon-steel ICMI-coded primary cyanide solution storage tank with epoxy or coal-tar-epoxy lining at the 100,000-2,000,000-gallon barren-solution tank + pregnant-solution tank scale, with HDPE 60-mil or 80-mil double-liner pond + leak-detection at the barren-pond + pregnant-pond + event-pond + stormwater-pond inventory, and HDPE SDR 11 or SDR 17 pipe at heap-pad solution distribution + drip-emitter + collection-sump piping. HDPE rotomolded tanks dominate at the process-water + lime-makedown + flocculant + reagent + analytical-lab + adjacency 1,500-10,000-gallon scale outside the primary cyanide circuit. OneSource Plastics' 5-brand HDPE network (Norwesco, Snyder Industries, Chem-Tainer, Enduraplas, Bushman) covers the process-water + lime + flocculant + reagent + makedown adjacency envelope at heap-leach mining; primary cyanide solution storage requires welded-carbon-steel ICMI-coded tank with epoxy lining + ICMI Standard of Practice 4 material specification at the 100,000-2,000,000-gallon scale OUTSIDE our HDPE 5-brand scope, and we refer those specifications to qualified ICMI-Signatory steel-tank fabricators.

2. Real-World Industrial Use Cases

Heap-Leach Gold and Silver Mining (Dominant Use). Heap-leach gold + silver mine operations crush low-grade ore at 0.3-2.0 g/t Au + 5-50 g/t Ag to 0.25-1.5 inch P80, agglomerate with cement or lime, stack at 30-200-foot lift on HDPE 60-mil or 80-mil double-liner pad with leak-detection + collection sump, and drip-irrigate at 0.005-0.015 gpm/ft2 with barren-cyanide solution at 100-500 ppm CN-free + pH 10.5-11.5 for 60-180-day leach cycle. Pregnant solution drains by gravity to pregnant solution pond + pregnant solution tank. Recovery via Merrill-Crowe zinc-precipitation press (Round Mountain, Castle Mountain, Goldstrike) or carbon-in-column CIC adsorption (high-grade gold belt, Cortez, Cripple Creek). Barren solution returns to barren-pond + barren-tank + heap-pad recirculation loop. Storage envelope: 100,000-2,000,000-gallon welded-steel epoxy-lined ICMI-coded tank; HDPE rotomolded tanks at process-water + lime-makedown + flocculant + reagent + analytical-lab + adjacency 1,500-10,000-gallon scale.

Cyanide-In-Leach (CIL) and Cyanide-In-Pulp (CIP) Mill Circuits. Mill-circuit gold + silver operations grind ore to 80% passing 75 micron + leach in agitated tank with sodium cyanide at 0.5-2.0 g/L NaCN + pH 10.5-11.5 + dissolved-oxygen sparge for 24-48 hour residence, then adsorb gold onto activated carbon in CIL or carbon downstream of leach in CIP, then strip + electrowin + smelt to dore bar. Storage envelope: same as heap-leach plus 50,000-500,000-gallon agitated leach + adsorption tank.

On-Site Sodium-Cyanide Solution Makedown Plant. Solid sodium-cyanide briquette delivery (1-tonne flow-bin or rail-car or 30% NaCN solution intermodal isotainer) is dissolved at on-site makedown plant in caustic-buffered process water at pH 12-13 to 30% NaCN solution + transferred to bulk-solution storage. Specialized HCN-vented enclosed makedown tank with double-wall + secondary-containment + emergency-deluge + HCN-monitoring + air-supplied-respirator + Buddy-system protocol per ICMI Standard of Practice 1.

Cyanide-Destruction (Detoxification) Tailings Treatment. Tailings discharge cyanide destruction via INCO SO2/Air process or alkaline-chlorination Cl2 process or peroxide H2O2 process at the tailings-disposal-area discharge point reduces WAD-CN to less-than-50 mg/L per ICMI + state mining-discharge permit + NPDES specification. Storage envelope: 5,000-50,000-gallon HDPE process-water + reagent makedown tank within OneSource scope, plus 50,000-500,000-gallon FRP or stainless reaction tank typically OUTSIDE HDPE scope.

Process Water and Adjacency Reagent. Process water + hydrated lime + xanthate + dithiophosphate flotation reagent + activated-carbon slurry + acid + caustic + flocculant + antifoam adjacency at the heap-leach + mill + tailings-treatment circuit uses HDPE rotomolded 1,500-10,000-gallon storage in the standard mining 5-brand network.

3. Regulatory Framework

OSHA 29 CFR 1910.1200 + 1910.1000 + 1910.151 Cyanide Standard. Sodium cyanide solid + solution is OSHA Acute Toxicity Cat 2 + Aquatic Toxicity Cat 1 + ceiling-limit at 5 mg/m3 NaCN as cyanide skin-notation. Hydrogen cyanide HCN gas is OSHA ceiling 4.7 ppm + ACGIH TLV-Ceiling 4.7 ppm + IDLH 50 ppm + acute-fatal at 100-300 ppm air concentration. Worker SDS + container labeling + PPE specification (full-face supplied-air respirator + chemical splash suit + double nitrile glove + steel-toe boots + buddy-system + emergency-shower-eye-wash within 10 seconds + cyanide-antidote kit at every work area + designated trained medical-response team + emergency-medical evacuation procedure per OSHA 29 CFR 1910.151 + 1910.146 confined-space + 1910.120 HAZWOPER framework + cyanide-poisoning awareness training annually for every cyanide-area worker) is mandatory.

MSHA 30 CFR 56/57 Surface-and-Underground Mine Standard. MSHA 30 CFR 56.5001 + 57.5001 cyanide air-contaminant ceiling 5 mg/m3 + escape-respirator + emergency-evacuation training per 30 CFR 56.13030 cyanide. Annual MSHA Part 46 + Part 48 cyanide-area worker refresher training.

International Cyanide Management Code + ICMI Signatory. The International Cyanide Management Code is a voluntary mining-industry program administered by the International Cyanide Management Institute that establishes Standard of Practice across nine principles: (1) Production, (2) Transportation, (3) Handling and Storage, (4) Operations, (5) Decommissioning, (6) Worker Safety, (7) Emergency Response, (8) Training, (9) Dialogue. Mine + producer + transporter Signatory commitment + triennial third-party audit + corrective-action-plan + public-disclosure framework. Most major U.S. + Canadian + Latin-American + Australian + African gold producers are ICMI Signatory at the mine-site + producer + transporter level.

EPA Method 9010 / 9012 / 9013 / 9015 Cyanide Analytical. Free-CN + WAD-CN + total-CN distillation + colorimetric + ion-selective-electrode + automated-flow-injection cyanide analytical methods per EPA SW-846 + ASTM D6888 free-CN + D7237 WAD-CN + Standard Methods 4500-CN framework at every NPDES + RCRA + ICMI compliance sample.

EPA NPDES + State Mining Discharge Permit. Heap-leach cyanide solution discharge to surface water is generally prohibited at greater-than-0.005 mg/L free-CN per state water-quality criterion; tailings-area cyanide-bearing solid + liquid discharge requires state-specific mining permit + EPA NPDES outfall + tailings-impoundment + reclamation-bond framework.

EPA SPCC + State Cyanide-Bearing Tailings Code. Cyanide-bearing solution storage requires double-liner + leak-detection + secondary-containment per state-specific cyanide-bearing tailings code (Nevada NAC 445A, Colorado Rule 11 cyanide closure + reclamation, Alaska Plan of Operations + ADEC mining permit, California SMARA + DPR Mine Plan, Montana Hard-Rock Mining DEQ-7, Arizona ADEQ Mining Aquifer Protection Permit, New Mexico Hard-Rock Mining + MMD reclamation + EMNRD).

RCRA Subtitle C Hazardous Waste. Cyanide-bearing solid + liquid waste at greater-than-1000 mg/L total-CN classifies as RCRA hazardous waste under D003 reactive characteristic + EPA waste-code F006 + F007 + F008 + F009 cyanide-plating-specific. Mining-extracted ore + tailings benefit from Bevill exemption to RCRA Subtitle C at most heap-leach + mill operations under 40 CFR 261.4(b)(7).

DOT 49 CFR 173 + UN 1689 Sodium Cyanide. Sodium cyanide solid + solution shipping is UN 1689 Sodium cyanide solid Class 6.1 PG I or UN 3414 Sodium cyanide solution Class 6.1 PG I at greater-than-2% NaCN. ICMI-certified intermodal cyanide-isotainer is the dominant rail + truck + ocean-freight shipping format. State-specific cyanide-route permitting + emergency-response framework + driver-training + routing-restriction.

4. Storage System Specification

Primary Heap-Leach Barren and Pregnant Cyanide Solution Tank (OUTSIDE OneSource HDPE Scope). Primary heap-leach barren + pregnant cyanide solution storage at 100,000-2,000,000-gallon scale uses welded-carbon-steel ICMI-coded vessel with epoxy or coal-tar-epoxy interior lining + double-wall or single-wall-with-secondary-containment-pond + leak-detection + emergency-overflow-to-event-pond per ICMI Standard of Practice 4 + state-specific cyanide-bearing tailings code. Construction at qualified ICMI-Signatory steel-tank fabricator with welded-seam radiographic-inspection + holiday-test on lining + cathodic protection at buried piping + stainless steel valve trim. This specification is OUTSIDE OneSource Plastics' HDPE 5-brand scope; we refer those specifications to qualified ICMI-Signatory steel-tank fabricators.

Heap-Pad and Solution Pond HDPE Geomembrane Liner. Heap-leach pad + barren-pond + pregnant-pond + event-pond + stormwater-pond uses HDPE 60-mil or 80-mil double-liner construction with primary + secondary liner separated by geonet drainage layer + leak-detection sump + GCL or compacted-clay subliner per state-specific cyanide-bearing tailings code. Liner installation by qualified geomembrane installer with electric leak-detection survey at acceptance per ASTM D7007. Heap-pad solution distribution piping is HDPE SDR 11 or SDR 17 with drip-emitter at the standard 0.005-0.015 gpm/ft2 application rate.

Process Water and Lime Makedown Tank (HDPE Scope). Process-water + lime-slurry-makedown + flocculant-makedown + xanthate + dithiophosphate + acid + caustic + antifoam reagent makedown at the mine site uses 1,500-10,000-gallon HDPE or XLPE rotomolded vertical flat-bottom or shallow-cone-bottom atmospheric tank, 1.85 specific-gravity rated, mounted on level reinforced-concrete pad with secondary containment via integral catch-basin or external concrete-bermed pad sized to 110% of largest-tank volume; 3-4 inch flanged top fill + atmospheric vent; 2-3 inch flanged bottom outlet with full-bore PVC ball valve; 18-24 inch top manway; ultrasonic level transmitter; sample valve; opaque-pigmented HDPE for UV protection at outdoor service; freeze-protection insulation + heat-trace at northern-state and Canadian operation.

Solution Makedown Plant Vented Enclosure. On-site sodium-cyanide solution makedown is conducted in vented enclosure with double-wall + secondary-containment + emergency-deluge + HCN-monitoring + supplied-air-respirator + Buddy-system + designated trained operator + cyanide-antidote kit + emergency-medical-response per ICMI Standard of Practice 1. Makedown vessel specification is welded-stainless or specially-engineered HDPE-lined steel typically OUTSIDE HDPE 5-brand scope.

Cyanide-Destruction Reaction Tank. INCO SO2/Air or alkaline-chlorination or peroxide cyanide-destruction reaction tank at 50,000-500,000-gallon scale uses FRP vinyl-ester or stainless-steel construction OUTSIDE HDPE scope. Reagent makedown for SO2 + Cu sulfate + chlorine + peroxide + lime is HDPE 5-brand scope at 1,500-10,000-gallon scale.

Containment and Spill Pad. All cyanide-bearing solution storage requires secondary containment per EPA SPCC + state-specific cyanide-bearing tailings code; concrete-bermed pad with HDPE primary + secondary liner + leak-detection sump + cyanide-resistant epoxy or polyurea topcoat.

5. Field Handling Reality

Handler PPE. Cyanide-area entry: full-face supplied-air respirator (SAR) with escape bottle for any approach to high-concentration solution makedown + transfer + sampling, half-mask air-purifying respirator with cyanide cartridge for routine open-system process-water + lime-makedown adjacency work, chemical splash suit + chemical-resistant apron at any open-system handling, double nitrile or neoprene chemical-resistant glove at any contact, chemical splash goggles + face shield, steel-toe boots with chemical-resistant overshoe, eye-wash + emergency shower per OSHA 29 CFR 1910.151 within 10 seconds of work area, cyanide-antidote kit (amyl nitrite + sodium nitrite + sodium thiosulfate or hydroxocobalamin Cyanokit) at every cyanide-area work zone with trained medical-response team on standby, Buddy-system mandatory at any high-concentration cyanide entry, continuous-personal HCN monitor at every cyanide-area worker.

HCN Detection and Alarm Discipline. Continuous fixed-point HCN gas detector at solution-pond + tank + makedown-plant + electrowinning-cell + Merrill-Crowe-press + sample-station + truck-load-out area at 4.7 ppm Ceiling alarm + 10 ppm shutdown + portable HCN monitor at every cyanide-area worker is mandatory. HCN-detector calibration + bump-test + battery-check at shift-start. HCN-alarm response per site-specific Cyanide Emergency Response Plan + ICMI Standard of Practice 7.

pH-Control Discipline. Continuous pH monitoring at every cyanide-bearing solution tank + pond + transfer point + heap-pad return + barren-tank + pregnant-tank with automated lime-dosing trim is mandatory; pH-low alarm at 9.5 + emergency-shutdown + lime-overdose at 9.0 with automated recirculation lockout. Alkaline pH 10.5-11.5 protect specification suppresses HCN gas evolution to less-than-1 ppm at the solution-air interface.

Cargo-Tank Receipt and Solid Briquette Off-Loading. Sodium-cyanide solid briquette receipt: 1-tonne flow-bin or rail-car solid delivery is off-loaded at vented-enclosure makedown plant with supplied-air-respirator + chemical-suit + double-glove + Buddy-system + ICMI-trained operator + emergency-deluge + HCN-monitoring + cyanide-antidote-kit. 30% NaCN solution intermodal isotainer receipt: ICMI-certified intermodal isotainer with bottom-discharge + pre-transfer site-survey + supplied-air-respirator + chemical-suit + Buddy + transfer-rate-monitoring + leak-detection + emergency-deluge.

Wildlife-Protection and Pond-Hazing Discipline. Open ponds at greater-than-50 ppm WAD-CN are prohibited under ICMI Standard of Practice 4.6 + state mining permit; open ponds at less-than-50 ppm WAD-CN must be netted with bird-exclusion netting + fenced + posted + hazed with propane-cannon + recorded-distress-call + scarecrow + LRAD + falconry to exclude waterfowl + raptor + mammal. Wildlife-mortality tracking + reporting is mandatory under ICMI + state permit + USFWS Migratory Bird Treaty Act + Bald and Golden Eagle Protection Act framework.

Process-Water Impurity Management. Copper + zinc + iron + nickel + cobalt + mercury cation impurities consume free-CN as metal-cyanide-complex + elevate WAD-CN + complicate cyanide-destruction; raw-water + recycled-water analysis at quarterly frequency with metal-impurity budget management is routine. High-impurity site (Cripple Creek elevated-Hg, Carlin elevated-Hg-Sb) implements ion-exchange + activated-carbon + sulfide-precipitation pre-treatment.

QC Sampling and Verification. Each barren-tank + pregnant-tank + makedown-batch + pond + outfall sample collection: free-CN per ASTM D6888, WAD-CN per ASTM D7237, total-CN per EPA Method 9010 distillation, Au + Ag assay per fire-assay or AAS, pH continuous + grab confirmation, dissolved-oxygen at leach circuit, conductivity, metal-impurity (Cu + Zn + Fe + Hg) at quarterly frequency.

Spill Response. Cyanide-solution spill response: small-volume spill is contained at secondary-containment + neutralized in place with hypochlorite or peroxide cyanide-destruction reagent + sampled to less-than-50 mg/L WAD-CN + transferred via vacuum-truck to event-pond. Large-volume spill triggers site Cyanide Emergency Response Plan + ICMI Standard of Practice 7 + state-agency notification + downstream water-quality sampling.

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