Dithiophosphate (Aerofloat) Storage — Mining Flotation Co-Collector Tank Selection
Dithiophosphate Storage — Aerofloat Tank Selection for Mining Flotation Co-Collector Service
Dithiophosphates — sodium and potassium salts of dialkyl dithiophosphoric acid, with general formula (RO)2P(=S)SNa or (RO)2P(=S)SK where R is methyl, ethyl, isopropyl, isobutyl, butyl, hexyl, or octyl — are the workhorse "secondary" sulfide-flotation collectors of the mining industry. Most dithiophosphates supply as 50-65% aqueous solutions in 200-liter drums, 1,000-liter IBC totes, or bulk tank-truck for large concentrators; some supply as solid pellet or flake (Aerofloat-31 dicresyl). Dithiophosphates are dosed at 5-50 g/t into the rougher conditioner box, often in conjunction with a primary xanthate (SIPX, SIBX, PAX) for combined collector strength. They are particularly strong for silver-bearing minerals (argentite, polybasite, tetrahedrite) and gold-bearing minerals where xanthates alone underperform. Importantly, dithiophosphates do NOT have the catastrophic CS2-decomposition pathway of xanthates — this is the operating-cost-vs-reagent-trade-off favoring dithiophosphates in safety-conscious modern operations despite the slightly higher reagent unit cost. This pillar covers honest material compatibility, real producer landscape, OSHA / MSHA hazard communication, storage system specification, and field handling reality for an Aerofloat / dithiophosphate flotation reagent installation.
Regulatory citations point to OSHA 29 CFR 1910.1200 GHS, MSHA 30 CFR 56/57 Subpart D mine air contaminant control, ACGIH TLV-TWA 1 ppm H2S with 5-ppm STEL (relevant to acid-contamination-induced H2S release), DOT UN 3265 (specific acidic-grade Aerofloat) or non-regulated transport for neutral sodium/potassium-salt aqueous solutions, EPA NPDES Multi-Sector General Permit (MSGP) Sector G for metal-mining stormwater, and Marpol Annex II marine pollutant classification for marine ocean shipment.
1. Material Compatibility Matrix
Dithiophosphate aqueous solutions are mildly alkaline (pH 8-10) for the sodium-and-potassium-salt forms and mildly acidic (pH 4-6) for the acidic-form Aerofloats. Material selection is constrained by tolerance of mild alkalinity or mild acidity (depending on grade), tolerance of low-level H2S vapor on long storage, and elimination of strong-acid contamination pathways which would liberate hydrogen sulfide.
| Material | Neutral Aerofloat 50% | Acidic Aerofloat 50% | Notes |
|---|---|---|---|
| HDPE / XLPE | A | A | Standard for storage tanks; opaque preferred |
| Polypropylene | A | A | Standard for fittings, valves, pump heads |
| PVC / CPVC | A | A | Standard for low-pressure piping |
| FRP vinyl ester | A | A | Standard for larger 3,000-15,000 gal storage |
| 316L stainless | A | B | Acceptable; passivate against sulfide pitting at hot spots |
| Carbon steel | C | NR | Sulfide attack; never in contact |
| Copper / brass | NR | NR | Sulfide attack and product contamination; never |
| Galvanized steel | NR | NR | Zinc reacts with dithiophosphate; never |
| EPDM | A | B | Acceptable for neutral; check OEM for acidic grade |
| Viton (FKM) | A | A | Premium gasket and pump diaphragm material |
| Buna-N (Nitrile) | B | B | Acceptable for short service |
| Natural rubber | NR | NR | Sulfide attack; never |
For the dominant secondary-collector use case, opaque HDPE rotomolded storage tanks with PP fittings, EPDM gaskets (for neutral grades) or Viton gaskets (for acidic grades), and FRP day-tanks for solution distribution to the rougher are the standard package. Carbon steel and copper-alloy materials are absolutely excluded from any dithiophosphate wetted-contact surface; sulfide chemistry consumes the reagent and contaminates the circuit.
2. Real-World Industrial Use Cases
Silver-Bearing Polymetallic Flotation (Strongest Use Case). Dithiophosphates outperform xanthates on silver minerals (argentite Ag2S, polybasite, tetrahedrite, freibergite) at typical 0.05-1 g/t silver feed grades. Operations such as Fresnillo (Mexico), Penasquito (Mexico), Greens Creek (Alaska), San Cristobal (Bolivia), and Kupol (Russia) run dithiophosphate co-collector chemistry with Aerofloat-208, -211, or -238 dosed at 5-25 g/t in addition to a xanthate primary at 30-60 g/t. The combined collector pull on silver-bearing concentrate exceeds either single-reagent chemistry alone.
Gold Sulfide Co-Collector. For refractory gold ores in pyrite or arsenopyrite, Aerofloat-31 (dicresyl) or Aerofloat-208 are dosed at 10-30 g/t alongside SIBX or PAX in the rougher to enhance gold-bearing-sulfide recovery. Witwatersrand (South Africa), high-grade gold belt (Nevada), and Australian gold operations run this chemistry. The dithiophosphate's selective gold-affinity is well-documented in SME Mineral Processing Plant Design.
Copper Sulfide Co-Collector. Selected primary copper porphyry concentrators add Aerofloat-208 or Aerofloat-238 at 5-15 g/t to the SIPX primary chemistry to improve recovery of partially-oxidized chalcocite, secondary covellite, and chalcopyrite-bornite blends. Operations include selected Chilean and Peruvian copper porphyries and selected African copperbelt operations.
PGM Flotation. Bushveld Complex platinum-group-metal flotation in South Africa frequently uses dithiophosphate co-collectors alongside xanthate primary collectors and thionocarbamate co-collectors for selective PGM-mineral pull. Dosing 5-20 g/t.
Lead-Zinc Selective Flotation. Aerofloat-211 (sodium diethyl, neutral) is used in the lead-cleaner stage at 5-15 g/t to improve galena selectivity vs sphalerite. The neutral grade is preferred to avoid pH disruption in the cleaner circuit.
Industrial-Mineral Flotation. Sulfide-removal flotation in coal preparation, kaolin processing, and iron ore concentrator beneficiation can use dithiophosphates as alternatives to xanthates when CS2-handling-infrastructure investment is uneconomic for the reagent volume.
3. Regulatory Hazard Communication
OSHA / GHS Classification. Dithiophosphate aqueous solutions carry GHS classifications H302 (harmful if swallowed), H315 (skin irritation), H318 (causes serious eye damage) for higher-strength solutions, H335 (respiratory irritation), H411 (toxic to aquatic life with long-lasting effects). The acidic-grade Aerofloats add H290 (may be corrosive to metals) and H314 (causes severe skin burns and eye damage at undiluted concentration). H2S vapor liberated by strong-acid contact is a separate hazard with ACGIH TLV-TWA 1 ppm 8-hour and STEL 5 ppm 15-minute — this is much lower than the H2S OSHA PEL ceiling 20 ppm 29 CFR 1910.1000 Z-2 reflecting modern toxicology.
NFPA 704 Diamond. Neutral sodium-salt Aerofloat aqueous solutions rate approximately Health 2, Flammability 0, Instability 0. Acidic-grade Aerofloats rate Health 3, Flammability 0, Instability 0 with H2S-on-strong-acid release. Storage building classification per IFC Chapter 50 and Marpol Annex II is corrosive-liquid storage for acidic grades; non-regulated for neutral aqueous-salt grades.
DOT and Shipping. Acidic-grade Aerofloats ship under UN 3265 (Corrosive Liquid, Acidic, Organic, NOS), Hazard Class 8, Packing Group II or III depending on concentration. Neutral sodium / potassium-salt aqueous solutions are typically non-regulated for transport (no UN number; LQ exempt). IBC tote and tank-truck shipping uses qualified corrosive-liquid packaging for the acidic grades. Marine ocean shipment for both grades requires Marpol Annex II marine-pollutant declaration.
MSHA 30 CFR 56/57 Mining Compliance. Surface metal/nonmetal mines (CFR 56) and underground metal/nonmetal mines (CFR 57) must control mine-air contaminants per Subpart D. The relevant air-contaminant limits apply to H2S vapor potentially generated from acid-contamination-induced dithiophosphate decomposition. Continuous H2S monitoring at the dosing station is recommended for acidic-grade installations.
EPA NPDES MSGP Sector G. Metal-mining stormwater discharges fall under EPA NPDES Multi-Sector General Permit Sector G. Aerofloat-storage building stormwater must be diverted to the tailings impoundment or to a process-water sump rather than to discharge.
4. Storage System Specification
Bulk Liquid Storage. Aerofloat aqueous solutions arrive at mine sites in 200-liter drums, 1,000-liter IBC totes, or 5,000-7,500-gallon tank-truck loads at large operations. Drum storage requires a covered indoor location with secondary containment; IBC and tank storage uses outdoor or sheltered installation with a containment pad sized to 110% of largest container. Bulk tank storage (3,000-15,000 gallons) uses opaque HDPE rotomolded or FRP vinyl-ester construction. Inventory turnover is targeted at 60-180 days; dithiophosphates have longer shelf life than xanthates due to absence of self-heating decomposition.
Day-Tank for Continuous Dosing. Concentrators typically use a smaller day-tank (200-500 gallons HDPE) decoupled from the bulk tank for steady metering pump suction to flotation cells. The day-tank refills from the bulk tank on level control. Solution residence time in the day-tank is targeted at less than 30 days.
Pump Selection. Diaphragm metering pumps (PTFE or EPDM diaphragm depending on grade, EPDM check valves, PP head) are standard for dithiophosphate dosing. ProMinent, LMI, and Grundfos brands have Aerofloat-service-rated configurations. For acidic grades, Viton elastomers throughout. NEVER use copper or brass pump bodies.
Secondary Containment. Per IFC Chapter 50 and most state mining regulations, reagent storage tanks above 1,000 gallons require secondary containment sized to 110% of the largest tank capacity. Acidic-grade Aerofloat installations require additional H2S vent management on the secondary containment to prevent vapor accumulation in low-lying spaces.
5. Field Handling Reality
The Dithiophosphate-vs-Xanthate Trade. The fundamental advantage of dithiophosphates over xanthates is the absence of the CS2-decomposition pathway. Dithiophosphates do NOT self-heat in damp warm storage, do NOT release violent CS2 vapor on acid contact, do NOT require the dedicated Class 4.2 storage-building infrastructure that xanthates demand. The trade-off is a slightly higher unit reagent cost ($3.20-$5.50 per pound for 50% active dithiophosphate vs $2.40-$3.80 per pound for 90% active SIPX, comparing on active-ingredient basis). For mining-investment economics, the trade-off favors dithiophosphates at smaller-scale or safety-conscious operations and favors xanthates at large-volume operations where the CS2-management infrastructure is already built. Many concentrators run BOTH chemistries simultaneously with combined-collector dosing for performance and risk-management balance.
The Odor Reality. Dithiophosphates have a characteristic sulfur / mercaptan odor at the bulk-tank breath level. The odor is mild compared to xanthate CS2 but is detectable at parts-per-million levels and triggers complaints from non-mining-trained operators encountering a dosing station for the first time. Mine-site SDS files and operator-training programs include a "this is normal odor, not a leak" note for the reagent.
Acid Contamination = H2S Release. Strong acid contact with dithiophosphate solution liberates H2S vapor. The release is much less violent than xanthate-CS2 release but is enough to require continuous H2S monitoring at acidic-grade installations. Reagent-room layout requires segregation from sulfuric-acid storage and from cyanide-circuit acid-spill-containment areas.
Marine Pollutant Reality. Dithiophosphate's H411 marine-toxicity classification means tailings-pond overflow, stormwater discharge, and accidental release to surface water are all regulatory events. Tailings-impoundment design considers dithiophosphate residual in the tailings water column.
PPE. Tank-fill and dosing-station operations require chemical-splash goggles, butyl rubber or Viton-coated gloves, Tyvek or equivalent disposable coveralls, and steel-toe boots. Acidic-grade Aerofloat handling additionally requires acid-resistant face shield and apron during drum-decanting. Eye-wash and emergency shower at the dosing station are mandatory.
Related Chemistries in the Severe-Hazard Specialty Cluster
Related chemistries in the severe-hazard specialty cluster (HF-related + Cr(VI) + heavy-metal + reactive amine + cyanide + hydrosulfide + reactive monomer + chlorinated acid + aromatic-amine intermediate + carbonyl-toxin + reactive-cyclic-diketone + quat-amine biocide + bromate oxidizer + reactive diene-monomer + acrylate-monomer + reactive vinyl-aromatic + acrylamide + xanthate + mining sulphidizing-agent + reactive isocyanate + reactive-epoxy + formaldehyde-resin chemistry):
- Potassium Amyl Xanthate (PAX) — Sulfur-collector companion chemistry
- Sodium Ethyl Xanthate (SEX) — Sulfur-collector companion chemistry
- Sodium Isopropyl Xanthate (SIPX) — Sulfur-collector companion chemistry
- Thionocarbamates — Sulfur-collector sister chemistry
- Sodium Hydrosulfide (NaSH Mining) — Sulphidizing-agent companion chemistry
Related Hub Pillars
For broader chemistry context, see the OneSource Plastics high-traffic chemical-compatibility hub pillars: