Mineral acids
An acid is bought on concentration and delivered on materials compatibility.
Get the first wrong and the process underperforms. Get the second wrong and the tank fails. Concentrated sulfuric acid can be carried in carbon steel; dilute sulfuric acid destroys it. That reversal is counter-intuitive, it is the single most common cause of damage in this trade, and it is why we confirm the receiving equipment before we confirm the fixture.
The programme
Three acids, three different industries, three different failure modes.
Into fertiliser production, metal leaching and treatment, steel pickling, water treatment and oilfield stimulation. Supplied in dedicated lined tanks and ISO containers, bought against a firm requirement rather than held.
- Sulfuric acid — technical, 93–98%
- The highest-tonnage industrial chemical in the world and the backbone of phosphate fertiliser production, copper and nickel leaching, and steel pickling. Concentration is not a detail: 98% and 93% behave differently in storage, in dilution and against your metallurgy.
- Nitric acid — non-concentrated, HNO₃ 57–60%
- Into nitrogen fertiliser production, metal treatment, passivation and pickling of stainless steel, and chemical synthesis. Non-concentrated grade is the industrial standard; it is also a restricted explosives precursor and carries end-use screening as standard.
- Hydrochloric acid — synthetic technical
- Synthetic route rather than by-product, which is what governs the impurity profile. Into steel pickling, water treatment, oilfield acidising, brine production and pH control. The acid whose vapour, not just whose liquid, damages the installation around it.
The one that costs money
Materials compatibility, confirmed before fixture.
We ask what the acid is going into — tank material, lining, gaskets, pump internals, vent arrangement — before quoting. Not to be difficult. Because a mismatch here writes off a tank, and occasionally rather more than a tank.
| Acid | Behaviour | What that means for the receiving equipment |
|---|---|---|
| Sulfuric, concentrated (93–98%) | Passivates carbon steel — a protective iron sulfate film forms and holds, provided velocity is low and the acid stays concentrated. | Carbon steel is standard for storage at these strengths. The film is fragile: high velocity, elevated temperature or dilution strips it and corrosion runs away. Hydrogen is generated as it does, which is why vents on sulfuric tanks matter. |
| Sulfuric, dilute | Aggressively attacks carbon steel. The concentration curve is not linear and the worst zone is not where people expect it. | Lined or alloy equipment. Any point where water can enter a concentrated system — a wash line, a rain ingress, a badly placed vent — creates dilute acid locally and starts the failure there. |
| Nitric, 57–60% | Strongly oxidising. It passivates austenitic stainless steel, which is the reason it can be handled at all, and attacks most other common metals. | 304L or 316L stainless is the normal specification. Aluminium is used at high concentrations and is not appropriate here. Carbon steel is not an option at any concentration. |
| Hydrochloric, synthetic technical | Attacks nearly all common metals including every grade of stainless steel, and the vapour above the liquid attacks the installation around the tank. | Rubber-lined steel, FRP, PVDF, PP or PTFE-lined equipment. Vapour management is part of the design, not an afterthought — unvented or badly vented HCl storage corrodes the building it sits in. |
Dilution is exothermic and the order is not optional. Acid into water, always, slowly, with agitation and cooling. Water into concentrated sulfuric acid boils locally and ejects acid from the vessel. This is basic, it is on every safety data sheet, and it still happens on sites where the person doing it was never told. If your team is new to concentrated acid handling, say so — we would rather arrange the briefing than read about it later.
Specification
What is on the certificate, and what the buyer actually cares about.
Assay is the headline. The impurities are what decide whether the acid can be used in your process at all — and which impurities matter is entirely application-dependent.
| Parameter | Why it is in the specification |
|---|---|
| Assay | Concentration as % w/w. The commercial basis, and often the basis of pricing per tonne of contained acid rather than per tonne of solution. |
| Iron | The impurity that matters most across the widest range of uses. In pickling it contaminates the bath; in leaching it changes solution chemistry; in electronics or battery applications it is disqualifying at levels that look trivial. |
| Chloride (in sulfuric and nitric) | Pitting corrosion of stainless steel. A low-chloride specification is what allows stainless equipment to be used at all in some services. |
| Sulfate (in hydrochloric) | Carries through into brine and water-treatment applications and precipitates where it is not wanted. |
| Heavy metals — arsenic, lead, mercury | Regulatory limits in fertiliser and water-treatment use, and process poisons in catalytic applications. |
| Nitrogen oxides (in nitric) | Dissolved NOx colours the acid and indicates how it was made and stored. Relevant to both handling and process behaviour. |
| Residue on ignition | Non-volatile matter. A general cleanliness indicator and a direct problem in any application where the acid is consumed. |
| Colour and appearance | The cheapest diagnostic available. Sulfuric acid darkened by organic contamination is telling you something before any laboratory does. |
Transport
Classification confirmed in writing before booking.
All three are Class 8 corrosives. Nitric acid additionally carries an oxidiser risk, and that changes what it can travel and be stored with.
- Sulfuric acid
- UN 1830, Class 8. Dedicated tanks; carbon steel at the concentrations supplied, with the velocity and temperature limits observed.
- Nitric acid
- UN 2031, Class 8, with an oxidiser subsidiary risk at higher concentrations. Stainless equipment, and segregation from combustibles and from reducing agents that is not negotiable.
- Hydrochloric acid
- UN 1789, Class 8. Lined tanks and ISO containers, with vapour management at both ends.
- Segregation
- Acids and cyanides must never be stowed or stored together in any circumstance — contact generates hydrogen cyanide gas. Where a buyer takes both from us, the consignments are planned separately and we say so in writing. See Mining Chemicals.
- Modal rules
- IMDG for sea, ADR for road, RID for rail, IATA where air is even possible. UN number, class, packing group, tank code and segregation group confirmed before booking rather than assumed from a previous shipment.
- Emergency response
- Documentation accompanies every consignment, in the language of the transit and destination countries, with a monitored contact that answers.
Regulatory
Two of these three are restricted explosives precursors.
Under the EU regulation on the marketing and use of explosives precursors, nitric acid and sulfuric acid are Annex I restricted substances. The restriction governs making them available to members of the general public; supply to professional users for a demonstrable business need is the normal industrial trade, and it comes with duties.
| Substance | Limit value | Upper limit for licensing |
|---|---|---|
| Nitric acid | 3% w/w | 10% w/w |
| Sulfuric acid | 15% w/w | 40% w/w |
| Sodium and potassium chlorate and perchlorate | 40% w/w | No licensing permitted |
| Hydrochloric acid | Not listed in Annex I or Annex II of the regulation. It is still screened here, because end-use screening is our practice rather than a compliance minimum. | |
- What a professional user is
- A person or company with a demonstrable need for the substance for purposes connected with its trade, business or profession. Demonstrable is the operative word: we ask what the acid is for, and a vague answer ends the enquiry rather than slowing it down.
- Suspicious transaction reporting
- Economic operators are required to report suspicious transactions, disappearances and thefts to the national contact point within 24 hours, and to have procedures for detecting them. We operate those procedures. It is worth knowing that we do, and it is worth knowing we will not discuss a report with the counterparty it concerns.
- Records
- Transaction data retained for the period the regulation requires — 18 months — and available to the competent authority on request.
- Outside the EU
- Destination controls differ and several jurisdictions apply tighter rules than the EU does. The import licence position at the destination is confirmed before shipment, not after arrival.
Straight answer
What it is not, said before you find out.
- We do not supply the general public, and we do not supply through intermediaries who will
- These are restricted substances. An enquiry that cannot evidence a professional end use does not get a price, and the commercial terms attached to it do not change that.
- We will not fix before the receiving equipment is confirmed
- Tank material, lining, gaskets, pumps, vents. This is the question that prevents the expensive failure, and asking it is not bureaucracy.
- Concentrations are not interchangeable
- 93% and 98% sulfuric are different products in storage behaviour, freezing point and metallurgy. Substituting one for the other because it is what was available is a decision, not a convenience, and it should be yours rather than ours.
- A type certificate is not a certificate of analysis
- Batch-specific, from the producing plant, tied to the consignment. A generic sheet with the product name on it tells you nothing about what is in the tank.
- Freight and equipment are most of the delivered cost
- Acid is heavy, low-value per tonne and needs dedicated lined equipment that does not backhaul. The routing decides the economics more than the acid price does, which is why we ask about the destination early.
- We will decline rather than pass an enquiry on
- Where an end use cannot be cleared, we do not refer it to someone else. That would be moving the problem, not solving it.
How to specify
Eight lines, and we can price it properly.
- 1 · Acid and concentration
- With the tolerance you can accept, not just the target.
- 2 · End use
- The process it is going into. This is a screening requirement and it is also how we tell you if the grade is wrong.
- 3 · Impurity limits
- The parameters your process actually cares about, with test methods. Iron and chloride at minimum.
- 4 · Receiving equipment
- Tank material and lining, gaskets, pump internals, vent arrangement, and whether the acid will be diluted on site.
- 5 · Quantity and pattern
- Parcel size and whether this is one shipment or a term supply. Dedicated equipment rewards a programme.
- 6 · Delivery format
- Bulk tank, ISO container, IBC or drum, and the discharge arrangement at your end.
- 7 · Destination
- Port and country, for the import licence position, the SDS language and the modal classification.
- 8 · Documentation required
- Which certificates have to travel with the goods and which are needed in advance for permitting.
Inspection
What we check, and what travels with the goods.
- Batch certificate of analysis
- Issued by the producing plant against the agreed parameter and test-method schedule, tied to the consignment rather than to the product name.
- Independent verification
- Where contracted, an agency appointed for the consignment — SGS, Bureau Veritas or Intertek — instructed jointly, sampling under supervision with the quality determination point named in the contract, and sealed retained samples held at both ends.
- Equipment cleanliness
- Previous cargo declaration and tank cleanliness certificate for the equipment used. On acids this is not a formality — residues from an incompatible previous cargo are a safety event, not a quality deduction.
- Documentation per shipment
- Safety data sheet in the destination format and language, REACH/CLP or GHS as applicable; batch certificate of analysis; dangerous goods declaration with UN number, class, packing group and tank code; emergency response documentation; import licence or permit where the destination requires one; certificate of origin; bill of lading; and the inspection report where an agency is appointed.
Enquiries
Every enquiry is answered by the desk that handles it.
Send the product, quantity, delivery basis, destination and timing. We revert with availability, an indication and the documentation that accompanies it. Specifications are released once we know who we are speaking with.