Sulfuric acid (CAS 7664-93-9, HS code 2807.00.00, UN 1830) is traded from China as 92.5% technical grade, 98.0% concentrated grade, and oleum with 20% or 25% free SO3. “Concentrated” alone is not a specification; a contract should fix total acidity, residue on ignition, iron, arsenic, mercury, lead, transparency, and colour under GB/T 534-2014, with methods cross-checked against ASTM E223-16 or ISO 910:1977. The commercial screen must also establish whether the Chinese supplier can lawfully export the acid or is domestic-only. Production origin at sulfur-burning contact plants, pyrite roasters, or zinc-lead smelter off-gas units changes the trace impurity fingerprint enough to affect phosphate digestion, alkylation, battery electrolyte, and sulfonation.

Full Export Licence or Domestic Only? How to Screen a Chinese Acid Supplier

Domestic-only status does not mean the supplier cannot produce acid; it means the legal entity lacks the export operating qualifications to declare an HS 2807.00.00 shipment directly. Such a supplier may hold a hazardous chemical operating permit and a valid industrial production licence, but the bill of lading would require another exporter to act as principal. Full export authority adds a Foreign Trade Operator Registration, a Customs Registration Certificate, and, where the specific acid is control-listed, an export licence reference issued by the Ministry of Commerce. A screening file should start with the unified social credit code and compare the declared business scope against the permit. The exporter name on the quotation must be the same entity on the customs declaration and the bill of lading. If a domestic-only supplier quotes CFR or CIF terms using an agent, the arrangement creates a title-transfer gap and increases dangerous-goods clearance risk.

Document authenticity matters more than the document list. Export licence numbers and hazardous chemical operating permits can be verified through the issuing authority or official portals; a PDF alone does not establish current validity. The chemical itself must move as UN 1830, IMO Class 8, Packing Group II, with a Dangerous Goods Packing Certificate for the chosen IBC or ISO tank. A safety data sheet prepared under GB/T 16483-2008 should accompany the cargo. For bulk ISO tanks, the current periodic inspection date, tank approval number, and previous lading compatibility record should be transmitted before loading. A supplier that cannot provide a valid packaging certificate or customs registration code should be treated as domestic-only, regardless of contract terms.

Destination jurisdiction also matters. Under REACH, sulfuric acid is a registered substance and the EU importer must confirm the registration number for the annual tonnage band; the Chinese supplier’s export permit does not satisfy REACH registration. Under US TSCA, sulfuric acid is listed on the inventory, but storage and transport can trigger state hazardous materials permits. A full export licence is only the export-side authorization; it does not transfer to destination permits.

Customs inspection in China for sulfuric acid focuses on dangerous goods packaging and, if applicable, export commodity inspection. A full export-licensed supplier should be able to produce a packaging performance test report for the 250 kg drum, 1.4 t IBC, or 25 t ISO tank type. The report should identify the certifying body, the container marking, the hydrostatic test date for IBCs, and the last periodic inspection date for ISO tanks. If the CoA is produced by the manufacturer but the loading is conducted at a third-party terminal, the buyer should request a terminal-issued loading certificate that records the tank number, line connections, and final volume. Discrepancies between the terminal certificate and the bill of lading volume often indicate a transshipment or blending event that was not declared.

Typical export packaging for Chinese acid includes 250 kg HDPE drums, 1.4 t IBC containers, and 25 t ISO tank containers. The 98.0% grade can solidify in unheated storage when ambient temperature falls below roughly 0–3 °C; 93.0% acid remains pumpable at substantially lower winter temperatures, which is why many mining leach operations specify 93.0% for uninsulated tanks. Bulk acid tanks and isotanks are usually constructed from carbon steel if the acid is kept in the concentrated range; dilute acid below approximately 65% is far more aggressive and requires HDPE, fiberglass-reinforced plastic, or lined steel. Discharge systems on Chinese export packages often use seal-less PTFE-lined magnetically coupled pumps to prevent mechanical seal failures. Gasketed joints on heated acid service should be PTFE or fluoropolymer-lined; black-rubber gaskets degrade rapidly above 35 °C and cause vapor leaks at the manway.

Phosphate Rock Digestion Demands Tight Filterability Control

Wet-process phosphoric acid reacts ground phosphate rock with sulfuric acid at 70–80 °C. The acid is diluted from 93.0% or 98.0% merchant strength before it contacts the rock slurry. The main process conflict is not P2O5 conversion but gypsum filtration: calcium sulfate dihydrate must form crystals that dewater on a horizontal vacuum belt filter without blinding the filter cloth. Operators control free sulfate in the slurry and wash water feed to keep the gypsum stable; excursions produce fine crystals, high cake moisture, and P2O5 losses. When the Chinese acid source changes from a sulfur-burning plant to smelter off-gas acid, the shift in fluoride, iron, and silica can alter filterability even if total acidity is unchanged. A supplier CoA that reports impurity values near the upper edge of the selected GB/T 534-2014 grade should trigger a bench-scale filterability test before vessel loading. Plant corrosion in the attack tank is managed with brick-lined steel and graphite or Hastelloy C276 heat exchangers; the acid-fed section must tolerate residual fluoride and sulfuric acid at digestion temperatures.

Alkylation service consumes 98.0–99.5% sulfuric acid as catalyst. In a stirred or contactor-based unit, the acid-to-hydrocarbon ratio is typically kept between 1.0:1 and 1.2:1 by volume at reactor temperatures of 4–10 °C. The feed isobutane-to-olefin ratio is held at 7:1 to 10:1 to suppress oligomerization and acid-soluble oils. Spent acid leaves the contactor at 88–90% acidity and carries water plus acid-soluble oils, so tight control of water in the fresh Chinese acid is commercially significant. A purchase specification for this service should express water content below 1.0% and iron below 50 mg/kg. Published data for specific Chinese smelter-acid performance in alkylation is limited; a pilot acid evaluation is warranted before a long-term contract.

When the Imported Acid Is Stored in Carbon Steel Tanks

Carbon steel is suitable for concentrated acid above roughly 93.0% at ambient temperature because the acid passivates the metal with a ferrous sulfate film. Dilution below approximately 65% removes that protection and can raise corrosion rates sharply, mandating lined vessels or nonmetallic tanks. When 98.0% acid is diluted in a mixing skid, the acid should be added to water in small proportion through a submerged diffuser to control the exotherm. Adiabatic dilution from 98% to 20% can raise solution temperature by more than 70 °C, so inline dilution with cooling water is required where the diluted stream feeds a continuous process. Tank vents should be fitted with mist eliminators to cut acid aerosol release; desiccated purge air should be considered to limit moisture absorption. Tanks fabricated from passivated carbon steel should not be reassigned to dilute acid service without a wall-thickness ultrasonic survey.

Because Chinese merchant acid is frequently blended from multiple production origins, a practical screen includes a source audit at the loading terminal and not only at the supplier’s office. The terminal should show segregation between acid from sulfur-burning, pyrite, and smelter acid tanks. Pyrite and smelter acid can carry elevated arsenic, mercury, selenium, and fluoride, which are irrelevant for pH neutralization but material for food-contact phosphate derivatives, battery electrolyte, and fine chemical sulfonation. Batch-to-batch variance in merchant acid is often larger than the difference between the supplier’s stated specification and the negotiated maximum. A buyer should request a minimum 7-lot trend chart for iron, arsenic, mercury, and residue on ignition rather than a single sample CoA.

Samples should be drawn from the top, middle, and bottom of the ISO tank before discharge, not from the road tanker bottom valve only, to check for acid stratification or water absorption at the vent. Analytical determination of total acidity by ISO 910:1977 or ASTM E223-16 should be repeated at the destination if transit time exceeds 30 days in high-humidity conditions.

Metallurgical Heap Leach and Battery Electrolyte Specifications

Heap leach circuits for copper oxide typically maintain raffinate pH between 1.5 and 2.0 and free acid near 5–10 g/L H2SO4. Acid for drip irrigation is filtered through 10 μm cartridge filters before dilution to prevent emitter plugging from suspended iron sulfate or silica particles. The acid itself is less critical than the clarified raffinate, but a consistent 93.0% assay simplifies pumping and freeze protection. Battery electrolyte is a more demanding application. Acid is diluted with deionized water to a density of 1.280 ± 0.010 g/cm³ at 25 °C, corresponding to a sulfuric acid mass fraction near 37%. Trace chloride, copper, iron, nitrate, and organic material accelerate self-discharge and plate-out on electrodes. A battery-grade Chinese acid should be analyzed by ASTM E223-16 and qualified through a full 1 L cell cycling test under the battery manufacturer’s internal protocol before production release.

Oleum supplied at 20% free SO3 is the standard sulfonation reagent for detergent-range dodecylbenzene. The free SO3 content of Chinese oleum should be determined by ISO 910:1977 or ASTM E223-16 before it is fed to a film reactor. A 1.05:1 molar ratio of SO3 to organic is typical for detergent sulfonation, with reactor jacket temperatures between 35 °C and 55 °C to control color-body formation. In sulfate-process titanium dioxide production, ilmenite or titanium slag is digested in strong sulfuric acid at 160–200 °C. Acid concentration, digestion temperature, and presence of ferrous iron influence hydrolysis and final particle size distribution. If 20% oleum is diluted too rapidly with condensate, local heat release can crack acid-brick linings and damage the agitator; controlled feed and continuous agitation are mandatory.

pH neutralization is the least demanding service; a single verified assay against the purchase order is sufficient.