Where Chinese Sulfuric Acid Goes: Chile, Indonesia, Morocco, Saudi and India

Sulfuric acid, H2SO4, CAS 7664-93-9, UN 1830, is the principal heavy industrial acid traded as 92.5 wt%, 96.0 wt%, 98.0 wt%, and oleum grades. Chinese export cargoes are classified under HS 2807.00.00 and are produced primarily from sulfur-burning double-contact double-absorption plants, with additional output from metallurgical off-gas and pyrite-roasting routes. The sulfur-burning route typically achieves sulfur dioxide conversion above 99.7% when four-stage vanadium pentoxide catalyst beds are operated within the design temperature band, and tail gas scrubbing is required under Chinese emission standards including GB 26132-2010. Physical properties relevant to handling include a density of approximately 1.84 g/cm³ at 20 °C for 98 wt% acid, high viscosity at terminal unloading temperatures, and a freezing point near -2 °C for the 98 wt% grade. These properties impose pump selection, tank lining, heating, and moisture exclusion requirements at destination terminals. The trade flow described here follows export destinations in Chile, Indonesia, Morocco, Saudi Arabia, and India, where downstream processing conditions determine acid grade, impurity limits, and handling systems.

What Quality, Sampling, and Storage Boundaries Govern Imported Acid?

Import terminals verify H2SO4 concentration by titration according to ASTM E223-16 and density by digital densitometry or hydrometer, with acceptance bands of ±0.2 wt% around the nominal concentration. Iron, chloride, arsenic, and residue-on-ignition limits are application-specific rather than uniform across all destinations. Copper heap leaching in Chile commonly requires Fe below 50 mg/kg and turbidity below 10 NTU to prevent drip emitter clogging, while Moroccan phosphate acidulation tolerates higher iron but penalizes organic impurities that increase foaming in reactor slurry. Storage tanks at receiving terminals are often rubber-lined carbon steel or fluoropolymer-lined carbon steel, with inert-gas blanketing or silica-gel vent dryers to limit moisture ingress. Dilution of 98 wt% acid must be performed by adding acid to water under agitation, never the reverse, to avoid localized boiling and steam eruption. Unloading pumps are typically magnetic-drive centrifugal units with dry-run protection and secondary containment, and flexible hoses are lined with EPDM or PTFE with documented visual inspection before each transfer. Vessel tanks are cleaned under IMO MARPOL Annex II category Y procedures, and cargo residues are prohibited from direct overboard discharge. Purchase specifications do not replace national standards such as GB/T 534-2014 for Chinese industrial sulfuric acid or ISO 910:1977 for titrimetric acidity determination, but they add destination-specific impurity thresholds and handling protocols.

On Chilean copper heap leach pads, imported Chinese acid is diluted to raffinate containing 10–20 g/L H2SO4 and distributed through drip emitter networks at 0.3–0.5 bar. Oxide and secondary sulfide ores are agglomerated in drums with concentrated acid and water to bind fines before stacking on HDPE-lined pads. Pregnant leach solution reporting copper concentrations of 1–5 g/L is processed by solvent extraction and electrowinning. Acid consumption varies with ore mineralogy; published engineering studies for chalcocite-dominated ores report 2.5–3.5 t H2SO4 per tonne of copper cathode, but published data for specific site configurations is limited. Large copper operations require steady acid deliveries because heap leach kinetics decline if the irrigated pH rises above 2.0. Acid quality issues in this use include suspended silica and colloidal iron that can blind drip emitters; terminal filtration at 25 µm nominal is often specified. Operational boundaries include avoidance of dilution water with high chloride, which promotes stainless steel corrosion in downstream solvent extraction and electrowinning circuits. Acid mist suppressants are added when tank vents and agitation produce aerosol at the perimeter, and personnel exposure is managed by facility-specific limits for sulfuric acid mist rather than by a single universal concentration.

When High-Pressure Acid Leaching Autoclaves Require 98 wt% Acid: Indonesian Nickel Laterites

In Indonesian HPAL plants processing limonitic nickel laterite, sulfuric acid is injected into titanium-lined autoclaves operating at 240–270 °C and 4.5–5.5 MPa. The acid dissolves nickel and cobalt from goethite and iron-rich laterite matrices while iron precipitates as hematite and alunite-type phases under high-temperature hydrolysis. Free acid in the discharge slurry is typically held at 30–50 g/L to maintain nickel extraction above 90%; however, excess free acid increases downstream neutralization with limestone and raises gypsum disposal volume. Acid consumption per tonne of nickel in limonitic ore can reach 25–35 t H2SO4 depending on iron and magnesium content, although published data for a specific HPAL line is limited to vendor engineering documents. High-magnesium saprolite ore is usually restricted because magnesium dissolution consumes acid without releasing nickel. Materials selection follows NACE MR0175/ISO 15156 for sour service, but additional corrosion testing per ASTM G31-72 is required for titanium and nickel-based alloys exposed to high-pressure sulfuric acid. Flash letdown valves use ceramic or tungsten carbide internals to resist erosion-corrosion from acid slurries at throttling velocities that generate localized wear. Operational boundaries include strict control of chloride in feed water to avoid pitting of titanium above 105 °C; chloride limits are often below 30 mg/kg. Acid storage at HPAL sites is usually in 10,000–20,000 m³ carbon-steel tanks with internal corrosion-resistant linings, with unloading from Chinese acid carriers via jacketed stainless-steel pipelines because acid viscosity increases as temperature falls below 10 °C.

Moroccan Phosphate Acidulation, Gypsum Filtration and Fluoride Recovery

In Morocco’s phosphate fertilizer complexes at Jorf Lasfar and Safi, sulfuric acid is used in the wet-process acidulation of phosphate rock. The primary reaction consumes 10 mol H2SO4 per mole of fluorapatite, producing phosphoric acid and calcium sulfate dihydrate. Reactor temperatures are maintained at 75–85 °C, with slurry solids content of 35–40 wt% to promote gypsum crystal growth before filtration. Chinese acid shipments supplement sulfur-burning acid plants and must meet sulfate and iron specifications compatible with Prayon tilting-pan filters; poor crystal habit from organic impurities or excessive free acid increases filter cloth blinding and reduces P2O5 recovery below 94%. Phosphoric acid concentration from the filter typically ranges 26–30% P2O5, and fluoride is recovered in wet scrubbers as fluosilicic acid rather than being vented. Acid flow to each reactor is ratio-controlled against phosphate rock feed; free sulfate is measured by ion chromatography and held between 2–4 wt% in the liquid phase. Operational limits include rock organic carbon below 0.5 wt% to avoid foaming, and excess sulfate above 5 wt% that can lead to gypsum scale on agitator shafts. Published data for the exact allocation of imported Chinese acid among Moroccan fertilizer sites is limited, but technical purchasing specifications at Moroccan ports specify 98 wt% acid with residue-on-ignition below 0.03% and chloride below 50 mg/kg to protect stainless steel reactors.

At Saudi Arabian integrated phosphate and desalination facilities, sulfuric acid is consumed for pH adjustment, scale control, and phosphate fertilizer production. In seawater reverse osmosis trains, 98 wt% acid is diluted to 0.5–2.0 wt% and injected ahead of static mixers to lower feed pH to 7.0–7.5, shifting carbonate equilibria toward bicarbonate and reducing calcium carbonate scaling on polyamide membranes. Membrane manufacturer technical bulletins require continuous pH monitoring and fail-safe shutoff if localized pH falls below 4.5, which can hydrolyze polyamide layers. Dosing rates depend on seawater alkalinity and temperature; Arabian Gulf seawater with alkalinity around 120–150 mg/L as CaCO3 typically requires 1–5 mg/L of concentrated acid equivalent. In phosphate complexes such as Ma’aden’s Ras Al Khair operation, sulfuric acid is produced from sulfur burning and supplemented by imported acid during maintenance or sulfur logistics interruptions. The acid is used in DAP/MAP production with reactor conditions and gypsum handling similar to Moroccan wet-process plants, but the local phosphate rock is often lower in organic carbon. Imported acid storage at Saudi ports must account for ambient temperatures above 45 °C; tank vents are fitted with acid mist arrestors and desiccant dryers to minimize corrosion. Chloride and iron limits are tighter for desalination use than for fertilizer use, requiring segregated unloading lines or sequential flushing between grades.

Indian Tender Documents Impose Chloride Limits Below 10 mg/kg for Battery Acid

Indian importers route Chinese sulfuric acid into three main application zones: lead-acid battery electrolyte, steel pickling, and phosphate fertilizer production. Battery-grade acid purchased under IS 266:1993 requires low iron, chloride, and nitrate content because impurities accelerate grid corrosion and gassing. Electrolyte is diluted to a relative density of 1.200–1.260 at 27 °C; automotive battery filling strength is typically 1.250. Steel pickling uses 5–10 vol% H2SO4 at 60–80 °C, with acid inhibitors added at 0.1–0.3 wt% to suppress base metal attack. Ferrous sulfate builds up in the bath and reduces pickling rate when iron exceeds 80–120 g/L, at which point the bath is cooled to crystallize ferrous sulfate heptahydrate or sent to neutralization. Indian fertilizer plants use sulfuric acid for single superphosphate and phosphoric acid routes; the acidulation follows the same fluorapatite reaction as in Morocco but often uses lower-cost rock with higher silica and iron. Silica in rock unites with fluoride to form fluorosilicic acid, which must be scrubbed from reactor vapors. Operational boundaries for imported acid in India include monsoon-season moisture control in storage tanks, because humid air entry raises iron dissolution from steel tank walls if linings are damaged. Published data for the exact end-use split of imported Chinese acid in India is limited; however, tender documents for battery-grade acid frequently specify 98 wt% minimum, residue below 0.03 wt%, Fe below 20 mg/kg, and Cl below 10 mg/kg.