Sulphur

Sulphur (S) ranks among the secondary nutrients in plant nutrition, although crops take it up in amounts comparable to phosphorus^[1]. Roots absorb it mainly as the sulphate ion (SO₄²⁻), and it plays a part in protein synthesis and chlorophyll formation^[1]. Within the fertiliser industry, sulphur is largely employed indirectly: roughly 90% of sulphur consumed is in the form of sulphuric acid^[2], a pivotal intermediate in the phosphate chain.

Manufacture and sources

Sulphuric acid (H₂SO₄) stands as the most widely produced chemical worldwide^[3]. Its manufacture draws on various sources of sulphur dioxide (SO₂): elemental sulphur leads, accounting for 43.7% of output in the EU-25, Norway and Switzerland in 2005, followed by non-ferrous metals (39.0%) and spent acid regeneration (7.5%)^[4]. Elemental sulphur comes from petroleum refining, natural gas processing and coking^[2]. In the United States in 2025, 86 sites producing recovered elemental sulphur and by-product sulphuric acid were spread across 26 states^[2]. Approximately half of domestic elemental sulphur output originated from two Gulf Coast states^[2]. The Claus process, often paired with a residual gas clean-up unit, extracts sulphur from gases arising from partial combustion operations^[5].

Agronomic uses

The principal outlet for sulphuric acid remains the phosphate fertiliser industry^[4]. Single superphosphate (SSP) is obtained by attacking phosphate rock with sulphuric acid, giving it a P₂O₅ content of 15–22% and a contribution of 10–12% S as sulphate^[6]. Producing one tonne of phosphoric acid (100% P₂O₅) calls for roughly one tonne of sulphur^[6]. Recommended sulphur application rates generally fall between 20 and 50 kg S/ha, depending on soil and crop; sandy soils and oilseed crops call for higher rates^[7]. Elemental sulphur oxidises slowly in the soil; the rate of conversion depends on particle size, temperature, moisture and soil contact^[7].

Market and trade

World sulphur production across all forms reached approximately 84 Mt in 2025, against 83.9 Mt in 2024^[8]. Leading producing countries include China (19 Mt), the United States (8.1 Mt), Russia (7.5 Mt) and Saudi Arabia (7.2 Mt)^[8]. Nearly 49% of global sulphur trade passes through the Strait of Hormuz^[9] — in spring 2025, some 400,000 t of sulphur held up on ten vessels was recorded west of the strait^[10]. Prices saw a sharp upward swing in 2025: on the Tampa, Florida benchmark market, contracts opened at USD 116/long ton in January and peaked at USD 310/long ton early in the fourth quarter, a high not seen since mid-2022^[8]. Across the Atlantic, total sulphur shipments were valued at roughly USD 1.4 billion in 2025, up by one billion on the previous year, with the tonne rising from USD 46 to USD 180^[2].

Regulation

Sulphuric acid manufacture is governed by the BREF LVIC-AAF document, which sets technical requirements to curb atmospheric releases^[5]. Producers must in particular combine Claus process units and residual gas treatment devices to meet the emission thresholds laid down^[5]. Recovery of spent sulphuric acid from petroleum refining and chemical processes amounts to 2.5–5 Mt annually^[2]. Sulphuric acid falls within the scope of the European Union's Carbon Border Adjustment Mechanism (CBAM).