TSP (triple superphosphate)

Triple superphosphate (TSP) is a straight phosphate fertiliser manufactured through the reaction of phosphate rock with phosphoric acid. It differs from SSP (single superphosphate) in both its production process and its high P2O5 concentration, which stands at 46% according to 2023 figures, compared with 15 to 22% for SSP^[1]. TSP contains only trace amounts of sulphur, marking a sharp contrast with SSP, which is rich in this secondary nutrient^[2]. It ranks among the three main finished phosphate fertilisers, alongside DAP (diammonium phosphate) and MAP (monoammonium phosphate)^[1].

Manufacturing

TSP production relies on attacking finely ground phosphate rock with phosphoric acid at a P2O5 concentration of 50 to 55%^[3]. The overall reaction yields monocalcium phosphate hydrate, with no calcium sulphate retained in the finished product, hence the near-total absence of sulphur in the resulting fertiliser^[3][4]. The reaction, which is exothermic and rapid (yield exceeding 96%), begins in a reactor where temperatures reach 90 to 100 °C^[3]. The resulting slurry is then discharged onto a slow-moving conveyor (the 'den') or into a holding tank for 10 to 40 minutes, after which it is ground and either granulated immediately or stored for a maturation period of up to six weeks^[3]. Product quality depends partly on the composition of the phosphate rock: the presence of aluminium, iron and magnesium reduces the water solubility of the phosphate^[3].

Agronomic uses

TSP supplies phosphorus in essentially water-soluble form, readily available to plants^[2]. Its principal application lies in compound fertiliser manufacture: it serves as a feedstock for producing PK and NPK fertilisers^[5]. As a straight fertiliser, it may also be applied directly to soils requiring a concentrated phosphorus input without nitrogen or potassium. Its very low sulphur content makes it less suited than SSP for sulphur-deficient soils, although its high P2O5 concentration renders it more economical to transport over long distances.

Market and trade

Superphosphates (SSP and TSP) account for one-quarter of global phosphate fertiliser output^[5]. In 2023, worldwide TSP production stood at 5 Mt (million tonnes of product), of which 4 Mt was exported^[1]. These volumes remain below those of DAP (85 Mt produced, 8 Mt exported) and MAP (35 Mt produced, 16 Mt exported)^[1]. Compared with 2021 data, TSP production held steady at 5 Mt, whilst exports rose from 3 to 4 Mt^[1][6]. SSP, with 19 Mt produced in 2020 (an older figure), remains a product of regional importance, notably for its sulphur and calcium contributions^[1]. During the 1999/2000 season, global consumption of normal single superphosphate reached 6.1 Mt of P2O5, whilst TSP consumption stood at 2.2 Mt of P2O5^[5].

Position in the phosphate industry

TSP exemplifies the production route incorporating phosphoric acid as an intermediate, as opposed to the sulphuric acid process used for SSP^[4]. This stream, dominated by vertically integrated producers from rock through acid to fertiliser, accounts for the bulk of international trade. The evolution of markets towards increasingly complex NPK formulations tends to reduce TSP's share as a finished product, in favour of its role as an intermediate component.