Cadmium management has become a scientific, industrial, commercial and geopolitical challenge. This heavy metal, present in phosphate fertilisers, is toxic and bioaccumulable, migrating from soil to roots, particularly in cereals and root vegetables. Faced with strict regulations — including EU rules limiting cadmium content to 60 mg/kg — and growing public alarm, the giants of the phosphate industry are developing a battery of commercial, industrial and organic strategies to achieve a cadmium level of 20 mg/kg in the medium to long term. Morocco’s OCP, Saudi Arabia’s Ma’aden, Norway’s Yara, Russia’s PhosAgro and America’s Mosaic are the main protagonists in a race to give their fertilisers a “green” label. Decadmiation is the most favoured strategy, particularly by the Moroccan OCP group and Prayon, its 50%-owned Belgian subsidiary.
THE STRATEGIES OF BIG GROUPS
OCP’s competitors are adopting different strategies based on the geological nature of their reserves and their geographical positioning.
1.PhosAgro (Russia): A Commercial Offensive on the “Naturally Pure” Theme
The Russian group PhosAgro holds one of the most competitive advantages in the market: its deposits on the Kola Peninsula are of magmatic, not sedimentary, origin. No decadmiation technique is required. The rock naturally contains cadmium levels below 10 mg/kg, placing it well below the European threshold (60 mg/kg) and the green label standard (below 20 mg/kg).
Rather than investing in purification R&D, the Russian group pursues an active commercial and lobbying strategy. It pushes international and European bodies to adopt stricter regulations in order to eliminate its Moroccan competitor. However, its strategy is complicated by tariff obstacles arising from the sanctions Russia has faced since the invasion of Ukraine.
2.Ma’aden (Saudi Arabia): Geopolitical Blending and Industrial Expansion
Ma’aden has become, within just a few years, OCP’s direct rival in Africa and Asia. The group exploits sedimentary phosphates (notably at Wa’ad Al Shamal) with cadmium levels ranging from moderate to high. Its strategy rests on two pillars:
- Optimised blending: with vast financial resources, Ma’aden manages the cadmium problem primarily through integrated logistics. It purchases or secures very low-cadmium rocks to blend industrially with its own resources in order to target demanding markets.
- Geographical pivot: rather than financing costly decadmiation plants for the European market, Ma’aden directs its exports towards markets with less stringent cadmium requirements but very high volume demand: India, China and South-East Asia.
3.The Mosaic Company (United States): Differentiation Through High Technology
The American giant is facing the gradual depletion of its high-quality deposits in Florida and rising extraction and raw material costs (sulphur). Its sedimentary rocks contain variable cadmium levels.
Rather than focusing solely on chemical cadmium removal from acid, Mosaic has chosen to reduce the impact of the problem by creating patented, high-value-added enhanced-efficiency fertilisers such as its MicroEssentials range. The principle is to incorporate sulphur directly (in two forms: sulphate and elemental) and zinc into the same phosphate coating or granule via its Fusion technology, thereby increasing the efficiency of phosphate absorption by the plant. This allows farmers to reduce overall fertiliser doses applied per hectare, consequently reducing the total quantity of cadmium introduced into the soil while maintaining yields.
4.Yara International (Norway): The “Nitric Route” Purification Model
Although Yara purchases a large proportion of its phosphates, the group owns mines (such as Siilinjärvi in Finland, of magmatic origin and therefore cadmium-free) and uses an industrial process unique in Europe: the nitric acid attack (Odda process).
Unlike OCP or Mosaic, which attack rock with sulphuric acid (generating phosphogypsum), Yara uses nitric acid. This process enables very effective separation of calcium in the form of calcium nitrate (a highly sought-after nitrogenous fertiliser) and isolation of the phosphate stream.
When Yara must process cadmium-bearing sedimentary rock, the chemical separation in the nitric phase facilitates the selective extraction of heavy metals by ion exchange or solvent extraction, prior to final granulation.
THE MAIN STRATEGIES FOR COMBATING CADMIUM
1.Blending :
Based on the geological nature of the rock, this is the simplest strategy. Magmatic rocks exploited by PhosAgro or Yara naturally contain very low cadmium levels (below 10 mg/kg). Sedimentary rocks from North Africa, the Middle East or the western United States, by contrast, often have levels exceeding 60 mg/kg. Producers using these rocks resort to blending — mixing their phosphate with purer imported ores or ores from clean seams — to dilute the cadmium content of their fertilisers in line with the requirements of importing countries.
2.Decadmiation :
This is, in the long term, the most promising strategy. There are two industrial decadmiation processes:
- Calcination of phosphate rock above 1,000°C followed by acid attack. Most of the cadmium is volatilised and captured in gas filters. This process has the drawback of being very energy-intensive and a major producer of carbon emissions.
- Treatment of phosphoric acid, an intermediate stage in fertiliser production. This is the preferred technique among researchers. Three processes are used:
- Co-precipitation with chemical additives: reagents such as the ACCO-PHOS range from Syensqo or Prayon’s solutions (in which OCP is a shareholder) are injected into the acid to form insoluble complexes with cadmium that bind to the gypsum and are removed during filtration. Tests show cadmium elimination rates exceeding 90%.
- Liquid solvent extraction: this technique purifies sulphuric acid to a “food grade” standard. It is effective but very costly.
- Additive-free technologies: the approach favoured by OCP and Prayon, which involves modifying physico-chemical parameters such as temperature or concentration to precipitate cadmium in the gypsum without the addition of costly chemicals.
3.Market Positioning and “Digital Passports” :
Cadmium management is redrawing the commercial landscape of fertilisers:
- Creation of premium segments: fertilisers with cadmium content below 20 mg/kg are sold at a premium as Food-Grade or ecological products for high-value crops: market gardening, organic produce, etc.
- Traceability and Blockchain: to reassure major food groups, fertiliser producers are implementing blockchain-based “digital passports” that track cadmium’s journey from rock extraction to fertiliser application in the field.
4.Agronomic Approaches :
Agronomically, it is known that cadmium migration towards roots does not depend solely on the quantity of fertiliser applied. Producers therefore advise farmers on mitigation practices in the field:
- Soil pH management: cadmium is more mobile and bioavailable in acidic soils. Farmers are therefore advised to practise liming to maintain pH above 6.0, thereby immobilising residual cadmium in the soil.
- Organic input management: optimising the balance between phosphate fertilisers and organic composts can help to sequester cadmium.
OCP’S STRATEGY: A TECHNOLOGICAL AND INDUSTRIAL APPROACH
The OCP group is the world’s leading exporter of phosphates and phosphoric acid. Holding 70% of the world’s phosphate rock reserves, it is directly exposed to the cadmium debate, as Morocco’s sedimentary deposits (Khouribga, Gantour, Boucraa, Mskala) contain variable cadmium levels that are, on average, higher than those found in magmatic rocks.
To protect its strategic market share in Europe and anticipate the global tightening of standards, OCP has deployed a cutting-edge industrial and technological strategy centred on flexibility and integrated R&D.
Detailed Deposit Mapping
OCP’s first response is not chemical but logistical and geological:
- 3D concentration mapping: OCP has modelled all of its mines to precisely map cadmium concentrations across the various sedimentary layers. Concentrations vary significantly from one zone to another (for example, certain levels at Khouribga are naturally lower in cadmium than elsewhere).
- Selective extraction and industrial blending: rocks with very low cadmium content are selectively extracted and reserved primarily for the production of fertilisers destined for the most regulated markets (the European Union, for example). OCP uses highly automated industrial mixing platforms to combine different quantities of rock and stabilise the final concentration below the authorised regulatory threshold.
Industrial R&D: Liquid-Phase Decadmiation
For the medium and long term, OCP has positioned itself at the forefront of global research into the decadmiation of wet process phosphoric acid (WPA). OCP Innovation teams, often in partnership with UM6P (Mohammed VI Polytechnic University) and Prayon’s chemical engineering specialists, favour three main approaches:
1.Co-crystallisation and gypsum modification (DA-HF route): rather than adding costly organic solvents, OCP is working on optimising the sulphuric acid attack. By modifying the temperature, concentration and reaction times during phosphoric acid production, cadmium ions are chemically forced to insert directly into the crystalline structure of phosphogypsum (the solid by-product) rather than remaining in the liquid acid. Cadmium is thus “naturally” extracted during gypsum filtration, leaving a purified acid.
2.Precipitation by organophosphate agents: OCP is patenting and testing processes involving the injection of complexing agents or specific ligands directly into medium-concentration phosphoric acid. These molecules specifically target heavy metals (cadmium, but also zinc and nickel) to form insoluble precipitates that are then easily filtered. The main challenge of this technique for OCP is its economic viability at very large scale.
3.Ion-exchange resins and adsorption: the group is running pilot projects using strong cationic resins. Phosphoric acid flows through resin columns that capture cadmium ions. This method can achieve ultra-purity levels (sometimes below 5 and even 1 mg Cd/kg), opening the door to specialty fertilisers with very high added value.
Market Diversification and Product Adaptation
Aware that full decadmiation carries an industrial cost, OCP adapts its product range according to regional requirements:
- High-demand markets (Europe): supply of products from naturally low-cadmium rocks, optimised blends or purified high-value acids.
- Large commodity markets (Africa, the Americas): formulation of tailor-made fertilisers (Nutri-Agri range or micronutrient-enriched fertilisers) adapted to local agronomic realities. OCP emphasises that in many tropical or highly fixing soils, the dynamics of cadmium transfer to plants are very different, shifting the problem towards soil-based agronomic management rather than systematic purification.
