Sodium molybdate (Na₂MoO₄·2H₂O) is an inorganic compound that serves as one of the most versatile sources of molybdenum across multiple industries. With a CAS number of 10102-40-6 and a molecular weight of 241.95 g/mol, this white crystalline powder dissolves readily in water and delivers molybdenum in a highly bioavailable, reactive form. From crop nutrition to industrial corrosion control, sodium molybdate plays a role that few chemicals can match in breadth.
What Is Sodium Molybdate?
Sodium molybdate dihydrate is produced by reacting molybdic acid with sodium hydroxide or sodium carbonate, yielding a stable, water-soluble salt. It appears as a white crystalline powder with a pH range of 7–9 in solution and an assay of 99.0% minimum in technical grades. The molybdenum content is typically 39.0% minimum — a high loading that makes it economical to use in trace-level applications.
Key physical properties:
- Appearance: White crystalline powder
- Molecular formula: H₄MoNa₂O₆
- Assay: ≥99.0%
- Molybdenum content: ≥39.0%
- Water solubility: ~560 g/L at 20°C
- pH (solution): 7–9
Sodium Molybdate in Agriculture: A Critical Micronutrient
Molybdenum is an essential micronutrient for plants, required in smaller quantities than any other mineral nutrient — yet deficiency causes severe crop damage. Sodium molybdate is the standard carrier for molybdenum fertilization because of its high solubility and clean dissolution.
Nitrogen Fixation and Legume Crops
Molybdenum is a cofactor in nitrogenase, the enzyme responsible for biological nitrogen fixation in legumes such as soybeans, clover, and alfalfa. Without adequate molybdenum, Rhizobium bacteria in root nodules cannot fix atmospheric nitrogen efficiently, forcing the plant to rely on soil nitrogen alone. A foliar spray or soil application of sodium molybdate at just 50–150 g/ha can dramatically improve nodulation and yield in molybdenum-deficient soils.
Nitrate Reductase Enzyme Activity
In non-legume crops — including wheat, corn, and brassicas — molybdenum activates nitrate reductase, the enzyme that converts nitrate (NO₃⁻) into ammonium for protein synthesis. Without this conversion, plants accumulate nitrate and show symptoms of molybdenum deficiency that mimic nitrogen deficiency: pale yellow leaves, stunted growth, and poor grain fill. Sodium molybdate applied via fertigation or foliar spray corrects this efficiently.
Sodium molybdate is commonly used alongside chelated micronutrients such as EDTA Fe, EDTA Mn, and EDTA Zn in complete micronutrient fertilizer blends. Complete fertigation programs often pair sodium molybdate with a nitrogen source such as ammonium sulphate and biostimulants such as humic and fulvic acids to improve micronutrient solubility and plant uptake.
Water Treatment: Corrosion Inhibitor
One of the largest non-agricultural uses of sodium molybdate is as a corrosion inhibitor in closed-loop cooling water systems, chilled water circuits, and heating systems. Molybdate ions adsorb onto metal surfaces and form a thin, protective oxide film that prevents oxidative corrosion of steel, copper, and aluminum components.
Compared to chromate-based inhibitors — which are highly toxic and heavily regulated — sodium molybdate offers a safer, environmentally acceptable alternative. It is effective at concentrations of 50–200 ppm molybdenum in the circulating water, and can be combined with other inhibitors such as zinc salts, phosphates, or benzotriazole for synergistic protection across mixed-metal systems.
Typical applications include:
- Industrial cooling towers
- HVAC chilled water circuits
- Engine coolant formulations (automotive and industrial)
- Boiler feed water pre-treatment
The non-toxic profile of sodium molybdate also makes it suitable for systems where incidental food or drinking water contact is possible, such as in food processing facility cooling circuits.
Pigments and Colorants: Molybdate Orange
Sodium molybdate is a precursor to molybdate orange (lead molybdate pigment, CAS 12656-85-8), one of the most durable and heat-stable orange-red pigments used in industrial coatings, plastics, and ceramics. The pigment is synthesized by co-precipitating lead chromate with lead molybdate and lead sulfate, producing a range of shades from yellow-orange to red-orange depending on the molybdate-to-chromate ratio.
Applications for molybdate-derived pigments include:
- Industrial and marine paints
- Automotive primer and topcoat systems
- Coloring of engineering plastics and masterbatches
- Ceramic glaze colorants
- Traffic paint and road marking materials
Although lead-containing pigments face increasing regulatory pressure in many markets, molybdate orange remains widely used in industrial segments where its performance characteristics — particularly heat stability above 200°C — are difficult to replicate with alternative pigments.
Other Industrial Applications
Catalysis
Sodium molybdate serves as a catalyst or catalyst precursor in several chemical processes. In the petroleum industry, molybdenum-based catalysts are used in hydrodesulfurization (HDS) to remove sulfur from crude oil fractions. In the chemical industry, molybdate is used in selective oxidation reactions, including the production of formaldehyde from methanol over iron-molybdate catalysts.
Flame Retardants
Ammonium molybdate and zinc molybdate — both derived from sodium molybdate as an intermediate — are used as smoke suppressants and flame retardants in PVC compounds and other halogenated plastics. They work synergistically with antimony trioxide to reduce smoke generation and improve the char structure during combustion.
Analytical Chemistry
In laboratory settings, sodium molybdate is a reagent for the colorimetric determination of phosphate and silicate in water and environmental samples (the molybdenum blue method). It is also used in the preparation of phosphomolybdic acid, a standard reagent for TLC staining and protein assays.
Grades and Specifications
Sodium molybdate is available in several grades depending on the application:
- Technical grade: ≥99.0% purity, suitable for water treatment, fertilizer, and pigment manufacture
- Fertilizer grade: Low heavy metal content (Pb ≤50 ppm, As ≤30 ppm, Hg ≤10 ppm) for crop and foliar applications
- Reagent/analytical grade: High purity (≥99.5%), used in laboratory applications
Packaging is typically in 25 kg woven bags with inner PE lining, stored in a cool, dry environment away from acids.
Sourcing Sodium Molybdate from China
China is the world’s largest producer of molybdenum, accounting for over 40% of global mine output, and Chinese manufacturers dominate the supply of downstream sodium molybdate. Technical and fertilizer grade material is available year-round with competitive pricing and flexible MOQs, making China the primary sourcing destination for buyers in Europe, Southeast Asia, and Latin America.
Unifarm Chemical supplies sodium molybdate dihydrate (99.0% min, Mo ≥39.0%) in fertilizer-compliant specification, with SGS inspection available on request. For pricing or sample inquiries, visit our contact page.