Manganese(II) Sulfate
Properties
| State | Solid (hygroscopic; usually as monohydrate or tetrahydrate) |
| Color | Pale pink |
| Solubility | Very soluble in water (620 g/L at 20 °C as monohydrate); insoluble in ethanol |
| Melting Point | 700 °C (anhydrous; decomposes) |
About Manganese(II) Sulfate
Manganese(II) sulfate is the pale-pink salt that shows up in three very different places: bagged fertilizer at a farm-supply store, the trace-mineral premix that goes into chicken feed, and the precursor tank at a lithium-ion cathode plant. The pink color is the textbook giveaway for high-spin d5 Mn(II) in octahedral coordination — every d-d transition is both spin-forbidden and Laporte-forbidden, so absorption is so weak you only see a hint of color even in concentrated solution. Anhydrous MnSO4 is 150.994 g/mol, but in practice the salt almost always shows up as the monohydrate (169.01 g/mol, the form sold as fertilizer-grade) or the tetrahydrate (223.06 g/mol). Global production runs north of 700,000 tonnes a year now, and the growth driver is not agriculture — it is the LiNiMnCoO2 (NMC) cathode boom for EV batteries. A typical NMC-622 cell needs about 0.6 kg of Mn per kWh of capacity, and that Mn comes from purified high-purity MnSO4·H2O. The fertilizer market is older and steady: Mn is the catalytic metal in the oxygen-evolving complex of Photosystem II, and on alkaline or peat soils it locks up as insoluble Mn(III)/Mn(IV) oxides where roots can't reach it. Foliar sprays of 2-5 kg/ha of MnSO4 fix the deficiency in soybeans, oats, and citrus within a couple of weeks.
Where you'll encounter it
If you have ever watched soybean leaves yellow between the veins on a high-pH field in Iowa — interveinal chlorosis — you have seen Mn deficiency, and the fix in the spray rig is MnSO4·H2O dissolved at 1-2 lb per acre. In a battery materials lab, you handle a different grade entirely: the same compound but purified to <1 ppm Ca, Mg, Na, and K, because anything else poisons the NMC cathode crystallization. The pink solution sits in a stirred tank coprecipitating with NiSO4 and CoSO4 at controlled pH 11 with NaOH and ammonia, growing the spherical Ni0.6Mn0.2Co0.2(OH)2 precursor particles that get calcined with Li2CO3 into cathode powder. Open the reactor lid and the smell of ammonia hits you immediately — that's how you know the chelation chemistry is running.
Common Uses
- Mn micronutrient fertilizer for soybeans, oats, and citrus on alkaline soils
- Trace-mineral supplement in poultry, swine, and dairy feed premixes
- High-purity precursor for NMC and LMO lithium-ion cathode coprecipitation
- Feedstock for electrolytic MnO2 used in alkaline dry-cell battery cathodes
- Mordant in textile dyeing and component of Bordeaux-style fungicides
Safety Information
GHS: Specific target organ toxicity (repeated exposure - nervous system, Category 2), Aquatic chronic hazard (Category 2). OSHA PEL for Mn dust is 5 mg/m3 ceiling; ACGIH TLV is 0.02 mg/m3 respirable. Chronic inhalation or ingestion produces manganism, a Parkinson-like neurological disorder first identified in Chilean miners in the 1830s. Acute oral toxicity is moderate (LD50 ~782 mg/kg in rats), but the real concern is cumulative neurotoxicity. P100 respirator and local exhaust required when handling powder. Toxic to aquatic invertebrates at >1 mg/L Mn — keep out of waterways. Compatible with most metals at neutral pH; corrodes aluminum and zinc.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.