The short answer
Magnesium chloride is the magnesium salt of hydrochloric acid. Anhydrous formula MgCl2, molecular weight 95.21 g/mol; the commercial form is the hexahydrate, MgCl2·6H2O, CAS 7791-18-6, molecular weight 203.30 g/mol.
It is white, extremely soluble, and strongly deliquescent — it absorbs water from the air until it dissolves in it. Most of its industrial uses trace back to that one property, together with the fact that it is recovered cheaply from seawater as a by-product of salt production.
Formula, molecular weight and identifiers
| Form | Formula | CAS | Molecular weight | Mg content |
|---|---|---|---|---|
| Anhydrous | MgCl2 | 7786-30-3 | 95.21 g/mol | 25.5 % |
| Hexahydrate (bischofite) | MgCl2·6H2O | 7791-18-6 | 203.30 g/mol | 11.9 % |
Other names: bischofite for the natural hexahydrate mineral, nigari for the food-grade material recovered from seawater bittern, and magnesium dichloride. HS code 2827.31. Commercial hexahydrate is usually quoted as a minimum MgCl2 percentage — 46 % or 47 % min is typical — alongside limits on sodium chloride, sulphate, calcium and water-insoluble matter.
Anhydrous and hexahydrate
The hexahydrate is what almost everyone buys: flakes, prills or granules, roughly 47 % MgCl2, cheap and easy to dissolve. The anhydrous salt is a specialist product, principally the feed for electrolytic magnesium metal production.
The reason anhydrous magnesium chloride is expensive is that you cannot make it simply by heating the hexahydrate. Drive the water off with heat alone and the salt hydrolyses — it reacts with its own water of crystallisation to give magnesium oxide and hydrogen chloride gas. Producing the anhydrous salt requires dehydration in a hydrogen chloride atmosphere or an equivalent route that suppresses that reaction, and that is what puts the cost in.
Why magnesium chloride is deliquescent
The magnesium ion is small and carries two positive charges, which gives it a very high charge density. That makes it bind water molecules tightly — in solution each Mg2+ holds six water molecules in a firm hydration shell, and in the crystal those same six waters are built into the lattice.
The energy released when the salt hydrates is large enough that magnesium chloride will strip water vapour out of air above roughly 33 % relative humidity, forming first a damp surface and then a saturated brine. Three uses follow directly:
- Dust suppression. Spread on an unpaved road, it keeps the surface permanently damp and binds fines, long after plain water would have evaporated.
- De-icing. It pulls in moisture and forms brine quickly, so it starts melting sooner than a salt that must wait for surface water.
- Desiccation. It is an effective, low-cost drying agent for gases and enclosed spaces.
The same property is the handling problem. An opened bag left in humid air will turn to slush.
Physical properties
| Property | Value |
|---|---|
| Appearance | White to off-white flakes, prills, granules or crystals |
| Odour | Odourless |
| Taste | Bitter, saline |
| Melting point | Hexahydrate about 117 °C with decomposition; anhydrous 714 °C |
| Density | Hexahydrate about 1.57 g/cm3 |
| Solubility in water | Very high, roughly 54 g anhydrous basis per 100 mL at 20 °C |
| pH of 5 % solution | Roughly 5 to 7 |
| Eutectic with water | About −33 °C at roughly 21 % MgCl2 |
The eutectic explains the de-icing performance. The theoretical limit is about −33 °C, though the practical working limit on a road is closer to −15 °C once dilution and heat transfer are accounted for — still well below what sodium chloride manages.
Bittern, bischofite and carnallite
Three sources, and all three are essentially concentrated seawater at different geological ages.
- Bittern. When seawater is evaporated for salt, sodium chloride crystallises first and leaves a magnesium-rich mother liquor behind. That bittern is the classic source, and it is the reason magnesium chloride and solar salt are produced side by side on the same coast.
- Brine and lake sources. The Dead Sea and the Great Salt Lake are worked directly for magnesium chloride, as are a number of continental subsurface brines.
- Bischofite and carnallite. Ancient evaporite beds are mined or solution-mined; carnallite, the mixed potassium magnesium chloride, is processed for both elements.
The impurity that follows from all of these is sodium chloride, together with sulphate, calcium and bromide. A specification that names only MgCl2 content leaves those open, and they matter — sulphate in particular causes problems in oxychloride cement and in plating.
Commercial grades and what separates them
| Grade | Typical MgCl2 | What is controlled |
|---|---|---|
| Industrial / de-icing | 44 to 47 % | Assay, insolubles, sodium chloride, particle size |
| Textile catalyst | Per process | Low iron and heavy metals, consistent pH, clarity in solution |
| Food grade (nigari) | Per FCC or local monograph | Heavy metals, sulphate, arsenic, potassium, sensory |
| Pharmacopoeial / AR | Per monograph | Full monograph or trace element profile |
| Anhydrous | 99 %+ | Residual water, magnesium oxide, particle size |
Scapex Exports supplies magnesium chloride hexahydrate, AR grade magnesium chloride hexahydrate and magnesium chloride DMDHEU catalyst grade for textile resin finishing.
What magnesium chloride is used for
- De-icing and dust control. Roads, runways and unpaved surfaces, applied as flake or as brine.
- Textile finishing. The standard latent acid catalyst for DMDHEU and other N-methylol crosslinking resins in easy-care cotton finishing. It stays inactive in the pad bath and releases acidity during curing, which is exactly what a resin finish needs.
- Magnesium metal. Anhydrous magnesium chloride is the electrolyte feed in the electrolytic production of magnesium.
- Construction. With magnesium oxide it forms magnesium oxychloride, or Sorel, cement — used in industrial flooring, grinding wheels and fire-resistant board.
- Food. Tofu coagulant, firming agent and mineral source; the traditional nigari of Japanese tofu making.
- Drilling fluids. Brine weighting and shale inhibition in oilfield and water well drilling.
- Agriculture and feed. A soluble magnesium source for magnesium-deficient soils and for ruminant rations.
- Water and wastewater. A magnesium source in struvite precipitation for phosphate recovery.
Handling, packing and export documents
- Hazard. Not classified as a dangerous good, no UN number, general cargo. Mild eye and skin irritant; use goggles and gloves when handling open material or hot solutions.
- Moisture. This is the whole handling story. Keep bags sealed and stored in a dry, covered warehouse off the floor, and use opened bags quickly. A caked or slumped bag is normally moisture pickup, not a quality defect, but it is still unusable in an automated feeder.
- Corrosion. Chloride solutions attack carbon steel and aluminium and drive chloride stress corrosion cracking in some stainless grades. Use FRP, HDPE, rubber-lined or correctly selected stainless equipment.
- Heating. Do not dry the hexahydrate with direct heat in a closed space: hydrolysis liberates hydrogen chloride.
- Packing. 25 kg and 50 kg PP laminated bags with inner liner, and 1000 to 1250 kg jumbo bags; food grade with a food-contact liner.
An export consignment should carry a certificate of analysis stating MgCl2 assay, moisture, sodium chloride, sulphate, calcium, water-insoluble matter, heavy metals and particle size; a 16-section GHS safety data sheet; commercial invoice and packing list; certificate of origin; and for food grade the FCC or local monograph reference with any Halal, Kosher or food-contact declarations required.
Enquire with a specification
Magnesium chloride hexahydrate is supplied by Scapex Exports as a manufacturer and supplier from qualified Indian producers, in industrial, textile catalyst, food and analytical grades, as flake, prill or granule, with certificate of analysis, safety data sheet and full export documentation.
Send the assay, sodium chloride and sulphate limits, physical form, packing and destination port, and you will get a quotation written against that specification rather than a generic one.
Frequently asked questions
What is the formula of magnesium chloride?
The anhydrous salt is MgCl2, CAS 7786-30-3, molecular weight 95.21 g/mol. The commercial form is almost always the hexahydrate, MgCl2 6H2O, CAS 7791-18-6, molecular weight 203.30 g/mol, which contains about 11.9 % magnesium against 25.5 % for the anhydrous salt.
Why does magnesium chloride absorb water from the air?
Because the magnesium ion is small and doubly charged, so it holds water molecules very strongly - strongly enough that the salt will take moisture out of humid air and eventually dissolve in it. That behaviour is called deliquescence. It is why magnesium chloride works as a dust suppressant and a desiccant, and why bags must be kept sealed.
What is nigari?
Nigari is the Japanese name for the bittern left after sodium chloride has been crystallised from seawater, and it is largely magnesium chloride. It is the traditional coagulant for tofu: the magnesium ions cross-link soy protein and make it set. Food grade magnesium chloride sold for this use is simply purified nigari.
Is magnesium chloride better than salt for de-icing?
It works at lower temperatures - down to roughly minus 15 degrees C in practice against about minus 9 for sodium chloride - and because it is deliquescent it starts working faster by pulling moisture in to form brine. It is more expensive per tonne, and like every chloride it still promotes corrosion of steel and reinforced concrete, so it is not a corrosion-free alternative.
Is magnesium chloride hazardous?
It is not classified as a dangerous good and needs no UN number for transport. It is a mild eye and skin irritant, and solutions are corrosive to carbon steel and aluminium over time, but as a solid it ships as general cargo in bags, jumbo bags or bulk.
What is magnesium chloride?
Magnesium Chloride Hexahydrate (CAS 7791-18-6) is supplied as white to colorless flakes, with the molecular formula H12Cl2MgO6 and a molecular weight of 203.30 g/mol. Its main applications include de-icing, dust control and dietary supplement. Scapex Exports exports and supplies it from India in ≥99% Technical grade, with a batch Certificate of Analysis (COA) and MSDS.
Where to buy magnesium chloride?
You can buy Magnesium Chloride Hexahydrate from Scapex Exports, an exporter and supplier based in Ahmedabad, India. Send the grade, quantity and destination port with the Request a Quotation button on the product page and we will confirm availability, packing and price, with the COA and MSDS.
What is the colour of magnesium chloride?
Magnesium Chloride Hexahydrate is supplied as white to colorless flakes.
What is magnesium chloride used for?
The main applications of Magnesium Chloride Hexahydrate are de-icing, dust control and dietary supplement.