Manganese

Typical wastewaters

• coal mine drainage (acid or ferruginous) dissolved Mn²⁺ that stays in solution after the iron has oxidised; 4.0 daily maximum and 2.0 mg/L monthly average
• ferroalloy smelting (open electric furnaces with wet scrubbers) total manganese in furnace off-gas scrubber water from ferromanganese and silicomanganese smelting BPT 0.064 kg/MWh daily maximum and 0.032 kg/MWh 30-day average, with chromium and TSS
• electrolytic manganese and manganese dioxide production dissolved Mn²⁺ with ammonia-N in cell liquor bleed and rinse water BPT 2.771 kg/t product daily maximum and 1.356 kg/t 30-day average for electrolytic manganese, ammonia-N 40.667 kg/t
• battery manufacture (zinc anode and Leclanche cells) manganese from manganese dioxide cathode paste in process wastewater BPT 2.58 mg/kg zinc daily maximum and 1.10 mg/kg monthly average for wet amalgamated powder anodes; NSPS 0.019 mg/kg of cells produced for Leclanche cells
• coal combustion residual leachate (ash landfills and impoundments) dissolved manganese among the BAT treated pollutants in combustion residual leachate; monitored as monthly minimum, maximum and average monitoring table lists Mn with V, As, Se, B and other ash metals
• blast furnace gas scrubbing water Mn 0.48 mg/L average in untreated scrubber water with Fe 6.77, Zn 0.1 to 29.4, NH₄⁺ 2 to 200 and cyanide 0.1 to 50 mg/L six EU blast furnaces, 1990 to 1992 data (Table 6.11)
• steelmaking plant wastewater manganese with iron, zinc and copper in raw steel making wastewater above the Malaysian Standard B limits 0.03 mg/L after an electric arc furnace slag column
• manganese contaminated mine drainage Mn²⁺ persisting after iron removal, precipitated as rhodochrosite, manganite and Mn(III, IV) oxides in steelmaking slag and limestone reactors 316 day pilot in Korea; no raw concentration in the abstract

1 · Identity

Symbol, number

Mn, 25

Oxidation states in water

+2 as Mn²⁺, the dissolved form of anoxic and acid groundwater and of hypolimnia (WHO: the divalent form predominates in most water at pH 4 to 7); +4 as MnO₂ and hydrous manganese oxides, the black solid that stains, coats mains and is the filter deposit; +7 as permanganate MnO₄⁻, the treatment oxidant, purple, and the species left by an ozone overdose; +3 only as a transient in oxide surfaces and in strong complexes.

Note

The element entry covers the eleven oxidation states, pyrolusite and the steel and battery uses. This chapter is about the Mn(II) to Mn(IV) step in water and what it costs to force it.

2 · Occurrence in water

Natural sources

Weathering of manganese bearing rock and soil; reductive dissolution of manganese oxides in anoxic aquifers, in lake and reservoir hypolimnia below a thermocline, and in acidic water. WHO: reducing conditions in groundwater and some lakes and reservoirs favour high manganese; in aerobic waters higher levels are usually associated with industrial pollution. Manganese is detected at about 70 percent of US groundwater sites and 97 percent of surface water sites.

Anthropogenic sources

Acid and ferruginous coal mine drainage (US limit 4.0 mg/L daily maximum); iron and steel and ferroalloy plants and manganese mining in the ledger's chapters; potassium and sodium permanganate used for cleaning, bleaching and water treatment; manganese as an impurity in coagulants (WHO fact sheet); permanganate overdosed in a treatment plant.

3 · Speciation

Manganese(II) is soluble and stable in water far longer than iron(II): oxygen alone oxidises it only above about pH 9 at useful rates, and the reaction is autocatalytic on the manganese oxide it produces, so a clean water without oxide surfaces holds Mn²⁺ for days in aerated water at neutral pH (Stumm and Morgan). Chlorine, permanganate, ozone and chlorine dioxide do the step in minutes at pH 7 to 8. The product is a hydrous Mn(IV) oxide, written MnO₂, that is insoluble, black, adsorbs other metals and catalyses further oxidation. In carbonate rich anoxic groundwater rhodochrosite MnCO₃ caps dissolved manganese; in sulfidic water MnS is far more soluble than FeS, so manganese stays dissolved where iron precipitates. Over-oxidation with ozone gives permanganate, which redissolves the manganese as a pink anion until it is reduced on a filter.

Solubility

MnO₂ is the controlling solid in oxic water and holds dissolved Mn(IV) at negligible levels; the practical solubility of manganese is that of Mn²⁺, which is high until it is oxidised. MnCO₃ (rhodochrosite) controls Mn(II) in anoxic carbonate water. No solubility products are quoted; the sources read print none.

Hydrolysis

Mn²⁺ hydrolyses only above pH 9 (Mn(OH)₂ is much more soluble than Fe(OH)₂), which is why the oxygenation rate, second order in hydroxide like that of iron, is so slow at neutral pH.

Complexation

Bicarbonate and sulfate ion pairs; natural organic matter binds Mn(II) weakly compared with Fe(III). WHO notes that adsorption on soil depends on organic content and cation exchange capacity. Constants not quoted.

Precipitates

MnO₂ and hydrous manganese oxides (oxic); MnCO₃ rhodochrosite (anoxic, carbonate); Mn₃O₄ hausmannite and Mn₂O₃ as ageing products; manganese oxide coatings on pipe walls that also hold arsenic, barium, chromium, lead and uranium (WHO fact sheet).

4 · Role in treatment

5 · Removal and control

6 · Analytics

Sampling pitfalls

Dissolved and particulate manganese answer different treatment questions (WHO: selection of treatment depends on the form), so filter 0.45 µm in the field for dissolved manganese and acidify both fractions at once; Mn(II) oxidises far more slowly than Fe(II) in the bottle but still deposits on walls over days. A tap sample after a hydraulic disturbance measures the deposit, not the water. Monitor after treatment where manganese is removed (WHO).

7 · Regulatory limits

Limits change, and many are set locally. Treat these as the published values to start from, not as your compliance target: check the standard in force at your site and the numbers written into your own permit.

8 · Health and environmental effects

Toxicity

Essential trace element; the central nervous system is the target of excess. WHO's provisional guideline rests on neurodevelopmental effects in juvenile rats (LOAEL 25 mg/kg per day) supported by epidemiology of reduced cognitive ability in children drinking manganese rich water; absorption and retention are higher in infants, and bottle fed infants get manganese from both formula and the water; no adequate evidence of oral carcinogenicity (WHO fact sheet). WHO advises exclusive breastfeeding or an alternative safe water for formula where the value is exceeded.

Bioaccumulation

Bioaccumulates in lower organisms (phytoplankton, algae, molluscs, some fish) but not in higher organisms; biomagnification in food chains not expected to be significant (WHO background document).

Ecotoxicity

No US EPA national recommended aquatic life criterion for manganese; the harm in mine drainage streams is the oxide coating of the bed, as with iron.

Flags

• The Mn(II) oxygenation rate law and its autocatalysis are cited to Stumm and Morgan chapter 11 from memory of the text, not re-read this session; MnCO₃ likewise to chapter 7.
• EPA Table 2-7 prints 0.77 mg Cl₂ per mg Mn; the Mn(II) to MnO₂ electron balance gives 1.29 mg Cl₂ per mg Mn. Both are given; the EPA figure comes from a 1986 compilation the manual cites.
• The chlorine, ozone and chlorine dioxide equations are electron balances written here; EPA prints the doses and the products, not the equations.
• USGS median and 99th percentile figures are 1990s NAWQA compilations quoted by the 2011 WHO background document; the 2021 WHO background document was not reachable (iris.who.int returned 403).
• The coal mining limit is reused from the book's iron chapter; the CFR section was not re-read this session.
• Abu Dhabi values cover two media (marine 0.2 mg/L, sewer 10 mg/L); other GCC states not read.
• Standard Methods and ISO method numbers other than those in the sources read (EPA 200.8, ISO 17294-2 and the methods the WHO documents cite) are quoted from memory and were not confirmed this session.

Gaps

• Biological manganese filtration design (pH, dissolved oxygen, start-up) is named by WHO but not described in any source read.
• The 2021 WHO background document (WHO/HEP/ECH/WSH/2021.5) behind the provisional guideline was not reachable; occurrence figures are from the 2011 revision.
• EU law was read on legislation.gov.uk mirrors because eur-lex did not respond to scripts; the eur-lex urls are kept for consistency with the other chapters.
• No EQS row: manganese is not an EU priority substance and the directive was not searched for it.
• Other GCC discharge standards (Saudi, Oman, Qatar) were not read.
• No solubility products, hydrolysis constants or rate constants are printed here. The hydroxide, sulfide, autocatalytic surface and permanganate half reaction equations and the lime softening and ion exchange stoichiometry are from Stumm and Morgan chapters 7, 8 and 11 and MWH chapters 16 and 22, from the chapter, not re-read.

Sources

Identity

Name and symbol

Manganese, Mn

Atomic number

25 protons

Position

group 7 · period 4 · d-block · transition metal

CAS number

7439-96-5

Atomic structure

Atomic mass

54.938 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵
[Ar] 4s²³d⁵

Electrons per shell

2, 8, 13, 2

Valence electrons

7 ns and (n-1)d

Physical properties

State at room temperature

Solid

Melting point

1,519 K (1,245.85 °C)

Boiling point

2,334 K (2,060.85 °C)

Density

7.3 g/cm3

Appearance

silvery metallic

Thermal conductivity

7.81 W/(m·K)

Electrical resistivity

1.44 µΩ·m at 20 °C

Electrical conductivity

694,444.444 S/m

Crystal structure

body-centered cubic

Molar heat capacity

26.32 J/(mol·K)

Chemical properties

Oxidation states

+7, +4, +3, +2

Electronegativity

1.55 (Pauling Scale)

Ionisation energy

7.434 eV
1st 717.3, 2nd 1,509, 3rd 3,248 kJ/mol

Electron affinity

0 eV

Atomic radius

van der Waals 197 pm

Ionic radius

Mn²⁺ 67 low spin; Mn³⁺ 58 low spin; Mn⁴⁺ 53 low spin; Mn⁵⁺ 33 (4-coordinate) low spin; Mn⁶⁺ 26 (4-coordinate) low spin; Mn⁷⁺ 46 low spin; Mn²⁺ 83 high spin; Mn³⁺ 65 high spin pm

Reactivity

A group 7 transition metal ([Ar] 3d5 4s2) with the widest range of oxidation states in the first row (+2, +4 and +7 the common ones); the hard, brittle metal is chemically reactive, a little less so toward air than its neighbours, and comparable to zinc in the reactivity series.

with water

Decomposes slowly in cold water at most, giving hydrogen; under normal conditions the attack is negligible.

with oxygen, air

Somewhat less reactive to air than its neighbours; heated in oxygen the metal burns to the mixed oxide $\ce{Mn3O4: 3 Mn + 2 O2 -> Mn3O4}$

with acids

Dissolves in dilute acids to pale pink manganese(II) salts and hydrogen: $\ce{Mn + 2 HCl -> MnCl2 + H2}$

with halogens

Combines with the halogens to manganese(II) halides, chlorine giving manganese(II) chloride and fluorine reacting similarly: $\ce{Mn + Cl2 -> MnCl2}$

Typical compounds

• MnO₂ manganese dioxide pyrolusite; dry-cell depolariser, glass decolouriser, oxidiser
• KMnO₄ potassium permanganate purple oxidiser for analysis, medicine, water treatment
• MnCO₃ manganese(II) carbonate rhodochrosite, a main ore
• MnSO₄ manganese(II) sulfate pale pink salt of the aquo ion; fertiliser additive
• MnCl₂ manganese(II) chloride from the metal and chlorine
• Mn₃O₄ trimanganese tetroxide hausmannite; the oxide from burning the metal

Occurrence, production and use

Crustal abundance

9.50×102 milligrams per kilogram

Oceanic abundance

2×10-4 milligrams per liter

Occurrence and sources

Manganese minerals are widely distributed, with oxides, silicates, and carbonates being the most common. Large quantities of manganese nodules are found on the ocean floor and may become a source of manganese. These nodules contain about 24% manganese, together with many other elements in lesser abundance.

Most manganese today is obtained from ores found in Russia, Brazil, Australia, South Africa, Gabon, and India. Pyrolusite and rhodochrosite are among the most common manganese minerals. The metal is obtained by reduction of the oxide with sodium, magnesium, aluminum, or by electrolysis.

• pyrolusite (MnO2) and rhodochrosite (MnCO3) the most common ore minerals, widely distributed; main mining areas in South Africa, Gabon, Australia, Ghana, India, China and Brazil
• manganese ore (35 to 54 percent manganese) land based resources large but irregular, South Africa about 70 percent of world resources; United States ores very low grade and not mined since 1970
• manganese nodules the deep ocean floor, about 24 percent manganese with cobalt, nickel and copper

Extraction, production

Smelting of manganese ore to ferromanganese and silicomanganese

$\ce{2 MnO (s) + C (s) -> 2 Mn (l) + CO2 (g)}$

Ore is reduced with carbon in furnaces to ferromanganese (74 to 95 percent manganese) or with silicon bearing charge to silicomanganese, the forms that steelmakers buy; the United States imports ferromanganese mainly from Malaysia, Australia, Norway and South Africa. The equation given is the carbothermic reduction step of ferromanganese smelting, taken from the added secondary source. World mine production about 20 million tonnes of manganese content in 2024 (estimate).

Electrolytic manganese metal and metallothermic reduction

The metal is obtained by electrolysis of manganese sulphate solution or by reducing the oxide with sodium, magnesium or aluminium; electrolytic manganese production consumes selenium dioxide as a yield additive. Battery grade high purity manganese is a growing product. Reactants only are stated, so no equation is written.

Uses

Nearly 90% of all of the manganese produced each year is used in the production of steel. Manganese is added to molten steel to remove oxygen and sulfur and is alloyed with steel to make it easier to form and work with and to increase steel's strength and resistance to impact. Railroad tracks, for example, are made with steel that contains as much as 1.2% manganese. Manganese is also used to give glass an amethyst color and is responsible for the color of amethyst gemstones.

Manganese dioxide (MnO2), the most common compound of manganese, makes up about 0.14% of the Earth's crust. It is used in dry cell batteries to prevent the formation of hydrogen, to remove the green color in glass that is caused by the presence of iron contaminants, and as a drying agent in black paints.

The dioxide (pyrolusite) is used as a depolarizer in dry cells and is used to "decolorize" glass that is colored green by impurities of iron. Manganese by itself colors glass an amethyst color and is responsible for the color of true amethyst. The dioxide is also used in the preparation of oxygen and chlorine and in drying black paints. The permanganate is a powerful oxidizing agent and is used in quantitative analysis and in medicine.

Manganese is widely distributed throughout the animal kingdom. It is an important trace element and may be essential for utilization of vitamin B1.

• Steel: about 1 percent manganese in ordinary steel for strength, workability and wear resistance; manganese steel with about 13 percent manganese for railway track, safes and rifle barrels; manganese dioxide for pig iron manufacture (three United States consumers) consumption closely follows the steel industry; manganese has no satisfactory substitute in its major applications (USGS)
• Batteries: manganese dioxide in dry cell batteries; high purity battery grade manganese for lithium ion cathodes, a strategic raw material under the EU Critical Raw Materials Act (in force May 2024)
• Chemicals: manganese containing catalyst for the transesterification step of PET made from dimethyl terephthalate, which ends up in the product (POL BREF); manganese(IV) oxide as a catalyst, rubber additive and glass decolouriser; potassium permanganate as an oxidant in synthesis and treatment
• Agriculture and food: manganese sulphate in fungicides and fertilisers for manganese poor soils; manganese as a mineral supplement in animal feed and in brick colorants (USGS lists animal feed among non metallurgical ore uses)
• Aluminium alloys: drinks can alloy with 1.5 percent manganese for corrosion resistance; highly magnetic alloys with aluminium, antimony and copper
• Mining: manganese ore extraction is grouped with iron ore in the MWEI BREF; manganese is a measured parameter in water discharged from base metal, precious metal, industrial mineral and coal extraction

Safety, toxicity

Exposure to manganese dusts, fume, and compounds should not exceed the ceiling value of 5 mg/m3 for even short periods because of the element's toxicity level.

GHS classification, signal word Danger

• H228 Flammable solid Flammable solids
• H319 Causes serious eye irritation Serious eye damage/eye irritation
• H411 Toxic to aquatic life with long lasting effects to the aquatic environment, long-term hazard
• H412 Harmful to aquatic life with long lasting effects to the aquatic environment, long-term hazard
• H360 May damage fertility or the unborn child Reproductive toxicity
• H372 Causes damage to organs through prolonged or repeated exposure Specific target organ toxicity, repeated exposure
• H401 Toxic to aquatic life to the aquatic environment, acute hazard
• H316 Causes mild skin irritation Skin corrosion/irritation
• H320 Causes eye irritation Serious eye damage/eye irritation
• H370 Causes damage to organs Specific target organ toxicity, single exposure

Discovery and name

Discovered by

Carl Wilhelm Scheele

Discovered

1774

First isolated

Johann Gottlieb Gahn

Named by

not in sources

Origin of the name

after Magnesia, Greece

It is gray-white, resembling iron, but is harder and very brittle. The metal is reactive chemically and decomposes slowly in cold water. Manganese is used to form many important alloys. Manganese improves rolling and forging qualities in steel, along with adding strength, stiffness, wear resistance, hardness.

With aluminum and antimony, and especially with small amounts of copper, it forms highly ferromagnetic alloys.

Manganese metal is ferromagnetic only after special treatment. The pure metal exists in four allotropic forms. The alpha form is stable at ordinary temperature; gamma manganese, which changes to alpha at ordinary temperatures, is said to be flexible, soft, easily cut, and capable of being bent.