chemistry

Mercury cycle

Mercury cycle is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mercury cycle rather than just read about it. In short: The mercury cycle is a biogeochemical cycle influenced by natural and anthropogenic processes that transform mercury through multiple chemical forms and environments. Mercury is present in the Earth's crust and in various forms on the Earth's surface.

Key takeaways

Mercury cycle belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mercury cycle to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mercury cycle from memory before moving on to harder problems.

Reference excerpt

The mercury cycle is a biogeochemical cycle influenced by natural and anthropogenic processes that transform mercury through multiple chemical forms and environments. Mercury is present in the Earth's crust and in various forms on the Earth's surface. It can be elemental, inorganic, or organic. Mercury exists in three oxidation states: 0 (elemental mercury), I (mercurous mercury), and II (mercuric mercury). Mercury emissions to the atmosphere can be primary sources, which release mercury from the lithosphere, or secondary sources, which exchange mercury between surface reservoirs. Annually, over 5000 metric tons of mercury is released to the atmosphere by primary emissions and secondary re-emissions.

Sources of mercury

Primary sources Primary sources of mercury emissions can be natural or anthropogenic. There are only a few significant mercury ores, most notably the mercury sulfide mineral, cinnabar. Organic-rich sedimentary rocks can also contain elevated mercury. Weathering of minerals and geothermal activity release mercury to the environment. Active volcanoes are another significant primary source of natural mercury. Anthropogenic primary sources of mercury include gold mining, burning coal, and production of non-iron metals, such as copper or lead.

Secondary sources Secondary natural sources, which re-emit previously deposited mercury, include vegetation, evasion from oceans and lakes, and biomass burning, including forest fires. Primary anthropogenic emissions are leading to increased sizes of mercury in surface reservoirs.

Processes Mercury is transported and distributed by atmospheric circulation, which moves elemental mercury from the land to the ocean. Elemental mercury in the atmosphere is returned to the Earth's surface by several routes. A major sink of elemental mercury (Hg(0)) in the atmosphere is through dry deposition. Some of elemental mercury, on the other hand, is photooxidized to gaseous mercury(II), and is returned to the Earth's surface by both dry and wet deposition. Because photooxidation is very slow, elemental mercury can circulate over the entire globe before being oxidized and deposited. Wet and dry deposition is responsible for 90% of the mercury of surface waters, including open ocean. A fraction of deposited mercury instantaneously re-volatilize back to the atmosphere. Inorganic mercury can be converted by bacteria and archaea into methylmercury ([CH3Hg]+), which bioaccumulates in marine species such as tuna and swordfish and biomagnifies further up the food chain. Certain xenophyophores have been found to have abnormally high concentrations of mercury within their bodies.

See also Mercury (element) Mercury in fish Minamata Convention on Mercury Mercury poisoning COLEX process (isotopic separation)

References

Illustrations

Worked examples

Example 1 — a first encounter with Mercury cycle

Start with the simplest possible case. Write down what Mercury cycle claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mercury cycle before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mercury cycle ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mercury cycle

In research: Mercury cycle appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mercury cycle in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mercury cycle is common in secondary-school and first-year university syllabi. It links to neighbouring topics Biogeochemical cycle, Mercury (element), so understanding it makes those chapters shorter.
In everyday life: Look for Mercury cycle outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mercury cycle in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mercury cycle means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mercury cycle out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mercury cycle in simple terms?

Why does Mercury cycle matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mercury cycle?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mercury cycle.