Copper

Typical wastewaters

• municipal sewage (plumbing corrosion) Cu²⁺ and its carbonate and hydroxo complexes; a four fold increase measured downstream of a sewage treatment plant on the River Stour
• copper plating and metal finishing Cu²⁺ in rinse water, complexed by ammonia or EDTA in some baths; 3.38 daily maximum and 2.07 mg/L monthly average
• copper mining and flotation mills total copper 0.30 daily maximum and 0.15 mg/L monthly average
• power plant metal cleaning wastes total copper with iron, 1.0 mg/L
• textile dyeing and leather tanning copper from dyes and auxiliaries; 1, 0.5 and 0.25 mg/L by ZDHC level
• chemical sector effluent total copper 5.0 to 50 µg/L after precipitation and solids separation

1 · Identity

Symbol, number

Cu, 29

Oxidation states in water

+2 as Cu²⁺ and its carbonate and hydroxo complexes, the dissolved form in oxic water and the blue green stain; +1 as Cu₂O cuprite in the scale on copper pipe and as CuCl₂⁻ in chloride rich or reducing water; 0 as the metal of tubes, fittings and roofs, which oxidises to both. The element entry sets out the two working states; here the +2 state does the dissolving and the solids on the pipe wall decide how much.

Note

Copper in drinking water is a plumbing problem: WHO reports raw water copper is rarely a contaminant and conventional treatment does not remove it, so the chapter is about release, control at the tap, and removal from industrial effluent.

2 · Occurrence in water

Natural sources

Weathering of copper sulfide and carbonate minerals; complexed with organic matter or particulate in surface water (WHO: copper is primarily present in complexes or as particulate matter). Background in an upper catchment control site 0.001 mg/L.

Anthropogenic sources

Corrosion of interior copper plumbing, the primary source in drinking water (WHO); copper sulfate pentahydrate added to reservoirs against algae; copper-silver ionisation in building hot water; copper plating and metal finishing (US limit 3.38 mg/L daily), copper mining and flotation mills (0.30 mg/L), power plant metal cleaning wastes (1.0 mg/L), copper in textile dye effluent (ZDHC), sewage effluent (four fold increase downstream of a treatment plant on the River Stour); the ledger's mining, chemical and textile chapters carry the plant figures.

3 · Speciation

Dissolved copper(II) in drinking water is mostly the neutral carbonate ion pair CuCO₃ and the hydroxo species, with free Cu²⁺ dominant only below about pH 6; natural organic matter binds copper strongly, which is why total and bioavailable copper differ and why the US freshwater criterion is a biotic ligand model rather than a number. Copper pipe corrodes to a scale of Cu₂O next to the metal with Cu(OH)₂, malachite Cu₂(OH)₂CO₃ and tenorite CuO above it; the solubility of that outer scale sets the tap concentration, so copper is highest in new pipe, in acid water and in high carbonate alkaline water (WHO: release increases in systems with an acid pH or in high carbonate waters with an alkaline pH), and falls as the scale ages to malachite and tenorite. Copper(I) matters in chloride: CuCl₂⁻ carries copper in seawater and brines, and Cu₂O is the first corrosion product.

Solubility

Controlled by the scale: Cu(OH)₂ is the most soluble of the pipe wall solids, malachite and tenorite the least, so copper release depends on scale age as much as on water chemistry. Carbonate raises copper solubility through the CuCO₃ ion pair, which is why high alkalinity alkaline waters are cuprosolvent (WHO). No solubility products quoted; the sources read print none (Stumm and Morgan chapter 7 has them).

Hydrolysis

Cu²⁺ hydrolyses from about pH 6 to Cu(OH)⁺ and Cu(OH)₂; copper salts are acidic in solution.

Complexation

Carbonate (CuCO₃ ion pair) and natural organic matter dominate in fresh water; chloride for Cu(I); ammonia, EDTA and citrate in plating rinses hold copper against precipitation; orthophosphate forms low solubility copper phosphate films, the basis of corrosion control (US EPA 1995 cuprosolvency study cited by WHO).

Precipitates

Cu₂O cuprite, Cu(OH)₂, Cu₂(OH)₂CO₃ malachite, CuO tenorite (pipe scale and treatment sludge); CuS and Cu₂S (sulfide); copper phosphate films (corrosion control); Cu co-precipitated in Fe(OH)₃ and Al(OH)₃ flocs.

4 · Role in treatment

5 · Removal and control

6 · Analytics

Sampling pitfalls

State the sampling protocol or the number means nothing: first draw after at least 6 hours of stagnation (the US rule) can be ten times the flushed value. Dissolved copper needs field filtration before acidification (WHO notes measurement of dissolved copper requires filtration); particulate copper from scale flakes is a total copper artefact. Copper adsorbs on unacidified container walls.

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 nutrient and a contaminant. The guideline rests on acute gastrointestinal effects: nausea NOAEL 2 to 4 mg/L and LOAEL 4 to 6 mg/L in volunteer studies, vomiting from 6 mg/L, with the response driven by concentration rather than daily mass (WHO background document). Tolerable upper intake 10 mg/day; carriers of Wilson disease and other copper homeostasis disorders are the uncertain sensitive group. Infants fed formula reconstituted with standing tap water carry the highest exposure.

Bioaccumulation

Homeostatically regulated in mammals; not addressed as a bioaccumulation concern in the sources read.

Ecotoxicity

Among the most toxic common metals to algae and invertebrates, which is why it is an algaecide. US EPA aquatic life criteria: saltwater 4.8 µg/L acute and 3.1 µg/L chronic (2007); freshwater criteria are calculated site by site with the biotic ligand model because organic matter, pH and hardness change copper bioavailability.

Flags

• The corrosion, carbonate complex, malachite and tenorite equations and the scale ageing sequence are cited to Stumm and Morgan chapters 6 and 7 from memory of the text, not re-read this session; the Lead and Copper Rule corrosion control detail and the EPA 1995 cuprosolvency study were not read beyond the WHO citation.
• The copper as oxidant interference item is general practice with no figure read.
• Mine drainage and metal cleaning limits are reused from the book's lead and iron chapters; the CFR sections were not re-read.
• No seawater copper concentration was read; the surveys quoted are 1990s and 2000s compilations by WHO.
• EU law was read on legislation.gov.uk mirrors because eur-lex did not respond; eur-lex urls kept for consistency.
• Abu Dhabi values cover two media (marine 0.5 mg/L, sewer 5 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

• No seawater, municipal wastewater or raw plating effluent copper concentration was read.
• Copper sulfate algaecide doses, cyanotoxin release on lysis and the aquatic side effects are not in the sources read.
• The EU textiles BAT conclusions (2022/2508) were not read for a copper BAT-AEL.
• The 2024 Lead and Copper Rule Improvements were read only as the effective date line on the Cornell page.
• EU law was read on legislation.gov.uk mirrors; other GCC discharge standards were not read.
• No solubility products or stability constants are quoted: Stumm and Morgan chapters 6, 7 and 8 were used for the hydrolysis, carbonate, chloride and redox forms only, from the chapter, not re-read, and the corrosion half reactions are from MWH chapter 22 on the same basis.
• The copper phosphate film of orthophosphate corrosion control is written as the simple phosphate solid; the real film composition and the dose response are in the US EPA 1995 cuprosolvency study, which was not read.

Sources

Identity

Name and symbol

Copper, Cu

Atomic number

29 protons

Position

group 11 · period 4 · d-block · transition metal

CAS number

7440-50-8

Atomic structure

Atomic mass

63.546 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰
[Ar] 4s¹³d¹⁰

Electrons per shell

2, 8, 18, 1

Valence electrons

11 ns and (n-1)d

Physical properties

State at room temperature

Solid

Melting point

1,357.77 K (1,084.62 °C)

Boiling point

2,835 K (2,561.85 °C)

Density

8.933 g/cm3

Appearance

Red-orange metallic luster

Thermal conductivity

401 W/(m·K)

Electrical resistivity

16.78 nΩ·m at 20 °C

Electrical conductivity

59.59 MS/m

Crystal structure

face-centered cubic

Molar heat capacity

24.44 J/(mol·K)

Chemical properties

Oxidation states

+2, +1

Electronegativity

1.9 (Pauling Scale)

Ionisation energy

7.726 eV
1st 745.5, 2nd 1,957.9, 3rd 3,555 kJ/mol

Electron affinity

1.228 eV

Atomic radius

empirical 132, covalent 132, van der Waals 140 pm

Ionic radius

Cu⁺ 77; Cu²⁺ 73; Cu³⁺ 54 ls pm

Reactivity

A group 11 coinage metal ([Ar] 3d10 4s1), rather inactive: it does not react with water or non-oxidising acids, oxidises only slowly in air and is found native, with a chemistry of the +1 and +2 states.

with water

Does not react with water.

with oxygen, air

Reacts slowly with atmospheric oxygen to a brown-black oxide film that protects the metal, and over years on roofs to a green patina (verdigris); it also tarnishes with sulfur compounds to sulfides: $\ce{2 Cu + O2 -> 2 CuO}$

with acids

Resists most acids, including hydrochloric, but dissolves readily in nitric acid and in hot concentrated sulfuric acid, which oxidise it to copper(II).

with halogens

Forms copper(II) fluoride, chloride and bromide and copper(I) chloride, bromide and iodide; copper(II) iodide cannot be made, iodide reducing Cu2+ to CuI and iodine: $\ce{Cu + Cl2 -> CuCl2}$

Typical compounds

• CuSO₄.5H₂O copper(II) sulfate pentahydrate blue vitriol, the familiar laboratory copper salt; algaecide
• Cu₂O copper(I) oxide red cuprite; Fehling and Benedict test product
• CuO copper(II) oxide black tenorite; the tarnish film
• CuFeS₂ chalcopyrite the main ore, smelted to the metal
• Cu₂CO₃(OH)₂ malachite green carbonate mineral and pigment
• CuCl₂ copper(II) chloride well characterised cupric halide

Occurrence, production and use

Crustal abundance

6.0×101 milligrams per kilogram

Oceanic abundance

2.5×10-4 milligrams per liter

Occurrence and sources

Copper occasionally occurs natively, and is found in many minerals such as cuprite, malachite, azurite, chalcopyrite, and bornite.

Large copper ore deposits are found in the U.S., Chile, Zambia, Zaire, Peru, and Canada. The most important copper ores are the sulfides, the oxides, and carbonates. From these, copper is obtained by smelting, leaching, and by electrolysis.

• chalcopyrite and bornite (sulphides); cuprite, malachite and azurite (oxide and carbonates); native copper porphyry and sediment hosted deposits in Chile, Peru, Congo (Kinshasa), China, Indonesia, the United States, Russia, Zambia, Kazakhstan, Mexico, Australia, Canada and Poland
• copper in reserves and resources reserves 980 million tonnes; identified resources 2.1 billion tonnes and undiscovered 3.5 billion tonnes (USGS assessment as of 2015)

Extraction, production

Smelting of sulphide concentrate, electrolytic refining and electrowinning

$\ce{2 Cu2O (l) + Cu2S (l) -> 6 Cu (l) + SO2 (g)}$

Sulphide ore is concentrated by flotation, smelted to blister and anodes and refined electrolytically to cathode; oxide and low grade ore is leached with sulphuric acid and the copper electrowon (14 electrowon refineries in the United States). Roasting the sulphides gives sulphur dioxide, and non ferrous smelting supplies 39 percent of sulphuric acid (LVIC-AAF BREF); anode slimes carry selenium and arsenic. No full reaction is stated, so no equation is written.

Cementation of copper sulphate on scrap iron (historic)

$\ce{CuSO4 + Fe -> Cu + FeSO4}$

The RSC describes roasting sulphide ore, leaching the copper sulphate with water and trickling it over scrap iron, on which copper deposits as a flaky layer; balanced from the stated reactants and copper product, with iron(II) sulphate as the only possible co product.

Uses

Used in large amounts by the electrical industry in the form of wire, copper is second only to silver in electrical conductance. Since it resists corrosion from the air, moisture and seawater, copper has been widely used in coins. Although once made nearly entirely from copper, American pennies are now made from zinc that has been coated with copper. Copper is also used to make water pipes and jewelry, as well as other items.

Pure copper is usually too soft for most uses. People first learned about 5,000 years ago that copper can be strengthened if it is mixed with other metals. The two most familiar alloys of copper are bronze and brass. Bronze, the first alloy created by people, is a mix of copper that contains as much as 25% tin. Early people used bronze to make tools, weaponry, containers and ornamental items. Brass, a mix of copper that contains between 5% and 45% zinc, was first used about 2,500 years ago. The Romans were the first to make extensive use of brass, using it to make such things as coins, kettles and ornamental objects. Today, brass is also used in some musical instruments, screws and other hardware that must resist corrosion.

Hydrated copper sulfate (CuSO4·H2O), also known as blue vitriol, is the best known copper compound. It is used as an agricultural poison, as an algicide in water purification and as a blue pigment for inks. Cuperic chloride (CuCl2), another copper compound, is used to fix dyes to fabrics. Cuprous chloride (CuCl) is a poisonous white powder that is chiefly used to absorb carbon dioxide (CO2). Copper cyanide (CuCN) is commonly used in electroplating.

The electrical industry is one of the greatest users of copper. Iron's alloys brass and bronze are very important: all American coins are copper alloys and gun metals also contain copper.

Copper has wide use as an agricultural poison and as an algaecide in water purification. Copper compounds, such as Fehling's solution, are widely used in analytical chemistry tests for sugar.

• Electrical and construction: wiring, motors and electronics; roofing, plumbing and heat exchangers; brass and bronze, coinage United States 2024: building construction 42 percent, electrical and electronic 23 percent, transport 18 percent, consumer 10 percent, machinery 7 percent (Copper Development Association via USGS)
• Textiles: copper complex dyes (phthalocyanine blues and turquoises among reactive dyes) so that the Textiles BREF lists copper among the metals discharged from reactive dyeing of cotton and from printing; copper bound in 1:1 and 1:2 metal complex dyes for wool; engraved copper rollers in roller printing
• Chemicals: copper salt catalyst for oxychlorination: $\ce{2 C2H4 + 4 HCl + O2 -> 2 C2H4Cl2 + 2 H2O}$ at 220 to 300 degrees C (balanced from the reactants and products the LVOC BREF states), with copper and catalyst fines removed from the waste water; copper catalyst for the direct synthesis of dimethyldichlorosilane from silicon and methyl chloride; copper oxide and zinc oxide low temperature shift catalyst in ammonia plants; copper discharged from EDC, phosphoric acid, pigment and silicone plants
• Pharmaceuticals and fine chemicals: metallisation of azo dyes with copper to form chelated complexes; copper is discharged from processes involving heavy metals
• Mining: copper ore is the first base metal ore of the MWEI BREF; sulphuric acid heap and dump leaching of copper; copper sulphate as a flotation activator and, with sodium metabisulphite, in SO2 and air cyanide destruction at gold plants; copper listed among substances discharged from base metal, precious metal, bauxite and industrial mineral extraction
• Agriculture and water: copper sulphate as an agricultural poison and algicide in water purification

Safety, toxicity

GHS classification, signal word Danger

• H400 Very toxic to aquatic life Hazardous to the aquatic environment, acute hazard
• H410 Very toxic to aquatic life with long lasting effects Hazardous to the aquatic environment, long-term hazard
• H302 Harmful if swallowed Acute toxicity, oral
• H411 Toxic to aquatic life with long lasting effects to the aquatic environment, long-term hazard
• H317 May cause an allergic skin reaction Sensitization, Skin
• H335 May cause respiratory irritation Specific target organ toxicity, single exposure; Respiratory tract irritation
• H370 Causes damage to organs Specific target organ toxicity, single exposure
• H372 Causes damage to organs through prolonged or repeated exposure Specific target organ toxicity, repeated exposure

Discovery and name

Discovered by

Middle East

Discovered

9000 BC

First isolated

not in sources

Named by

not in sources

Origin of the name

after Cyprus, principal mining place in Roman era (Cyprium)

Copper is reddish and takes on a bright metallic luster. It is malleable, ductile, and a good conductor of heat and electricity (second only to silver in electrical conductivity).