Quantum chromodynamics

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Quantum_chromodynamics 

In theoretical physics, quantum chromodynamics (QCD) is the theory of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type of quantum field theory called a non-abelian gauge theory, with symmetry group SU(3). The QCD analog of electric charge is a property called color. Gluons are the force carriers of the theory, just as photons are for the electromagnetic force in quantum electrodynamics. The theory is an important part of the Standard Model of particle physics. A large body of experimental evidence for QCD has been gathered over the years.

QCD exhibits three salient properties:

• Color confinement. Due to the force between two color charges remaining constant as they are separated, the energy grows until a quark–antiquark pair is spontaneously produced, turning the initial hadron into a pair of hadrons instead of isolating a color charge. Although analytically unproven, color confinement is well established from lattice QCD calculations and decades of experiments.
• Asymptotic freedom, a steady reduction in the strength of interactions between quarks and gluons as the energy scale of those interactions increases (and the corresponding length scale decreases). The asymptotic freedom of QCD was discovered in 1973 by David Gross and Frank Wilczek, and independently by David Politzer in the same year. For this work, all three shared the 2004 Nobel Prize in Physics.
• Chiral symmetry breaking, the spontaneous symmetry breaking of an important global symmetry of quarks, detailed below, with the result of generating masses for hadrons far above the masses of the quarks, and making pseudoscalar mesons exceptionally light. Yoichiro Nambu was awarded the 2008 Nobel Prize in Physics for elucidating the phenomenon, a dozen years before the advent of QCD. Lattice simulations have confirmed all his generic predictions.

Terminology

Physicist Murray Gell-Mann coined the word quark in its present sense. It originally comes from the phrase "Three quarks for Muster Mark" in Finnegans Wake by James Joyce. On June 27, 1978, Gell-Mann wrote a private letter to the editor of the Oxford English Dictionary, in which he related that he had been influenced by Joyce's words: "The allusion to three quarks seemed perfect." (Originally, only three quarks had been discovered.)

The three kinds of charge in QCD (as opposed to one in quantum electrodynamics or QED) are usually referred to as "color charge" by loose analogy to the three kinds of color (red, green and blue) perceived by humans. Other than this nomenclature, the quantum parameter "color" is completely unrelated to the everyday, familiar phenomenon of color.

The force between quarks is known as the colour force (or color force) or strong interaction, and is responsible for the nuclear force.

Since the theory of electric charge is dubbed "electrodynamics", the Greek word χρῶμα chroma "color" is applied to the theory of color charge, "chromodynamics".

History

Main articles: History of quantum mechanics and History of quantum field theory

With the invention of bubble chambers and spark chambers in the 1950s, experimental particle physics discovered a large and ever-growing number of particles called hadrons. It seemed that such a large number of particles could not all be fundamental. First, the particles were classified by charge and isospin by Eugene Wigner and Werner Heisenberg; then, in 1953–56, according to strangeness by Murray Gell-Mann and Kazuhiko Nishijima (see Gell-Mann–Nishijima formula). To gain greater insight, the hadrons were sorted into groups having similar properties and masses using the eightfold way, invented in 1961 by Gell-Mann and Yuval Ne'eman. Gell-Mann and George Zweig, correcting an earlier approach of Shoichi Sakata, went on to propose in 1963 that the structure of the groups could be explained by the existence of three flavors of smaller particles inside the hadrons: the quarks. Gell-Mann also briefly discussed a field theory model in which quarks interact with gluons.

Perhaps the first remark that quarks should possess an additional quantum number was made as a short footnote in the preprint of Boris Struminsky in connection with the Ω⁻ hyperon being composed of three strange quarks with parallel spins (this situation was peculiar, because since quarks are fermions, such a combination is forbidden by the Pauli exclusion principle):

Three identical quarks cannot form an antisymmetric S-state. In order to realize an antisymmetric orbital S-state, it is necessary for the quark to have an additional quantum number.

— B. V. Struminsky, Magnetic moments of barions in the quark model, JINR-Preprint P-1939, Dubna, Submitted on January 7, 1965

Boris Struminsky was a PhD student of Nikolay Bogolyubov. The problem considered in this preprint was suggested by Nikolay Bogolyubov, who advised Boris Struminsky in this research. In the beginning of 1965, Nikolay Bogolyubov, Boris Struminsky and Albert Tavkhelidze wrote a preprint with a more detailed discussion of the additional quark quantum degree of freedom. This work was also presented by Albert Tavkhelidze without obtaining consent of his collaborators for doing so at an international conference in Trieste (Italy), in May 1965.

A similar mysterious situation was with the Δ⁺⁺ baryon; in the quark model, it is composed of three up quarks with parallel spins. In 1964–65, Greenberg and Han–Nambu independently resolved the problem by proposing that quarks possess an additional SU(3) gauge degree of freedom, later called color charge. Han and Nambu noted that quarks might interact via an octet of vector gauge bosons: the gluons.

Since free quark searches consistently failed to turn up any evidence for the new particles, and because an elementary particle back then was defined as a particle that could be separated and isolated, Gell-Mann often said that quarks were merely convenient mathematical constructs, not real particles. The meaning of this statement was usually clear in context: He meant quarks are confined, but he also was implying that the strong interactions could probably not be fully described by quantum field theory.

Richard Feynman argued that high energy experiments showed quarks are real particles: he called them partons (since they were parts of hadrons). By particles, Feynman meant objects that travel along paths, elementary particles in a field theory.

The difference between Feynman's and Gell-Mann's approaches reflected a deep split in the theoretical physics community. Feynman thought the quarks have a distribution of position or momentum, like any other particle, and he (correctly) believed that the diffusion of parton momentum explained diffractive scattering. Although Gell-Mann believed that certain quark charges could be localized, he was open to the possibility that the quarks themselves could not be localized because space and time break down. This was the more radical approach of S-matrix theory.

James Bjorken proposed that pointlike partons would imply certain relations in deep inelastic scattering of electrons and protons, which were verified in experiments at SLAC in 1969. This led physicists to abandon the S-matrix approach for the strong interactions.

In 1973 the concept of color as the source of a "strong field" was developed into the theory of QCD by physicists Harald Fritzsch and Heinrich Leutwyler, together with physicist Murray Gell-Mann. In particular, they employed the general field theory developed in 1954 by Chen Ning Yang and Robert Mills (see Yang–Mills theory), in which the carrier particles of a force can themselves radiate further carrier particles. (This is different from QED, where the photons that carry the electromagnetic force do not radiate further photons.)

The discovery of asymptotic freedom in the strong interactions by David Gross, David Politzer and Frank Wilczek allowed physicists to make precise predictions of the results of many high energy experiments using the quantum field theory technique of perturbation theory. Evidence of gluons was discovered in three-jet events at PETRA in 1979. These experiments became more and more precise, culminating in the verification of perturbative QCD at the level of a few percent at LEP, at CERN.

The other side of asymptotic freedom is confinement. Since the force between color charges does not decrease with distance, it is believed that quarks and gluons can never be liberated from hadrons. This aspect of the theory is verified within lattice QCD computations, but is not mathematically proven. One of the Millennium Prize Problems announced by the Clay Mathematics Institute requires a claimant to produce such a proof. Other aspects of non-perturbative QCD are the exploration of phases of quark matter, including the quark–gluon plasma.

The relation between the short-distance particle limit and the confining long-distance limit is one of the topics recently explored using string theory, the modern form of S-matrix theory.

Theory

Some definitions

Unsolved problem in physics:

QCD in the non-perturbative regime:

• Confinement: the equations of QCD remain unsolved at energy scales relevant for describing atomic nuclei. How does QCD give rise to the physics of nuclei and nuclear constituents?
• Quark matter: the equations of QCD predict that a plasma (or soup) of quarks and gluons should be formed at high temperature and density. What are the properties of this phase of matter?

Every field theory of particle physics is based on certain symmetries of nature whose existence is deduced from observations. These can be

• local symmetries, which are the symmetries that act independently at each point in spacetime. Each such symmetry is the basis of a gauge theory and requires the introduction of its own gauge bosons.
• global symmetries, which are symmetries whose operations must be simultaneously applied to all points of spacetime.

QCD is a non-abelian gauge theory (or Yang–Mills theory) of the SU(3) gauge group obtained by taking the color charge to define a local symmetry.

Since the strong interaction does not discriminate between different flavors of quark, QCD has approximate flavor symmetry, which is broken by the differing masses of the quarks.

There are additional global symmetries whose definitions require the notion of chirality, discrimination between left and right-handed. If the spin of a particle has a positive projection on its direction of motion then it is called right-handed; otherwise, it is left-handed. Chirality and handedness are not the same, but become approximately equivalent at high energies.

• Chiral symmetries involve independent transformations of these two types of particle.
• Vector symmetries (also called diagonal symmetries) mean the same transformation is applied on the two chiralities.
• Axial symmetries are those in which one transformation is applied on left-handed particles and the inverse on the right-handed particles.

Additional remarks: duality

As mentioned, asymptotic freedom means that at large energy – this corresponds also to short distances – there is practically no interaction between the particles. This is in contrast – more precisely one would say dual– to what one is used to, since usually one connects the absence of interactions with large distances. However, as already mentioned in the original paper of Franz Wegner, a solid state theorist who introduced 1971 simple gauge invariant lattice models, the high-temperature behaviour of the original model, e.g. the strong decay of correlations at large distances, corresponds to the low-temperature behaviour of the (usually ordered!) dual model, namely the asymptotic decay of non-trivial correlations, e.g. short-range deviations from almost perfect arrangements, for short distances. Here, in contrast to Wegner, we have only the dual model, which is that one described in this article.

Symmetry groups

The color group SU(3) corresponds to the local symmetry whose gauging gives rise to QCD. The electric charge labels a representation of the local symmetry group U(1), which is gauged to give QED: this is an abelian group. If one considers a version of QCD with N_f flavors of massless quarks, then there is a global (chiral) flavor symmetry group SU_L(N_f) × SU_R(N_f) × U_B(1) × U_A(1). The chiral symmetry is spontaneously broken by the QCD vacuum to the vector (L+R) SU_V(N_f) with the formation of a chiral condensate. The vector symmetry, U_B(1) corresponds to the baryon number of quarks and is an exact symmetry. The axial symmetry U_A(1) is exact in the classical theory, but broken in the quantum theory, an occurrence called an anomaly. Gluon field configurations called instantons are closely related to this anomaly.

There are two different types of SU(3) symmetry: there is the symmetry that acts on the different colors of quarks, and this is an exact gauge symmetry mediated by the gluons, and there is also a flavor symmetry that rotates different flavors of quarks to each other, or flavor SU(3). Flavor SU(3) is an approximate symmetry of the vacuum of QCD, and is not a fundamental symmetry at all. It is an accidental consequence of the small mass of the three lightest quarks.

In the QCD vacuum there are vacuum condensates of all the quarks whose mass is less than the QCD scale. This includes the up and down quarks, and to a lesser extent the strange quark, but not any of the others. The vacuum is symmetric under SU(2) isospin rotations of up and down, and to a lesser extent under rotations of up, down, and strange, or full flavor group SU(3), and the observed particles make isospin and SU(3) multiplets.

The approximate flavor symmetries do have associated gauge bosons, observed particles like the rho and the omega, but these particles are nothing like the gluons and they are not massless. They are emergent gauge bosons in an approximate string description of QCD.

Lagrangian

The dynamics of the quarks and gluons are controlled by the quantum chromodynamics Lagrangian. The gauge invariant QCD Lagrangian is

${\displaystyle {\mathcal{L}}_{\mathrm{Q}\mathrm{C}\mathrm{D}}={\overline{\psi }}_i\left(i{\gamma }^{\mu }(D_{\mu }{)}_{ij}-m{\delta }_{ij}\right){\psi }_j-\frac{1}{4}{G}_{\mu \nu }^a{G}_a^{\mu \nu }}$

where ${\displaystyle {\psi }_i(x)}$ is the quark field, a dynamical function of spacetime, in the fundamental representation of the SU(3) gauge group, indexed by ${\displaystyle i}$ and ${\displaystyle j}$ running from ${\displaystyle 1}$ to ${\displaystyle 3}$; ${\displaystyle D_{\mu }}$ is the gauge covariant derivative; the γ^μ are Dirac matrices connecting the spinor representation to the vector representation of the Lorentz group.

Herein, the gauge covariant derivative ${\displaystyle {\left(D_{\mu }\right)}_{ij}={\mathrm{\partial }}_{\mu }{\delta }_{ij}-ig{\left(T_a\right)}_{ij}{\mathcal{A}}_{\mu }^a}$couples the quark field with a coupling strength ${\displaystyle g}$to the gluon fields via the infinitesimal SU(3) generators ${\displaystyle T_a}$in the fundamental representation. An explicit representation of these generators is given by ${\displaystyle T_a={\lambda }_a/2}$, wherein the ${\displaystyle {\lambda }_a(a=1\dots 8)}$are the Gell-Mann matrices.

The symbol ${\displaystyle G_{\mu \nu }^a}$ represents the gauge invariant gluon field strength tensor, analogous to the electromagnetic field strength tensor, F^μν, in quantum electrodynamics. It is given by:

${\displaystyle G_{\mu \nu }^a={\mathrm{\partial }}_{\mu }{\mathcal{A}}_{\nu }^a-{\mathrm{\partial }}_{\nu }{\mathcal{A}}_{\mu }^a+g{f}^{abc}{\mathcal{A}}_{\mu }^b{\mathcal{A}}_{\nu }^c,}$

where ${\displaystyle {\mathcal{A}}_{\mu }^a(x)}$ are the gluon fields, dynamical functions of spacetime, in the adjoint representation of the SU(3) gauge group, indexed by a, b and c running from ${\displaystyle 1}$ to ${\displaystyle 8}$; and f_abc are the structure constants of SU(3). Note that the rules to move-up or pull-down the a, b, or c indices are trivial, (+, ..., +), so that f^abc = f_abc = f^a_bc whereas for the μ or ν indices one has the non-trivial relativistic rules corresponding to the metric signature (+ − − −).

The variables m and g correspond to the quark mass and coupling of the theory, respectively, which are subject to renormalization.

An important theoretical concept is the Wilson loop (named after Kenneth G. Wilson). In lattice QCD, the final term of the above Lagrangian is discretized via Wilson loops, and more generally the behavior of Wilson loops can distinguish confined and deconfined phases.

Fields

The pattern of strong charges for the three colors of quark, three antiquarks, and eight gluons (with two of zero charge overlapping).

Quarks are massive spin-1⁄2 fermions that carry a color charge whose gauging is the content of QCD. Quarks are represented by Dirac fields in the fundamental representation 3 of the gauge group SU(3). They also carry electric charge (either −1⁄3 or +2⁄3) and participate in weak interactions as part of weak isospin doublets. They carry global quantum numbers including the baryon number, which is 1⁄3 for each quark, hypercharge and one of the flavor quantum numbers.

Gluons are spin-1 bosons that also carry color charges, since they lie in the adjoint representation 8 of SU(3). They have no electric charge, do not participate in the weak interactions, and have no flavor. They lie in the singlet representation 1 of all these symmetry groups.

Each type of quark has a corresponding antiquark, of which the charge is exactly opposite. They transform in the conjugate representation to quarks, denoted ${\displaystyle \overline{\mathbf{3}}}$.

Dynamics

According to the rules of quantum field theory, and the associated Feynman diagrams, the above theory gives rise to three basic interactions: a quark may emit (or absorb) a gluon, a gluon may emit (or absorb) a gluon, and two gluons may directly interact. This contrasts with QED, in which only the first kind of interaction occurs, since photons have no charge. Diagrams involving Faddeev–Popov ghosts must be considered too (except in the unitarity gauge).

Area law and confinement

Detailed computations with the above-mentioned Lagrangian show that the effective potential between a quark and its anti-quark in a meson contains a term that increases in proportion to the distance between the quark and anti-quark (${\displaystyle \propto r}$), which represents some kind of "stiffness" of the interaction between the particle and its anti-particle at large distances, similar to the entropic elasticity of a rubber band (see below). This leads to confinement  of the quarks to the interior of hadrons, i.e. mesons and nucleons, with typical radii R_c, corresponding to former "Bag models" of the hadrons The order of magnitude of the "bag radius" is 1 fm (= 10⁻¹⁵ m). Moreover, the above-mentioned stiffness is quantitatively related to the so-called "area law" behavior of the expectation value of the Wilson loop product P_W of the ordered coupling constants around a closed loop W; i.e. ${\displaystyle ⟨P_W⟩}$ is proportional to the area enclosed by the loop. For this behavior the non-abelian behavior of the gauge group is essential.

Methods

Further analysis of the content of the theory is complicated. Various techniques have been developed to work with QCD. Some of them are discussed briefly below.

Perturbative QCD

Main article: Perturbative QCD

This approach is based on asymptotic freedom, which allows perturbation theory to be used accurately in experiments performed at very high energies. Although limited in scope, this approach has resulted in the most precise tests of QCD to date.

Lattice QCD

Main article: Lattice QCD

 

⟨E²⟩ plot for static quark–antiquark system held at a fixed separation, where blue is zero and red is the highest value (result of a lattice QCD simulation by M. Cardoso et al.)

Among non-perturbative approaches to QCD, the most well established is lattice QCD. This approach uses a discrete set of spacetime points (called the lattice) to reduce the analytically intractable path integrals of the continuum theory to a very difficult numerical computation that is then carried out on supercomputers like the QCDOC, which was constructed for precisely this purpose. While it is a slow and resource-intensive approach, it has wide applicability, giving insight into parts of the theory inaccessible by other means, in particular into the explicit forces acting between quarks and antiquarks in a meson. However, the numerical sign problem makes it difficult to use lattice methods to study QCD at high density and low temperature (e.g. nuclear matter or the interior of neutron stars).

1/N expansion

Main article: 1/N expansion

A well-known approximation scheme, the 1⁄N expansion, starts from the idea that the number of colors is infinite, and makes a series of corrections to account for the fact that it is not. Until now, it has been the source of qualitative insight rather than a method for quantitative predictions. Modern variants include the AdS/CFT approach.

Effective theories

For specific problems, effective theories may be written down that give qualitatively correct results in certain limits. In the best of cases, these may then be obtained as systematic expansions in some parameters of the QCD Lagrangian. One such effective field theory is chiral perturbation theory or ChiPT, which is the QCD effective theory at low energies. More precisely, it is a low energy expansion based on the spontaneous chiral symmetry breaking of QCD, which is an exact symmetry when quark masses are equal to zero, but for the u, d and s quark, which have small mass, it is still a good approximate symmetry. Depending on the number of quarks that are treated as light, one uses either SU(2) ChiPT or SU(3) ChiPT. Other effective theories are heavy quark effective theory (which expands around heavy quark mass near infinity), and soft-collinear effective theory (which expands around large ratios of energy scales). In addition to effective theories, models like the Nambu–Jona-Lasinio model and the chiral model are often used when discussing general features.

QCD sum rules

Main article: QCD sum rules

Based on an Operator product expansion one can derive sets of relations that connect different observables with each other.

Experimental tests

The notion of quark flavors was prompted by the necessity of explaining the properties of hadrons during the development of the quark model. The notion of color was necessitated by the puzzle of the
Δ⁺⁺
. This has been dealt with in the section on the history of QCD.

The first evidence for quarks as real constituent elements of hadrons was obtained in deep inelastic scattering experiments at SLAC. The first evidence for gluons came in three-jet events at PETRA.

Several good quantitative tests of perturbative QCD exist:

• The running of the QCD coupling as deduced from many observations
• Scaling violation in polarized and unpolarized deep inelastic scattering
• Vector boson production at colliders (this includes the Drell–Yan process)
• Direct photons produced in hadronic collisions
• Jet cross sections in colliders
• Event shape observables at the LEP
• Heavy-quark production in colliders

Quantitative tests of non-perturbative QCD are fewer, because the predictions are harder to make. The best is probably the running of the QCD coupling as probed through lattice computations of heavy-quarkonium spectra. There is a recent claim about the mass of the heavy meson B_c . Other non-perturbative tests are currently at the level of 5% at best. Continuing work on masses and form factors of hadrons and their weak matrix elements are promising candidates for future quantitative tests. The whole subject of quark matter and the quark–gluon plasma is a non-perturbative test bed for QCD that still remains to be properly exploited.

One qualitative prediction of QCD is that there exist composite particles made solely of gluons called glueballs that have not yet been definitively observed experimentally. A definitive observation of a glueball with the properties predicted by QCD would strongly confirm the theory. In principle, if glueballs could be definitively ruled out, this would be a serious experimental blow to QCD. But, as of 2013, scientists are unable to confirm or deny the existence of glueballs definitively, despite the fact that particle accelerators have sufficient energy to generate them.

Cross-relations to condensed matter physics

There are unexpected cross-relations to condensed matter physics. For example, the notion of gauge invariance forms the basis of the well-known Mattis spin glasses, which are systems with the usual spin degrees of freedom ${\displaystyle s_i=\pm 1}$ for i =1,...,N, with the special fixed "random" couplings ${\displaystyle J_{i,k}={ϵ}_i{J}_0{ϵ}_k.}$ Here the ε_i and ε_k quantities can independently and "randomly" take the values ±1, which corresponds to a most-simple gauge transformation ${\displaystyle (s_i\to s_i\cdot {ϵ}_i{J}_{i,k}\to {ϵ}_i{J}_{i,k}{ϵ}_k{s}_k\to s_k\cdot {ϵ}_k).}$ This means that thermodynamic expectation values of measurable quantities, e.g. of the energy $\mathcal{H}:=-\sum s_i{J}_{i,k}{s}_k,$ are invariant.

However, here the coupling degrees of freedom ${\displaystyle J_{i,k}}$, which in the QCD correspond to the gluons, are "frozen" to fixed values (quenching). In contrast, in the QCD they "fluctuate" (annealing), and through the large number of gauge degrees of freedom the entropy plays an important role (see below).

For positive J₀ the thermodynamics of the Mattis spin glass corresponds in fact simply to a "ferromagnet in disguise", just because these systems have no "frustration" at all. This term is a basic measure in spin glass theory. Quantitatively it is identical with the loop product ${\displaystyle P_W:=J_{i,k}{J}_{k,l}...J_{n,m}{J}_{m,i}}$ along a closed loop W. However, for a Mattis spin glass – in contrast to "genuine" spin glasses – the quantity P_W never becomes negative.

The basic notion "frustration" of the spin-glass is actually similar to the Wilson loop quantity of the QCD. The only difference is again that in the QCD one is dealing with SU(3) matrices, and that one is dealing with a "fluctuating" quantity. Energetically, perfect absence of frustration should be non-favorable and atypical for a spin glass, which means that one should add the loop product to the Hamiltonian, by some kind of term representing a "punishment". In the QCD the Wilson loop is essential for the Lagrangian rightaway.

The relation between the QCD and "disordered magnetic systems" (the spin glasses belong to them) were additionally stressed in a paper by Fradkin, Huberman and Shenker, which also stresses the notion of duality.

A further analogy consists in the already mentioned similarity to polymer physics, where, analogously to Wilson loops, so-called "entangled nets" appear, which are important for the formation of the entropy-elasticity (force proportional to the length) of a rubber band. The non-abelian character of the SU(3) corresponds thereby to the non-trivial "chemical links", which glue different loop segments together, and "asymptotic freedom" means in the polymer analogy simply the fact that in the short-wave limit, i.e. for ${\displaystyle 0\leftarrow {\lambda }_w\ll R_c}$ (where R_c is a characteristic correlation length for the glued loops, corresponding to the above-mentioned "bag radius", while λ_w is the wavelength of an excitation) any non-trivial correlation vanishes totally, as if the system had crystallized.

There is also a correspondence between confinement in QCD – the fact that the color field is only different from zero in the interior of hadrons – and the behaviour of the usual magnetic field in the theory of type-II superconductors: there the magnetism is confined to the interior of the Abrikosov flux-line lattice, i.e., the London penetration depth λ of that theory is analogous to the confinement radius R_c of quantum chromodynamics. Mathematically, this correspondendence is supported by the second term, ${\displaystyle \propto g{G}_{\mu }^a{\overline{\psi }}_i{\gamma }^{\mu }{T}_{ij}^a{\psi }_j,}$ on the r.h.s. of the Lagrangian.

Environmental effects of mining

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Environmental_effects_of_mining 

Environmental effects of mining can occur at local, regional, and global scales through direct and indirect mining practices. The effects can result in erosion, sinkholes, loss of biodiversity, or the contamination of soil, groundwater, and surface water by the chemicals emitted from mining processes. These processes also affect the atmosphere from the emissions of carbon which have an effect on the quality of human health and biodiversity. Some mining methods (lithium mining, phosphate mining, coal mining, mountaintop removal mining, and sand mining) may have such significant environmental and public health effects that mining companies in some countries are required to follow strict environmental and rehabilitation codes to ensure that the mined area returns to its original state.

Erosion

Erosion of exposed hillsides, mine dumps, tailings dams and resultant siltation of drainages, creeks and rivers can significantly affect the surrounding areas, a prime example being the giant Ok Tedi Mine in Papua New Guinea. Soil erosion can decrease the water availability for plant growth, resulting in a population decline in the plant ecosystem. Soil erosion is mainly caused by excessive rainfall, lack of soil management and chemical exposure from mining. In wilderness areas mining may cause destruction of ecosystems and habitats, and in areas of farming it may disturb or destroy productive grazing and croplands.

Sinkholes

House in Gladbeck, Germany, with fissures caused by gravity erosion due to mining

A sinkhole at or near a mine site is typically caused from the failure of a mine roof from the extraction of resources, weak overburden or geological discontinuities. The overburden at the mine site can develop cavities in the subsoil or rock, which can infill with sand and soil from the overlying strata. These cavities in the overburden have the potential to eventually cave in, forming a sinkhole at the surface. The sudden failure of earth creates a large depression at the surface without warning, this can be seriously hazardous to life and property. Sinkholes at a mine site can be mitigated with the proper design of infrastructure such as mining supports and better construction of walls to create a barrier around an area prone to sinkholes. Back-filling and grouting can be done to stabilize abandoned underground workings.

Water pollution

Mining can have harmful effects on surrounding surface and groundwater. If proper precautions are not taken, unnaturally high concentrations of chemicals, such as arsenic, sulfuric acid, and mercury can spread over a significant area of surface or subsurface water. Large amounts of water used for mine drainage, mine cooling, aqueous extraction and other mining processes increases the potential for these chemicals to contaminate ground and surface water. As mining produces copious amounts of waste water, disposal methods are limited due to contaminates within the waste water. Runoff containing these chemicals can lead to the devastation of the surrounding vegetation. The dumping of the runoff in surface waters or in a lot of forests is the worst option. Therefore, submarine tailings disposal are regarded as a better option (if the waste is pumped to great depth). Land storage and refilling of the mine after it has been depleted is even better, if no forests need to be cleared for the storage of debris. The contamination of watersheds resulting from the leakage of chemicals also has an effect on the health of the local population.

In well-regulated mines, hydrologists and geologists take careful measurements of water to take precaution to exclude any type of water contamination that could be caused by the mine's operations. The minimization of environmental degradation is enforced in American mining practices by federal and state law, by restricting operators to meet standards for the protection of surface and groundwater from contamination. This is best done through the use of non-toxic extraction processes as bioleaching.

Air pollution

Air pollutants have a negative impact on plant growth, primarily through interfering with resource accumulation. Once leaves are in close contact with the atmosphere, many air pollutants, such as O3 and NOx, affect the metabolic function of the leaves and interfere with net carbon fixation by the plant canopy. Air pollutants that are first deposited on the soil, such as heavy metals, first affect the functioning of roots and interfere with soil resource capture by the plant. These reductions in resource capture (production of carbohydrate through photosynthesis, mineral nutrient uptake and water uptake from the soil) will affect plant growth through changes in resource allocation to the various plant structures. When air pollution stress co-occurs with other stresses, e.g. water stress, the outcome on growth will depend on a complex interaction of processes within the plant. At the ecosystem level, air pollution can shift the competitive balance among the species present and may lead to changes in the composition of the plant community. In agroecosystems, these changes may be manifest in reduced economic yield.

Acid rock drainage

Main article: Acid mine drainage

Sub-surface mining often progresses below the water table, so water must be constantly pumped out of the mine in order to prevent flooding. When a mine is abandoned, the pumping ceases, and water floods the mine. This introduction of water is the initial step in most acid rock drainage situations.

Acid mine drainage in Portugal

Acid rock drainage occurs naturally within some environments as part of the rock weathering process but is exacerbated by large-scale earth disturbances characteristic of mining and other large construction activities, usually within rocks containing an abundance of sulfide minerals. Areas where the earth has been disturbed (e.g. construction sites, subdivisions, and transportation corridors) may create acid rock drainage. In many localities, the liquid that drains from coal stocks, coal handling facilities, coal washeries, and coal waste tips can be highly acidic, and in such cases it is treated as acid mine drainage (AMD). The same type of chemical reactions and processes may occur through the disturbance of acid sulfate soils formed under coastal or estuarine conditions after the last major sea level rise, and constitutes a similar environmental hazard.

The five principal technologies used to monitor and control water flow at mine sites are diversion systems, containment ponds, groundwater pumping systems, subsurface drainage systems, and subsurface barriers. In the case of AMD, contaminated water is generally pumped to a treatment facility that neutralizes the contaminants. A 2006 review of environmental impact statements found that "water quality predictions made after considering the effects of mitigation largely underestimated actual impacts to groundwater, seeps, and surface water".

Heavy metals

Heavy metals are naturally occurring elements that have a high atomic weight and a density at least 5 times greater than that of water. Their multiple industrial, domestic, agricultural, medical and technological applications have led to their wide distribution in the environment; raising concerns over their potential effects on human health and the environment.

Naturally occurring heavy metals are displayed in shapes that are not promptly accessible for uptake by plants. They are ordinarily displayed in insoluble shapes, like in mineral structures, or in precipitated or complex shapes that are not promptly accessible for plant take-up. Normally happening heavy metals have an awesome adsorption capacity in soil and are hence not promptly accessible for living organisms. The holding vitality between normally happening heavy metals and soil is exceptionally high compared to that with anthropogenic sources.

Dissolution and transport of metals and heavy metals by run-off and ground water is another example of environmental problems with mining, such as the Britannia Mine, a former copper mine near Vancouver, British Columbia. Tar Creek, an abandoned mining area in Picher, Oklahoma that is now an Environmental Protection Agency Superfund site, also suffers from heavy metal contamination. Water in the mine containing dissolved heavy metals such as lead and cadmium leaked into local groundwater, contaminating it. Long-term storage of tailings and dust can lead to additional problems, as they can be easily blown off site by wind, as occurred at Skouriotissa, an abandoned copper mine in Cyprus. Environmental changes such as global warming and increased mining activity may increase the content of heavy metals in the stream sediments.

Effect on biodiversity

The Ok Tedi River is contaminated by tailings from a nearby mine.

The implantation of a mine is a major habitat modification, and smaller perturbations occur on a larger scale than exploitation site, mine-waste residuals contamination of the environment for example. Adverse effects can be observed long after the end of the mine activity. Destruction or drastic modification of the original site and anthropogenic substances release can have major impact on biodiversity in the area. Destruction of the habitat is the main component of biodiversity losses, but direct poisoning caused by mine-extracted material, and indirect poisoning through food and water, can also affect animals, vegetation and microorganisms. Habitat modification such as pH and temperature modification disturb communities in the surrounding area. Endemic species are especially sensitive, since they require very specific environmental conditions. Destruction or slight modification of their habitat put them at the risk of extinction. Habitats can be damaged when there is not enough terrestrial product as well as by non-chemical products, such as large rocks from the mines that are discarded in the surrounding landscape with no concern for impacts on natural habitat.

Concentrations of heavy metals are known to decrease with distance from the mine, and effects on biodiversity tend to follow the same pattern. Impacts can vary greatly depending on mobility and bioavailability of the contaminant: less-mobile molecules will stay inert in the environment while highly mobile molecules will easily move into another compartment or be taken up by organisms. For example, speciation of metals in sediments could modify their bioavailability, and thus their toxicity for aquatic organisms.

Biomagnification plays an important role in polluted habitats: mining impacts on biodiversity, assuming that concentration levels are not high enough to directly kill exposed organisms, should be greater to the species on top of the food chain because of this phenomenon.

Adverse mining effects on biodiversity depend a great extent on the nature of the contaminant, the level of concentration at which it can be found in the environment, and the nature of the ecosystem itself. Some species are quite resistant to anthropogenic disturbances, while some others will completely disappear from the contaminated zone. Time alone does not seem to allow the habitat to recover completely from the contamination. Remediation practices take time, and in most cases will not enable the recovery of the original diversity present before the mining activity took place.

Aquatic organisms

The mining industry can impact aquatic biodiversity through different ways. One way can be direct poisoning; a higher risk for this occurs when contaminants are mobile in the sediment or bioavailable in the water. Mine drainage can modify water pH, making it hard to differentiate direct impact on organisms from impacts caused by pH changes. Effects can nonetheless be observed and proven to be caused by pH modifications. Contaminants can also affect aquatic organisms through physical effects: streams with high concentrations of suspended sediment limit light, thus diminishing algae biomass. Metal oxide deposition can limit biomass by coating algae or their substrate, thereby preventing colonization.

Contaminated Osisko lake in Rouyn-Noranda

Factors that impact communities in acid mine drainage sites vary temporarily and seasonally: temperature, rainfall, pH, salinisation and metal quantity all display variations on the long term, and can heavily affect communities. Changes in pH or temperature can affect metal solubility, and thereby the bioavailable quantity that directly impact organisms. Moreover, contamination persists over time: ninety years after a pyrite mine closure, water pH was still very low and microorganisms populations consisted mainly of acidophil bacteria.

One big case study that was considered extremely toxic to aquatic organisms was the contamination that occurred in Minamata Bay. Methylmercury was released into wastewater by industrial chemical company's and a disease called Minamata disease was discovered in Kumamoto, Japan. This resulted in mercury poisoning in fishes and shellfishes and it was contaminating surrounding species and many died from it and it impacted anyone that ate the contaminated fishes.

Microorganisms

Algae communities are less diverse in acidic water containing high zinc concentration, and mine drainage stress decrease their primary production. Diatoms' community is greatly modified by any chemical change, pH phytoplankton assemblage, and high metal concentration diminishes the abundance of planktonic species. Some diatom species may grow in high-metal-concentration sediments. In sediments close to the surface, cysts suffer from corrosion and heavy coating. In very polluted conditions, total algae biomass is quite low, and the planktonic diatom community is missing. Similarly to phytoplankton, the zooplankton communities are heavily altered in cases where the mining impact is severe. In case of functional complementary, however, it is possible that the phytoplankton and zooplankton mass remains stable.

Macro-organisms

Water insect and crustacean communities are modified around a mine, resulting in a low tropic completeness and their community being dominated by predators. However, biodiversity of macroinvertebrates can remain high, if sensitive species are replaced with tolerant ones. When diversity within the area is reduced, there is sometimes no effect of stream contamination on abundance or biomass, suggesting that tolerant species fulfilling the same function take the place of sensible species in polluted sites. pH diminution in addition to elevated metal concentration can also have adverse effects on macroinvertebrates' behaviour, showing that direct toxicity is not the only issue. Fish can also be affected by pH, temperature variations, and chemical concentrations.

Terrestrial organisms

Vegetation

Soil texture and water content can be greatly modified in disturbed sites, leading to plants community changes in the area. Most of the plants have a low concentration tolerance for metals in the soil, but sensitivity differs among species. Grass diversity and total coverage is less affected by high contaminant concentration than forbs and shrubs. Mine waste-materials rejects or traces due to mining activity can be found in the vicinity of the mine, sometimes far away from the source. Established plants cannot move away from perturbations, and will eventually die if their habitat is contaminated by heavy metals or metalloids at a concentration that is too elevated for their physiology. Some species are more resistant and will survive these levels, and some non-native species that can tolerate these concentrations in the soil, will migrate in the surrounding lands of the mine to occupy the ecological niche. This can also leave the soil vulnerable to potential soil erosion, which would make it inhabitable for plants.

Plants can be affected through direct poisoning, for example arsenic soil content reduces bryophyte diversity. Vegetation can also be contaminated from other metals as well such as nickel and copper. Soil acidification through pH diminution by chemical contamination can also lead to a diminished species number. Contaminants can modify or disturb microorganisms, thus modifying nutrient availability, causing a loss of vegetation in the area. Some tree roots divert away from deeper soil layers in order to avoid the contaminated zone, therefore lacking anchorage within the deep soil layers, resulting in the potential uprooting by the wind when their height and shoot weight increase. In general, root exploration is reduced in contaminated areas compared to non-polluted ones. Plant species diversity will remain lower in reclaimed habitats than in undisturbed areas. Depending on what specific type of mining is done, all vegetation can be initially removed from the area before the actual mining is started. 

Cultivated crops might be a problem near mines. Most crops can grow on weakly contaminated sites, but yield is generally lower than it would have been in regular growing conditions. Plants also tend to accumulate heavy metals in their aerian organs, possibly leading to human intake through fruits and vegetables. Regular consumption of contaminated crops might lead to health problems caused by long-term metal exposure. Cigarettes made from tobacco growing on contaminated sites might also possibly have adverse effects on human population, as tobacco tends to accumulate cadmium and zinc in its leaves.

Animals

Malartic mine - Osisko

Habitat destruction is one of the main issues of mining activity. Huge areas of natural habitat are destroyed during mine construction and exploitation, forcing animals to leave the site.

Animals can be poisoned directly by mine products and residuals. Bioaccumulation in the plants or the smaller organisms they eat can also lead to poisoning: horses, goats and sheep are exposed in certain areas to potentially toxic concentration of copper and lead in grass. There are fewer ant species in soil containing high copper levels, in the vicinity of a copper mine. If fewer ants are found, chances are higher that other organisms living in the surrounding landscape are strongly affected by the high copper levels as well. Ants have good judgement whether an area is habitual as they live directly in the soil and are thus sensitive to environmental disruptions.

Microorganisms

Microorganisms are extremely sensitive to environmental modification, such as modified pH, temperature changes or chemical concentrations due to their size. For example, the presence of arsenic and antimony in soils have led to diminution in total soil bacteria. Much like waters sensitivity, a small change in the soil pH can provoke the remobilization of contaminants, in addition to the direct impact on pH-sensitive organisms.

Microorganisms have a wide variety of genes among their total population, so there is a greater chance of survival of the species due to the resistance or tolerance genes in that some colonies possess, as long as modifications are not too extreme. Nevertheless, survival in these conditions will imply a big loss of gene diversity, resulting in a reduced potential for adaptations to subsequent changes. Undeveloped soil in heavy metal contaminated areas could be a sign of reduced activity by soils microfauna and microflora, indicating a reduced number of individuals or diminished activity. Twenty years after disturbance, even in rehabilitation area, microbial biomass is still greatly reduced compared to undisturbed habitat.

Arbuscular mycorrhiza fungi are especially sensitive to the presence of chemicals, and the soil is sometimes so disturbed that they are no longer able to associate with root plants. However, some fungi possess contaminant accumulation capacity and soil cleaning ability by changing the biodisponibility of pollutants, this can protect plants from potential damages that could be caused by chemicals. Their presence in contaminated sites could prevent loss of biodiversity due to mine-waste contamination, or allow for bioremediation, the removal of undesired chemicals from contaminated soils. On the contrary, some microbes can deteriorate the environment: which can lead to elevated SO4 in the water and can also increase microbial production of hydrogen sulfide, a toxin for many aquatic plants and organisms.

Rubbish

Tailings

Main articles: Tailings and Tailings dam

Mining processes produce an excess of waste materials known as tailings. The materials that are left over after are a result of separating the valuable fraction from the uneconomic fraction of ore. These large amounts of waste are a mixture of water, sand, clay, and residual bitumen. Tailings are commonly stored in tailings ponds made from naturally existing valleys or large engineered dams and dyke systems. Tailings ponds can remain part of an active mine operation for 30–40 years. This allows for tailings deposits to settle, or for storage and water recycling.

Tailings have great potential to damage the environment by releasing toxic metals by acid mine drainage or by damaging aquatic wildlife; these both require constant monitoring and treatment of water passing through the dam. However, the greatest danger of tailings ponds is dam failure. Tailings ponds are typically formed by locally derived fills (soil, coarse waste, or overburden from mining operations and tailings) and the dam walls are often built up on to sustain greater amounts of tailings. The lack of regulation for design criteria of the tailings ponds are what put the environment at risk for flooding from the tailings ponds.

Spoil tip

A spoil tip is a pile of accumulated overburden that was removed from a mine site during the extraction of coal or ore. These waste materials are composed of ordinary soil and rocks, with the potential to be contaminated with chemical waster. Spoil is much different from tailings, as it is processed material that remains after the valuable components have been extracted from ore. Spoil tip combustion can happen fairly commonly as, older spoil tips tend to be loose and tip over the edge of a pile. As spoil is mainly composed of carbonaceous material that is highly combustible, it can be accidentally ignited by the lighting fire or the tipping of hot ashes. Spoil tips can often catch fire and be left burning underground or within the spoil piles for many years.

Mining activities

Mining activities, including prospecting, exploration, construction, operation, maintenance, expansion, abandonment, decommissioning and repurposing of a mine can impact social and environmental systems in a range of positive and negative, and direct and indirect ways.

Effects of mine pollution on humans

Further information: Coalworker's pneumoconiosis, Toroku arsenic disease, and Itai-itai disease

Humans are also affected by mining. There are many diseases that can come from the pollutants that are released into the air and water during the mining process. For example, during smelting operations large quantities of air pollutants, such as the suspended particulate matter, SO_x, arsenic particles and cadmium, are emitted. Metals are usually emitted into the air as particulates as well. There are also many occupational health hazards that miners face. Most of miners suffer from various respiratory and skin diseases such as asbestosis, silicosis, or black lung disease.

Furthermore, one of the biggest subset of mining that impacts humans is the pollutants that end up in the water, which results in poor water quality. About 30% of the world has access to renewable freshwater which is used by industries that generate large amounts of waste containing chemicals in various concentrations that are deposited into the freshwater. The concern of active chemicals in the water can pose a great risk to human health as it can accumulate within the water and fishes. There was a study done on an abandon mine in China, Dabaoshan mine and this mine was not active to many years yet the impact of how metals can accumulate in water and soil was a major concern for neighboring villages. Due to the lack of proper care of waste materials 56% of mortality rate is estimated within the regions around this mining sites, and many have been diagnosed with esophageal cancer and liver cancer. It resulted that this mine till this day still has negative impacts on human health through crops and it is evident that there needs to be more cleaning up measures around surrounding areas.

The long-term effects associated with air pollution are plenty including chronic asthma, pulmonary insufficiency, and cardiovascular mortality. According to a Swedish cohort study, diabetes seems to be induced after long-term air pollution exposure. Furthermore, air pollution seems to have various malign health effects in early human life, such as respiratory, cardiovascular, mental, and perinatal disorders, leading to infant mortality or chronic disease in adult age. Discuss contamination basically influences those living in huge urban zones, where street outflows contribute the foremost to the degradation of discuss quality. There's moreover a threat of mechanical mishaps, where the spread of a harmful haze can be lethal to the populaces of the encompassing regions. The scattering of poisons is decided by numerous parameters, most outstandingly barometrical soundness and wind.

Deforestation

With open cast mining the overburden, which may be covered in forest, must be removed before the mining can commence. Although the deforestation due to mining may be small compared to the total amount it may lead to species extinction if there is a high level of local endemism. The lifecycle of mining coal is one of the filthiest cycles that causes deforestation due to the amount of toxins, and heavy metals that are released soil and water environment. Although the effects of coal mining take a long time to impact the environment the burning of coals and fires which can burn up to decades can release flying ash and increase the greenhouse gasses. Specifically strip mining that can destroy landscapes, forests, and wildlife habitats that are near the sites. Trees, plants and topsoil are cleared from the mining area and this can lead to destruction of agricultural land. Furthermore, when rainfall occurs the ashes and other materials are washed into streams that can hurt fish. These impacts can still occur after the mining site is completed which disturbs the presences of the land and restoration of the deforestation takes longer than usual because the quality of the land is degraded. Legal mining, albeit more environmentally-controlled than illegal mining, contributes to some substantial percentage to the deforestation of tropical countries 

Impacts associated with specific types of mining

Coal mining

Further information: Environmental effects of coal

The environmental factors of the coal industry are not only impacting air pollution, water management and land use but also is causing severe health effects by the burning of the coal. Air pollution is increasing in numbers of toxins such as mercury, lead, sulfur dioxide, nitrogen oxides and other heavy metals. This is causing health issues involving breathing difficulties and is impacting the wildlife around the surrounding areas that needs clean air to survive. The future of air pollution remains unclear as the Environmental Protection Agency have tried to prevent some emissions but don't have control measures in place for all plants producing mining of coal. Water pollution is another factor that is being damaged throughout this process of mining coals, the ashes from coal is usually carried away in rainwater which streams into larger water sites. It can take up to 10 years to clean water sites that have coal waste and the potential of damaging clean water can only make the filtration much more difficult.

Deep sea mining

Main article: Deep sea mining

Deep sea mining for manganese nodules and other resources have led to concerns from marine scientists and environmental groups over the impact on fragile deep sea ecosystems. Knowledge of potential impacts is limited due to limited research on deep sea life.

Lithium mining

Lithium mining at Salar del Hombre Muerto, Argentina.

Lithium does not occur as the metal naturally since it is highly reactive, but is found combined in small amounts in rocks, soils, and bodies of water. The extraction of lithium in rock form can be exposed to air, water, and soil. Furthermore, batteries are globally demanded for containing lithium in regards to manufacturing, the toxic chemicals that lithium produce can negatively impact humans, soils, and marine species. Lithium production increased by 25% between 2000 and 2007 for the use of batteries, and the major sources of lithium are found in brine lake deposits. Lithium is discovered and extracted from 150 minerals, clays, numerous brines, and sea water, and although lithium extraction from rock-form is twice as expensive from that of lithium extracted from brines, the average brine deposit is greater than in comparison to an average lithium hard rock deposit.

Phosphate mining

A limestone karst on Nauru Island influenced by phosphate mining.

Phosphate-bearing rocks are mined to produce phosphorus, an essential element used in industry and agriculture. The process of extraction includes removal of surface vegetation, thereby exposing phosphorus rocks to the terrestrial ecosystem, damaging the land area with exposed phosphorus, resulting in ground erosion. The products released from phosphate ore mining are wastes, and tailings, resulting in human exposure to particulate matter from contaminated tailings via inhalation and the toxic elements that impact human health are (Cd, Cr, Zn, Cu and Pb).

Oil shale mining

Main article: Environmental impact of the oil shale industry

Oil shale is a sedimentary rock containing kerogen which hydrocarbons can be produced. Mining oil shale impacts the environment it can damage the biological land and ecosystems. The thermal heating and combustion generate a lot of material and waste that includes carbon dioxide and greenhouse gas. Many environmentalists are against the production and usage of oil shale because it creates large amounts of greenhouse gasses. Among air pollution, water contamination is a huge factor mainly because oil shales are dealing with oxygen and hydrocarbons. There is changes in the landscape with mining sites due to oil shale mining and the production using chemical products. The ground movements within the area of underground mining is a problem that is long-term because it causes non-stabilized areas. Underground mining causes a new formation that can be suitable for some plant growth, but rehabilitation could be required. 

Mountaintop removal mining

Main article: Mountaintop removal mining

Mountaintop removal mining (MTR) occurs when trees are cut down, and coal seams are removed by machines and explosives. As a result the landscape is more susceptible to flash flooding and causing potential pollution from the chemicals. The critical zone disturbed by mountaintop removal causes degraded stream water quality towards the marine and terrestrial ecosystems and thus mountaintop removal mining affect hydrologic response and long-term watersheds.

Sand mining

Main article: Sand mining

Sand mining and gravel mining creates large pits and fissures in the earth's surface. At times, mining can extend so deeply that it affects ground water, springs, underground wells, and the water table. The major threats of sand mining activities include channel bed degradation, river formation and erosion. Sand mining has resulted in an increase of water turbidity in the majority offshore of Lake Hongze, the fourth largest freshwater lake located in China.

Mitigation

See also: Responsible mining and Restoration ecology

To ensure completion of reclamation, or restoring mine land for future use, many governments and regulatory authorities around the world require that mining companies post a bond to be held in escrow until productivity of reclaimed land has been convincingly demonstrated, although if cleanup procedures are more expensive than the size of the bond, the bond may simply be abandoned. Since 1978 the mining industry has reclaimed more than 2 million acres (8,000 km²) of land in the United States alone. This reclaimed land has renewed vegetation and wildlife in previous mining lands and can even be used for farming and ranching.

Specific sites

• Tui mine in New Zealand
• Stockton mine in New Zealand
• Northland Pyrite Mine in Temagami, Ontario, Canada
• Sherman Mine in Temagami, Ontario, Canada
• Ok Tedi Mine in Western Province, Papua New Guinea
• The Berkeley Pit
• Wheal Jane Mines

Film and literature

• Burning the Future: Coal in America
• Coal River
• Mountain Top Removal
• Moving Mountains: How One Woman and Her Community Won Justice From Big Coal
• Tar Creek
• Trou story