Download Cink, kadmium, ólom, gallium, indium, tallium

Zinc, cadmium, lead, tin,
gallium, indium, thallium
Zinc (Zn)
Universe: 0.3 ppm (by weight)
Sun: 2 ppm (by weight)
Carbonaceous meteorite: 180 ppm
Earth's Crust: 75 ppm
Seawater:
Atlantic surface: 5 x 10-5 ppm
Atlantic deep: 1 x 10-4 ppm
Zinc in magmatic processes
Zinc abundance in different minerals is a function of the
zinc concentration in the magma and the ability of the
crystal structure to incorporate this element. It is a major
constituent of more than 80 minerals, but there are only a
few important commercial ores. The principal Zn sulphide
minerals are sphalerite (cubic ZnS) and wurtzite
(hexagonal ZnS). The occurrence of zinc in some rockforming ferrous iron and magnesium silicates and oxides
(magnetite, pyroxenes, amphiboles, micas, spinel (gahnite,
franklinite) and staurolite) is far more important for the
crustal abundance of this element than zinc in ore deposits.
Most of the zinc deposits occur as fillings and replacements
formed by low-temperature hydrothermal solutions.
Zinc in magmatic processes
There are many substitution in sphalerite structure. The
most important is Fe and Cd. The concentration of other
elements in sphalerite depends on the temperature: Co,
Mn, Fe, In, Ga, Ge, Tl (order in decreasing temperature).
The unique zinc deposit is Franklin Furnace in New
Jersey. The ore minerals there are zincite (ZnO), willemite
(Zn2SiO4 ) and franklinite (Fe,Zn,Mn)(Fe,Mn)2O4
occurring as grains in calcite and high temperature and
high pressure of their origin is suggested.
Zinc in weathering and sedimentary
processes
The concentration of zinc in weathering solutions is
controlled rather by adsorption (on clay minerals, Fe, Mn,
AI hydroxides and organic matter) than by solubility of zinc
carbonates, hydroxides and phosphates. The Zn content in
soils depends on the nature of parent rocks, texture,
organic matter and pH and ranges from 10 to 300 ppm.
Several soil profile studies show that extractable zinc
content generally decreases with depth, while total Zn is
uniformly distributed throughout the profile. Higher content
of zinc is present in soils in the vicinity of deposits and
smelters. Addition of phosphate fertilizers and atmospheric
deposition increases zinc concentration in the soils.
Zinc in weathering and sedimentary
processes
In aqueous solutions it exists as Zn2+ and some complex
ions. Zn chloride, sulfate and nitrate are readily soluble in
water, whereas Zn oxide, carbonate, phosphate, silicate
and sulfide are practically insoluble in water.
Common Zn minerals in the oxidation zone of Zn ore
deposits are: smithsonite (ZnCO3), hemimorphite
(Zn4Si2O7(OH)2•H2O), aurichalcite (Zn,Cu)5(CO3)2(OH)6
and hydrozincite Zn5(CO3)2(OH)6.
Zinc in weathering and sedimentary
processes
In surface waters zinc occurs mainly bound to suspended
matter (clays, AI, Fe, Mn, Si hydrous oxides). High
concentrations of zinc are found in sludge. Freshwaters,
especially rivers, are frequently contaminated by sewage
and waste water and contain considerable zinc levels. Acid
mine water can locally accumulate zinc up to a high
concentration.
Zinc occurs in the atmosphere mainly as fine particles
(<21-1m). Atmospheric zinc results from the production and
processing of zinc, non-ferrous smelters, fossil fuel
combustion and car emissions.
Zinc in the biosphere
Zinc plays an important role as an essential trace metal in
all living systems from bacteria to humans. Zinc is found in
all human tissues and all body fluids. The metal is essential
for growth, development and reproduction in man.
Compared to other elements such as cadmium, mercury,
lead, zinc has a low toxicity.
Cadmium (Cd)
Universe: 0.002 ppm (by weight)
Sun: 0.006 ppm (by weight)
Carbonaceous meteorite: 0.45 ppm
Earth's Crust: 0.11 ppm
Seawater:
Atlantic surface: 1.1 x 10-6 ppm
Atlantic deep: 3.8 x 10-5 ppm
Cadmium in magmatic processes
Cadmium concentration in igneous rocks is generally low
(0.07-0.25 ppm). It is a chalcophile element, favoring an
association with sulfur, and is closely associated with zinc.
The bulk of cadmium in nature is dispersed as isomorphic
impurities in various other minerals, usually sulfide
minerals. The principal carrier is in sphalerite.
Common Cd-containing minerals are: greenockite,
hexagonal CdS, hawleyite, cubic CdS, otavite, trigonal
CdCO3.
It always substitutes Zn in different minerals (sphalerite,
smithsonite, hemimorphite etc.).
Cadmium in weathering and
sedimentary processes
It is relatively mobile in the surficial environment. Cadmium
often forms complexes with natural organic matter.
In many natural environments, aqueous cadmium
concentrations are controlled primarily by sorption
reactions. It to be enriched in shales, oceanic and
lacustrine sediments, and phosphorites, and depleted in
red shales, sandstones, and limestones. Carbonaceous
shales, formed under reducing conditions, tend to contain
the most cadmium. In oxidized zones of ore deposits, it is
found in smithsonite, hemimorphite, manganese oxides,
and hydrous iron oxides. During weathering, cadmium
forms complexes with sulfate and chloride in solution.
Lead (Pb)
Universe: 0.01 ppm (by weight)
Sun: 0.01 ppm (by weight)
Carbonaceous meteorite: 1.4 ppm
Earth's Crust: 14 ppm
Seawater:
Atlantic surface: 3 x 10-5 ppm
Atlantic deep: 4 x 10-6 ppm
Lead in magmatic processes
It is widely distributed throughout the Earth and can be
found in all environmental media (air, soil, rocks,
sediments, waters). The average crustal abundance of lead
is 16 ppm. In the Earth's crust, Pb is the most abundant of
the heavy elements with atomic number > 60.
Lead occurs in rocks as a discrete mineral, or the major
portion of the metal in the Earth's crust replaces K, Sr, Ba
and even Ca and Na in the mineral lattice of silicate
minerals. Among silicates potassium feldspars and micas
are notable accumulators of Pb, therefore granitic rocks
tend to have higher levels than basaltic ones.
Lead in magmatic processes
It can substitutes Ca in some phosphates (apatites),
carbonates (aragonite). The largest accumulations connect
to post-magmatic hydrothermal processes. The most
important Pb-sulphide mineral is galena (cubic PbS), but it
forms many Pb-bearing sulphosalts (e.g. boulangerite,
bournonite, jamesonite). More than 200 other minerals are
known.
Lead in weathering and sedimentary
processes
In the oxidation zone of Pb-bearing ore deposit found many
secondary Pb-minerals, the most common are cerussite
(orthorhombic PbCO3 ) and anglesite (orthorhombic
PbSO4). However, we know many other compounds in this
environments, oxides (minium, litarge, plattnerite),
phosphates (pyromorfite), arsenates (beudantite,
carminite), chromates (crocoite), molybdates (wulfenite),
and vanadates (vanadinite).
It can concentrates in sedimentary rocks, which contain
organic matters.
Lead in weathering and sedimentary
processes
Lead in surface run-off comes from chemical weathering,
municipal and industrial water discharges and largely from
atmospheric deposition. The concentration of lead in
natural waters is much lower than would be expected from
the inputs because of adsorption of the element onto
particulate matter (clay minerals, oxides and hydroxides of
aluminum, iron and manganese). The adsorption
decreases with lowering pH of the water. Under reducing
conditions lead precipitates as highly insoluble sulfide.
Lead occurs in atmosphere as fine particulates ( < 1 1-1m),
generated mainly by anthropogenic high temperature
sources.
Tin (Sn)
Universe: 0.004 ppm (by weight)
Sun: 0.009 ppm (by weight)
Carbonaceous meteorite: 1.2 ppm
Earth's Crust: 2.2 ppm
Seawater:
Atlantic surface: 2.3 x 10-6 ppm
Atlantic deep: 5.8 x 10-6 ppm
Tin in magmatic processes
The main tin carriers in granitic rocks are hornblende,
biotite, muscovite, garnet, ilmenite and magnetite. Common
substitution are in complex oxides, as niobates, tantalates
(Sn2+Ca2+, Sn4+  Ti4+ or Fe2+) in high temperature
processes. Cassiterite (tetragonal SnO2, the most common
tin mineral) occurs in pegmatites, high temperature quartz
veins and metasomatic deposits (greisens and tin skarns),
generally genetically associated with granitic rocks.
Postmagmatic hydrothermal interaction and chemical
alteration of granitic rocks produce greisen enriched in tin.
It also occurs in a few volcanogenic massive sulfide
deposits related to felsic rocks. At relatively low
temperatures the affinity of tin for sulfur increases (e.g.
stannite, cylindrite).
Tin in weathering and sedimentary
processes
Because of the cassiterite chemical stability, it concentrates
in clastic sediments. Most tin is produced from secondary
alluvial placers, which were eroded from cassiterite
deposits.
Except for alluvial placers, the abundance of tin is very low
in the sediments.
Gallium (Ga)
Universe: 0.01 ppm (by
weight)
Sun: 0.04 ppm (by weight)
Earth's Crust: 18 ppm
Seawater: 3 x 10-5 ppm
Gallium in magmatic processes
Concentration of Ga in most of the igneous rocks
varies between 1-40 ppm. The Al/Ga ratio decreases
only slightly from ultramafic to mafic and felsic rocks.
Volatile components and fluoride complexing cause the
enrichment of Ga in the late stages of magmatic processes.
Together with rare alkali elements it is enriched in
pegmatites, and sometimes in minerals of greisens and
skarns. The chalcophile character is emphasized especially
under hydrothermal, sulfur-rich conditions. Gallium is
enriched mainly in sphalerite (up to 0.16%). The gallium
concentration is temperature dependent and typical for
mesothermal ore associations. (1.88% Ga).
Gallium in weathering and
sedimentary processes
Gallium is dispersed in the oxidation zone of sulfide
mineralizations. The average concentration of Ga in shales
and the Al/Ga ratio of the latter remain similar to igneous
rocks. Ga, like AI, is enriched in weathering. It is more
mobile and the Al/Ga ratio tends to decrease in residual
materials. Coal may be a collector for Ga.
The content of Ga in bauxites (20-200 ppm) is of economic
importance. The concentration of Ga depends on the
weathered rock materials. The highest values are reported
from bauxites originating from alkali rocks. The carbonatederived bauxites display average contents around 50 ppm
Ga.
Indium (In)
Universe: 0.0003 ppm (by
weight)
Sun: 0.004 ppm (by weight)
Earth's Crust: 0.049 ppm
Seawater: 1 x 10-7 ppm
Indium in magmatic processes
Indium is a rare elements, it occurs mostly as a trace
constituent of other minerals. Indium minerals are very
rare. Indium prefers tin minerals, especially cassiterite,
cylindrite and teallite, as well as minerals with tetrahedral
covalent bonds, such as sphalerite, chalcopyrite and
stannite. Concentrations in silicates are low, frequently in
the range of ppb.
Significant concentration of In takes place only in the late
fluid-rich stages of magmatic processes, notably in tin-rich
associations. Indium is enriched during the formation of
greisens, skams and high temperature hydrothermal sulfide
mineralizations. In addition to tin minerals, dark iron-rich
sphalerites are the most common host mineral.
Indium in weathering and
sedimentary processes
In indium-rich ore deposits, secondary In minerals may be
expected to occur in the oxidation zone; however, only the
hydroxide dzahlindite has been described so far. Most of
the indium is dispersed in minerals of the oxidation zone.
Iron hydroxides have a high sorption capacity for the
negatively charged ln(OH)4 anion complex which might
help indium to be enriched like germanium or gallium.
In fossil organic matter like coal, the carbonate sedimenst,
and shales have very low concentration of In.
Thallium (Tl)
Universe: 0.0005 ppm (by weight)
Sun: 0.001 ppm (by weight)
Carbonaceous meteorite: 0.08 ppm
Earth's Crust: 0.6 ppm
Seawater: 1.4 x 10-5 ppm
Thallium in magmatic processes
Thallium is both a chalcophile and a lithophile element. Its
chalcophile character is expressed in the formation of a
number of independent sulfides, sulfosalts and selenides
with As, Sb, Cu, Pb, Fe, Hg, and Ag (e.g. lorándite TlAsS2,
vrbaite, hutchinsonite), and in trace amounts in sulfides
(galena, sphalerite, pyrite, etc.). These chalcophile
minerals are formed by hydrothermal (epithermal stage) or
by supergene processes. Thallium shows lithophile
character in K-minerals in igneous and metamorphic rocks.
It is concentrated in K-minerals because of their similar
size.
Thallium in weathering and
sedimentary processes
Thallium may be easily released during weathering, but
because of its large ionic radius it will be fixed by clay
minerals and the oxides of Fe and Mn in the weathering
products. It is very mobile in oxidized conditions, and in the
oxidizing zone of sulfide deposits it is often enriched in
jarosite and manganese oxides. Because of the higher
concentrations of Th in hydrothermal altered rocks, it can
be used as an indicator element for hydrothermal deposits,
especially for epithermal gold deposits.